&EPA
           United States
           Environmental Protection
           Agency

           Research and Development
           Municipal Environmental Research EPA-600/2-78-090
           Laboratory        May 1 978
           Cincinnati OH 45268
Conventional and
Advanced Sewer
Design Concepts for
Dual Purpose
Flood and
Pollution  Control
A Preliminary
Case Study,
Elizabeth,  NJ

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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 nine series. These nine broad cate-
 gories were established to facilitate further development and application of en-
 vironmental technology. Elimination  of  traditional grouping was  consciously
 planned to foster technology transfer and a maximum interface in related fields.
 The nine series are:

      1.  Environmental Health Effects Research
      2.  Environmental Protection Technology
      3.  Ecological Research
      4.  Environmental Monitoring
      5.  Socioeconomic  Environmental Studies
      6.  Scientific and Technical Assessment Reports (STAR)
      7.  Interagency Energy-Environment Research and Development
      8.  "Special" Reports
      9.  Miscellaneous Reports

 This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
 NOLOGY series. This series describes research performed to develop and dem-
 onstrate instrumentation, equipment,  and methodology to repair or prevent en-
 vironmental 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-600/2-78-090
                                             May 1978
     CONVENTIONAL AND ADVANCED SEWER DESIGN CONCEPTS
      FOR DUAL PURPOSE FLOOD AND POLLUTION CONTROL

     A Preliminary Case Study, Elizabeth, New Jersey
                           by

                   Herbert L. Kaufman
                      Fu-Hsiung Lai
                Clinton Bogert Associates
               Fort Lee, New Jersey  07024
                   Grant No. S-802971
                     Project Officer

                    Anthony N. Tafuri
            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
     This  report  has been  reviewed  by the Municipal  Environmental  Research
Laboratory, U.S.  Environmental  Protection Agency, and  approved  for  publica-
tion. 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.  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,  treat-
ment,  and management of wastewater and  solid  and hazardous waste pollutant
discharges  from municipal and  community sources.  This work  is to  facilitate
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;  part of
a most  vital communications  link between the  researcher  and  the  user  com-
munity.

     Alleviation  of  the deleterious  effects  of  combined  sewer  overflows
and storm water discharges on the nation's waterways  depends  upon  characteri-
zation of the pattern, quantity and quality of  these  flows and evaluation of
alternative methods to achieve cost-effective  control.   This  report compares,
using the urban area of  the  City of Elizabeth, New Jersey,  the  cost-effec-
tiveness  of alternatives  for  a community-wide  sewer system.   Advanced  sewer
designs,   providing  controlled flow routing,  are compared with conventional
combined  and  separate sewer  systems.   The report also describes a practical
methodology for planning cost-effective  facilities  to abate  pollution  from
wet-weather flows.
                                                  Francis T.  Mayo
                                                  Director
                                                  Municipal Environmental
                                                  Research Laboratory
                                     iii

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                               PREFACE
     The study was made specifically for Elizabeth, N.J.  Because of funding
limitations, some  approximate  analytical methods  were  used.   These approxi-
mate methods were evaluated to insure the validity of the conclusion reached
as  to  the  main  purpose of  the  report; i.e.,  the development  of  relative
cost/benefit relationships  for  various  types  of  sewer systems under identical
inputs.   In Step 1  (Section 201)  Facility Planning,  with adequate funding,
more  exact methods x^ould be  used to determine combined  sewage overflow
pollutant characteristics and to  route  flows  through the system.

     Determination  of  the preferred  method  of handling rainfall  data was
outside  the scope of this work.   In addition,  the discrete rainfall/runoff
data required for "fine" temporal and distributional analysis and correlation
was not  available,  nor were the  funds  for their development.   However, the
importance  of runoff volume, as  opposed to runoff rate, to achieve combined
sewage  overflow  pollution abatement  was  recognized.   Hence,  the rainfall
handling was based  on  synthetic  hyetographs  which were designed to approxi-
mate the runoff  volume for the stated  return interval at all time segments,
rather than peak runoff rates.

     The alternative  systems developed  using the synthetic hyetographs
were  tested for pollution  abatement benefits using  STORM and available
hourly real rainfall records  for  a continuous 12 year period.

     Although the rainfall input  data may not be based on  the preferred  deter-
mination methodology, it still offered  a consistent/convenient means for com-
paratively  evaluating the most  cost-effective alternative  drainage system for
combined sewer overflow pollution control.

     The concepts developed have  been used  and the results accepted for
Steps 1, 2 and 3 grants for Trenton,  New Je'rsey.  Step 1 planning is also
proceeding  in Elizabeth,  New Jersey,  based  on the findings of this study.

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                                 ABSTRACT
     Alternatives  for  pollution  abatement  from  combined  sewer  overflows
and  stormwater  discharges  were evaluated.   The following  types  of  systems
were  compared:  separate storm and  sanitary  system,    conventional combined
system, and advanced combined systems with varying amounts of in-pipe and/or
satellite storage and controlled flow  routing.  The  cost-effectiveness
comparison was based  on achieving  a desired  effluent quality assuming a new
sewer  system.   In addition, the effects  on  pollution  abatement  and  cost of
changing  various  elements   (collection  system,  interceptors,  storage  and
treatment works)  of  the system were investigated.  Manning's  equation was
also  compared qualitatively  with   the  complete  momentum  equation for  the
hydraulic design of sewers.

     Two  mathematical  models, SWMM and STORM,  were employed.  SWMM was
used to design sewers and to analyze the  characteristics of the quantity and
quality  of  combined  sewage  and  stormwater  runoff  for  selected  synthetic
storms.  STORM was used to  analyze a continuous  12-year, real rainfall record
to determine  the frequency  of overflow events, the  mass  of pollutants  dis-
charged in  the  overflows for the alternatives  considered,  and  the duration
and quantity of  the overflows.  The runoff and  overflow characteristics  were
developed for  one .drainage  district  (about  265  hectares  or 655  acres)  in
Elizabeth, New Jersey.   A  method was developed to use these characteristics
to determine runoff  and overflow characteristics from  the remaining 24
drainage  districts  in  the  City so  that  a  city-wide sewer system could be
planned.

     The  study   (a)  evaluated the  effects  of  differing  rainfall  patterns
and  intensities  on pollutant concentrations, the  effects  of  varying  inter-
ceptor and treatment capacity on pollutants discharged,  and the economics of
peak  flow equalizing for different levels  of treatment;  (b)  quantified
the  long-term pollutional  loads  from  combined  sewage  overflows;  and  (c)
evaluated the effect-  on overflow control  of  varying  the  amounts  of upstream
and downstream storage.  The  report concluded that for Elizabeth,  N.J.,  the
most  economical  systems were  those which  included  substantial amounts  of
upstream storage  to  minimize the  size  of  trunk and interceptor sewers,
pumping stations and  treatment  facilities.

     While  the  study  was made  for  the City  of Elizabeth, New  Jersey,  the
methodology  should be  generally applicable to other urban areas.
                                     v

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     This  report was submitted in fulfillment of Grant No. S-802971 by
the City of Elizabeth, New Jersey under the partial sponsorship of the
U.S. Environmental Protection Agency.  Work was completed as of August
1976.
                                  vi

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                            CONTENTS

Foreword	ħħħ
Preface	iv
Abstract	 v
List of Figures	ix
List of Tables	;	xii
Acknowledgments	xv

  Sections
     I.  Summary	 1
    II.  Specific Conclusions-City of Elizabeth	 5
              Pollution Characteristics - Combined Sewage	 5
              Pollution Control Potential - Conventional
               and Existing Combined System	 6
              Pollution Control - Advanced Combined Systems	 8
              The "Normalized Hydrograph" - a Planning Aid	 9
              Costs	10
              Additional Hydraulic Studies	13
   III.  Recommendations	'.	..14
    TV.  Introduction	................16
     V.  Objectives and Scope of the Study	19
    VI.  Description of Study Area	,.,.21.
   VII.  Suggested Methodology.	25
  VIII.  Design and Cost Comparison of Sewer Systems in District A....30
              Design Philosophy	31
              Conventional Combined Sewer System	35
                   Design	35
                   Outflow Hydrographs and Pollutographs	41
              Separate Storm Sewer System	57
            ,  Separate Sanitary Sewer System	59
            '  Combined System with In-system Storage	....62
                   Design with In-pipe Storage	62
                   Outflow Hydrographs and Pollutographs	.....67
              Sewers with Satellite Storage.	67
                   Design	*	70
                   Outfow Hydrographs and Pollutographs	76
              Pollution Control Potential of Conventional
                   Combined System	83
                                  vii

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           Cost Comparison of Alternative Collection Systems	  83
                Cost of Conventional Sewer Systems	..........  85
                Cost of Advanced Sewer Systems	.....,,	  87

  IX. Design and Cost Comparison of Alternative City-Wide Sewer
      Systems	•	.	  89
           Synthetic Storm Runoff	  89
           Design of Intercepting Sewers.....	  96
           Amount of Storage Required vs. Treatment  Rate...	  97
           Cost Comparison of Alternative Sewer Systems..	100
   X. Analysis of Overflow Quantity and Quality,	105
           Effect of Storage and Interceptor Capacity.	106
           Effect of Street Sweeping Practice.	 Ill
  XI. Interceptors for Pollution Control	115
           The "First Flush" Phenomena.	,.115
 XII. Alternative Pollution Control Programs	118
           Conventional Combined System...	 .118
           Advanced Combined System.	120
           Selection of Design Storm for Separate and Combined
            Systems	124

XIII. Appendices	126

           A.  Alternative Model Evaluation	127
           B.  Modification of SWMM and STORM Programs	147

           C.  Quantity and Quality Considerations,  SWMM vs
               STORM	150
           D.  Model Input Data	..154
           E.  Calibration of STORM Runoff Coefficients	197

 XIV. References	202

  XV. Glossary, Abbreviations and Symbols	206
                                viii

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                                 FIGURES
Number
          Study area, Elizabeth, New Jersey.
                                                           Page

                                                          ..22
10


11

12

13

14

15
Hyetograph and outflow hydrograph, District A (5-year
intermediate pattern storm)	42

Mass rate SS pollutographs, 4 dry days (5-year intermediate
pattern storm)	,45

Mass rate. BOD pollutographs, 4 dry days (5-year interme-
diate pattern storm)	45

Mass rate SS pollutographs, 30 dry days (5-year interme-
diate pattern storm)	47

Mass rate BOD pollutographs, 30 dry days (5-year interme-
diate pattern storm)	....47

SS, BOD concentration pollutographs, 5^-year intermediate
pattern storm	49

Outflow hydrograph and pollutographs, 1-year intermediate
pattern storm	50

Outflow hydrograph and pollutographs, 1.3-month interme-
diate pattern storm	.51

Outflow hydrograph and pollutographs, 5-year advanced
pattern storm	52

Combined sewage pollutographs for various storms	55

Stormwater runoff pollutographs for various storms	56

Sanitary sewer layout, subareas I and II	60

Sanitary sewer layout, subareas III, IV and V	61

Incremental cost of pipe storage.	63
                                   ix

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                           FIGURES (continued)

Number                                                                Page

16        Weir-orifice regulator	 64

17        Hydrographs modified by in-pipe storage..	 66

18        Outflow hydrographs with in-pipe storage (5-year interme-
          diate pattern storm)	Ğ	 68

19        Wet-weather BOD variation, Trenton, New Jersey	 69

20        Outflow hydrographs with satellite storage at various
          locations (5-year intermediate pattern storm).....	 71

21        Schematic diagram of satellite storage locations,
          District A	 73

22        Outflow hydrographs with satellite storage (5-year
          intermediate pattern storm)	•	 75

23        Outflow pollutographs with satellite storage (5-year
          intermediate pattern storm)	 77

24        Outflow hydrographs and pollutographs with satellite
          storage (1-year intermediate pattern storm)	 79

25        Outflow hydrographs and pollutographs with satellite
          storage (1 • 3-raonth intermediate pattern storm)	 80

26        Outflow hydrographs and pollutographs with satellite
          storage (1-year advanced pattern storm)	-	 81

27        Normalized hydrographs	 93

28        Outflow hydrographs, Districts A, E and H	 95

29        Total cost comparison-city sewer system, in-pipe vs.
          satellite storage	•	103

30        Correlation of annual SS overflow with annual precipi-
          tation	107

31        Annual number of overflow events for various storage and
          interceptor capacities	Ğ	109

32        Annual SS overflow for various storage and interceptor
          capacities	•	HO

33        Effect of street cleaning interval on SS street washout	113
                                     x

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                           FIGURES  ( Continued)

Number                                                               Page

34        Pollution  control  costs - conventional system	121

35        Pollution  control  costs - advanced system	,	123

A-l       Definition sketch  for equations of motion	....128

A-2       Uniform flow rating curve and loop rating curve	132

A-3       Surcharged simple  pipe system.	135

C-l       Street SS  accumulation, SWMM vs. STORM.,	153

D-l       Frequency  distribution of precipitation amounts	156

D-2       Frequency  distribution of precipitation duration	157

D-3       Frequency  distribution of antecedent dry hours......	158

D-4       Rainfall intensity-duration-frequency curves	160

D-5       5-year design storm hyetographs and infiltration curve	161

D-6       Frequency  of hourly rainfalls	163

D-7       Subareas of drainage District A	166

D-8       Combined sewer system layout, subarea I	167

D-9       Combined sewer system layout, subarea II	168

D-10      Combined sewer system layout, subarea III	169

D-ll      Combined sewer system layout, subarea V	169

D-12      Combined sewer system layout, subarea IV	..170

D-13      Separate storm sewer system layout.	171

D-14      Definition of drainage districts and interceptor system in
          Elizabeth	T. ..	.186

D-15      Unit cost of sewers	193

D-16      Cost of treatment vs.  % of BOD removal	196

E-l       STORM runoff coefficient C,  vs..  rainfall	,.200
                                  xi

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                                  TABLES
Number

  1

  2

  3

  4


  5


  6
  10
  11
  12
  13
  14
  15
                                                         Page

Lateral Sewer Design Diameters (inches)	• •	37

Trunk Sewer Design Diameters (feet)	40

Comparison of Design Diameters and Peak Hydrographs	43

Solids Deposit (Ibs) in Sewers with Four Antecedent
Dry Days	-	4"

Summary of Runoff Quantity and Quality Characteristics
for Various Storms	•	54

Comparison of Pipe Diameter, Slope, and Excavation
Depth, Separate Storm versus Combined Systems	58

Peak Flow Comparison for Separate  Storm and Combined
Sewer Design	•	^9

Comparison of Trunk Sewer Sizes  (feet) for Storage
Basin at Various Locations	72

Summary of Runoff Quantity and Quality for Combined
System with  Satellite  Storage	.. .82

Storage Volume  in Sewer  Pipes and  Storage Basins,
District A	84

Cost  Comparison of  Conventional  Combined and  Separate
Sewer system ($10 )  of District  A	86

Cost  Summary of Combined System  with In-system
 Storage	•	88

 Summary  of  Normalized Hydrograph Development  from
District A  Data	• • •	91

 Adjustment  of Peaking Time  with  Respect  to  that of
District A	•	92

 Development of Outflow Hydrographs	94
                                   xix

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                            TABLES (continued)
Number

 16

 17


 18


 19

 20


 21


 22 .


 23

A-l


A-2

C-l

D-l

D-2

D-3

D-4

D-5

D-6

D-7

D-8

D-9
 Intercepting Sewer Pipe Element Data.,
 Page

.,.96
 Summary of Intercepting Sewer Diameters (feet) and
 Cost ($10 ).'	
  .98
Off-line Storage Required (10  gallons) and Cost for
Equal Weight of SS Discharged to Receiving Waters	99
Total Cost of City-Wide Sewer Systems	101

Effect of Storage and Flow Interception on District A
Sewer Sys tern Discharges	108

Pollutant Overflow as Affected by Street Sweeping Inter-
val and Efficiency	.	112

Interceptor Capacity Required to Contain First Flush from
District A	116

Comparison of Alternative Combined Sewer Systems	119

Range of Typical Values for Each Term in Momentum Equa-
tion	:	130

Peak Flow Comparison between Rational Method and SWMM......144

Pollutant Default Values for SWMM and STORM		...151

Annual Precipitation and Runoff Events	155

Hourly Rainfall versus Return Interval	164

Storm Characteristics.	164

Area of Land Use Distribution in Each Subarea (acres)	165

Total Sewer Length Comparison	 172

Sub catchment Data for SWMM	173

Pipe Element Data for Combined Sewer System	177

Subcatchment Water Quality Input Data for SWMM..	179

Subarea Curb Length (feet) versus Land Use	182
                                 xiii

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                                  TABLES
Number

D-10

D-ll

D-12

D-13

D-14


D-15


D-16


D-17

E-l


E-2
                                                          Page

Summary of Drainage District A Land Use Data.	182

Monthly Evaporation Rate.	-	-•••,.•• 184

Summary of Land Use in The City of Elizabeth..	187

Population	188

Average Daily Pollutant Concentration of Domestic Waste-
water	189

Diurnal Variation of Domestic Wastewater Quantity :and
Quality for District A	190

SWMM Input Data for Domestic Wastewater Computation,
District A	191

Unit Cos t of Sewers	194

Sensitivity of Hyetographs and Integration Interval on
Runoff Volume		198

Calibration of Runoff Coefficient C	199
                                   xiv

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                             ACKNOWLEDGEMENT S
     The  support of  the  project by  the City  of  Elizabeth  and  the Office
of  Research  and  Development, U.S. Environmental Protection Agency is acknow-
ledged and appreciated.

     The  assistance  and  cooperation of  Messrs.  Richard  Field  and Anthony
N.  Tafuri, Chief and Grant Project  Officer,  respectively,  Storm and Combined
Sewer  Section, Municipal Environmental  Research  Laboratory,  U.S.
Environmental Protection Agency, has been invaluable.

     This project was directed  by Mr. Herbert L. Kaufman,  Partner-In-Charge.
Messrs.  John H.  Scarino, Principal  Associate  arid Director  of Engineering
Management,  and  William Wheeler, Associate, provided valuable criticism and
review.   Dr.  Fu-hsiung Lai served  as  Project Engineer  and Mr.  Gerald G.
Gardner  as  Engineer.   Dr.  Lai  developed original  and innovative  analyses,
which resulted in  significant  findings  as to practical methods for reducing
pollution from combined sewage overflows.

     Dr.  Brendan M. Harley, Dr.  Guillermo J. Vicens  and Mr. Richard L.
Laramie of  Resource Analysis, Inc.,  Cambridge, Massachusetts,  provided
computer program changes  to  SWMM and STORM and prepared drafts for parts of
Appendix A in late  1974.   Dr. Harley  also participated in the preparation of
the "Design  Philosophy" described in Section VIII.

     Dr.  Wayne  C.  Huber  of the University of  Florida  and Mr..  Harry C.
Torno  of the  U.S.   Environmental  Protection Agency  reviewed the  draft of
this  report.  Their  comments  and  constructive  criticism  are  appreciated.
Dr. Huber  also  freely  contributed his  expertise  in  many discussions during
the preparation of  the  report for which  we express our sincere thanks.

     Finally,  the  authors  are grateful to Mr. M.B. McPherson,  Director
of  ASCE Urban Water Resources  Research Program,  and Mr. Chi-Yuan Fan,  Storm
and Combined  Sewer  Section, Municipal Environmental Research Laboratory,  U.S.
Environmental Protection Agency,  who also  contributed constructive comment.
                                     xv

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                                  SECTION I

                                   SUMMARY
     Pollution resulting from the discharge of untreated wastes from combined
sewers  is  a  national problem  which  requires  correction  if  the  objective
of  clean  waters  is  to be  achieved.   Such discharges  are now  experienced
from systems serving a population of 54 million located in some 1,300 munici-
palities.  They  occur, on  average,  about .every  5 to  10 days, depending  on
location,  a'nd can reduce the efficiency  of pollutant removal from  about  90
percent to 15 to 25 percent.

     Using computer technology, tools  to  investigate  and analyze  the various
elements required  for planning  cost-effective solutions  for combined  sewage
overflow  pollution abatement  have been developed.   This study modifies
and improves existing tools and develops new tools.   It organizes  these tools
into a systematic methodology that can have broad application.

     This  study  developed  appropriate criteria  for  sewerage  improvements.
The criteria are to be used to:

        identify alternative  corrective  programs for  abating  pollution  from
        combined sewage overflows, and

   -    select the most cost-effective solution.

STUDY PROCEDURE

     Initially,   alternatives for  combined  and   separate  sewage  collection
systems to  serve a 1.6-square-kilometer  (1.0-square-mile) area in Elizabeth
were  analyzed.  , The systems were designed to  convey, without flooding,
flows resulting  from  a two-minute interval,  synthetic  storm hyetograph which
matched the  intensity-duration curve  applicable to  the area  at each  time
interval for  a   5-year  return frequency  rainfall.    The characteristics  of
the  hydrographs  and  pollutographs   for  the  alternative collection  systems
were  determined  and  applied to  the  remaining  11.0-square-kilometer  (6.9-
square-mile) urban area of the City.  The alternatives, including  interceptor
and  treatment/storage  systems,   which would  provide  essentially  complete
capture and treatment of pollutants  for each of  the  collection system alter-
natives, were then screened  by  comparing costs of  the  total  systems.  The
reduced cost  resulting from  reducing  the amount of  pollutant captured for
treatment  were   then  estimated  and  an evaluation  made  of  the  pollutional
impact of  the resulting discharges.

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     The 5-year  return  interval,  synthetic storm  hyetograph  developed  does
not  represent the  5-year return frequency  runoff.  However, since  this
study emphasized  pollution  abatement,  and, since  the  calculated  amounts  of
mass pollutants  in the  runoff  from a  similarly  synthesized  1-year  return
interval storm  hyetograph are  not  significantly  different  (TABLE 9),  the
amount of pollutants determined may be expected to represent the quantity to
be expected  from a 5-year return frequency runoff volume  computed by other
methods. The  function served  by the selected  5-year  synthetic  storm  hyeto-
graph was  to permit design  of  alternative facilities that were  tested for
effectiveness in pollution abatement with a 12-year continuous real rainfall
record.

     For the  City  of  Elizabeth, the quantity  of  pollutants  in urban  runoff
and combined  sewage, which can be  intercepted  for treatment with alternative
facilities  were relatively quantified.  The alternatives considered included:

     1.    Separate sewer systems;

     2.    Combined  sewer systems designed to convey urban runoff  from a
          synthetic, 5-year  return frequency rainfall  (Figure D-5);

     3.    Combined sewer systems with flow routing and storage  in the trunk
          sewer;

     4.    Combined  sewer systems with enlarged lateral  sewers   to  permit
          storing various  amounts  of  runoff   from an intermediate  pattern
          storm  (peak rainfall  in the middle  half of the  storm  duration);

     5.    Combined sewer  systems,  similar to   4, except  that  storage  basins
          were provided  along  the  trunk sewer;  and  •

     6.    Interceptor sewers of varying  capacity  together with storage and
          treatment facilities.

     Evaluation  of 32  alternatives for  collection system modifications
and  of  27 alternatives  for total  sewer system modifications  was made,
assuming all new  construction,  to  determine relative cost-effectiveness.   The
interdependent relations between flood alleviation  and pollution control in a
combined sewer system were described.

METHODOLOGY
     A suggested flexible methodology  has been developed which can be applied
for analysis and screening of many alternatives to determine the cost-effec-
tive  solution  for abatement  of  combined  sewer  overflows.   It  modifies  to
some  extent  the procedures  used in  this  study.    The methodology  did  not
develop a  "design  storm" for pollution control.   It  used a long-term,  con-
tinuous rainfall record and calculated runoff and quality characteristics  of
real  rainfalls  to determine the  relative effectiveness  of alternative
facilities.

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     The EPA Storm Water Management Model (SWMM) was used to:

     1.   design the many alternative systems for a common synthetic rainfall
          event (Figure D-5),  and

     2.   quantify relatively the quality and quantity of combined sewage for
          a broad  range of specific, lesser, synthetic  rainfall  events with
          varying patterns.

     The Corps  of  Engineers'  Storage,  Treatment,  Overflow  and Runoff  Model
(STORM) was used to  compare the  performance of  the various systems q-uantita-
tively with  respect  to pollution  abatement for a  12-year  continuous  period
of real rainfall events.  It determined:

     1.   the number of annual combined sewer overflow events;

     2.   the mass loading (weight) of pollutants discharged in the overflows
          for the different facilities considered;  and

     3.   the duration and quantity of the overflows.

     The study evaluated the effects of:

     1.   random rainfall patterns and intensities;

     2.   the  long-term and  shock  pollutional loads  from combined  sewage
          overflows;

     3.   varying  amounts, modes  of  operation,  and  locations  of  storage;

     4.   varying interceptor and treatment capacity;

     5.   peak flow equalization; and

     6.   rainfall patterns on pollutant concentration.

     The  SWMM RUNOFF  Block was  modified  to   include  design capability  in
sizing sewers.   STORM was modified  to extend its  use to  combined  sewage.

SIGNIFICANT FINDINGS

     1.   Capture  of  the  low-volume,  high-concentration  first  flush  from
          combined systems is essential for pollution abatement.

     2.   Annual discharges of moderate rainfalls contain more pollutant with
          higher concentrations  than do  discharges from  severe  storms.  The
          combined  sewage  discharges  of  moderate  rainfalls should be  con-
          trolled and treated for protection of the environment.

     3.   Storage of combined sewage should reduce pollutant concentration as
          a  result of  mixing  the  highly  polluted  first  flush with  later,

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          less polluted  flows.   Storage is  effective  in abating pollution.

     4.    If storage cannot be  provided,  diversion of  combined sewage flows
          of 17 or more times the peak dry-weather flow  for  treatment should
          result in significant  pollution abatement benefits.

     5.    A combined system can be designed to discharge less pollutant than
          a conventional separate system in which the storm  sewers discharge
          all urban runoff directly  to water  courses.

     6.    Providing  additional  storage  in a  combined   sewer  system should
          result  in the  least-cost  system  for pollution control.   This
          storage can be provided by enlarging the  size of  the upstream sewer
          reaches  if  site restrictions  result in costly  satellite storage
          basins.

     The  ability of  SWMM and  STORM  to  simulate the  pollutant components
reliably  in urban  runoff  and  combined  sewage is questionable.   This also
applies to all known presently  available models.  However,  the  "first flush"
phenomenon has been observed, as well  as the  substantial reduction in pollu-
tant concentrations after the "first flush".   Hence,  the  relative  quantifica-
tion of  pollutants, through  SWMM  and STORM,  offers  a   practical, available
measurement  by  which  alternatives  for  combined  sewage overflow abatement
facilities can be developed and evaluated.

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                          SECTION II

            SPECIFIC  CONCLUSIONS - CITY OF ELIZABETH



POLLUTION CHARACTERISTICS - COMBINED SEWAGE

1.   The magnitude of  pollution resulting  from  combined sewage  over-
     flows in Elizabeth  is indicated by:

     (a)  the probability  of  about  66  overflows of  raw,  combined  sewage
          annually, or about  one every 5 or 6 days;

     (b)  an average of about 60  percent  of the  raw sewage  entering
          the sewer system during the  overflow periods being  discharged
          untreated;  and

     (c)  the  concentration  of pollutants  in the initial  discharges
          possibly  being an  order  of  magnitude  greater than in  normal
          dry-weather flow.

2.   Combined  sewage generated  by  an "intermediate"  (typical) pattern
     storm  (peak rainfall  in  the  middle  half of  the storm  duration)
     exhibits  two  peak flushes  of mass pollutants.  The first,peak
     flush includes  the washout of  solids deposited in  combined  sewers
     from  sanitary  wastes  during  dry  days.  The second  peak flush
     includes  the washout of  street pollutants.   The first peak is  of
     low-flow  volume but high-pollutant concentration.   The second
     peak  is of high-flow  volume but low-pollutant  concentration.

     Combined  sewage generated by  an  "advanced"  pattern  storm  (peak
     rainfall  in the first  quarter of the storm duration)  exhibits
     only a single  peak flush.  When compared to  the peaks  of  an  inter-
     mediate "pattern storm,  this peak  has  less . flow  volume but  a much
     higher  pollutant  concentration than  the second  peak  and a  lower
     concentration  than  the first peak.

     With  either storm  pattern,  however,  the highest concentration  of
     pollutants occurs  early  in the storm.

3.   The mass  washout  of  combined sewage  solids from  an individual
     major  storm  (5-year  rainfall  return  frequency)  is greater than
     from  individual frequent rainfalls  (1.3 and  0.35-month  rainfall
     return frequencies).    However,  the  total pollution resulting

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     from frequent rainfalls is greater.   Rainfalls with an individual
     cumulative  depth of  less  than 25.4  mm (1.0  inch)  produce  about
     93 percent  of the total annual precipitation and about: 73 percent
     of the total pollutant  washout for the  year. A storm of 0.35-month
     (about 10  days)  return frequency,  which  has  a peak  runoff  rate
     about ten  times  the  average  dry-weather  flow,  should  cleanse the
     sewer of most solids  deposits.   Hence,  capturing runoff  from
     frequent  storms is essential for pollution control.

4.    A 5-year  return frequency rainfall may  be  expected to remove
     about 96 percent of the  total  suspended solids accumulated on
     streets; a 1-year rainfall,  87 percent;  and a 1.3-month  rain-
     fall, 35 percent.  However, except when  preceded  by a protracted
     dry period,  street washout  should  contain substantially  lower
     pollutant  concentrations than the  sewer   solids washout  since it
     usually  occurs at a  time when high  flow  rates  provide dilution.

5.    With  the synthetic 5-year  storm hyetograph used, treatment of
     essentially all pollutants  in  the  combined  sewage and street
     washout  would require capture for treatment  of  the first 90
     minutes  of  flow  from  the  storm.   Such  facilities  may  be justi-
     fied  only  where  the  receiving  water  requires  an  extremely high
     quality  discharge to preserve the environment.

6.    In  a combined sewer system,  the  lower the  flow  velocity  in dry
     weather,  the greater would  be the amount  of solids  deposit.
     Maintaining  or  creating  flushing velocities  in combined systems
     during dry  weather  should  provide  a  significant reduction in the
     pollutant concentration in the initial storm flush.

7.    Both  SWMM  and STORM provide  an  option with internally specified
     default  values  (see  TABLE  C-l)  for computation of  suspended
     solids (SS),  biochemical  oxygen  demand (BOD),  and coliforms from
     the mass of dust and dirt in the street washouts.  Use of the SWMM
     default  values results in SS and  BOD mass  discharges  about ten
     and  five  times,  respectively,  that  computed  using  STORM default
     values.

POLLUTION CONTROL POTENTIAL  - CONVENTIONAL AND  EXISTING COMBINED
SYSTEMS

1.    Flow  routing  devices  can be used to reduce the number of annual
     combined sewage overflow events.   When installed in  a  conven-
     tional combined  sewer  system, designed using SWMM for a synthetic
     intermediate pattern storm,  and having interceptor  capacity  equal
     to the peak dry-weather flow, reductions for Elizabeth  proved  to be
     as follows:

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2.
       Design Storm
         Return
        Frequency

       10 years

        5 years

        2 years
                         Reduction of
                           Overflow
                            Events

                              80%

                              65%

                             small
Mass Reduction
 of Overflow
  Pollutants

      75%

      55%

     small
The  ineffectiveness  of the  system designed with  a 2-year return
interval storm  in  abating  pollution results from the reduction in
volume  of  about 40  percent for storage  of  flows during a 1.3-
month storm.   Analysis of  real rainfall  events,  based  on a con-
tinuous  12-year record,  indicates  the  available  storage volume
would be exceeded  frequently,  substantially increasing the number
of overflow events  and the  mass of  pollutants discharged.

The  cost of sewer facilities  to prevent  flooding  from  a 10-year
return frequency rainfall  is about  25  percent  greater than from a
5-year  return  frequency rainfall.   Since less costly  means are
available in  the  design of  new systems to  reduce pollution from
combined sewage overflows  and  urban runoff, the use  of  a 10-year
return interval storm for  pollution control can not be justified.

Increasing   interceptor  sewer  size can reduce  the  number of  over-
flows and  pollutants discharged  in combined sewage overflows.
Based on analysis using actual rainfall events  over  a  12-year
continuous   period, the calculated relative amounts of  SS  and BOD
discharged   for various interceptor  capacities were determined.
The analysis assumed  no storage upstream of the interceptor.   The
results for  a drainage area of about 1.6 square  kilometers (1.0
square mile) are summarized as  follows:
Interceptor
Capacity
(Times Peak
Dry-Weather
Flow)
1.0*
3.8
6.2
8.2
Average Annual Overflows
Number of
Events
Longer than
1 Hour
65.8
40.3
28.5
18.5
Volume
(%)
100.
50.40
32.50
24.20
Relative
Amounts of Pollutants
SS BOD
(%) (%)
100. 100.
41.70 29.30
26.30 15.00
18.10 10.00
                               (continued)
          Conventional  design  capacity based on Harmon's Ratio.

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Interceptor
Capacity
(Times Peak
Dry-Weather
Flow)
16.5
22.3
23.1
26.8
59.2
151.7

Number of
Events
Longer than
1 Hour
6.6
3.8
3.5
2.3
0.2
0.0



Vo lume
(%)
8.90
4.30
4.00
3.30
0.04
0.00



SS
(%)
5.20
2.30
1.90
1.20
0.04
0.00



BOD
(%)
2.50
1.10
0.90
0.60
0.04
0.00
     The mass of  pollutants  discharged reduced at a  faster  rate than
     the volume  due  to greater capture of the initial flush.

3.   Where the  capacity  of  an existing combined  system  is  such as to
     result in  frequent combined sewage flooding, but where the  system
     is adequate  to convey  dry-weather flows,  and adequate  storage
     facilities  cannot be provided economically upstream,  it is  cost-ef-
     fective by  a large margin to divert urban runoff in excess  of the
     combined system capacity to. a  separate stormwater  system for the
     same level  of pollution  abatement.

4.   Based on data developed for Elizabeth, use of the Rational  Method
     to determine peak runoff rates results in values 30 to 60 percent
     less than  those obtained using SWMC1 for  a synthetic 5-year  return
     frequency storm (Figure  D-5).  In a separate study by the U.S. Army
     Corps  of Engineers at  Louisville, Kentucky in 1949  (33), peak
     runoff  rates obtained with the Rational  Method were  20 to 43
     percent less than those obtained  with  the Unit Hydrograph Method.
     Sewers  sized  in  accordance with such  values would not permit
     effective  use  of  flow control  devices for pollution  control
     because of  the  limited  storage volume available.

POLLUTION CONTROL -  ADVANCED  COMBINED  SYSTEMS

1.   Storage of wet-weather  flows  in the collection system, either in
     the  pipe   (in-pipe)  or  in  storage basins  (satellite) ,  is  an ef-
     fective pollution' control method.    By mixing the highly pol-
     luted  initial  flushes  with the  later, less polluted runoff, the
     concentration of pollutants discharged in the untreated wastes is
     reduced.   By  reducing the peak  flow  rate,  more of  the waste
     can  be  diverted to  the  interceptor and subsequent treatment.  The
     following  presents  the SS  diverted  to  treatment for the various
     synthetic  storms  selected  with  varying  amounts'  of  storage (also
     see  TABLE  9):

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       Rainfall
       Return
       Frequency

       5 years

       1 year

       1.3 month
0*

0

0

0
SS Diverted in Percent

     9.4*         17.0*
     34

     37

     55
37

46

56
41.3*

 51

 78

 91
     * Storage in percent  of  5-year  synthetic storm runoff volume. The
     pollution control  benefits  increase  with  the amount  of  storage
     provided and with a shorter return interval  storm.

2.   In a combined  system,  upstream  storage  reduces the size of trunk,
     interceptor  and  treatment  facilities.   For a  1.6-square-kilometer
     (1.0-square-mile)  area in Elizabeth,  about  99  percent of the
     pollutants that would  overflow from a conventional combined system
     could be captured  for  treatment  with  storage  equal to 9.4 percent
     of the  5-year  synthetic storm runoff and  an interceptor capacity
     of 17 times peak  dry-weather  flow.  If the storage is increased to
     41.3 percent,  the  interceptor capacity could  be  reduced to  about
     four times peak  dry-weather flow for the same amount of capture.
     With 41.3 percent storage  and  interceptor  capacity  equal to the
     peak dry-weather  flow,  (the conventional capacity), about 95
     percent  of   the  pollutants  should be  captured  for treatment.
     Storage for pollution  control provides  flood  protection  as  a side
     benefit.

3.   The manner  of  flow routing through  storage influences  both  costs
     and the degree of pollution control achieved.   If upstream storage
     is bypassed  until the  downstream  trunk sewer capacity is exceeded,
     interceptor  and downstream  storage  and  treatment  capacity  must be
     much larger  for a  desired  pollution  abatement  goal as compared to
     the facilities  required if  all  flow is routed  through upstream
     storage.   For  a  given facility,  bypassing upstream storage basins
     until the trunk  sewer capacity  is reached  would  result  in lowest
     operating costs,  but  routing all  flow through  upstream  storage
     basins  would result in greatest  pollution  control.   The preferred
     method  of operation might consider bypassing upstream  storage until
     interceptor  capacity is exceeded.

THE "NORMALIZED HYDROGRAPH" - A  PLANNING AID

1.   For a  given rainfall  pattern,   the  primary factors  defining the
     outflow hydrograph of  a  combined drainage  system  serving, an  urban
     environment,  are  area  and  percent imperviousness.   The  area
     influences peak  flow   reduction  and  time of occurrence.   Percent
     imperviousness  affects  flow volume.   Within  reasonable  ranges of
     area and  percent  imperviousness, the shape of  the hydrographs is
     sufficiently  similar  to  permit  development of   a  family  of

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     "normalized hydrographs" whose ordinates are  defined by  a percen-
     tage of  the peak runoff  rate and whose area is measured in seconds.
     The volume of  runoff of a storm event  may be  determined by  a
     simple computation  (as  in STORM).   The  runoff  at each  ordinate
     then is determined  so  that  this volume is obtained.   These ordi-
     nates provide an adequate  representation of the hydrograph from the
     given area for flow  routing through an interceptor. This concept is
     an aid  in reducing  the amount of  segmentation  required and  the
     costs for  planning.
COSTS

1.
     The amount  of  in-pipe  storage  which may  be  provided is  limited
     by cost since:

     (a)  The incremental unit cost of in-pipe storage volume  increases
          with sewer size (Figure 15),

     (b)  storage resulting  from  a  large increase  in sewer  diameter
          should be  more costly per  unit of volume  than for  a  rela-
          tively small  increase,

     (c)  pipe storage in the  smaller  lateral sewers  provides  not only
          lower costs  for  in-pipe storage but  also  permits  reduction
          in the size of  the  more costly trunk sewers, and

     (d)  satellite (off-line)  storage,  which is  located  so as  to
          reduce trunk sewer sizes,  would probably be a cost-effective
          alternative  since  its  cost  per unit  of  volume  may be  as
          little as  30  percent  of in-pipe  storage. .

2.   Storage to reduce  costs  should result  in:

     (a)  reduction  of the peak  flow of  the outflow  hydrograph  to  the
          extent practical  and  economical,

     (b)  the multiple peaks of  the  hydrograph  being relatively equal,
          and

     (c)  reduction  of the  concentration  of  pollutants  in the initial
          peak by dilution.

3.   Comparative costs  of  the  alternative  collection systems  con-
     sidered are as  follows (TABLE  11,  TABLE 12):

     (a)  a  conventional combined  system  should  cost  about the same as
          separate  systems  when  surcharge  of the  separate  drainage
          system is  permitted,

     (b)  the  combined system  permitting  significant overland drainage
          flow is the least cost  conventional system,
                                  10

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     (c)   separate systems  in which  surcharge  of  the  storm  drainage
          system is not  permitted are most costly,

     (d)   surcharge of  a  separate  storm drainage  system  reduces
          costs  by about 20 percent,
its
     (e)   in the  case of  the  City of  Elizabeth storing about  eight
          percent  of  the 5-year  synthetic storm runoff  volume  in
          the upstream  lateral system  results  in  the  least  cost  for
          in-pipe  storage systems since the  increased  cost of  the
          lateral  sewers  is more than compensated by the reduced cost of
          trunk  sewers.    However,  the  increased  cost  resulting  from
          doubling or tripling  the  amount of  storage in  the laterals is
          relatively  small,

     (f)   if satellite storage basins  can be built at  low cost,  about
          $0.08  per  liter  ($0.3 per  gallon),  the least-cost collection
          system results  from  storing   about  17 percent of  the  5-year
          synthetic storm runoff volume,  and

     (g)   if satellite storage  is  costly, about $0.26  per liter  ($1.0
          per gallon), the cost of  the  collection system increases with
          the increase in storage volume.                           '

4.   Comparative   costs  of  the alternative systems  considered  for
     control of  urban runoff  and  combined  sewage  overflows  from  the
     entire City,  assuming essentially  complete  capture  (92% using  the 5
     year synthetic hyetograph) of pollutants in both sewage and  urban
     runoff for  treatment,  are:(TABLE 19  and Figure 29)

     (a)   Where  the  cost  of  off-line storage is high,  $0.26  per  liter
          ($1.0  per  gallon),  and   in-pipe  storage  cannot  be provided,
          separate sewers would be  more  economical than combined sewers.
          However,  where  the  storage  cost is  low,  $0.08  per liter  ($0.3
          per gallon), the combined system is more economical.

     (b)   The amount   of  in-pipe storage  that  may be optimally provided
          is about 30 percent of the runoff  developed using  the  5-year
          synthetic storm hyetograph with the assumed range  in cost of
          off-line (downstream) storage.      ,

     (c)   The conventional  separate  system  would  be  the most  costly
          choice if  storage  (off-line  or satellite)  can be  built  at  a
          cost of  $0.08 or less per liter  ($0-30 per gallon).

     (d)   At a  satellite  storage  cost  of  $0.26 per liter  ($1.0  per
          gallon), the  conventional  separate system would be more
          economical   than any  alternative  advanced  combined  system.

     (e)   In all instances,  the advanced combined  system  offers  advan-
          tage over the conventional system.
                                  11

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5.   The least-cost  system  for essentially complete  control  of  pollu-
     tants from   urban  runoff and combined sewage  is expensive,  being
     estimated at  more  than  $114,000 per  hectare  ($29.5 million  per
     square mile)  (ENR Construction Cost Index equals  1800).

6.   The  criteria of  removing essentially all  pollutants from  urban
     runoff  and  combined sewage overflows  is economically imprac-
     tical.  Capturing  about  97.5  percent  of  the wet-weather BOD  for
     treatment,  rather   than  substantially 100  percent,   would  reduce
     costs of  the overall system by  about 25 percent.   Hence,  alter-
     native  criteria were  explored  which  would result  in  acceptable
     pollution control at a more  reasonable cost.   These_ are tabulated
     below:
        Description

             A
             A
             B
             C
             A
Interception
   Rate
 % of Peak
    DWF

    380
   2310
   1380   .
    220
    100
                                              Pollutant*
                                               Capture
58
98
98+
98
 0
   Cost
$/Hectare

  79,000
  96,000
  90,000
  80,000
  75,500
A.   Conventional combined system.

B.   Conventional  combined  system with flow routing to utilize  storage
     capacity available in sewers during normal rainfalls.

C.   Advanced combined system with about 40% in-system storage.

*    With  respect to  SS  overflow  from  a conventional combined  system
     with  intercepting rate equal to peak dry-weather flow.

     A conventional combined system,  without  provision  for pollu-
     tion  control,  would cost about $75,500 per  hectare  ($19.6  million
     per square mile).   Upgrading this system by  increasing  interceptor
     capacity from 1.0 to 3.8 times peak dry-weather flow would increase
     costs by about  five  percent  but provide about 58 percent pollutant
     capture.   Increasing interceptor  capacity,  only,  to obtain  98
     percent pollutant capture  would  increase base costs  by about ^27
     percent.    Using  a  conventional  system with flow routing  and  in-
     creased interceptor capacity  to  obtain a pollutant capture  of  98
     percent would increase  the base  cost by about  20 percent.   If
     in-system  storage equal to about  40 percent of  the 5-year synthetic
     storm runoff can be provided,  98 percent  of the annual pollutants
     in the combined wastes should be captured with an increase of base
      cost  of about  seven  percent.

     The  cost  of providing pollution  control  by  in-system  storage
                                   12

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     and flow control  devices  for  urban runoff and  combined  sewage  is
     quite small  when considering the  overall investment  in  sewerage
     systems.

7.   The optimum  cost  relation between off-line  storage  and  treatment
     capacity  depends  on the  degree  of treatment required.  If  simple
     processes such as  micros training will suffice,  the  cost  of  addi-
     tional storage would  about  balance the cost  of  reduced  treatment
     facilities  so  that  the total  cost is  about the same within  any
     reasonable  range (TABLE 19).   Should  more sophisticated  treatment
     be required,  larger storage and smaller treatment facilities  would
     afford greatest economy.

ADDITIONAL HYDRAULIC STUDIES

1.   Overland flow can  be  adequately  modeled by retaining only  the
     bottom slope  and friction  slope  terms  in  the  complete  momentum
     equation  (Kinematic  Wave Model).

2.   Simulation  of pipes in urban system may  require  that the gravita-
     tional and convective  acceleration terms  be retained, as done  in
     the  SWMM TRANSPORT Block  over   individual  pipe segments.   These
     terms will  introduce  dynamic effects  which  exist in  urban  sewer
     routing.

3.   In cases where backwater effect  (say,  near a  control structure)
     or surcharging  of  pipes  is  present,  it  is  inappropriate to  use
     the assumption that  the  pipe slope  and the friction slope  are
     equal.  Manning's equation can only be  used  in  these cases  if  the
     appropriate friction slope  is computed.   But in  these cases,  the
     friction slope depends  on flow conditions and  is  not known  in
     advance.  In  the absence of  such  effects, use of Manning's equation
     and assuming  friction  slope  equals  pipe slope, appears to  be  a good
     approximation in sewer  design.

4.   No detailed  comparison of  cost  reduction versus number  of  terms
     modeled  for  the momentum  equation  has  been  published.   Most
     evaluations and  comparisons have  focused on overall  differences
     between  models and not on a  comparison of the details of  the
     solutions to  the  basic equations.   However, models  which include
     more  than  the  bottom  and  friction slope  terms would increase -the
     cost  of  computer  use.   These "full equation" models need be used
     only when extreme accuracy can be justified.

     However,  other factors  such as  inaccurate  rainfall  data,  inaccu-
     rate  modeling  of control structures,  and the  modifications  used
     to model a prototype system with  a limited set  of model  elements,
     may  produce errors more significant  than those  introduced  by
     using a  simple  model  such as  the Kinematic  Wave Model which
     neglects the  gravitational  and  convective acceleration  terms
     in momentum equation.
                                  13

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                           SECTION III

                        RECOMMENDATIONS
The Rational  Method should be  used with  extreme  caution.   It  should
not be  used  for  systems  in  which controlled  routing  or storage  for
pollution control  is desired.

In  urban areas with relatively high  imperviousness,  combined  sewers
should be considered for  new development.

New combined sewers should  be designed  to maintain flushing velo-
city for dry—weather flows.

Urban  runoff  and  combined sewage overflow  pollution  control  should
be predicated on  containing  pollution from  the less intense,  frequent
storms rather than from intense  rare storms.

The storage  contained  in trunk  sewers of  a  combined  sewer system
designed with SWMM for a 5-year  or greater return frequency storm
hyetograph should  be exploited by  installing suitable  regulators  for
pollution control  of runoff  from  less  intense,  frequent  storms.   De-
velopment of  simple inexpensive regulators  for utilization of  in-pipe
storage is needed.

Upstream storage in  the collection  system (either  in—pipe  or  satellite)
should be required in new combined  systems and, where practical,  for  the
improvement of existing systems.

More reliable quantification of  runoff in urban areas would be  desirable
to  determine  absolute rather than relative quantities  of  pollutants
discharged  in urban  runoff   and  combined   sewage  overflows.    Further
investigations might include  street washout  mechanisms,  pollutant
constituents in dust and dirt,  and  the  contribution  of  solids  deposits
in combined sewers to BOD loading.

Based  on computed data,  control  of first flush pollutants appears
to be a better criterion  for Elizabeth than  control of the  total mass of
pollutants.

To  achieve pollution control benefits from  controlled  routing  in
Elizabeth,  design  based  on  a  5-year  return interval  synthetic  storm
                                14

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hyetograph using SWMM can be justified.  Use of a 2-year return interval
storm largely forfeits the benefits of  flow routing,  and the additional
storage obtained from using a 10-year  return interval storm may be more
economically achieved by satellite basins.
                                 15

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                                SECTION IV

                               INTRODUCTION
     Concern with  storm  runoff  primarily has  considered  street and  base-
ment  flooding.   Sewers  were installed to correct such problems.  With
recognition of  the pollutants contained  in  storm runoff,  reduction of  the
amounts of  pollutants  reaching natural  water  bodies has become  a  signifi-
cant  factor.   The pollution  load placed on  a stream  or  other receiving
waters by  combined sewer overflows  is  substantial.   It has  been estimated
in a  study  conducted at  Northhampton,  England,  that  the total pounds of  BOD
contributed yearly  to  receiving  waters by storm  generated  overflows may be
equal to about  15  percent of the BOD in  the dry-weather flows  (1).  A U.S.
Environmental Protection Agency (EPA)  funded  study in Durham, North Carolina,
resulted in similar findings (2).

     The earliest  sewers were  built to  convey stormwater  runoff.  They
were  converted  to  combined sewers in  later  years as waterborne wastes were
discharged  to  them.   Subsequently, the  use  of  combined sewers became  wide-
spread.  A  nationwide survey by the American Public  Works Association  (APWA)
indicated  that  drainage areas totalling  over  1,214,100 hectares (3,000,000
acres) in more  than 1,300 municipalities and a population of  54 million are
served by some  875,000 kilometers  (550,000 miles) of combined sewers. Of the
641 jurisdictions surveyed, 493 reported  about  14,200 combined sewer overflow
points.   Three hundred  and forty reported infiltration problems during
wet  weather and  96 indicated combined  sewer  overflows during  dry weather
(3). The cost of sewer separation in the  U.S. has  been estimated at about $96
billion  in 1974  (4).   The  merit  of  sewer separation  has  been argued with
respect to  effectiveness in storm runoff  pollution abatement (4).

      Elimination  of all  pollution from wet-weather flow  could be  prohibi-
tively  expensive.   There  is,  however,  an optimal  level of expenditure for
pollution  control that  should be justified  by environmental  benefits.   To
enhance  the urban  environment and to  conserve water  and  other resources,
the design  of either combined or separate sewer systems  should:

      1.   provide  sufficient  relief  of  street  and basement  flooding  from
          urban runoff or combined sewage,

      2.    limit pollution from  municipal wastes  and urban  runoff  that may
           enter natural waterways  to  an acceptable  level that  will not
           adversely affect the environment, and
                                      16

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     3.   be economically feasible in context with society's needs.

     Alternatives for the alleviation of  street  flooding include:

     1.   gutter inlets and collection sewers of adequate capacity to collect
          and convey the defined peak urban  runoff,

     2.   storage basins for the  containment of urban runoff  to reduce peak
          flow entering or flowing in sewers,

     3.   a  combination  of collection sewer  capacity and  in-pipe  storage,
          and

     4.'   source control, including porous pavement  to  reduce runoff volumes,
          and roof detention or ponding over designated areas to reduce peak
          flows.

     Alternatives  for pollution control  in  the  natural  waterways  from
wet-weather flow include:

     1.   increased interceptor  and  treatment  capacity to  convey  and treat
          wet-weather flows before discharge,

     2.   off-line storage for equalization of  the treatment rate and reduc-
          tion  of  capital  investment in interceptors  and  treatment plants,

     3.   in-pipe  storage  for  containment   of  pollutants  in runoff  and  for
          modulating the runoff  hydrograph of flow to  the interceptor system,
          and

     4.   source control,  including  sewer  flushing  to reduce solids deposit
          in sewers=,  street sweeping  to  reduce  the  pollutant washout and/or
          porous pavement to reduce the runoff quantity.

     The alternatives for alleviation of  urban flooding and for urban runoff
and  combined  sewage  pollution  abatement  are  interdependent.   The  upstream
sewer  facilities  planned for  flood  control determine the character  of  the
flow  hydrographs  and  pollutographs  reaching  the  downstream  interceptor,
storage  and treatment facilities and impacting on  the  receiving  water.
Upstream  storage,  source  control  or  other quantity   control measures  have
potential benefits  in both pollution and flood control.   A  plan  for a com-
munity-wide sewer  collection  system should include optimum  exploitation of
those benefits.

     The  complex nature of the  urban rainfall/runoff and the pollutant
accumulation/washout/transport  processes, and  evaluation  of the many manage-
ment  alternatives  have  made  use  of  computer  models advantageous.  Tradi-
tionally,  storm  sewers  are  designed  using the Rational  Method.    It
provides an estimated  peak  flow  but  not   the  runoff  hydrograph  and
                                     17

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pollutograph needed for the  evaluation of runoff pollutants and the design of
facilities  for  their  control  and treatment.   Several  more recent  design
nethods for drainage systems have  been proposed (5,6,7). These methods  employ
nonentun equations for computing unsteady storm runoff in overland catchments
and in  sewers  and  utilize  the  micro (fine discretization)  approach  in  the
application of  hydrologic and hydraulic theory.

     This  study was  undertaken  to analyze  the  effects  of  alternatives
available  for  the  design of sewer  systems  considering  both pollution  and
flood  control.   The  alternatives  were analyzed for  the urban area  of
Elizabeth, New Jersey, but  the principles and  general  conclusions  should be
applicable to other urban areas.
                                    18

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                                   SECTION V

                       OBJECTIVES AND SCOPE OF THE STUDY
     This study compares:

     1.   sewer system  design flows  using conventional  and  advance hydro-
          logic and hydraulic methodology,  and

     2.   the cost-effectiveness  of

          (a)  a conventional separate storm and  sanitary  system,

          (b) -a conventional combined system,  and

          (c)  advanced  combined systems  with  varying  amounts  of  in-pipe
               and/or satellite storage and controlled  flow routing.

     The  cost-effectiveness  comparison was initially  based on  achieving a
very high standard  of  pollution  abatement.   As  the study  progressed,  it
became apparent that to provide an. effective basis for  evaluation of alterna-
tives  for pollution  abatement,   the  scope required  extension  to evaluate
facilities for  less complete, but  acceptable, pollutant  capture for treat-
ment.

     The  components of  a  sewer  system include collection  sewers,  storage
(both  in-pipe  and  satellite)  facilities  in  the collection  systems,  inter-
ceptors,  and downstream  off-line  storage  and  treatment facilities.    New
systems were  assumed  to  provide  a  uniform  basis of comparison  between
the  alternatives  and permit  application  of  the findings to  other  cities.
However,  the study also includes the case  (applicable to Elizabeth and
other cities) in which  the  existing system can be  used as a sanitary system
and  a  new storm system provided  for  pollution abatement  and alleviation of
combined sewage flooding.

     The scope of  the study  includes:

     1.   comparison of sewer design equations,

     2.   review and selection  of mathematical models  for evaluation of
          alternatives,

     3.   development of synthetic storm hyetographs, hydrographs and pollu-
          tographs,
                                     19

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 4.    alternative  sewer  designs  at  a master  planning  level  for  Drainage
      District A  of  the  City of Elizabeth, with an area of  265  hectares
      (655 acres),

 5.    economic evaluation  of the  alternative  designs for Drainage
      District A,

 6.    development  of  quantity  and quality parameters  for application  to
      the entire City,

 7.    design  of  interceptors  and  downstream  facilities for  pollution
      abatement,

 8.    cost-effective comparison of the  alternative  systems for  the
      entire  City,

 9.    determination  of  the facilities required to provide an acceptable
      level of pollution abatement,  and

10.    the development of  a methodology  for planning facilities  for
      pollution abatement.
                                  20

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                                  SECTION VI

                           DESCRIPTION OF STUDY AREA
     The  City of  Elizabeth,  New Jersey (Figure 1) encompasses a  total
urban  area  of  about  1,780 hectares  (4,400 acres) and  has been divided
into 25 drainage districts for planning sewerage improvements.  The existing
sewers  are  largely combined.   Approximately  90 percent,  by  length,  of the
sewers are from 50 to  100 years  old, and  the  expected deterioration in their
condition has  occurred.   This  is evidenced by  occasional sewer collapses,
joint  deterioration,   and  physical inspection  when  sewers  are  exposed  in
excavations.   In  1973,  the base sewage flow  in the  City  was estimated
as follows:
              Flow Category

              Residential
              Commercial
              Industrial
              Municipal

                    Total
Amount (mgd)

 6.5
 1.1
 3.4
 0.6

11.6
     There are  37  points in  the  system at which  combined  sewage overflows
to natural water  courses during wet weather.   In  1973,  the principal over-
flows on the Westerly Interceptor discharged combined sewage during 61 storm
events while the principal  overflows  on the Easterly Interceptor discharged
sewage during  44 storm  events.   Discharges  from the  Westerly  Interceptor
entered the Elizabeth River  while  those  from the Easterly Interceptor entered
the Peripheral Ditch around Newark Airport,  the Great Ditch, Newark Bay,  the
Arthur Kill  and the Elizabeth River.   Overflows  during  dry weather  were
experienced at Westfield Avenue,  the upstream terminus  of the Westerly
Interceptor.   These  overflows may extend for  about 18 hours per  day and may
be the  result of  a blockage  in  the Westerly  Interceptor  or of  very  high
infiltration in its  tributary  area.

     Average infiltration in  1973 was  estimated  as  0.28 m3/sec  (6.4 mgd),
or about 8.7 million m  (2.3 billion gallons)  per year.   Infiltration
equals about  55  percent of the average dry-weather flow and indicates  the
deterioration of the system' with age.   Excluding dry-weather discharge  of
wastes at Westfield  Avenue, the total amount  of infiltration jirom Elizabeth
treated at  the Joint Meeting  Plant  was about  7.6  million
gallons) in 1973.
          m
(2,0  billion
                                     21

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                                                               EASTERLY
                                                              INTERCEPTOR
      WESTERLY ,
     INTERCEPTOR
   JOINT  MEETING  i
       PLANT
           Figure 1,   Study  area,  Elizabeth, New Jersey
                                   22

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     Because the  increased  infiltration,  as  noted in  other studies,  is
 coincident  with peak  inflow  rates,  the  amount of  inflow treated  in  1973
 was  only about  1.9 million  m  (500 million  gallons)  per year.   Assuming
 an  average  number of about  60 events per year  during which combined sewage
 overflow  occurs,  t|ie average quantity of inflow accepted  to the Plant would
 be  about 30,300 m   (8  million gallons) per event.   The  quantity  of wastes
 discharged'  as  untreated combined  sewage during  1973,  including  the  dry-
 weather  Westfield Avenue  discharge,  is  estimated  at about 7.6 million  m3
 (2.0 billion gallons).   Approximately  80 percent  of  this  discharge entered
 the Elizabeth River, with the remainder discharging to the Arthur Kill, Great
 Ditch, Peripheral  Ditch and Newark Bay.   Since such  discharges  can contain
 significant  quantities  of  pollutants,  including  oxygen demanding substances,
 suspended solids and coliforms, they exert an adverse environmental effect on
 the receiving waterways.  The inadequacy of the existing system also resulted
 in frequent  flooding of  streets and cellars  with combined sewage.  Hence,  an
 environmentally  effective solution  for  correction  of  the Elizabeth  sewer
 system requires:

     (1)   a  reduction of infiltration, and

     (2)   alleviation  of the  overflows and  street and  cellar  flooding  by
          combined sewage,

 to the extent justified as cost-effective.

     Detailed studies were made in Drainage  District A (Figure  1) to develop
 criteria for water quality management  for the entire City.   The  drainage  area
 contains  265 hectares  (655 acres); with  47  hectares  (115  acres)  located  in
 Rosalie Park; 2  hectares (5  acres)  in Union and the  remainder  in Elizabeth.
 The area  is  largely developed for  residential use (about  90 percent),  with
 some neighborhood  commercial  (about  5 percent) and  small  industrial areas
 (about 3 percent).   It  includes most  of  the  northwest  region of the City and
 is served almost entirely by  combined sewers.  Dry-weather flow from most  of
 the District is  conveyed to  the Westerly  Interceptor which generally follows
 the course of the  Elizabeth  River.   Part of the District,  generally west  of
 Elmora Avenue and south  of Park Avenue,  is served  by  the Joint  Meeting Trunk
 Sewers, which traverse the District.  Dry-weather flows  and limited combined
 sewage flows are  treated at the'Joint  Meeting Treatment Plant, located
 east of  Bayway  Avenue  and north of South  First  Street in the City.   Excess
 combined  sewage  flows discharge to  the  Elizabeth River.    The existing sewer
 system in the District is badly undersized and six areas  flood  with combined
 sewage at almost every  significant  rainfall.   A preliminary design has  been
prepared  for  a  separate drainage system  to  relieve  the overloaded combined
 system.  This system provides for  the  drainage  of the  six frequently flooding
areas plus  other low  spots,  and for  the separation  of  urban  drainage and
municipal wastes.   A storm drain  is  not provided on  every street, but re-
 liance is placed, wherever possible without detrimental effects,  on overland
flow for  the collection of urban  drainage.

     The population of  the City  is  close  to  saturation and  is  expected
 to have  only a  moderate future growth.   Inadequacies  in  the existing sewer
                                     23

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system result  in numerous complaints  of  street and  basement  flooding and
of pollution  in the Elizabeth  River.   Secondary  treatment  facilities are
now under  construction  at the  Joint Meeting Plant.   These  facilities are
designed to provide  secondary  treatment  for a  nominal  average  flow of 3.3
m  /sec  (75  mgd)  of which  0.9 m /sec (20 mgd)  is  assigned  to
Elizabeth.    By  installation  of a  low head effluent  pumping  station, the
plant  would,  during  wet  weather,  hydraulically provide  secondary treat-
ment  for flows  of up  to 7.9 ja. /sec (180 mgd)  and  primary treatment for
flows  between  7.9 and 9.6 m /sec  (180  and 220 mgd)  at all  tide eleva-
tions.   The City has  allocated to it,  a peak  wet-weather flow  capacity
of 1.8  m /sec (40 mgd).   The  Corps of Engineers  has also planned a  diked
storage area,  with a total capacity  of about 80,000  m  (21 million  gallons)
along the Elizabeth River  near the Joint Meeting Plant.

     The Elizabeth River  is  tidal from its  mouth  at Arthur  Kill for  about
4,900 m  (16,000 feet)   to  the  Penn-Central Railroad.   The river is small,
draining only a total of 60 square kilometers (23 square miles) at its
mouth.   The analysis of  the  flow  records at Westfield Avenue,  about  5,500
m  (18,000 feet)  upstream  from the ..mouth indicated  the 7-day, 10-year return
interval low flow to  be 0.21 m  /sec (4.8 mgd).   Samples 'taken during
slack periods  at both low and high tides  showed the river was polluted  below
the location of combined sewage  overflow outlets.
                                    24

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                                  SECTION VII

                              SUGGESTED METHODOLOGY


REQUIREMENTS TO BE MET

     The need to evaluate  the  effects of:

     1.   random rainfall  patterns and intensity,

     2.   the  long-term  and  shock  pollutional loads  from combined  sewage
          overflows,

     3.   varying  amounts,  modes of  operation,  and  locations  of  storage,

     4.   varying interceptor  and  treatment capacity,

     5.   peak flow equalization,  and

     6.   rainfall patterns  on pollutant concentration

to  develop  cost-effective  facilities  for  combined  sewage overflow  pollu-
tion abatement  is apparent.   This  need  arises from  the following  under-
standing  of combined  sewage pollution characteristics as developed for
Elizabeth:

     1.   Approximately  three out  of four storms  have peak rainfall  rates
          during the  last  three quarters of the rainfall period.   Such  storms
          exhibit two peaks  of  mass pollutant washout.   The first peak is
         .of high-concentration,  but  low-flow  volume, and  the second of low-
          concentration, but high-flow volume peak.

     2.   The remaining one  in four storms have the unusual pattern with peak
          rainfall rates  occurring  in the first  quarter of the rainfall
          period.   Such storms have only one peak with the maximum SS concen-
          tration about  one order of magnitude less than the first peak of
          the usual  storm  pattern, but  a substantially greater volume.

     3.   Most of the pollutant washout in the first peak of all  the usual
          pattern  storms,  and  in the  frequent return interval, unusual
          pattern  storms,  results  from solids deposition in  the sewers
          during dry weather  and is dependent  upon the dry-weather  sewage
          characteristics.
                                    25

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     4.   Significant amounts  of  street pollutant  washout  occur with  more
          intense storms  than  those causing the  severe  pollutant discharge
          from sewer solids deposits.  Urban runoff, therefore, is generally
          lower in pollutant concentration  than  the first  flush of  combined
          sewer flow.
     5.   Every one or two weeks,  on  an average,  a rainfall can be expected
          to cleanse essentially all  dry-weather  solids  deposits in sewers.

     Hence, capturing  for treatment  combined  sewage generated  by  ordinary
rainfalls is the primary  requirement for effective, combined sewage pollution
abatement.

     The variables  that  affect the pollutants  contained  in combined sewage
overflow resulting  from  average rainfalls  are  many  and  complex.   The most
significant are


     1.   Time of day when rainfall occurs.   Combined sewage  generated  by a
          rainfall between 3  and 6  a.m.  will contain relatively small amounts
          of  low-strength  municipal   sewage,  (excepting  pollution  from dry
          x^eather flow  solids deposit) and hence will be weaker than combined
          sewage generated by the same amount of rainfall between noon and 2
          p.m., when the  greatest  amounts  and  higher strengths of municipal
          sewage are usually  experienced.

     2.   Day  of  the week.   Municipal  sewage is usually stronger  and of
          greater volume  on weekdays than on Saturdays, Sundays and holidays.

     3.   Sewer  slopes.   The flatter  the  sewer slope,  the lower  will be
          the  velocity of dry—weather  flows  and the more solids  will be
          settled and later resuspended  and  discharged in  the combined sewage
          overflows.

     4.   Rainfall pattern  and intensity.  The overflows from storms of
          frequent return  interval contain  a  higher  concentration of pollu-
          tants than do the greater storms.

     5.   Period since  last rainfall.   The  amount of pollutants deposited in
          sewers increases with the duration of the antecedent dry period as
          does the street pollutant accumulation.   There are large masses of
          data existing in the  literature indicating pollutant concentration
          for  various  combined  systems  and rainfall  amounts.   Much  of the
          available data has  not been correlated,  because the nature of the
          phenomenon may not  have  been  fully  understood,  and all the neces-
          sary information may not  have  been obtained. (10,15)

     The  selection  of a  "design storm"   or  a series of "design  storms"
would  not  assess  adequately many of  the significant  pollutional aspects
of  combined sewage overflows.   Hence,  development of a  "design storm" for
                                     26

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pollution control is not a viable approach.   A long-term (12-year)  continuous
rainfall record  and calculated runoff and quality characteristics, based  on
STORM  default  values,  were used  in this  study to  determine  the relative
effectiveness of alternative facilities  for  pollution abatement.

METHODOLOGY OUTLINE

     A practical methodology has  been developed in this study for the anal-
ysis required  to determine cost-effective sewer systems  in urban areas for
combined sewage  overflow  pollution  abatement.   The  following  outlines the
tasks of the suggested methodology:

     1.   Delineate the  drainage  districts  of  the  study area and select  a
          typical drainage district  for  detailed analysis.

     2.   Prepare data for the  typical district  for input  to  computer models.

          This  would include:

          (a)   The existing  long-term  (10-year)  precipitation and  air
                temperature data  applicable  to  the area  to  account  for the
                random nature of  rainfall  events.

          (b)   Development of  synthetic  storms  of  1-month, 6-month,  1-year
                and 5-year  return intervals  to  determine overflow quantity
                and quality for  the various  alternatives for  pollution
                control.

          (c)   Subdivision of  the typical drainage district and development
                of  data  such as  land use,  street  length, population,  sewer
                network and sizes, and street sweeping practice for input to
                SWMM.

          (d)   Preparation of  district-wide data (land use,  population, area
                and street length, etc.) of all  drainage districts to develop
                the total combined sewage  flows  for the City.

          (e)   Development of  dry-weather flow quantity and quality includ-
                ing infiltration.

          (f)   Preparation of  cost  data, including  costs   of sewer  pipes,
                storage,  pumping stations, treatment, flushing, chemicals and
                regulators.

     3.   Evaluate  alternatives  in  the  typical  drainage  district  using
          computer  technology.

         This  would include:

          (a)   Field  sampling  and  calibration  of  computer  models  for both
                quantity  and quality of  combined sewage.
                                    27

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          (b)   Analyzing the capacity of existing sewer systems.

          (c)   Establishing  the characteristics of  runoff  quantity and
               quality  from the  existing  system for  various synthetic  or
               real storm events.

          (d)   Using  STORM and  SWMM  to evaluate the combined sewage  over-
               flows  pollution reductions  to be achieved by  various  alter-
               natives, including:

                 1)  upstream storage  either  in detention basins  or  sewers,

                 2) controlled  routing in sewers,

                 3) sewer separation,

                 4) sewer rehabilitation,

                 5) overflow containment,

                 6) overflow  treatment  with  and without  containment,  and

                 7) interceptor capacity upgrading.

          (e)   Comparing the  cost-effectiveness of alternatives.

          (f)   Developing  parameters  of runoff  quantity  and  quality (i.e.,
               normalized  hydrographs and pollutant loading for various land
               uses) for  application  to the  remaining  districts  of  the
               planning area.
     4.   Cost-effectiveness  evaluation  of alternatives  for the  entire
          planning area.   The "Effectiveness" and  "Efficiency" Indices may
          be used for scanning the various alternatives.
          Index" is obtained as follows:
             The "Effectiveness
               x BOD(mg/l)
x   Annual Overflow Volume (MG)
    Average Overflow Return Interval (Days)
          Physically,  it represents  the  relative quantities of pollutant mass
          per day in  the combined sewage overflows during overflow periods.
          The "Efficiency  Index"  is the product  of  the Effectiveness Index
          and the cost of the sewer  system  in dollar units.  These parameters
          also permit  development of the  optimum level of treatment beyond
          which effectiveness diminishes markedly with  increased cost incre-
          ments.

RESULTS ATTAINED

     The  methodology   develops,  for the  various   alternatives,  the  average
                                     28

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number of annual  overflows,  the  annual volume of combined sewage  overflows,
the duration of the overflows, and the  annual mass  of  BOD  and  SS discharged.

     Combined sewage  discharges  are, by  their  nature, a  severe  shock  load
on the receiving waters.

     The effectiveness of the various alternatives with respect to  mitigating
shock discharge  loads are  compared  using  the  "Effectiveness  Index".   The
logic for selecting the parameters which comprise  this  index  follows:

     1.    The longer  the return  interval between overflows,  the less should
          be the impact of such flows on the river system.

     2.    The impact on the river system would be  proportional  to the concen-
          tration of  pollutants  discharged  thereto.   Hence,  the  use of the
          geometric mean weights  the  effects of  both SS and BOD.

     3.    The total volume  of  overflow would also affect  the  river quality.

     The  lower the value of  the "Effectiveness  Index", the less  should
be the impact of combined sewage  overflows on the  receiving water.

     The  "Efficiency  Index"  determines the  most efficient alternative.   The
higher  the  "Efficiency Index",  the less  desirable  is  the  alternative.
The "Efficiency Index" is a measure  of  cost-effectiveness.   The relationship
of the "Efficiency" and  "Effectiveness" Indices should also be compared for
the various alternatives.  If Alternative A  has  a  lower "Effectiveness Index"
but a higher "Efficiency Index"  than Alternative  B,  it means  the incremental
work proposed to  achieve Alternative A may  be too expensive  and other alter-
natives should be explored.

SUPPORTING APPENDICES

     This report  contains  five appendices which provide background data for
the methods  used  in  this  study.   Appendix  A presents  the justification for
using SWMM  and  STORM.   Appendix B discusses modifications made to SWMM and
STORM.  Appendix C compares the differences  in the two  models with  respect  to
determinations of quantity and quality.  Appendix  D  describes,  in detail, the
required  data . for computer models,  including meteorological data,- the  syn-
thetic hyetograph development, sewer  network configuration, hydraulic proper-
ties and  land use of  District A for both SWMM  and  STORM,  discrete data, the
area  and land  use characters  for  the  remaining urban area  of  Elizabeth,
dry—weather flow  quantity, quality and  characteristics, and basic  cost data.
Appendix  E describes  the method  of calibrating  the  STORM runoff coefficient.
                                    29

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                                 SECTION VIII

           DESIGN AND COST COMPARISON OF SEWER SYSTEMS IN DISTRICT A
     Designs of  the three  types  of alternative sewer  systems  (conventional
combined, conventional  separate,  and advanced combined with  varying amounts
of storage)  were made for District A and respective costs estimated, assuming
new  sewer  systems.   The effectiveness of  the alternative sewer  systems  in
District A in  controlling wet-weather  flow  problems  (flooding and pollution)
were also  evaluated.   New  sewer systems were assumed in  the  evaluation  to
permit a uniform comparison and the transfer  of the  study findings to other
districts within the City and to other urban areas.        —

     The conventional separate  sewer system consisted  of  two  systems,  one  to
carry wastes  from  domestic,  commercial  and industrial  discharges  together
with such infiltration/inflow as must be anticipated,  and the second to carry
storm runoff.   There are no storage facilities  or flow regulators in either
system.   In  the sanitary  sewer  system,  almost every street  contains  a
sewer,  while in  a storm sewer  system,  street gutter and overland flow to the
maximum extent  practical is allowed.   Consequently, the  total  length of the
storm sewer  system is  shorter  than that of  the sanitary sewer system.   In
newly developing areas, where ponding for urban runoff can be provided, storm
sewer sizes can also be significantly reduced.

     In a conventional  combined system,  sewers receive both municipal waste-
water and  stormwater.    In  this study,  by  definition, flow  control devices
and/or  storage facilities  were not provided in  the  collection  system for
control of  combined sewage flow rates  and  quality.   Collection  sewers (in-
cluding laterals and trunks) were used for conveyance of both dry-weather and
wet-weather flows.   Combined  sewage flow rates  in excess of  the capacity  of
the  intercepting sewers  (which carry  flow  to storage/treatment  facilities)
overflow to  receiving  waters.   A combined  sewer system and a separate sani-
tary sewer  system  have the same  total length.   As  street  runoff normally
enters  inlets  located at the  downstream end  of a street, the sewer  in the
upstream reach of a sewer network  branch would usually carry sanitary waste-
water  only.   Consequently, the length of sewers carrying combined sewage is
less than  the total length of a separate  sanitary  system.  In  the case  of
District A,  about  40 percent  of the length of sewers  in the combined system
would  accept  only  sanitary sewage.    Modification of  the  combined  system
which permitted  the same amount of overland  flow  as  the separate system was
also evaluated.

     The advanced   combined sewer  systems  were  designed  to  provide various
amounts of  storage  for wet-weather flow  control.   Two types  of storage were
                                      30

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considered:  in-pipe storage and satellite storage.   In  in-pipe storage
systems, sewers are increased in  size to provide volumetric storage  in
addition  to  flow  conveyance.   Regulators  are  installed ,to  permit use  of
in-pipe  storage  to reduce  peak  flows,  thus  increasing the amount of polluted
runoff intercepted and later treated for equal  interceptor  capacities.
In-pipe  storage  has been  successfully implemented  in the  existing combined
sewer  systems  of Seattle,  Detroit,  Cleveland and Minneapolis-St. Paul.  The
storage  may be  incorporated  in upstream lateral sewers or  downstream  trunk
sewers or both.   In  this study,  in-pipe storage  was found to be  more econom-
ically located in upstream lateral  sewers,  as  will  be described more  fully
hereinafter.   There  is  only about  half the  volume in  the lateral  sewers
as in the larger size trunk sewers in a conventional combined system, and the
additional  storage  for both  pollution  abatement  and flood  control may  be
obtained  more economically  by  enlarging  smaller  size  rather  than  larger
size sewers.

     In  a satellite  storage  system,  collection sewers are designed  for flow
conveyance,  but  detention  basins  are located in the  collection  sewer  system
to reduce peak flows.   There would  be little volume  available in the  sewers
for storage because of the small volume in  the laterals and reduced size and
volume in the trunks.   The detention  basins could  be open, covered or tun-
neled  structures.    In  the   literature,  "satellite  storage"  is frequently
referred to  as "off-line   storage".    In this study, however, the term  "off-
line  storage" is  reserved for  flow  equalization  basins located  near the
sewage  treatment plant.    In  both   the conventional and  advanced  combined
systems,  off-line  storage  may be provided.  Satellite storage  can be con-
structed at any location within a drainage district  where  there is sufficient
flow  to  use it  effectively.   With   respect  to  the  city-wide sewer  network,
satellite storage  should   be  viewed  as  upstream as  opposed to  off-line  or
downstream storage.  There could  be several satellite storage structures  at
strategic locations in each of the  25 drainage  districts in Elizabeth.
The number  of  off-line storage  basins  would be much  fewer.  As  both in-pipe
and satellite  storages are located in  the collection  sewer system,  both will
be generally termed as "in-system" storage.

     Since the basic difference between  an  advanced and a  conventional sewer
system is the in-system  storage provided,  the sewer layout and  total sewer
length of the  two systems  are identical.  However,  the pipe  diameters differ
significantly.

DESIGN PHILOSOPHY

     The selection  of  the rainfall  event  or  events on  which  to  base the
design of a  combined or separate  system for urban runoff  is of  major impor-
tance, and  has,  too often, been  only  casually  addressed.   The  traditional
approach  has been to:

     1.   develop the  intensity-duration-frequency  curves for the   location
          under  study.   These  are  normally available from U.S.  National
          Weather Service  Technical  Paper No-s.  25 and 40  (37,38),  or other
          such sources.
                                     31

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     2.   select a return interval for which  it  is  desired to provide flood
          protection.   Typically,  a return interval of two, five or ten years
          has been used.

     3.   develop a design storm hyetograph from  the intensity-duration curve
          for  the selected  return  interval.   This  storin  is a synthetic
          rainfall  event  which may  be  based on meteorological  probabili-
          ties or  may  be an  envelope  storm which contains  within  a single
          event the depth—duration characteristics of all naturally occurring
          events likely within the chosen return  interval  (9)•

     4.   Use  the  intensity-duration curve directly  in situations  where  a
          synthetic storm hyetograph is not developed,  e.g., when the analy-
          sis  of  the  system  is  to  be performed using  the Rational Method.
          This use has  similar characteristics as an envelope event.

     During  the  past   five  years, as  use  of relatively  powerful computer-
based models such as SWMM has grown, users continued to develop the required
"design storm" input in  the  manner  described above.   However, the .increased
capabilities of the model compared to hand-computation techniques has led to
numerous questions concerning the "shape" of the design storm and the appro-
priateness  of  any  single  storm  for  the design of  the system.   The usual
questions are related  to the following  items:

     1.   Where  should the  peak of  the "design  storm"  be located?   The
          intensity-duration—frequency  curves do not include any information
          on  the  "shape"  characteristics  of  naturally  occurring  rainfall
          events.

     2.   What antecedent conditions  should be used?

At  the same time as  these  issues  were being  raised,  the developemnt of
the various  Water Quality Control Acts  has  forced  the designer to consider
quality  as  well as quantity  in  the design  of  a storm  sewer  system.   Only
recently has it been  appreciated that  the  return  interval  appropriate for
quantity control is  not appropriate for  the  elimination of the  typical
pollution-causing  discharge.   The runoff quality from  any event  is largely
a  function  of the  pollutant  which has accumulated  in the sewer  and on the
overland surface since  the  last rainfall  event.  The following  aspects
of storm selection now have been recognized:

     1.   Rainfall  rates  of  about 25-4 mra/hr (1.0. in./hr) are sufficient to
          washoff about 90% of  the pollutant from the surface  (6) .  Slightly
          lower  rates  will be  sufficient  for paved  surfaces,  while higher
          rates may be required to  cause significant erosion from non-urban
          areas.   Substantially lower  rates should  flush out  most sewer
          solids deposits.

     2.   Rainfall depths of between 5.1  and  12.7 trim (0.2  and 0.5  inches) are
          sufficient to  washoff  most  of the accumulated  pollutants  from a
                                     32

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          typical  urban  area.

     3.   Since the available pollutant is largely a function of the inter-
          vals between rainfall events, the distribution of  storms within the
          typical  year is significant.

     The majority of the  polluting overflows result  from small  events
(as  compared to  the traditional  design event).   Hence,  the  system must
be  able  to handle  the  hydraulic  design  storm  without excessive flooding,
while,  at the same time,  it must be capable  of  regulating the  frequent
rainfall  runoff which, if allowed to discharge  freely,  would result in
major pollution.  Several models  such as STORM were  developed  to  allow analy-
sis of the performance  of  the proposed/present  system  under  long-tern rain-
fall behavior.  These models employ  simplified hydraulics,  and  little or no
sewer  network  data,  and  can not  adequately estimate the  response  of  the
system to  the large storm event.    Rather,  they  serve as  a mechanism for
evaluating the type of control strategies which should be employed.

     The availability of both  SWMM and  STORM  provides the mechanisms  to
evaluate  both the  "day-to-day" and "rare-design-storm" characteristics
of  this system.   However,  the  inputs to the models must be  both compatible
and  representative  of  the rainfall  characteristics  of the  area.   For the
present study, the following  inputs were adopted:

     1.   The  continuous hourly  precipitation  data  at  the Newark
          International  Airport gauge was used as input to the STORM program.
          This location  is quite close  to the study area,  and  its rainfall
          characteristics are quite similar.   Rainfall data  for the 12-year
          period  from 1963 to 1974 was used, and was assumed to be uniform
          within the study  area.

     2.   A 5-year return  interval intermediate  patterns  envelope type
          storm hyetograph  was used as  the design  criteria for flood protec-
          tion for the City of Elizabeth.   The intensity-duration curves for
          Sandy Hook,  New  Jersey,  were  used as a basis  for the synthetic
          storm generation.  An  analysis of  the 12-year Newark  Airport data
          used, indicated  close  agreement  between  the intensity-duration
          curves for Newark and Sandy Hook.  However, the latter  was used for
          the development of  the hyetograph since  they  represent an analysis
          of  a much  longer period of  record than the 12-year  Newark data.

     It is felt that this  combination  of  rainfall  inputs can confidently be
used  to  design a system  which  is  capable  of  controlling  the pollutional
aspects of typical daily or  weekly flows, while at the same time providing
runoff control capabilities sufficient to handle the hydraulic  flows of the
5-year event.

     The synthetic hyetograph, as  developed  in  Appendix  D,  was  used to
design alternative facilities for  evaluation.   This type of hyetograph was
conceived in 1959 by the  senior  author after investigation  of  failures
resulting  with  drainage  structures   designed  using   meterological
                                    33

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hyetograph  (9)  or other methods.   The  total  rainfall precipitation repre-
sented in this hyetograph at any elapsed time should  about equal the histori-
cal  total  for  that  time interval,  and the total  volume of  runoff  may be
expected to  equal,  within reasonable limits,  the  total  for the interval at
the stated return period interval.  However, the actual rainfall intensities
for shorter  increments within  the selected time interval nay be expected to
vary  from,  and  be less  than, those  assumed  in  the  synthetic ,_hyetograph.
Hence, the peak flows  experienced will probably be less than flows computed
with the hyetograph.

     The magnitude  of  the difference between  the  flow rates obtained using
the  synthetic  rainfall  hyetograph  and  the  probable  5-year peak  runoff
flows is  influenced by the short  time  of  travel for peak runoff flows  from
the  upstream  reaches  to the  overflow point.   Previous  studies in
Elizabeth  (8)  determined that, for  93 drainage areas  containing  less  than
49 hectares  (120 acres)  each,  the time of travel  was  less than 12 minutes.
For District A,  the time  of  travel is  about  20 minutes.   Such  short times of
travel are  frequently  found in cities  with  populations  of about 100,000 or
less.  Based on analyses by others (9), the short increment  rainfall rates of
5—year storms of  various  durations would be as  follows, when expressed  as a
multiple of the increments of a 360-minute duration rainfall.
Time
Increment
(minutes)

   5

  10

  15

  20
         <
  30

  60

  180
Total Rainfall Duration (Minutes)
5 30
1.37 1.22
1.20
1.18
1.18
1.16
-
_ _
60
1.16
1.15
1.14
1.13
1.11
1.10
_
180
1.06
1.05
1.04
1.05
1.05
1.04
1.03
360
1.0
1.0
1.0
1.0
1.0
1.0
1.0
     Hence,  at the  point where  a  system would  be stressed  by a  5-ninute
peak rainfall rate, computations using the synthetic hyetograph, which
satisfies the  intensity-duration  curve at  each time  interval,  would  be  about
30  percent  greater  than that obtained  from the peak  5-minute  flow from  a
180-minute  duration storni.   By  extrapolation,  the  following  relations  with
respect  to  the  180^-minute  storm were developed  for reaches which would be
stressed by other time intervals.
                                     34

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                 Time
                 Interval (min.)
% Greater Flow from
Synthetic Hydrograph
                    10

                    15

                    20

                    25

                    30
        27

        24

        21

        18

        15
     It  is improbable that  a 5-year  return frequency storm  of  duration
equal  to  the  most severe flow generating time for each sewer reach would be
experienced every five years.   Hence,  the  synthetic  hyetograph chosen may
generate  peak flow rates  that are,  perhaps, 15  to  30 percent greater than
those  experienced,  although  the total  runoff volume  required  for design of
pollution abatement facilities should  be about right.  As demonstrated
hereinafter,  the use  of  the  180-minute  duration hyetograph  should permit
determination  of  the runoff volume  required to  develop  pollution abatement
facilities.

     The  design  philosophy and methodology  developed  in this study is based
on  a synthetic  hyetograph,  which reasonably establishes runoff  volumes
required  for  effective  pollution abatement  for  design of alternatives.   The
methodology permits determination of   the  effects  of  a wide  variation  in
storage volumes on  the  design  of facilities.  The alternatives developed are
tested using  a long-term continuous record  of real rainfall  events to deter-
mine  their effectiveness  for abatement  of pollution  from  combined sewage
overflows.   No  attempt is made  to  develop  a  design  storm or < storms  with
respect to pollution abatement.
.CONVENTIONAL COMBINED SEWER SYSTEM
Design

     The new conventional  combined  sewers  in District A were designed using
SWMM with  capacity to  convey  runoff from a 5-year  return interval, inter-
mediate pattern  synthetic  storm.   The combined sewer system layout is shown
in Figures D-8 to D-12.  The total  length  of the  system  is  32,308 m  (106,000
feet), of  which  19,397 m  (63,640  feet) carry combined  sewage  and  12,911 m
                                     35

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(42,360 feet)  carry sanitary sewage.   The sewers  carrying  sanitary sewage
are all 0.2 m (8 inches)  diameter.                                      >

     The total length of  lateral sewers conveying  combined sewage  (those pipe
elements numbered  less  than  300)  is  15,651  m  (51,350  feet) and  of trunk
sewers  3,746 m  (12,290 feet).   There are 139 designated lateral sewers
conveying combined  sewage and  31 trunk sewers in District A, with pertinent
pipe  elements  shown in  TABLE D-7.   These sewers  receive  runoff  from 279
subcatchments  with  subcatchment  characteristics  tabulated  in  TABLE  D-6.

     SWMM allows  routing rainfall runoff  in  sequence from overland  through
lateral sewers  and trunk sewers to  the outfall.   Lateral sewers were sized
with  the SWMM RUNOFF Block and  trunk sewers  with the SWMM TRANSPORT Block.
The design diameters of  the lateral  sewers  for  the  combined  system are shown
in TABLE 1 and  of the  trunk sewers  in  TABLE 2,  under 0 percent  in-pipe
storage.  Design diameters  for  the  advanced  combined system are also shown
for comparison and  later discussion.

     Two sets of design diameters are shown in TABLE 1 (laterals)  and TABLE  2
(trunks), for the combined system.   The lateral sewers were  designed  with two
methods of flow routing.   In both  cases, the  hydrographs of  the 5-year
synthetic storm from tributary  subcatchments  to  lateral sewers  (gutter and
pipes)  are  identical  and  are  computed with   the  SWMM RUNOFF  Block (up to
Subroutine  WSHED).   In  computing the set of  design diameters  for  lateral
sewers  not  in  parentheses, the  design flow was the  peak  of  the  inflow hydro-
graph developed by  adding the  inflow hydrographs  of  upstream pipes and  local
tributary  subcatchments  using  a  subroutine  derived  for  this  study.   The
design  flow, without  reduction  due to pipe storage,  was  assumed to  enter the
upstream end of the  pipe.   Manning's  equation was  used to compute  the re<-
quired  pipe diameter  for full  flow condition  and  the next largest commercial
size  was  used as  the  design  diameter.  This  method was  developed to permit
determination  of peak  flow  with  in-pipe storage as  later  described.   The
lateral sewer  sizes in. parentheses were  computed with the  Subroutine GUTTER
of the  SWMM RUNOFF Block which  uses  Manning's  equation  to  determine maximum
pipe  flow together  with  storage  routing using the continuity equation.  Where
only  numbers not  in  parentheses are  shown,  there  is no difference  in  pipe
diameter under  the  two methods.

      Sewers  sized  assuming  no storage  routing  or time lag  in the hydrograph
are generally  at least as large  as those  sized considering storage routing  or
time  lag  of hydrograph.   Of  the 139 lateral  sewers considered,  111  have  the
same  sewer  diameter and 19 designed  with the first method  are  greater  and  9
are smaller  in diameter  than those designed with the second method.   However,
some  significant reductions  are found  in element numbers  210,  225,  239,  237
and 219, which are the larger diameter  and more costly pipe reaches.

      With  respect to in-pipe  storage pipe  sizes, discussed later, pipe
element number  105  decreases in  diameter  with  increased  total  volumes
of in-pipe  storage.  This results  because of the moderating effect of outflow
from  pipe  element number 49  and  no  tributary  area directly drains to  it.
Pipe  element  number  77 is  the minimum  size  used  in a combined  sewer  and
                                      36

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    TABLE  1.   LATERAL SEWER DESIGN DIAMETERS  (inches)
Pipe
Element
No.
82
101
99
98
95
94
92
91
189
187
85
104
103
108
112
119
78
,80
83
121
123
125
126
84
128
148
149
147
146
143
141
139
138
135
87
89
133
1
3
4
7
8
0%*
27
36
30
27
36 (42)
36
42 (48)
36 (30)
48
36 (40)
36
21
27
36
36 (30)
30
36
36
30 (36)
27
30
36
42
42
36
27
18
21
36
48
48
60
21 (18)
48
48
54
54
27
30 (36)
27
18
24
In-pipe
8.3%
60
48
48
48
36
42
48
42
48
65
48
42 '
36
48
48
48
36
42
24
48
42
42
30
60
54
36
24
42
60
60
60
66
30
60
42
60
48
48
48
54
36
36
Storage
16.5%
84
60
60
60
42
54
60
48
60
90
60
60
48
60
60
60
42
54
21
60
54
54
27
78
66
42
36
54
72
72
78
78
42
72
48
66
48
60
66
66
48
48
Volume**
25.0%
102 .
72
66
72
42
60
66
60
66
108
66
72
54
72
66
72
48
60
18
72
60
60
24
96
78
48
42
66
90
84
90
84
48
84
54
78
54
72
78
78
54
54
41.3%
126
90
84
90
54
72
84
72
84
132
84
90
72
90
84
90
60
72
18
90
78
72
18
120
96
60
48
84
114
108
114
108
60
102
60
96
60
90
96
102
66
66
NOTE:
          Conventional Combined Sewer System.   Numbers in the
          parenthesis are pipe sizes obtained from SWMM and
          should replace the numbers not in parenthesis as
          the combined sewer sizes.

          Advanced  Combined Sewer System.  Storage volumes as
          percent of  119,000 m  (31.5 million gallons) (runoff
          volume of the 5-year synthetic storm for District A).
                              37

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TABLE 1.  (continued)
Pipe
Element
No.
10
13
14
15
20
19
24
25
29
30
33
31
35
42
40
38
36
47
49
56
52
54
55
114
117
59
72
74
75
67
105
109
129
77
76
71
69
64
62
60
58
201
202
203
204
205
206
207
208
212
213
214
215
0%*
27 (30)
27 (24)
30
21
27
30
36 (30)
21
24
36
27
36
30
21
27
30
48
24
27 (24)
27
36
36
42
42
27
36
27
27
36 (30)
27 (24)
27 (24)
36
21
18
21 (18)
36
42
54
54
54
48
36
54
54
54
54
54
42
30
42
42
48
27
In-pipe
8.3%
48
48
36
42
42
48
48
36
42
54
48
48
24
42
42
42
48
42
36
42
54
42
42
36
42
42
42
54
36
42
21
48
24
18
36
36
60
54
54
50
42
84
54
96
48
60
54
42
48
60
42
60
54
Storage
16.5%
60
60
42
54
54
60
60
48
60
72
66
66
21
54
60
54
54
54
42
54
66
48
54
27
54
48
60
72
42
60
18
54
27
18
42
42
72
60
54
72
48
114
60
132
48
72
60
48
60
84
48
78
66
Volume**
25.0%
72
72
54
60
60
66
72
60
66
84 •
78
78
18
66
66
66
60
60
48
66
78
54
60
24
66
54
66
84
54
66
18
66
30
18
48
42
84
66
60
78
48
138
72
156
54
84
66
48
72
96
54
90
78
41.3%
90
90
60
78
78
84
84
78
84
108
102
96
18
78
84
84
72
78
60
84
96
56
72
21
84
66
84
108
60
84
18
84
42
18
60
54
108
84
72
102
60
174
84
192
60
108
84
60
84
120
66
114
102
         38

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                      TABLE 1.   (continued)
Pipe
Element
No.
216
209
210
211
220
221
227
226
225
228 ,
229
230
233
222
232
235
234
231
224
223
236
238
246
249
251
253
252
250
248
247
245
244
243
242
241
240
239
237
260
261
262
263
264
219
0%*
. 36
48 (54)
60 (54)
48
30
36
27 (24)
30
42 (36.)
27 (24)
30
36
30
36 (42)
42
24
27
42 (36)
48
66
24
27 (30)
24
27
27
27
36
42
48
54
60
24
66
54
54
54
60 (54)
66 (60)
36
36
54 (48)
21
36
102 (96)
In-pipe
8.3%
42
48
54
42
48
60
30
48
54
' 42
54
36
60
66
48
36
30
54
36
60
36
60
36
42
42
42
48
42
36
54
60
36
60
60
60
60
48
60
54
54
54
30
60
84
Storage
16.5%
48
48
54
48
66
84
36
54
66
54
72
42
78
84
60
48
36
66
30
60
48
78
48
54
60
54
60 .
48
36
60
66
48
66
66
72
72
54
72
72
66
66
42
78
78
Volume**
25.0%
54
54
60
54
78
96
42
66
78
60
84
48
90
102
66
60
42
78
27
66
54
90
60
66
66
66
72
54
42
66
72
60
78
78
84
84
60
78
84
78
78
48
90
78
41.3%
66
66
72
60
96
126
54
84
96
78
108
54
114
126
•78
72
48
102
24
72
66
120
72
84
84
84
90
60
42
84
84
72
90
96
102
102
66
96
108
96
96
60
120
84
NOTE:
          Conventional Combined  Sewer  System.  Numbers in the
          parenthesis  are pipe sizes obtained from SWMM and
          should replace the  numbers not  in parenthesis as
          the combined sewer  sizes.

          Advanced Combined Sewer System.  Storage volumes as
          percent of  119,000  m   (31.5  million gallons) (runoff
          volume of the 5-year synthetic  storm for District A).
                                 39

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is not  reduced  in size as  a  result of moderated outflows from pipe  element
number  129.  Pipe element number  219  is  reduced  in size with in-pipe  storage
because of the moderating effects of outflow from upstream pipes.

     A similar comparison of trunk  sewer sizes for  the  conventional combined
system is given in TABLE  2.  The difference in sewer sizes,  with  four excep-
tions,  is  no more  than  one  commercial size  and is due to differences  in
hydrographs entering  the  trunk sewer  inlet  points  since the same TRANSPORT
Block was used to size the diameters.   Of the 31 trunk sewer  conduit elements
considered, 13 have the same sizes.   Twelve associated  with  the first method
are  greater and  six  are smaller  than those associated with  the  second
method.   However, the  increases are  in  the larger  size pipe although  the
largest  and  second  largest size  pipes, (element  numbers 349 and  351)  are
reduced in size.  The difference in  diameters sized  with two design  methods
reflects the small pipe  storage effect for a  5-year  synthetic storm.   Those
diameters obtained with subroutine  GUTTER of SWMM  (as modified) were  used as
the combined sewer sizes.

     The initial diameters specified for each conduit element when using SWMM
for conduit sizing affect the  final design diameters as  well as  the  outflow
hydrograph and pollutograph.  This  results  since SWMM does not recompute the
previously computed portion of  the  hydrograph when pipes are resized  due to
the occurrence of surcharge at  a  later time in the design storm.  Generally,
the effect on  the design diameter  is small but  could be significant  on the
peak outflow hydrograph.

     The trunk sewer decreases  as the amount of  in-system storage increases.
This results from the reduced  peaks  of  the outflow  hydrographs  from  either
satellite storage or  in-pipe  storage.  This characteristic  is a  significant
factor  in  determining the  least-cost system  for  both  pollution and  flood
control.

Outflow Hydrographs  and Pollutographs

     The 5-year return interval synthetic  storm and  outflow hydrograph from
District A for  the  conventional combined system is  shown in Figure 2.   The
peak  outflow rate  is 39.8 m  /sec (1,407  cfs).   A 2-minute integration
interval was used.   The  outflow hydrograph maintains a  relatively low value
until about  one  hour after the rainfall starts.  The  time  lag  between  the
peak of  the  hyetograph and the peak  of the outflow  hydrograph  is  about  12
minutes, indicating  a short  response  time of  the   drainage system  to  the
synthetic storm.   The  time of travel  in  the trunk  sewers, estimated assuming
all pipes flowing full,  is  about twice as long as the  time  required for  the
peak flow to be generated at the downstream outlet.

     As discussed  previously,   the  initial diameters specified as  input  to
SWMM affect  the  design diameters and  the  flow routing.  Hence,   the  outflow
hydrograph and pollutographs are influenced.  For example, Case A of TABLE 3
specified initial pipe diameters to  be about one-half  of the final  design
diameter  and results in a peak hydrograph  of value 44.4 m /sec  (1,569
cfs).  In Case B, initial diameters were assumed to  be  one or two commercial
                                     41

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TABLE   3.  COMPARISON  OF  DESIGN DIAMETERS AND PEAK
           HYDROGRAPHS
Trunk
Sewer
No.
301
303
305
307
309
311
313
315
317
319
321
323
325
327
329
331
333
335
337
339
341
343
345
347
349
351
353
357
359
361
363
Case A
(1) (2)
1.5
1.5
1.5
1.5
2.0
2.0
3.0
3.0
3.0
2.5
4.0
4.0
4.0
3.0
3.0
4.0
3.0
3.0
3.0
4.0
4.0
4.0
5.0
4.0
4.5
4.5
6.0
5.0
5.0
5.0
5.0
3.0
4.0
4.0
4.5
5.0
6.0
6.5
7.0
7.5
6.0
8.5
8.0
• 8.5
6.5
7.5
9.0
6.5
7.5
7.5
9.0
10.0
10.0
10.0
12.0
13.0
14.0
12.5
11.0
11.0
11.0
11.5
Case B
(1) (2)
2.5
3.5
* 3.5
4.0
4.5
5.5
6.0
6.5
7.0
5.5
8.0
7.5
8.0
6.0
7.0
8.5
6.0
7.0
7.0
8.5
9.5
9.5
9.5
12.0
13.0
13.0
11.0
10.5
10.5
10.5
10.5
3.0
3.5
4.0
4.5
5.0
6.0
6.0
6.5
7.0
6.0
8.0
8.0
9.0
6.5
8.0
9.0
6.5
7.5
7.5
9.5
10.0
10.0
10.0
13.5
13.0
14.0
12.5
11.0
11.0
11.5
11.5
Case C
(1) (2)
3.0
3.5
4.0
4.5
5.0
6.0
6.0
6.5
7.0
6.0
8.0
8.0
9.0
6.5
8.0
9.0
6.5
7.5
7.5
9.5
10.0
10.0
10.0
13.5
13.0
14.0
12.5
11.0
11.0
11.5
11.5
3.0
3.5
4.0
4.5
5.0
6.0
6.0
6.5
7.0
6.0
8.0
8.0
9.0
6.5
8.0
9.0
6.5
7.5
7.5
9.5
10.0
10.0
10.0
13.5
13.0
14.0
12.5
11.0
11.0
11.5
11.5
Peak hydro-
graph flow

     Note:
 1569  cfs
1509 cfs
(1)   Input diameters in feet
(2)   Design diameter in feet

     1  foot = 0.3048 meters
     1  cfs  = 0.0283 m /sec
1407 cfs
                         43

-------
sizes  less (using  Case A  as a guide)  than the  final design diameters.
The  final  design diameters  were  generally  the same  as  or  one  commercial
size different  from those of  Case A and the peak  outflow  hydrograph  value
from District  A was  reduced  from 44.4  to 42.7  m /sec  (1,569 to  1,509
cfs). In Case C, the initial pipe diameters were specified to be equal to the
final  design  diameters of  Case B.   Sewer routings were  consistently made
throughout  the  duration of  the synthetic storm.   Because of  proper  sewer
routing, of  design storm flow,  the  peak  flow rate was reduced  from  42.7  to
39.8 .BI /sec  (1,509  to 1,407 cfs).   The  hydrographs  corresponding  to Case C
of TABLE 3 were used for analysis.
                                         +
     Figures 3  and  4  preserit the outflow pollutographs in pounds per minute
from the  combined sewer system for SS and BOD, respectively.   They assume
four dry  days  prior , to  the occurrence  of  the  storm.   The street sweeping
interval assumed was  seven  days   (as now practiced in Elizabeth)  and the
sweeping efficiency 75 percent.  STORM default values were used in computing
pollutant  constituents (SS, BOD)  from the amount  of  dust  and dirt  in the
street washout.

     Figure 3  illustrates  the two  flushes in  a combined  sewer  system.
The  first  flush ends  about  50  minutes from the start of the storm and the
second flush, about  40 minutes later.  The first flush reflects the deposit
of solids  in  combined sewers from sanitary wastes during dry days and their
resuspension  in the initial phase  of  the storm.   TABLE 4  shows  the  amount
of  solids  deposited  in  each trunk sewer segment in District A during four
antecedent  dry  days  as computed with the SWMM TRANSPORT Block.  The average
daily  solids  deposit  is about  127  kg  (281 pounds).   Most  of these .deposits
occur  in  pipe  element numbers 347, 349  and  351, which  have the relatively
flat slope of  0.0004.   The solids deposits  in these three elements account
for  about  84  percent  of  the  total.   This  indicates the advantage  of
maintaining flushing  velocities for dry-weather flows.  A  rainfall with an
intensity  of  about  1/16 of  the 5-year   synthetic  storm  and with  a  return
frequency  of  less than one month  (about ten days)-  should cleanse  these
deposits  in the sewers.    The peak  runoff  rate  from this  small,  frequent
rainfall  is 0.76 m /sec (27  cfs)  as compared  to  39.8 m  /sec  (1,407 cfs)
for  the  5-year  design storm.   This  flow  rate is about ten times the average
dry—weather flow.

     Figure 4  presents mass  rate  BOD  pollutographs associated with the
5_year synthetic storm  for both  the separate storm  and  combined  systems.
The  double peak, observed in the  SS  pollutograph,  is  not as  apparent  since,
in the SWMM used, solids deposited  in sewers are assumed to  contribute only
to SS  and not  to BOD.  Such contribution should be considered based  on  the
anticipated organic content  associated with all sewer solids.

     Had  the number  of  antecedent dry days  been more than four, the  first
peak of the mass rate SS pollutograph would be increased  since solids deposit
in combined sewers  would become a  dominant factor  in total  runoff  polutants.
The  pollutograph, shown  in Figure 5, .assumes  30  antecedent  dry days.   The
BOD  for  either  the  combined  or  separate system would  mainly result from
street washout as shown in Figure 6 by the  similarity of pollutographs
for  both  the  combined and separate  systems.
                                     44

-------
  in
  XI
	  CONVENTIONAL
               COMBINED SYSTEM

	CONVENTIONAL
               SEPARATE  SYSTEM

ASSUME:
   7 DAY  STREET SWEEPING INTERVAL
   0.75  SWEEPING  EFFICIENCY
   STORM DEFAULT  VALUES FOR
   POLLUTANT CONVERSION FROM DD
                                                5-YEAR INTERMEDIATE
                                                  PATTERN STORM
                         6O                 |20
                 TIME SINCE START OF STORM (minutes)
                      180
Figure  3.  Mass rate SS pollutographs, 4 dry days  (5-year intermediate
           pattern storm)
                                                        CONVENTIONAL
                                                        COMBINED SYSTEM

                                                        CONVENTIONAL
                                                        SEPARATE SYSTEM
                                              5-YEAR INTERMEDIATE
                                                PATTERN STORM
                        60                 120
                 TIME SINCE START OF STORM (minutes)
                     ISO
 Figure 4.  Mass  rate BOD pollutographs, 4 dry days  (5-year interme-
            diate pattern storm)
                                   45

-------
TABLE  4.  SOLIDS DEPOSIT  (LBS)  IN  SEWER WITH FOUR
           ANTECEDENT DRY  DAYS
Element
Number
301
303
305
307
309
311
313
315
317
319
321
323
325
327
329
331
333
335
337
339
341
343
345
347
349
351
353
357
359
361
363
Solids
fibs)
6.48
4.88
3.52
3.61
4.23
5.65
5.87
6.53
7.18
0.37
15.36
12.41
11'. 66
0.40
0.67
12.78
0.29
0.52
0.51
2.60
13.80
13.76
13.75
311.61
306.40
322.76
28.69
1.73
1.86
1.92
1.92
 Note:   1 Ib = 0.453 kg
                        46

-------
400
300
 100
                                                  CONVENTIONAL
                                                  COMBINED SYSTEM

                                                  CONVENTIONAL
                                                  SEPARATE SYSTEM
                        ASSUME:
                          7 DAY STREET SWEEPING INTERVAL
                          0.75 SWEEPING  EFFICIENCY
                          STORM  DEFAULT  VALUES FOR
                          POLLUTANT CONVERSION FROM DD


                                5-YEAR INTERMEDIATE
                                              PATTERN STORM
Figure 5.
                      60                  120

              TIME SINCE START OF STORM  (minutes)
                                                  180
Mass rate SS pollutographs,  30 dry  days  (5-year interme-
diate pattern storm)
  20 i-
                                                   CONVENT10NAL
                                                   COMBINED SYSTEM

                                                   CONVENTIONAL
                                                   SEPARATE SYSTEM
                                            5-YEAR INTERMEDIATE
                                               PATTERN STORM
                       60                 120

               TIME SINCE START OF STORM (minutes)
                                                   180
 Figure 6.
 Mass  rate  BOD pollutographs, 30 dry days (5-year interme-
 diate pattern storm)
                                47

-------
     To control the initial flush  of pollution from solids  deposits in
the sewers,  it would be necessary to store and treat a volume of  about  1.6 mm
(0.063  inches) over the drainage  basin for a  5-year synthetic storm of
intermediate pattern.   The  volume  requiring storage is small since most of
the  solids  are deposited in the larger  and  more flatly  sloped  downstream
reaches of  the sewer  system.   This  condition is generally typical in  most
urban areas.   If the  solids are distributed more uniformly  throughout  the
system, the  volume  to  be stored  could be  larger.   If the pollutants  from
street  washout are to be controlled, a runoff volume of 23.0 mm  (0.906
inches) should be stored and treated for the 5-year synthetic storm.

     In terms  of pollutant  concentration  (mg/1), a  different  pollutograph
character is observed.   Figure 7 shows  the concentration pollutographs  of the
5-year synthetic storm for BOD and SS for both the conventional combined and
separate storm systems.  The pollutograph contains only one peak which  occurs
early  in the  storm when the runoff quantity  is small.   In the combined
system, the  peak  SS concentration of  1,972  mg/1  occurs 18  minutes after the
start of rainfall and  38 minutes later (or 56 minutes after the start  of the
storm) the concentration drops below  20 mg/1.  The peak SS concentration from
the separate storm system occurs 50 minutes  after the storm starts.  The peak
has  a  relatively low value of 17  mg/1 using  STORM default values.   The
BOD  concentration pollutograph has  a  similar general  character  except  that
the  peak  of pollutograph occurs earlier since there  is  no consideration of
the BOD fraction in the solids deposit  in storm sewers in SWMM.

     The  pollutographs associated  with the separate storm sewer  system
were  obtained using  the combined  sewer  network  and  design diameters  but
without  the DWF  inputs to   the  SWMM TRANSPORT   Block.   Although  there  are
differences  in sewer network and design diameters between  the  two systems,
the resulting differences in outflow hydrographs  and pollutographs are within
the  range of  accuracy required in this study  for the comparison  of  the
alternative  systems.

     Figures  8 and  9  present the outflow hydrographs and  pollutographs  of
1-year  and   1.3-month  synthetic  storms,  respectively.   They  are  similar  to
those  of  the 5-year synthetic storm except  in flow and pollutant magnitude.

     Runoff  characteristics  from storms of advanced pattern were also inves-
tigated.  Figure  10 shows the District  A outflow  hydrograph and pollutographs
for  a 5-year return interval storm with the  advanced pattern hyetograph shown
in Figure D-5.   The peak runoff rate from District A occurs about 18 minutes
(as  compared to 74 minutes for intermediate  pattern storm) after the start of
the  storm with a peak rate of 21.7  m  /sec (766 cfs),  about one-half of
the  corresponding intermediate pattern storm.    The peak  combined sewage SS
concentration  (138 mg/1) is one order of magnitude less than the peak concen-
tration (1,972 mg/1)  for the intermediate pattern storm.  This results since
peak runoff from an advanced  storm occurs  in the early  stages  of the storm
event  when  the  results of  sewer flushing  is combined with street washout.
However,  the peak  SS  concentration  of stprmwater runoff  alone  is 92 mg/1,
about  five  times higher  than the peak (17mg/l)  for an intermediate pattern
storm.  There is  one peak  flush  of pollutant mass in  advanced pattern
storm  runoff.   The peak flush  ends about 45 minutes after the .storm starts.
                                     48

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Characteristics of  runoff from  1-year  and  1.3-month synthetic  storms  are
similar to  those  of  the the 5-year  synthetic  storm except for magnitude of
runoff rate and pollutant amounts.

     Although  runoff   characteristics  between  storms  of  intermediate  and
advanced patterns  are substantially different,  differences appear insigni-
ficant  in  the total  pounds  of  pollutants reaching the outlet  of the sewer
system as shown in TABLE 5.  The computed SS loadings in District A combined
system are 1,331 and.1,329 kg (2,939  and  2,933 pounds), respectively, for the
synthetic 5-year  intermediate and, advanced  pattern storms.   For  a separate
storm  system,  the  computed values are 506 and  500 kg  (1,116 and  1,104
pounds),  respectively.  For BOD,  the  values are 321 versus 320 kg (709
versus  707  pounds)  for  a  combined  sewer system,  and  58  versus  57  kg (128
versus  126 pounds) for  a storm  sewer systems.   However, the peak concentra-
tions  for  the  advanced pattern  are much lower  than for the intermediate
pattern due to the dilution afforded  to the first flush.

     The following is  noted from TABLE  5:

     (1)  For a given  rainfall amount,  both the  runoff volume and peak runoff
          rate from an intermediate pattern storm are greater than those from
          an advanced  pattern storm with the exception 6f  the runoff volumes
          for 1.3-month return frequency storms, which are  equal,  since most
          of the runoff from  this  storm is from  impervious  areas.

     (2)  Frequent,  smaller storms, regardless of pattern,  generally produce
          higher pollutant concentrations than infrequent,  rare storms.  This
          is  illustrated  in  Figures  11 and  12,  which, respectively, compare
          the SS concentration pollutographs versus storm  return frequencies
          for the combined and  separate  storm sewer  systems  in District A.
          Conclusions from  BOD  concentration pollutographs are similar.

     (3)  Rains with a return interval  of about  10  days  (0.35 months) (inten-
          sity 0.1 inches/hour)  should  cleanse combined sewers.  The total SS
          loading reaching the  drainage district outlet  from  this  storm is
          computed as  827 kg (1,826 pounds),  of which 325  kg (718 pounds) is
          estimated to be  from DWF.   The remaining pollutant mass is attri-
          butable to  the sewer  solid  deposits,  as the street  washout from
          this small storm would be insignificant.   During  the four dry days
          assumed in  the  computation,  the total  amount  of solids  deposit is
          estimated to be 509 kg (1,124 pounds).

     (4)  The total SS  accumulation  on  the' streets  of  District A, assuming
          four  antecedent  dry  days,  a 7-day street  sweeping  interval,  and
          75  percent  sweeping  efficiency,  is  computed  as 525 kg  (1,160
          pounds).  A  5—year  synthetic  storm would  remove  about 96 percent of
          the total,  a  1-year  synthetic storm, 87  percent, and a 1.3-month
          synthetic storm,   35  percent.    Corresponding  synthetic  advanced
          storms would remove slightly  less pollutant.

     Effective pollution control in an urban area associated with wet-weather
                                    53

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 4000

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  1000
  800

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  500
  400

  300

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   30

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                              •I-YEAR
INTERMEDIATE PATTERN STORM

ADVANCED PATTERN STORM
                5-YEAR
                              I
                                          1
                                                       I
                 30          60           90          120
                        TIME  SINCE START OF  STORM  (minutes)
                                                                  150
                                                                              180
         Figure 11.  Combined sewage  pollutographs  for various storms
                                       55

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flows can  be largely achieved by the  containment  and  treatment  of  the first
flush from frequently occurring storms.

SEPARATE STORM SEWER SYSTEM

     In  1972, a  separate  storm  sewer  system was designed  for  District
A  (11).   The existing  combined sewers were  to  be maintained as a separate
sanitary sewer system  accepting limited amounts of urban  runoff.   The storm
sewer layout is  shown  in Figure D-13.  Its  function was  to relieve combined
sewage flooding by  intercepting runoff.   The new combined sewer layouts were
extensions of the  separate  storm system.   Storm  sewer slopes,  diameters and
average  excavation depths  for  the  trunk sewer elements  in the system are
listed  in  TABLE 6.   Also  listed  is  the corresponding information for the
combined sewer  system.   The effect of  eliminating  surcharges in  combined
sewer  systems is  apparent.   The storm  sewer  slopes  were determined  from
detailed topographic surveys and field inspection of underground utilities to
eliminate interference.   The average excavation depth  for  each  pipe  element
is computed  taking into account the upstream and downstream pipes.

     The separate  storm sewer system was  designed with surcharged  sewers to
reduce  sizes and  excavation cost.   The following was  used  to  determine the
flows and hydraulic grade in the system.  Hydrographs  for  both impervious and
pervious areas  were developed  from the  5-year  synthetic  storm hyetograph.
These hydrographs  were  determined  for  a 0.405 hectare  (1.0  acre) area and a
ground slope of one  percent,  by subtracting  surface infiltration, depression
storage  and   surface detention  from the  rainfall,  for each  minute  of  the
storm.   The  flow  in any particular  section of the  trunk  sewer  at any  minute
was determined by  time  routing  the  incremental volumes from upstream  hydro-
graphs.  For each  minute  of  the storm,  the  flow in each section of  the trunk
was successively determined.   For trial  pipe sizes,  the  hydraulic gradient
was determined for each minute of 'the storm based on  flowing  full friction
and secondary losses calculated for each section of  trunk sewer.   The  pipe
sizes selected were  those which raised the peak hydraulic  gradient to about
one foot below  the  drain inlet grating at the  lowest point in the  system.
This would  still  allow  design  flow  from the  critical low points to  simul-
taneously  enter  the system.  Different  trunk sewer sizes  necessitated
reevaluating  the  time   of  travel in each section  for proper time routing.

     TABLE 7 compares peak flows at several locations of District A  generated
for the  storm sewer  design  and  for the design of combined sewer  system using
SWMM.   The peak  flow rate used in the  separate  storm  sewer  design  is  gener-
ally ten percent less than  the  flow  used  in  the  design of combined  sewers to
reduce the frequency of combined  sewer surcharging.  This  results  since the
critical factor in  a surcharged system is the hydraulic gradient.  The  peak
hydraulic gradient in any sewer reach, except the most downstream  reach,  is
influenced by backwater effects and occurs  after  the  peak flow has  passed
downstream.
                                     57

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    TABLE  6.   COMPARISON OF PIPE DIAMETER,  SLOPE, AND EXCAVATION DEPTH,
                    SEPARATE STORM VS.  COMBINED  SYSTEMS
Trunk
Sewer
Element
301
303
305
307
309
311
313
315
317
319
321
323
325
327
329
331
333
335
337
339
341
343
345
347
349
351
353
357
359
361
363
Separate Storm
Diameter
(feet)
3.0
3.5
4.0
4.5
5.0
6.0
6.0
6.5
7.0
7.0
7.0
7.0
7.5
7.5
7.5
7.5
7.5
7.5
7.5
8.0
8.0
8.0
8.0
10.0
10.0
10.0
11.0
11.5
11.5
11.5
11.5
Slope
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0013
.0010
.0013
.0017
.0020
.0090
.0090
.0005
.0100
.0094
.0094
.0034
.0034
.0088
.0088
.0004
.0004
.0004
.0013
.0003
.0003
.0003
.0003
System
Excavation
Depth (feet)
9.0
9.6
9.8
10.4
10.9
12.2
14.3
13.5
14.4
13.7
13.4
13.5
14.2
13.6
14.0
14.8
14.1
15.3
16.3
17.0
16.4
17.6
18.7
19.9
22.6
25.9
28.0
28.5
29.5
32.3
31.0
Combined System
Diameter
(feet)
3.0
3.5
4.0 .
4.5
5.0
6.0
6.0
6.5
7.0
6.0
8.0
8.0
9.0
6.5
8.0
9.0
6.5
7.5
7.5
9.5
10.0
10.0
10.0
13.5
13.0
14.0
13.0
11.0
11.0
11.5
11.5
Slope
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0090
.0013
.0017
.0025
.0099
.0048
.0019
.0133
.0089
.0091
.0034
.0019
.0019
.0019
.0004
.0004
.0004
.0013
.0030
.0030
.0030
.0030
Excavation
Depth (feet)
9.2
9.8
10.0
10.6
11.0
12.7
14.3
14.4
14.8
13.3
15.4
15.4
16.2
13.1
14.5
16.0
13.8
16.5
17.4
23.1
22.8
22.4
20.8
22.4
24.7
29.0
30.2
28.5
29.5
32.8
31.5
Note:  1 foot = 0.3048 meters
                                  58

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                      TABLE 7.  PEAK FLOW COMPARISON FOR
                   SEPARATE STORM AND COMBINED SEWER DESIGN
                         (5 YEAR RETURN FREQUENCY)
Trunk Sewer
Inlet No.
338
342
356
364
Drainage Area
(Acres)
349.6
360.0
600.4
655.1
Peak Flow
Separate Storm
System
766
795
1259
1276
(cfs)
Combined
System
898
909
1321
1407
       Note:  1 acre = 0.405 hectare
              1 cfs  = 0.0283 m /sec

     There are noted differences of sewer  sizes  for  the conveyance of storm-
water runoff and combined sewage as shown in TABLE 6.  The differences result
from allowing  surcharged flow  in  the separate  sewer  system and not  in  the
combined  system  under design  flows.    All  other  conditions being  similar,
design diameters for a combined sewer system are generally equal to or larger
than those for a separate storm system.

     There is little difference in  runoff  hydrographs  for the separate storm
and combined  system since dry—weather flow  quantity is  a  small  fraction of
total runoff during wet  weather.   For instance,  the  peak 1.3-month synthetic
storm  runoff rates are  6.08  and  5.95  m /sec  (215 and 210  cfs), respec-
tively, for the combined and separate storm system.

SEPARATE SANITARY SEWER SYSTEM

     The  layout  of the  separate  sanitary sewer  system (Figures 13  and  14)
generally follows  the  existing  sanitary  or combined sewers,  except  that  the
existing three outlets have been reduced  to  two.   Each city street is served
by one sanitary sewer.  There are 260 sewer pipe elements with a total length
of about 32,308 m (106,000 feet).

     The  quantity  of  domestic  sewage was  determined  using the  estimated
saturation  population  and  the  estimated  daily  wastewater  flow  per  capita.
For District A,  the total saturation population was estimated  at 16,500  and
the average daily  domestic  flow  was  calculated as  4.34 m  per min.  (0.65
mgd),   assuming  a rate of 379  liters  (100 gallons)  per  capita per  day  in-
cluding  infiltration.    The ratio  of  peak  flow to  average  daily flow  was
estimated using the formula suggested by Harmon (12)
                     M
                     Q
1 +
14
(1)
where:
     M = the instantaneous peak flow,
     Q = the average daily domestic flow, and
     P = the tributary population in thousands.
                                     59

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     The formula indicates that relatively higher maximum  rates  of  flow are
expected from small numbers of people than from large numbers.  This formula
was found  applicable  to  Elizabeth in previous studies(S).   For  District A,
the ratio  of  peak  daily  flow to average daily flow  is  computed  as  2.74 and
peak  daily flow,  as 11.82  m  per  min.  (4.50 mgd).   For  commercial and
industrial areas, peak sewage flow was assumed as 187,000 liters  per hectare
(20,000 gallons per acre) and  equaled 2.76 m  per min.  (1. 05  mgd).   The
peak  dry-weather  flow at the outlets was about  14.58 m   per min.  (5.5
mgd).    This  peak  was rounded up  to 15.8 m per  min.  (6.0 mgd)   for  compu-
tations in this report.

     The minimum  size  used  for sanitary sewers  was 0.20  m (8 inches).
The minimum pipe slopes  selected  assured a minimum flowing full  velocity of
0.61  m (2.0  feet)  per  second.   Sewer diameters  were calculated based on
Manning's equation with  a roughness  coefficient of 0.013.

     The sanitary  sewer  diameters  are shown in Figures 13 and 14.   Most of
the pipes  are 0.20 m (8 inches) in  diameter with  the  largest being  0.381 m
(15 inches).                                                            .

COMBINED SYSTEM WITH IN-SYSTEM STORAGE

     As discussed previously,  in-system storage, as considered in this study,
includes  (a)  storage provided  in enlarged upstream lateral sewers  due to
the economy achieved, and (b) satellite storage provided  in the collection
system along  the  trunk sewer.   Both storage schemes have the effect of
reducing the  size  of  trunk sewers.   In some cases, trunk sewers  designed to
convey  peak flows  are  the  practical maximum that  can be  physically  con-
structed due  to space limitations.    Pipe  storage  provided in upstream lat-
erals  and  satellite storage  would permit a reduction  in  trunk sewer sizes.
Such  storage  serves  to reduce the peak  of  outflow hydrograph and modify the
outflow  pollutograph  from a  drainage basin  thus  reducing the  capacity of
interceptors required to  abate overflow pollution.
   I
Design with In-Pipe Storage

      In-pipe  storage can be  provided in  both  lateral  and trunk  sewers.
Preliminary cost analysis indicates storage  in  the  laterals,  rather   than
in the trunks,  to  be less  costly   for either  pollution or  flood  control.

      Figure 15 shows the  incremental cost of  pipe storage  resulting  from
increasing the  diameters  of  the  pipes required to convey storm runoff.   The
pipe  cost  is  obtained from Figure D-15 or TABLE D-17 for an excavation depth
allowing 1.52 meters (5 feet) of  cover  over  sewers.  The  following  can be
observed:

      1.   A slight  enlargement  of sewers  to provide storage  volume  is   less
          costly than a large sewer  enlargement,

      2.   Pipe  storage  in the smaller  lateral  sewers  would  be  less costly
          than pipe storage in large trunk  sewers, and
                                     62

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     3.   Satellite storage which  also'reduces trunk sewer sizes may  be  the
          least  costly  alternative since  in-pipe  storage  costs average
          about $0.26 per liter ($1.00 per gallon).
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NOTES:
 NUMBER ARE BASIC PIPE SIZES
 REQUIRED FOR CONVEYANCE OF
 DESIGN STORM RUNOFF.
 GRAPHS INDICATE-COST OF STORAGE
 OBTAINED BY INCREASING PIPE
 DIAMETER TO SIZE INDICATED
 BY THE  ABSCISSA.
   I
               I
                        67      8     9     10    II

                      INCREASED  PIPE  DIAMETER (feet)
                                                           12-
               13
                                                                       14
                  Figure  15.   Incremental  cost  of  pipe  storage
     In-pipe storage reduces peak runoff  rates  while  permitting  flow convey-
ance.   The pipe volume,  in  excess  of that  required  to pass peak  flow,  can
provide regulation by installing either a  downstream  orifice  coupled with an
overflow weir  (Figure  16)  or a  collapsible dam  coupled  with  a  regulator.
Other  devices  such as the  "Hydro-Brake" (13) and  the VBB  Flow Regulator
(14) have  been proposed.   The backwater  created  by the  regulators results
in  storing flows  in excess  of  the  desired downstream rate  reaching  £he
regulator.    This reduces  the  design  flow rate in  the downstream sewers.   It
may  also  be  designed  to  moderate the  initial pollutant concentration  by
diluting the concentrated pollutant in the first flush  with  subsequent,  less
concentrated runoff.
     The in-pipe storage analysis was accomplished in three steps.
                                     63

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         LENGTH AND  DIAMETER AS  REQUIRED
         TO PROVIDE DESIRED. FLOW CONTROL
                                                -MANHOLE
 OVERFLOW WEIR
 ELEVATION AND LENGTH
 DETERMINED  TO PREVENT
 SURCHARGE  OF
 UPSTREAM  SEWER
CONTROL
STRUCTURE
                           PLAN
         OVERFLOW
         WEIR
FLOW  CONTROL SEWER
              -c
                      SECTION  A-A
                Figure ,16.  Weir-orifice  regulator
                            64

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          Step  I  - The overland flow hydrograph  to  lateral  sewers from each
          subcatctment  was generated for  the  5-year  synthetic  storm using a
          computer program adapted from the SV7MM RUNOFF  Block.   Summing
          arithmetically the  corresponding time  steps of  the tributary
          subcatchment  hydrographs, the  overland flow hydrograph  to a pipe
          element was derived.   This hydrograph was integrated to obtain the
          total direct runoff.   The volume that  should  be  stored to obtain
          the desired outflow peak  rate was  then  determined by integration of
          the flow in  the overland flow hydrograph  in  excess  of that rate.
          The peak constant flow  rate  shown  in  the  modified  hydrographs of
          Figure  17 assumes  a variable orifice outlet  control.

;          Step II - The desired peak flows  of the upstream tributary sewers
          were sumried to  obtain the peak  flow  to  be passed for the pipe under
          consideration.   Manning's equation was used to  compute  the pipe
          diameter and slope required  to convey  the  peak  design flow.  The
          pipe diameter required for storage was  separately  computed  and then
          was combined with the pipe diameter for flow conveyance to obtain
          an aggregate design pipe size having the same cross-sectional area
          as the  two  separate pipes. The next available 'commercial pipe size
          was used as the design diameter.

          Step III - The design of trunk  sewers was  made using  the SUMM
          TRANSPORT Block with the modified  hydrographs  entering the trunk
          sewer from  the  lateral sewer branches.   No  surcharge was allowed in
          either  the  lateral or trunk sewers.

     Figure  17 illustrates  the controlled  hydrographs  to  be  routed  through
the pipe  element  201  for  storage of 0,10, 20 and 50 percent of  total runoff
volume drained to that pipe element from its tributary subcatchment.  Zero
percent storage represents the  case without  in-pipe  storage.  Storage reduces
the magnitude of  the  peak flow  but  extends its duration.

     The  design  diameters of  lateral and trunk  sewers  for ,in-pipe  storage
volumes equal  to 8.3, 16.5,  25.0  and  41.3 percent  of  the 5-year  synthetic
storm runoff volume in District A  are.listed  in  TABLE 1  and TABLE 2,  respec-
tively.   These percentages  correspond  to a total of  10,200; 20,100;  30,300;
and  50,300  m   (2-7,  5.3,  8.0 and 13.3 million gallons),  respectively,
stored in  the  lateral  sewer pipes.  The  respective  percentages  of  tributary
subcatchment runoff volume stored in each lateral sewer  element  are,  however,
10,  20,  30 and  50 since  about 14  percent  of District  A drains  directly to
t runk s ewe rs.

     As  the volume  stored  in  lateral  sewers increases,  the  lateral sewer
sizes are  consistently increased except  for some  at  the  lower  end of lateral
sewer branches.   Trunk sewer,  sizes are  consistently reduced  because of  the
reduction in peak flox/s discharged by  the branches.   The reduction in size is
reasonably  uniform  over  the  entire length  of   trunk  sewer.    This  type of
design provides  storage  for pollution control at least cost,  as previously
described.       •
                                     65

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                                    PIPE ELEMENT 201
                                    TRIBUTARY  AREA = 8.9 ACRES
                                    % IMPERVIOUSNESS = 80
                                    NUMBERS ON CURVES ARE
                                    PERCENTAGES OF TOTAL
                                    RUNOFF STORED IN PIPE
                                    FROM AREA DIRECTLY TRIBUTARY
                                    TO THE PIPE
                                         5-YEAR INTERMEDIATE
                                            PATTERN STORM
                                                   50
30
          60        90        120        150        180
             TIME SINCE  START OF  STORM  (minutes)
210
          240
Figure  17.   Hydrographs modified by in-pipe storage
                          66

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Outflow Hydrographs and Pollutographs

     Figure  18  presents outflow  hydrographs  for various  amounts  of runoff
temporarily stored^in upstream laterals.   The  peak runoff  rates  are 293, 228,
162, 126 and  93  m /sec (1,407, 1,096, 788, 607, and 448 cfs) for amounts of
storage eq,ual to  0,  8.3,  16.5, 25.0, and  41.3 percent -respectively of about
119,000 m   (31.5  million gallons).   The  computer program developed in this
project for  in-pipe  storage  does not currently  permit routing pollutants.
Therefore",  pollutographs were not  generated.

     The pollution  abatement benefits  of in-pipe s.torage depend  on the
flow  rate  selected at which  storage of combined waste begins.   Where a
pollutant sink does not exist, the higher  the flow-through rate, the smaller
would be the benefit achieved and  the smaller  the  amount of storage required.
Less  pollution  abatement benefit  results since  less  dilution of  the high
pollutant concentration in the first  flush would occur.

     Increasing  the  amount  of in-pipe  storage  reduces  the  flow velocity
and may  result  in  solids  settlement  in  the sewers.   About  60  percent  of
the pipes, when  in-pipe storage equals  8-3 percent  of the  total  5-year
synthetic  storm  runoff volume, would  have a flowing  full  velocity greater
than 0-30 m  (1.0  feet)  per second.   As the amount of storage increases to 25
percent, less  than 20  percent have  flowing  full velocity  exceeding  0.30 m
(1.0 feet)  per second with about  40  percent have  a velocity less than 0.06 m
(0.2  feet)  per second.   Solids  deposited in  sewer  pipes during  the pipe
full,   low  velocity period may be resuspended as flow  recedes and velocity
increases.   However, where in-pipe storage of about 40% of the  overland flow
volume is provided, additional maintenance for cleaning  may be  required.  The
Boston sewer flushing study  (15)   indicates that sewage  impounded in upstream
sewer  segments by manhole stoppers  are  self-cleansing  upon stopper release
due to sudden increase in velocity with pipe drawdown.

     In a  wastewater  facilities  plan study  for  Trenton, New  Jersey "(16),
several wet-weather  flows  were sampled  to find  the values  of BOD  and  SS
in combined sewage.   Automatic samplers were  used and  started at the begin-
ning of the rainfall with samples  taken at 15-minute intervals.  The results
of  two sampling   periods  during   small storms  are shown  in Figure 19.   An
increase  in BOD  occurred in  a short time as  the storm runoff  increased
flow to the treatment plant.   The  BOD then receded as the  sewage flow exceed-
ed the treatment  plant's pumping,  capacity and sedimentation occurred in the
interceptor due  to  reduced  velocities resulting from storage  in  the sewer.
After  the  end  of the  rainfall, wastes stored in  the interceptor  were drawn
upon,  the sewer velocity increased, settled material was resuspended and peak
concentrations of BOD reached the  plant.

     The deposition  and resuspension  of  solids  would  be reflected  in  the
 outflow pollutographs.

SEWERS WITH SATELLITE STORAGE

     Satellite  storage along the trunk  was investigated using the ST7MM
TRANSPORT Block.   The  simulation included  no more  than  two such basins.  The
                                     67

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effect of storage quantity and location on the  trunk  sewer  sizes and outflow
hydrographs and pollutographs was  studied.   All flows were assumed diverted
to  storage  basins with  outflow  occurring  only after storage  was  full.   In
addition, at  any  point  in time,  the flow contained  in  a storage  basin was
assumed  to  be completely mixed.    After  storage basin locations were deter-
mined  for  various amounts  of storage capacity,  runoff  characteristics for
various  combinations of  storm intensity  and  patterns  were developed.   These
runoff characteristics were used  in determining comparative  costs.

Design

     Design of trunk  sewers with satellite storage was made with  SWMM.
Cylindrical storage  basins were  assumed  with outlets controlled by overflow
weirs.  The width of the overflow weir was  determined  to  minimize the hydrau-
lic  head above the  crest of  the weir  and  reduce the  effect of surcharge
volume on the routing of storm runoff.  Since the  flow divider  option in SWMM
was not  used, dry-weather flows above  a storage basin are  intercepted by the
basin.  Consequently, the amount  of solids  deposit in  the sewer reflected the
location of storage basins.   In practice,  dry-weather  flows  would be diverted
from the basin.

     The locations and volumes of storage  basins in a  drainage  watershed were
selected to conform to the following criteria:

     1.   The peak  of  outflow hydrograph  should  be  attenuated as  much as
          practical.

     2.   For outflow  hydrographs  with multiple  peaks,  the peaks  should be
          relatively equal to reduce intercepting  sewer sizes.

     3.   The rising limb of  the  outflow hydrograph should  be delayed as much
          as  possible  to provide  reduction  of the  high  concentrations of
          pollutants  in the  initial flush  by dilution  with  later runoff.

     Figure 20 shows  the outflow hydrographs for  storage  basins_at six
different  locations  in  District  A.   In. each  case,  about 50,300  m   (13.3
million  gallons)  of  the total 119,000 m   (31.5 million gallons) of assumed
storm  runoff  is captured.   TABLE 8  compares  the corresponding trunk sewer
sizes.   The  curve labeled  "no  storage" applies  to a conventional combined
system and is shown for reference only.  Figure 21 presents  schematically the
various alternatives for storage  location.

     Case A assumes a single basin  located at  the  downstream end  of the
system.  Overflow occurs 82 minutes  after  the  start of rainfall assuming the
5-year synthetic storm hyetograph.  The  peak  overflow rate is 25 m  /
sec  (890 cfs).  The trunk sewer  diameters  are the  same as in the conventional
combined system, and the cost is  about 75  percent  more than  Case B, the least
expensive.

     In  Case  B,  the  two storage  basins  of  equal  capacity were located at
points where  26 and  54 percent of  the watershed  drained to them.   The peak
runoff  is  about  the  same as Case A  but  the peak occurs  about 20 minutes
                                     70

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         TABLE  8.   COMPARISON  OF  TRUNK SEWER SIZES  (FEET)  FOR STORAGE
                             BASIN AT  VARIOUS LOCATIONS
Sewer
Element No
301
303
305
307
309
311
313
315
317
319
321
323
325
327
329
331
333
335
337
339
341
343
345
347
349
351
353
357
359
361
363
A
3.0
3.50
4.00
4.50
5. 00
6.00
6.00
6.50
7.00
6.00
8.00
8.00
9.00
6.50
8.00
9.00
6.50
7.50
7.50
9.50
10.00
10.00
10.00
13.50
13.00
14.00
12.50
11.00
11.00
11.50
11.50
B
3.0
4.00
4.00
4.50
5.00
6.00
6.50
7.00
4.00
3.50
4.50
4.50
6.00
5.00
5.50
7.00
5.00
6.00
6.00
7.50
5.00
5.00
5.00
6.50
7.00
7.00
9.00
8.50
8.50
9.00
9.50
C
2.75
3.50
4.00
4.50
5.00
5.50
6.00
6.50
7.50
6.00
8.00
8.00
5.00
4. 00 •
.4.50
5.00
4.00
4.50
4.50
6.50
7.00
7.00
7.00
9.50
9.00
10.50
9.50
8.50
8.00
8.50
8.50
D
2.75
3.50
4.00
4.50
5.00
5.50
6.00
6.^50
7.50
6.00
8.00
8.00
9.50
7.00
7.50
8.50
6.00
7.00
7.00
8.50
9.00
9.00
9.00
12.00
12.00
12.00
9.50
8.50
8.50
8.00
8.50
E
2.75
3.50
4.00
4.50
5.00
5.50
6.00
6.50
7.50
6.00
8.00
8.00
8.00
6.50
7.50
8.50
6.50
7.00
7.00
9.00
10.00
10.00
10.00
13.00
13.00
13.50
9.50
8.50
8.00
8.00
8.50
F
, 2.75
3.50
4.00
4.50
5.00
5.50
6.00
6.50
7.50
6.00
5.00
4.50
5.00
4.00
5.00
6.00
4.50
4.50
5.50
7.00
8.00
8.00
8.00
10.00
11.00
10.50
9.50
8.00
8.00
8.00
8.00
Peak Runoff
Rate (cfs)
890
897
665
644
                                             630
                                            607
          TOTAL STORAGE VOLUME = 13.3 MILLION GALLONS OR 41.3% OF
           TOTAL 5-YEAR SYNTHETIC STORM RUNOFF VOLUME

NOTE: Case A - One basin at downstream end of watershed
           B - Two basins of equal capacity at 26 and 54% of watershed area
           C - Two basins at 35 and 82% of watershed area, capacity ratio 3:2
           D - Two basins at 35 and 82% of watershed area, capacity ratio 1:3
           E - One basin at 82% of watershed area
           F - Two basins of equal capacity at 28 and 82% of watershed area.
                                        3                                 3
1 foot * 0.3048 meters; 1 cfs = 0.0283 m /sec; 1 million gallons = 3,785 m
                                     72

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earlier.  Hence,  more polluted runoff would have  to be  intercepted  and  more
off—line storage  capacity would be  required.   On  the  other hand,  trunk sewer
sizes are substantially reduced.

     Case C  has  a lower peak in  the  outflow hydrograph  than  Case B  with
about the same cost of  trunk  sewers.  Two  basins,  having a capacity  ratio  of
3:2, were located where 35 and 82  percent of  the watershed drains  to them.
Further improvements of the outflow hydrograph is  achieved  by  using  the  same
basin locations  but  with a capacity  ratio of  1:3 (Case D).   However, trunk
sewer sizes  are  generally greater  than  those  in Case C.   Case E,  with one
large basin located where 82  percent  of  the area  drains  to it, has a compar-
able outflow hydrograph and trunk sewer  sizes (except  for the reaches immedi-
ately upstream of the basin)  as those of Case D.

     Case F  assumes  two  basins  of equal  capacity located  where  28 and  82
percent of the watershed drains to  them  (trunk sewer  element numbers 320 and
352).   The  outflow  hydrograph improved somewhat  over that  of  Case C  with
trunk sewer  sizes generally  comparable.   Based  on the  criteria stated  pre-
viously for the selection of  basin location, Case  F offers most advantage and
was  used  to  represent  the desirable locations  for  storage  equalling  41.3
percent of the 5-year synthetic storm runoff.  In  practice,  the locations for
storage would be dictated by  site conditions.

     For satellite storage volumes equal   to  9.4 and 17 percent of  5-year
storm runoff, two basins of equal capacity  located where  26 and 54 percent  of
watershed drains  to  them,  or at  trunk sewer  element numbers  316  and 340
respectively, appear  to  result  in reasonably good outflow  hydrographs
(Figure 22).   The two peaks  in the hydrographs are of about  the same  magni-
tude and  the  reduction in peak  flow rate  is appreciable.   An additional
computer run was made for 17  percent storage with  basins  located  where  28 and
82 percent of  the watershed drained to  them.   The peak of the outflow  hydro-
graph was about 15 percent greater and  the trunk  sewer sizes  slightly
greater.

     The  trunk sewer  diameters   for  three  different amounts of satellite
storage are  listed in TABLE  2 together  with the  sewer  sizes for a conven-
tional  combined  system and  advanced systems with  in-pipe  storage.  The
effect of storage on  sewer  sizes  is.more  pronounced for  capacities  of about
17 or more  percent of  the total  runoff.   A major reduction  in sewer sizes
results  as  the  storage capacity  increases to  41.3  percent  of  the  5-year
synthetic storm runoff  volume.   For a storage capacity  equal  to 9.4 percent
of  the  total  5-year  synthetic  storm runoff  volume,  the  trunk sewer  dia-
meters are generally less than that for  conventional combined  system but not
by a  significant  amount.   Similar findings have been  reported  by  Yen and
Sevuk(17).

     The sewer size of  element number 317  for 9.4 percent  satellite storage
is greater  than  for  a  conventional combined system.   This is caused by the
release of waste  over a gravity weir after  the  storage  basin is full.  The
rate of release  is affected  by the plan area of the basin  and the characte-
ristics  of the overflow weir.   In  this  particular case,  the effect  of basin
                                     74

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volume  on  discharge rate  is of  particular  significance since  the storage
basin becomes full  at  about  the same time as the peak inflow, and hence, is
not available for  storage.   The  same explanation applies in the case of 17
percent  storage  to pipe  elements numbers  321  and 323  whose diameters are
greater than those of 9.4 percent storage.

Outflow Hydrographs and Pollutographs

     The outflow hydrographs from District A,  for satellite  storage amounts
equal  to 0, 9.4,  17,  and 41.3 percent  of  5-year synthetic storm runoff
(about  119,000 m   or  31.5 million gallons),  are in Figure 22. 3The peaks of
hydrographs are  respectively  39.8,  34.2, 24.9  and  17.2 m  /sec  (1,407
,1,208,  879  and  607 cfs).   There are two peaks in the  outflow  hydrographs.
The first peak results from  runoff below  the downstream storage basin.  The
first  60 minutes  of  the hydrograph rising limbs for  9.4  and 17 percent
storage  are  identical, since the  storage  basins  are  identically located in
each case.  The shape  of hydrograph following the first peak  is influenced by
the modulating effect  of  the unfilled storage volume remaining, if any, and
the  reduction  in  local runoff  from areas  downstream of  the second  basin.
Overflow from  the  storage basin  can result  in  a' second  peak.   With greater
storage  (41.3  percent), the first peak is  less  than with  less storage  (17
percent) due to  the further  downstream location of storage.  The first  peak
for  9.4 percent  storage is  greater  than  for 17 percent  storage, due  to the
small  storage volume and  earlier  spillage  from  basins.   The  time lag between
the two peaks increases as the storage capacity increases.

     Figure  23 presents  the  5-year,  intermediate-pattern,   synthetic  storm
outflow SS  concentration  and mass  rate  pollutographs   from  District  A for
various  amounts  of satellite  storage.   The effect of   satellite storage on
pollutant loadings  discharged  is  indicated.  The  peak concentration of SS is
lower  with  satellite  storage.   Although  the peak SS concentration  for  41.3
percent storage  is higher than  for  9.4 and 17 percent  storage, this  is not
significant  with  respect to  pollution  control  since  the flow rates are  low
when the high  concentrations occur.   For  example,  at  the time of the peak SS
concentrations for 0,  9.4,   17, and  41.3 percent  storage, the flow  rates are
respectively  0.13,  0.07,  0.07 and 0.02 m /sec (4.6,  2.6, 2.6 and  0.6 cfs).
At the time of peak outflow,  the  SS  concentrations are respectively  7.9,  8.6,
5.8 and 13.4 mg/1.

     Based  on  the current SWMM program, the low  discharge  pollutant  concen-
trations of  intense  storms imply  that  intercepting  of urban runoff for
treatment  during  such times may not be  required  where the concentration,
rather than mass,  of  pollutants  discharged is governing and there  is not  a
need for extremely high quality water.

     The higher SS concentration  with 41.3 percent storage is coincident with
peak storage basin spillage. The same peak  concentrations are found with 9.4
percent and 17 percent storage but at an earlier  time  since spillage takes
place  earlier.  The  mass rate pollutograph for  41.3 percent storage during
 the  first 70 minutes  of  storm runoff is  substantially less  than for 9.4 and
 17 percent  storage.  No storage  results in highest pollutant levels.  Hence,
                                     76

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1,000 -
                           -NO STORAGE
mg/I
Ibs/min
                                                 5-YEAR INTERMEDIATE
                                                   PATTERN STORM
                                                                    41.3%
               20-X       40          60          80
                      TIME SINCE  START OF STORM  (minutes)
100
            120
            Figure 23.  Outflow pollutographs with satellite  storage
                        (5—year intermediate pattern storm)
                                    77

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satellite storage provides benefit in controlling both storm runoff quantity
and quality.

     Figures 24 and 25 present the 1-year and 1.3-month intermediate pattern
storm outflow hydrographs  and SS concentration pollutographs, respectively,
for satellite  storage amounts equal  to  0,  9.4, and  41.3  percent  of 5-year
synthetic storm runoff.    Their  characteristics are similar to those of the
5—year synthetic storm.   Differences are in the magnitude of flow rate and
pollutant concentration.   If  satellite storage  is  located  downstream of the
system,  storage capacity equal to 17  percent of  5-year synthetic storm runoff
volume may  contain all  combined sewage  from  a 1.3-month  return  frequency
rainfall.

     The effect of  satellite storage on  runoff characteristics  from storms
of  advanced  pattern was also  investigated.   Figure  26  presents  the
District A outflow hydrographs and pollutographs  for  a 1-year  return
interval storm.   The shapes  of  the  hydrographs and pollutographs  from ad-
vanced pattern  synthetic storms  of  5-year and  1.3-month  return frequencies
are similar.  Runoff from  the  1.3-month synthetic storm would be fully
contained by a satellite storage  basin of  capacity equal to 17 percent of the
5-year synthetic storm  runoff located at the downstream end of  the system.

     TABLE  9  provides a  summary of  peak discharge, peak  SS concentration
and the  total SS  mass  loading  from a combined  system serving District  A
with various amounts  of satellite storage for  5-year,  1-year and  1.3-month
return frequency storms  of intermediate and advanced  patterns.  The amount of
solids deposited in sewers during  dry days,  as  computed with SWMM is depen-
dent upon  the  storage basin  locations  selected.   For the  cases  being com-
pared, the total pounds  of solids deposited in sewers during  the assumed four
antecedent dry days  are 509, 172, 172 and  395  kg  (1,124,  380,  380 and 872
pounds)  respectively for 0, 9.4,  17.0 and 41.3  percent of  satellite storage.

     The following may be noted from  TABLE 9:

     1.  Peak runoff   rates are  effectively  reduced  by satellite  storage.

     2.  Satellite  storage is  an effective  pollution  control device.

     3.  The difference  between  the  total pounds  of SS  discharged  from  5
        -year  and 1.3-month intermediate  pattern storms  is 328 kg  (724
        pounds)  for a conventional combined system.   For a system storing 9.4
        percent,  17 percent and  41.3 percent of  5-year  synthetic  storm
        runoff,  the differences are  429,  396 and  553 kg (948, 875 and 1,221
        pounds)  respectively.

     4.  The peak flow,  peak  pollutant concentration,  and  total mass loading
        discharge  is less for an advanced pattern storm than for an interme-
        diate pattern storm of the same frequency.

     Satellite storage  basins along  the trunk line of  a  combined  system
result in  the  reduction  of  trunk sewer  sizes   to control  both flooding and
                                    78

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 pollution.   The cost-effectiveness of  providing satellite storage also
 requires  consideration  of  downstream  interceptors,  storage  and  treatment
 facilities as discussed hereinafter.

 POLLUTION CONTROL POTENTIAL OF CONVENTIONAL COMBINED SYSTEMS

     Pollution from  combined  sewage  overflows  has been abated by installing
 flow control systems in large trunks or interceptors  of existing,  well
 designed,  conventional systems  to  contain  peak  flows for  later  discharge
 to  treatment  facilities.   The Cities  of  Seattle,  Washington, Minneapolis-
 St.  Paul, Minnesota, and Cleveland, Ohio have installed dynamic flow control
 systems and  demonstrated  the  feasibility of  remote,  computer directed
 control.  In Seattle, the cost of each  flow control device ranged  from
 about  $60,000 to $450,000 with $150,000 being a  representative  value (18).

     The  above   approach  originated  the  concept  of  the  "advanced  system"
 which  provides  either in-pipe  or  satellite storage  in the  design  process.
 TABLE  10 summarizes the total volume in sewer pipes and storage  basins
 for  both conventional and advanced  sewer  systems.   That part of  the total
 pipe volume available  for storage  would be dependent  upon the number and/or
 location of flow control devices, the pipe  slopes and sewer network configu-
 ration.  The  trunk sewer  of  the  conventional  combined system designed  for
 District A has  a  total storage capacity%f  9.4 mm  (0.37 inches).   This
 storage, if  fully effective, would contain the  total runoff  of  6.6  mm
 (0.26  inches)  which  is  equivalent  to  a  1.3-month  synthetic storm  runoff
 volume  (See TABLE 5).  The 1.3-month  synthetic storm represents a high return
 frequency storm.   By capturing and treating its runoff significant  pollution
 control  can  be  achieved.  The conventional combined system  designed using
 SWMM for a 5-year or more return frequency  contains as much storage (14.2 mm
 or 0.56  inches for District A) as the minimum size advanced combined system
 investigated and  could be equally  effective for pollution control.

 COST COMPARISON OF ALTERNATIVE  COLLECTION SYSTEMS

     The collection system includes the  lateral and trunk  sewers  and  storage
 facilities within each drainage district.   House connections are  practically
 the  same  for  all alternatives  and  were therefore not considered in  making
 comparison.

     The number of  manholes was estimated assuming a uniform spacing  interval
 of 91 m  (300 feet).  For excavation depths  of less than 8.5 m (28 feet),  the
 estimated unit cost was $2,500  and of more  than 8.5 m (28 feet), $5,000.   The
 excavation depth  of a manhole  is measured  as the average.excavation  depth  of
 the sewer it  serves.

     The cost of sewers  is  computed in  accordance with  the unit prices
 of Figure D-15 or  TABLE D-17.   The  excavation depth was determined  as  the
 average of the depths of  the upstream and downstream ends of the sewer at  the
 junction manholes.    The  sewer  depth is determined by  its  invert elevation.
At a junction manhole,  where  more  than   one  upstream  sewer  connects,  the
 lowest  crown  elevation of the  upstream connecting  sewers  was taken  as  the
                                    83

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 TABLE 10.  VOLUME* IN SEWER PIPES AND STORAGE BASINS, DISTRICT A
Description
Separate Storm
Conventional Combined
8.3% In-Pipe
16.5% In-pipe
25.0% In-pipe
41.3% In-pipe
9.4% Satellite
17.0% Satellite
41.3% Satellite
Lateral
Sewer
(inches)
-
0.19
0.28
0.41
0.55
0.83
0.19
0*19
0.19
Trunk
Sewer
(inches)
-
0.37
0.28
0.23
0.18
0.15
0.43**
0.61**
0.94**
Total
(inches)
0.39
0.56
0.56
0.64
0.73
0.98
0.62**
0.80**
1.13**
 *  Total Volume expressed as inches of runoff over the entire watershed
    of District A.

**  Includes satellite storage volume. Note:  1 inch = 25.4 mm
                                  84

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crown  of  the downstream  sewer to  avoid surcharging  upstream sewers  above
their  crown when  the  downstream sewer flows full or near  full.   The minimum
sewer  cover was 1.8 m (6 feet).  Reduction of the minimum cover  to  1.52 and
1.22 m (5  and 4  feet)  would reduce  the  cost  of District A sewer system by
about five and eight percent respectively.

     A  computer  program  was written to estimate  sewer  system  cost.    The
same computer program was used for  all  sewer system  alternatives including
the  separate  storm system.   Although the  assumption  of matching the  down*-
stream sewer  crown with  the lowest of the  upstream sewer  crowns  would  some-
what  increase the  cost  of  the separate  storm sewer  system,  the  increase
should not alter the conclusion.

Cost of Conventional Sewer Systems

     TABLE.  11 summarizes  the  costs  of alternative  conventional  separate
and  combined sewer  systems in District  A.   Compared are the following
alternative systems:

   1.    A  conventional  combined system  with a minimal amount  of  overland
         flow permitted for  urban  runoff.   In this system,  all sewers  would
         carry combined sewage except those at the extreme upstream  end of a
         sewer branch.    These upstream  sewers  would  convey  sanitary  flow
         only as previously described (Case 1).

   2.    A  combined  system with  the same amount  of  overland  flow as  a
         separate storm sewer  system.  The  total  length  of sewers  carrying
         combined sewage  is the same as the  toal  length of separate  storm
         sewers (Case 2).

         Separate sanitary and storm systems with storm sewers  surcharged. In
         this alternative, a significant  amount of  overland flow is permitted
         to  reduce  the length  of  storm  sewers  required  (Cases  3 plus  4).

         A  separate   sanitary  and  storm  system with  storm sewers  designed
         without surcharge (Cases 3 plus  5).

     The costs summarized in TABLE  11 indicate:

   1.    A conventional combined system (Case 1)  would  cost about  the same as
         a separate system with surcharge (Cases  3 plus 4).

   2.    The combined system permitting significant overland flow  (Case  2) is
         the  least-cost   system  with an  estimated cost  about  five  percent
         lower than the cost of Case 1 and Cases  3 plus 4.

   3.    The most expensive  system is Cases  3 plus  5 with  a cost  of  about 13
         percent greater than for Case 1  and Cases  3 plus 4.

   4.    Surcharging  storm  drains  permits  reducing their  costs by  about 20
         percent.
3.
4.
                                     85

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     For urban areas  requiring  storm  and sanitary sewers,  a  combined  sewer
system  (Case 2) would be more  economical  than  separate  systems with  respect
to the  cost of collection sewers.   For areas  where the existing sewers
can be  used to convey  sanitary wastes,  as  in District A, sewer  separation
is the  least-cost alternative  (Case  4 as  compared  to case  2).   However,
where an  existing system  contains  substantial capacity to  convey  part of
the storm flows,  it  may be desirable to intercept in a separate system
only  sufficient  runoff  to  prevent  frequent  flooding.   As  previously  dis-
cussed,  combined  systems,  designed as  described  in this report,   also  offer
advantages for pollution abatement because  of  the storage that can be  made
available in the  pipes.

     In the subsequent cost comparisons of conventional'systems with advanced
combined  systems,  Case  1  is  used since  the  configuration  of the advanced
combined system was compatible with this case.

Cost of Advanced  Sewer Systems

     TABLE 12  presents  a  cost  comparison of  combined systems with various
amounts of  either in-pipe  storage  provided  in  upstream  lateral  sewers to
achieve greatest economy  or  satellite  storage  along the  trunk  sewers.
The costs of collection sewers  for  the entire City were projected from
District  A sewer costs by the ratio of drainage areas.  These costs do
not include interceptors, downstream storage  and treatment facilities.
Storing about  8.3 percent  of  the overland runoff  from a 5-year synthetic
storm in  the lateral sewers would  result  in   the  least  cost  for trunk and
lateral sewers in District A.   The  increased  cost of lateral  sewers is
more  than offset  by  the reduced cost  of  trunk  sewers.   However, while  there
is a  small  increase  in cost (about $1.1 and $1.9  million, respectively) as
the storage volume is doubled and  tripled,  there is  a substantial reduction
of peak outflow which the downstream interceptors and subsequently  downstream
storage and treatment  facilities  may be required to accept.   Depending
on specific  circumstances,  this  increase  on  collection system  costs may
be offset  by capital  investment  required  for  downstream sewer facilities.
For a combined system with  satellite  storage,   the  potential cost  savings of
providing storage may  be  greater than  for  a system with  in-pipe storage
depending on the  unit cost  and  location of  the storage.  In TABLE 12,  sewer
system  costs are presented with  unit costs  equal to $0.08 to  $0.26 per
liter ($0.30 and  $1.00 per gallon) of storage.    This  cost  could vary de-
pending upon the  type  of  storage  basin  required and the environmental re-
straints.   With respect  to  District A,  a satellite storage capacity of  20,800
m  (5.5 million  gallons)  or about  17 percent  of 5-year synthetic storm
runoff  should  result  in the least cost in  the three cases  compared if the
unit  storage cost is $0.08 per  liter ($0.03 per gallon) of storage. At
a unit  cost of $0.26 per liter  ($1.00  per gallon) of storage,  the cost
of collection  sewer  system increases  with  an   increase in storage capacity.
                                    87

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                                 SECTION IX
              DESIGN AND COST  COMPARISON OF ALTERNATIVE CITY-WIDE
                               SEWER SYSTEMS
     An objective of this study was the evaluation of the cost—effectiveness
of alternative sewer system  designs for  a given level of pollution control.
For  the  various alternative  collection  systems developed  (a total  of  9),
the  level  of  pollution control  would  determine  the requirements for  (a)
interception and  treatment  of  runoff  and combined  sewage  before discharge
and  (b)  capital  investment   required  for interceptors,  downstream  storage
and treatment facilities.  Since  the hydrographs and  pollutographs generated
for  the  alternative collection sewers are different,  the downstream system
facilities to  achieve  the  same level  of pollution control can,also be
different.   That  alternative which achieves  the desired  level of pollution
control with  the  least  total  cost  for collector, interceptor,  storage  and
treatment systems,  is the cost-effective system.

     Examination of the  outflow  characteristics  of the various synthetic
storms  from the alternative collection  systems provided insight  to  the
interception and  treatment  requirements.   The effectiveness  in pollution
abatement  of  varying amounts  of  interceptor  capacity and  upstream storage
was evaluated using real rainfall  events over a  period long enough to provide
statistically significant information.

     Near  total elimination  of  runoff  pollutants  from District A associated
with  runoff from  the  5-year synthetic storm with intermediate pattern
would require  the  first 90  minutes  of runoff  from  a conventional combined
system to  be captured  and  conveyed  by interceptors to storage and treatment
facilities  (Figures 3 and 4).  The costs of systems  meeting this severe cri-
terion were estimated.

SYNTHETIC STORM RUNOFF

     City-wide planning requires  development of  runoff  hydrographs  and
pollutographs for  each of the  City's  drainage districts for  the storms of
interest to  develop the required interceptor  and  treatment storage facili-
ties.  The  necessary hydrographs and pollutographs  for each drainage district
were derived from information developed in the detailed study of District A.

     The two  primary  factors governing  the  shape  and  peak flow rate of
the hydrograph for a given drainage basin  are area  and percent of impervious-
ness. The area affects  the peak flow rate, the  flow  duration and the peaking
time of the hydrograph.   The  percent İf imperviousness, which is dependent on
                                     89

-------
land use, affects the runoff volume and the peak flow rate.  Study of 5-year
synthetic  storm hydrographs  computed with  SWMM  for  various  areas  within
District A indicated that  hydrographs  are relatively  similar  in character
within  a reasonable range of -variation  in  drainage  area and percent of
imperviousnesSj and that dividing the  volume by  the peak runoff rate yields a
relatively constant  value in time  units.   Such hydrographs may  be "norma-
lized" by  equating  the  defining ordinates to values  based on Q/^peak where
Q is  the flow rate at given time and  %eak,  the peak flow rate.  The runoff
volume for the synthetic storm was estimated as in  STORM.   With  the hydro-
graph constant  determined from  the data developed for  District A,  the peak
flow was obtained by dividing  the volume by the hydrograph constant and the
values of  the  5-year synthetic  storm  hydrograph obtained  by multiplying the
peak flow  by  the ordinates  of  the appropriate "normalized" .hydrograph.  The
maximum ordinate is  equal to  1  (peak/ peak)  and the  hydrograph  con-
stant equals  the area of the  normalized hydrograph.   Five normalized hydro-
graphs were  developed with data  as summarized in TABLE  13.  The  normalized
hydrograph No. 1 is  based on the hydrographs for sewer  element^ numbers 205,
209,  219 and  223 with  drainage areas of  13.2,  21.8,  58.3 and 21.0 hectares
(32.5, 53.9,  144.0 and  52.0 acres)  respectively.  The corresponding percents
of  imperviousness  of the areas  drained to these  elements  are respectively
60.0, 55.3, 53.5, and 43.0.   The estimated peak flow of 3.14 m / sec (111.0
cfs) for ,sewer element  number 205 was obtained by  dividing the runoff volume
of  634  m  (22,400 cubic  feet) by  the hydrograph  constant of the normalized
hydrograph No. 1 in seconds.
     The  estimated peak flow  for element  numbers  209,  219 and  223 were
computed  in  the same manner.   The agreement between the peak flow computed
with SWMM and that computed using  the  normalized hydrograph,  indicates the
percent of imperviousness affects  the runoff volume more than the hydrograph
shape within  the range of variation considered.   For  other normalized hydro-
graphs, the agreement between the  estimated  peak  flow and that obtained from
SWMM is also  good.   The adjustment of the time of peak flow occurrence with
respect to District A  is listed  in TABLE  14 for four  ranges  of drainage
areas.  The peak outflow from District A occurs 74 minutes after the start of
the  5-year synthetic storm.   Figure  27 presents  two  of  the normalized
hydrographs,  one for  a drainage area greater  than 215 hectares (530 acres)
and one for  area  less  than 60 hectares (150 acres).  The hydrograph for the
larger drainage area has a greater spread and  later  peaking time.   The
peaking time  of the other normalized hydrographs  fall between the two peaks
shown in Figure 27.

     The  5-year synthetic storm  runoff volume in drainage  districts other
than District A were  computed  using the  calibrated  runoff  coefficients of
0.55 for  the pervious  area and 1.0 for  the  impervious  area.   TABLE 15 sum-
marizes the relevant data involved in the  computation of outflow hydrographs
for 24 drainage districts.   Runoff from District  Y drains toward the City of
Newark, and is not served by the Easterly or  Westerly  Interceptor.

     Figure  28 shows  the  outflow  hydrographs  for Districts A, E  and H
respectively.   To  develop outflow hydrographs for drainage  districts other
                                     90

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TABLE 14.   ADJUSTMENT OF PEAKING TIME WITH RESPECT
           TO THAT OF DISTRICT A
           of Drainage
        Area  A
        (Acres)
 Peaking  Time  Ahead of
      District  A
	(minutes)
         A <70

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 TABLE 15.   DEVELOPMENT OF OUTFLOW HYDROGRAPHS
Drainage
District
A
B
C
D
E
F
G
H
I
J
K
L
M
N
0
P
Q
R
S
T
U
V
W
X
Area
(acres)
655
112
111
117
229
88
34
122
70
420
65
66
67
79
103
37
83
303
207
62
331
440
415
138
Normalized
Hydrograph
Used
5
1
1
1
2
1
1
1
1
4
1
1
1
1
1
1
1
3
2
1
3
4
4
1
5-Year Storm
Runoff Volume
(106 ft3)
4.18 :
0.71
0.76
. 0.81
1.57
0.61
0.27
0.92
0.48
2.82
0.46
0.48
0.44
0.52
0.67
0.28
0.60
2.36
1.37
0.44
2.37
3.16
2.77
0.85
Peak
Flow
(cfs)
; 1407
351
376
401
671
302
134
455
237
1015
228
237
218
257
331
- 139
297
967
555
218
971
1137
997
421
Downstream
Inlet
204
200
202
202
202
206
206
208
210
212
210
110
212
: 212
300
300
300
300
108
106
104
102
102
100
Note:   1 acre =.405- hectares; 1 ft3  =0.283 m3
                       94

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than District A for systems with in-pipe or satellite storage,  the respective
ratios of  outflow  hydrographs  of the  various  advanced combined systems  to
the conventional combined  system in District A were used.

DESIGN OF INTERCEPTING SEWERS

     A computer program was  developed  to  obtain the  5-year synthetic  storm
outflow  hydrographs  for  the  24  drainage districts  using the  appropriate
normalized hydrograph, runoff volume, and peaking time.   The  program  output
was stored and used as input to the SWMM TRANSPORT Block for sizing  inter-
cepting  sewers.   The  layout  of  the intercepting sewer system is shown  in
Figure D-14.  It follows  the existing  Westerly and  Easterly Interceptors.
Runoff from  a drainage district  is assumed to  enter  the  interceptor  at  one
inlet  only as indicated in TABLE 15.   TABLE 16 .summarizes the  pipe  slope,
length and ground elevation at the upstream non-conduit element.   The  ground
elevation of  each  pipe element  is used to compute  the excavation  depth  for
the cost estimate of intercepting sewers.   The Easterly Interceptor is about
6.4 km (4 miles)  in length and the  Westerly Interceptor,  4.8 km (3 miles).
The capacity of the existing  interceptor is a small fraction of that required
to convey the peak 5-year  synthetic storm  runoff.

       TABLE 16.    INTERCEPTING SEWER PIPE  ELEMENT  DATA
Pipe
Element
No.
101
103
105
107
109
111
201
203
205
207
209
211
213
Slope
.0005
.0005
.0007
.0005
.0005
.0010
.0010
.0015
.0007
.0002
.0050
.0010
.0018
Length
(ft)
2517
5769
3982
3125
3470
2950
2500
2500
1000
2000
2000
3000
2970
Ground*
Elevation
(ft. MSL)
5.
10.
15.
17.
13.
8.
30.
27.
24.
16.
12.
10.
11.
         *   at upstream non-conduit element
      In the analysis, new  interceptors  were assumed to be required and
 only one  storage basin  and one treatment facility  located near  element
 number  300.   As mentioned  before,  the  U.S. Army  Corps of Engineers has
 planned several  diked  storage basins with an estimated  total  storage  capacity
 of  80,000 m   (21 million gallons)  near  this location.   The Join^ Meeting
 Sewage  Treatment Plant,  now being  upgraded,  will provide  1.76  m /sec (40
 mgd)  of its  wet-weather flow  capacity  for use  by  Elizabeth.    Hence, the
                                     96

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assumption of centralizing storage  and  treatment  facilities is appropriate to
the actual condition.

     TABLE 17 presents a summary of intercepting  sewer sizes for the alterna-
tives investigated defined  by  the  type of  collection  system and  the amount
and types of in-system storage.  Except for sewers carrying sanitary wastes,
all  other  sewers were  sized with  the SWMM TRANSPORT  Block.   Intercepting
sewers for the  conventional  separate system were assumed to have dual pipes
in each pipe  element,  one carrying sanitary waste and the other storm flow.
This dual pipe  sewer  system would  be more economical than one pipe carrying
both  sanitary  waste  and  storm flow because  the off-line  storage required
would be  substantially less (TABLE  18).   The  sewers  intercepting sanitary
wastes  were  designed using Equation 1 to determine  peak domestic  flow
plus  peak  commercial  and  industrial flows.   The peak  domestic  flow  of  a
drainage district was  computed  using the  district population shown in TABLE
D-13. The  peak  commercial  and industrial  flows were  calculated  from  land
use distribution shown in TABLE D-12 and the assumed rate of 187,000 liters
per  hectare  (20,000  gallons per acre).   The intercepting  sewer  sizes for
carrying storm  flow  only  and   for  combined sewage  are  the same  since the
difference of flow rate  between the two systems is  the  sanitary wastewater,
which is  small  in comparison  with the 5-year  synthetic storm runoff rate.

     The  sewer  sizes  required  for  the advanced combined  systems decrease
as  the  amounts  of  in—system storage  increase,  since the  peaks  of outflow
hydrograph from a drainage district decrease.

AMOUNT OF STORAGE REQUIRED VERSUS TREATMENT  RATE

     Ninety-two percent of the  SS would be treated if the initial 90 minutes.
of  runoff  of  the  5-year synthetic  storm  were captured assuming  a
conventional  combined  system is provided in  District A.   The remaining SS
would  be discharged  untreated to the receiving waters.  Since  in-system
storage modifies  the  outflow pollutograph  characteristics,  the duration of
runoff to be captured for equal amounts of pollutant  overflow varies with the
amount  of  storage provided.    In  District  A,  satellite storage  capacities
equal to  9.4,  17.0 and  41.3 percent  of  the 5—year  synthetic  storm runoff
would require   the  capture of  the  initial 92,  100 and 124 minutes of runoff
respectively  to capture  for  the treatment the  same amount  (92  percent of
the  total  in the 5-year  synthetic storm)  of  SS.    The  greater duration of
runoff  to  be  captured results  since  the  period of  significant  pollutant
spillage from storage basins is extended  as the  storage  volume increases.

     For advanced combined  systems with various amounts of in—pipe storage,
the  duration of runoff  to  be  captured was  assumed  to be the initial 90
minutes for  the 5-year synthetic storm.  This is  the  same  as for a conven-
tional combined system.   In—pipe storage, using  a fixed  orifice and overflow
weir  (Figure  16) for  control,  can be  effective during  the  peak  portion of
runoff  hydrograph  starting about 60 minutes after  the  beginning  of the
storm. During this period, dry-weather sewer deposits should be fully clean-
sed  and most of  the  pollutants washed  off the streets would be contained
in  the  next  30 minutes  of  runoff.  In-pipe  storage would delay somewhat the
                                    97

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TABLE 18.  OFFLINE STORAGE REQUIRED  (106 GALLONS) AND COST FOR EQUAL
             WEIGHT OF SS DISCHARGED TO RECEIVING WATERS
Case
No.
1
2
3
4
5
6
7
8
9
Sewer
System
Conventional*
Separate
Conventional**
Combined
8.3% In-pipe**
16.5% In-pipe**
25.0% In-pipe**
41.3% In-pipe**,
9.4% Satellite ***
17.0% Satellite +
41.3% Satellite"1"1"
Treatment Rate
40 mgd
26.67
(7.88)
84.87
(25.46)
78.80
(23.64)
59.91
(17.97).
49.20
(14.76)
37.66
(11.30)
74.21
(22.26)
f
74.81 .
(22.44)
56.98
(17.09)
200 mgd
22.44
(6.73)
78.32
(23.50)
72.28
(21.68)
53.40 ,
(16.02)
42.63
(12.79)
31.14
(9.34)
67.68
(20.30)
67.44
(20.33)
48.45
(14.54)
400 mgd
18 .'43
(5.53)
71.51
(21.45)
65.51
(19.65)
46 . 6.3
(13.99)
35.85
(10.76)
24.37
(7.31)
61.70
(18.51)
60.33
(18.10)
39.62
(11.89)
   Number in the parenthesis are storage costs ($10^) for a unit
   cost of $0.30 per gallon of storage.
  *Capture of runoff starts 30 minutes and ends 70 minutes after
   the start of storm.
 **Capture the initial 90 minutes of runoff.
***Capture the initial 92 minutes of runoff.
  +Capture the initial 100 minutes of runoff.
 ++Capture the initial 124 minutes of runoff.
   Note:   1 million gallons = 3785 m3
          1 mgd = 0.0438 m3/sec
                               99

-------
discharge of  pollutant  mass, but  this  delay would  not  be as  long as with
satellite storage since, under the assumed operating mode, storage would not
be utilized  until  flows in  excess of  interceptor pipe capacity are experi-
enced.

     Runoff  from the  separate  storm system for the 5-year  intermediate
pattern  synthetic  storm,  as  computed by  SWMM,  for  the  first  30 minutes is
practically pollution-free  (Figure 3), and  capture of this small portion of
runoff  (Figure  2),  should  not  be required.   The dry-weather  flow would be
fully  captured  in the  separate  system and  only  stormwater  would  overflow.
Since  stormwater is less  polluted  than  the combined sewage,  less storage
should  be required or  a greater  amount  of  overflow may be  allowed.   The
treatment of 92 percent of the SS would require  storing runoff  for  a duration
of 40 minutes,  from 30  to 70 minutes after  the  start of  the synthetic  storm.

     The  amount of  storage  required  would also  depend upon  the rates of
stormwater  runoff  and  combined  sewage treatment.   Runoff rate,  up to the
treatment capacity, would bypass the storage to  treatment.  TABLE 18 presents
the  appropriate off-line storage  capacity  for  treatment rates  of  1.75,8.77
and  17.54 m /sec (40,200  and  400  mgd).   This range  of treatment  rates
indicates the  effect  of treatment capacity on;downstream storage  costs  of  a
city-wide sewer  system.

     It  was assumed  that  the  required  off-line  storage volume would be
provided near element number  300.

     The off-line storage volume required  generally decreases with the  amount
of  in-system storage provided.   The off-line  storage volumes  required for
9.4  percent  and 17.0 percent of satellite storage are about  the  same  since
the  outflow  hydrographs and  pollutographs  from these two  systems are similar.
 (Figures  22  and  23)

     The  preceding analysis was  calculated  using  SWMM with   STORM default
values.   The  values  have  not  been  verified  by  testing  of   field  samples.
However,  the  relative  relationships developed should be adequate  for  this
stage  of planning.

COST COMPARISON  OF ALTERNATIVE SEWER SYSTEMS

     The cost  of  intercepting  sewers  was  estimated as  described for  the
 collection  sewers.   Sewer   sizes  greater than  4.3  m (14 feet)  in diameter
were replaced  by  multiple  parallel sewer  pipes with  sizes  less  than 4.3
m (14  feet) while  maintaining  the  same total  cross-sectional area.   For
 example,  a  5.8  m  (19  feet)  diameter pipe  as  required for the pipe element
number  205  in a conventional  combined  system  was replaced by two  4.1  m
 (13.5  feet)  diameter' pipes; and  one 7.2,m (23.5  feet)  diameter  pipe for
 element number  207 was  replaced by three 4.1 m  (13.5 feet)  diameter  pipes.
This enabled the use of  the unit costs shown in Figure  D-15  and TABLE D-17.

      The cost  of  the  intercepting  sewers for  the alternative  systems are
 shown in TABLE 19.  The cost of  intercepting sewers  for the advanced combined
                                     100

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systems  is  less  than for  the conventional  separate  or  combined  systems.
The  cost of off-line  storage  was estimated  using  unit  costs of  $0.08 and
$0.26 per liter  ($0.30 and  $1,00  per gallon)  of storage provided.   TABLE 18
uses only a storage  cost  for $0.08 per liter ($0.30 per gallon)  of storage.
Capital cost of treatment  for facilities was estimated using the SWMM STORAGE
/TREATMENT Block.  The treatment processes were assumed to include bar racks
and microstrainers. Sedimentation is assumed to occur in the storage basins.
This essentially conforms  to the contemplated operation of the Joint Meeting
Plant  since  peak wet-weather  flows  are  proposed  to bypass  the  biological
treatment units.  The unit cost of the treatment processes and land, and the
amortization period and interest rate used, were the default values provided
in  SWMM.   The  computed  costs were  converted to the ENR  construction cost
index  of 1800.   The  computed capital costs of treatment  facilities were
$1.07, $3.47 and $6.71 million respectively for  treatment capacities of 1.75,
8.77 and  17.54 m /sec (40,   200 and  400 mgd).   If  more sophisticated  treat-
ment  is  required, these  costs could increase  by  about  40 times  and would
favor larger basins and lower treatment capacities.

     TABLE 19 presents the  total  cost  of  the nine alternative sewer systems
including collection sewers,  in-system  storage,  intercepting sewers, off-line
storage and treatment  facilities.   Two  cost totals  are given, one assumes a
storage  cost of  $0.08 per liter  ($0.30 per gallon)  and  the other $0.26 per
liter  ($1.00 per gallon).   For  each alternative, the  total cost  of the
sewerage system  is about  the same for  the minimum treatment assumed regard-
less of treatment rate. However,  if more  sophisticated treatment is required
(such  as  activated sludge at  the  Joint Meeting Plant),,  the lower treatment
rate would provide substantial cost advantage.   The total costs are presented
in  Figure 29 for the various amounts of in-pipe  and  satellite  storage.
Points A and B  are a conventional separate system computed with a unit cost
of  off-line storage  equal to $0.08 and $0.26 per liter ($0.30 and $1.00 per
gallon), respectively.  The  following conclusions can be drawn:

     1.   In areas where  the  cost  of  off-line storage  is relatively high,
          sewer  separation  would be more economical  than a conventional
          combined system.   On the  other hand, when storage  can be  econo-
          mically  provided,  a  conventional  combined system  would  be more
          economical than a  conventional separate system.

     2.   The maximum  amount of in-pipe  storage that may  be  optimally pro-
          vided  is  about  30 percent of   the  5-year  synthetic storm runoff,
          within the range of costs assumed for  off-line storage. •

     3.   The conventional separate system would be  the most expensive  system
          if storage  (off-line and satellite) can be provided  at a cost of
          $0.08 or less per  liter  ($0.30 or less per  gallon).               ,

     4.   At a  storage cost of  $0.26 per liter  ($1.00  per gallon), the
          conventional separate system  would be more  economical  than an
          advanced combined system with any amount of  satellite  storage
          provided.
                                    102

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     5.    In all instances, an  advanced combined system offers economic
          advantage over the  conventional  combined system.   If  the  storage
          cost is $0.26 per liter  ($1.00 per  gallon),  the total system cost
          would be  reduced  by about  four  percent  when an  optimal  storage
          volume of about  20 percent of the  runoff is provided.  The cost
          would be  reduced  by 20  percent  if  the storage  cost  is  $0.08 per
          liter ($0.30 per gallon)  and the storage volume about 40 percent of
          the 5-year synthetic  storm runoff.

     The above  comparison  demonstrates  the effect  of  storage costs  on the
cost-effectiveness   of  the  alternative  systems.   Assuming  a cost of $0.08
per liter ($0.30 per gallon) of  storage, the least-cost system for Elizabeth
for  treating 92 percent  of  the combined sewage  pollutants from a 5-year
synthetic storm would be about  $200 million.   This cost  is excessive and
alternatives are explored  in Section XII.
                                     104

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                                  SECTION X

                  ANALYSIS OF OVERFLOW QUANTITY AND QUALITY
     In previous analyses, collection sewers,  storage basins  and  interceptors
have been  developed to  essentially  provide treatment  for  about 92  percent
of  the  computed pollutants  in runoff  and municipal  wastes resulting  from
a  long  return  interval,  synthetic,  intermediate  pattern storm  hyetograph.
Pollutants  in  combined   sewage  are  subject  to  random  hydrometeorological
fluctuations. Use of the  same  "design storm" for pollution and flood  control
implies the  desired degree of water  quality protection can  be equated  to  a
level of flood protection in an urban area. This  is not valid.   The severity
and frequency of critical storms  for the planning  of  facilities  for  control
of urban flooding and  of pollution is different.    While  the  total pounds of
pollutants contained in  the  runoff from a 5-year  synthetic  storm is  greater
than, in the  runoff from individual frequent  storms,  the  total pollution
generated  by the frequent storms  is greater  when weighted by the  number
of expected occurrences  per  year. The  concentration of pollutants  in  a
frequent storm may  also be greater.   In  the Elizabeth, area,  about 93  percent
of the  precipitation events  have  a gross rainfall  amount of  less than  25 mm
(1.0 inch)  with the accompanying  street  pollutant washout  aggregating  more
than 73 percent of  the  total.

     To develop reasonable criteria for pollution control,  the  charac-
teristics of runoff quantity  and  quality from frequent storms (1.3 and  0.35
month return frequencies) were evaluated quantitatively using SWIM.  Overflow
control effectiveness  was also  studied,  using STORM, to evaluate   (a) the
dynamic response of the catchment  to  a  series of historical  rainfall  events,
(b) the consequences (overflow quantity and quality)  of  such events,  and (c)
the results in  terms of an average performance  characteristic.   The benefits
of  a  combination of  storage  and  treatment (or  interceptor)  capacity  were
also comparatively  quantified  in  terms   of  overall  performance under the
variety of  hydrometeorological conditions experienced in nature.  The  bene-
fits were  based on the  characteristics  of overflow  quantity  and quality,
using long-term precipitation records.    Statistical analysis developed the
probable  number of  annual overflow  events,  their total volume and  their
discharge quality (total pounds of pollutants)  for  32 alternatives.

     Treatment  rate, as  normally  referred to  in  STORM,  was used as  inter-
ceptor  capacity.  Overflow from each  drainage district was controlled by the
interceptor capacity selected.  Because storage basins  are possible near the
treatment plant  for flow equalization,  treatment  rate  and interceptor  capa-
city could be different.
                                     105

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     Since STORM considers pollutant accumulation on streets, it was used  to
evaluate  the  effectiveness  of street sweeping practices for  source  control.
Data, developed  for District A, was  used to determine the  effectiveness  of
overflow control measures by  extension  to other drainage districts  in
the  City.   Simulation  of  urban runoff from a separate  system  was made  by
specifying zero  storage and bypassing  the  dry—weather  flow (which would  be
entirely  diverted  to  treatment)  routines.   Figure  30 presents  the  annual
amount  of SS  in  street  washout  and  combined sewage  overflows  versus the
amount  of  annual rainfall.   More  pollutants should be removed from streets
and greater pollutant loads  discharged  in combined  sewage overflows  during a
wet year than a dry year.

EFFECT OF STORAGE AND INTERCEPTOR CAPACITY

     On the basis  of a  continuous  12-year precipitation record at  the  Newark
International Airport  and  an  assumed  capture  rate for  treatment  equal  to
the  peak dry-weather flow,  65.8 combined sewage overflow events should
be  expected  annually  from  a  conventional   combined  sewer   system.    Yearly
overflows should  have  lasted a  total of  more than  3.2 percent of the  time.
The  yearly  total  overflow  volume  should have equaled-343  mm (13.5 inches)
over the  entire watershed  of  District  A or  908,000 m  (240.0 million  gal-
lons).   Based on STORM default values,  the  pollutant overflow yearly  should
equal  23,300 kg (51,300 pounds)  of SS  and 11,000 kg (24,300 pounds)  of
BOD.   All sanitary  wastes  were assumed  to be treated  during dry  periods.

     TABLE 20 summarizes  the results  of computer  simulations over a 12-year
period for various combinations of  storage capacity  and  rates of interception
for  treatment.   The  number of  overflow  events,  their volume and the  mass
discharges of  SS and BOD are  listed.   Computer  runs  were  made for storage
capacities ranging from 0 to 50,300  m   (0 to  13.3  million gallons) and
interceptor capacities  from 0.10 to 40 m /sec  (2.4 to  910  mgd).   Case  No.l
in TABLE  20 represents  discharge from a conventional separate storm system.
                                     i
     Figures 31  and  32  present the annual average  number of  overflow  events
and mass SS discharged for  various combinations of  storage volume  and  inter-
ceptor capacity.   The number of  overflow  events and the amount of  pollutants
discharged could be controlled by  increasing  storage or interception rate  or
a combination of  both.   For a given storage volume, ah increasingly greater
interceptor capacity would be required to attain each successive increment  of
pollutant  reduction.    This diminishing  return   also  applies,  for  a   given
interceptor capacity, to storage volume.

     The  amount  of  SS  and  BOD  contained in  street washout  in  District  A
is estimated  as  15,300 and  2,600  kg  (33,800 and 5,800 pounds) respectively
(Case No.  1 of  TABLE  20)  based on  the STORM  default  values for computing
pollutants from  dust and  dirt washed off the street.   This  much SS and BOD
would reach  the  receiving  waters  through  a separate storm system  with  no
treatment.  With  an assumed interception rate of 0.26 m /sec  (6.0 mgd), the
peak DWF,  a  conventional  combined  system  would  annually  discharge   about
23,300 kg  (51,300 pounds)  of  SS and  11,000 kg (24,300 pounds) of BOD  (Case
No.  3).   These  amounts  are substantially  greater  than those estimated for
                                    106

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     TABLE  20.   EFFECT  OF STORAGE AND FLOW INTERCEPTION  OF DISTRICT A
                              SEWER SYSTEM DISCHARGES
Case
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16*
17
18
19
20
21
22
23
24
25
26*
27
28
29
30
31
32
Storage
(MG)
0
0
0
0
0
0
0
0
0
2.7
2.7
2.7
3.0
3.0
3.0
5.3
5.3
5.3
5.3
5.3
8.9
8.0
8.0
8.0
8.0
13.3
13.3
13.3
13.3
13.3
13.3
13.3
Intercepting DWF
Rate
	 (mad) 	
0
2.4
6.0
22.6
41.0
98.9
161.0
355.0
910.0
2.4
6.0
41.0
69.8
82.7
140.9
2.4
6.0
69.8
82.7
140.9
2.4
6.0
22.6
41.0
88.6
2.4
6.0
12.9
22.6
31.7
41.0
69.8
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Number
of
Overflow
Events
. 69.5
68.5
65.8
40.3
22.6
6.6
2.3
0.2
0.
28.0
24.4
7.8
3,3
2.7
1.1
16.0
13.1
1.6
1.4
0.6
9.0
7.8
3.3
1.8
0.8
5.0
3.7
1.8
1.3
1.1
0.8
0.5
Quantity
(MG)
298.7
285.5
240.0
121.0
69.4
21.3
7.8
0.9
0.
185.0
138,7
34.5
16.4
13.0
5,3
131.6
90.4
11.0 .
•8.7
3.7
90.2
63,5
26.5
14.4
5.5
62.1
35.0
23.7
16.2
11.6
7.8
4.1
SS
(Ibs.)
33822
68242
51337
21387
11335
2702
611
23
0
37631
23466
3665
1215
859
203
21658
11913
449
313
92
12962
6670
1355
468
122
6373
2345
995
451
268
162
83
BOD
(Ibs.)
5803
35528
24345
7138
3113
620
149
9
0
18573
10199
1002
336
242
73
11315
5542
169
126
46
7588
3592
622
234
75
4109
1496
630
310
192
119
61
NOTE:   (a)   Assumed Street Sweeping frequency is 7 days  and efficiency
            is  75 percent.
       (b)   STORM default values were used in computing  pollutants from streets
       (c)   *Runs made with precipitation data (1965-1971), otherwise (1963-
            1974)
    Note:   1 mgd
2.628 m3/min;  1 MG = 3785 m3;  1 Ib =  0.453 kg
                                      108

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                                           CURVE A-STORAGE
                                           CURVE B-STORAGE
                                           CURVE C-STORAGE
                                           CURVE D-STORAGE
                                           CURVE E-STORAGE
                                           CURVE F-STORAGE
CAPACITY
CAPACITY
CAPACITY
CAPACITY
CAPACITY
CAPACITY
= 0
= 2.7MG (8.3 % OF*)
= 3.0 MG (9.4 % OF *)
= 5.3 MG (16.5 % OF *)
= 8.0 MG (25.0% OF*)
= I3.3M6(4I.3% OF *•)
                                              * 5-YEAR SYNTHETIC STORM RUNOFF VOLUME

                                              • DATA  POINT
         0     20    40     60     80     100    120   140    160    180   200   220   240   260
                                   INTERCEPTOR CAPACITY  (mgd)
Figure  31.   Annual number of  overflow events  for  various  storage  and
               interceptor  capacities
                                          109

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  100,000
                                     CURVE A-STORAGE CAPACITY = O
                                     CURVE B-STORAGE CAPACITY = 2,7 MG (8.3% OF*}
                                     CURVE C- STORAGE CAPACITY =3.0 MG (9.4% OF *)
                                     CURVE D-STORAGE CAPACITY = 5.3 MG (16.5 % OF *)
                                     CURVE E -STORAGE CAPACITY = 8.0 MG (25.0% OF #)
                                     CURVE F-STORAGE CAPACITY =13.3 MG (41.3% OF *)

                                        * 5-YEAR SYNTHETIC STORM RUNOFF VOLUME

                                        • DATA POINT
o: 10,000
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              80    100   120   140   160   180  200   220  240   260   280
                 INTERCEPTOR  CAPACITY  (mgd)
Annual SS overflow for various storage  and interceptor
capacities
                                         110

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 a separate  system indicating the pollutant contribution of DWF.   The  sanitary
 waste  lost  through  overflows  is estimated  to  be about  two  percent of  the
 total.   Since overflows may be experienced  about 3.2 percent or more of  the
 time,  it appears that as much as 60 percent of  the sanitary wastes  might be
 lost  during overflow periods.   These percentages were  determined  from  the
 estimated total weight of annual SS and BOD contained  in the sewerage wastes.
 The  high percent of  sanitary  waste  lost in the overflows, coupled  with  the
 fact that  most  of the  loss  occurs during the frequent rainfalls and is
 accompanied by high  concentrations of  pollutants, makes  their control signi-
 ficant  to upgrading receiving water quality.

     To reduce  the  SS  in  the overflow from District A by two  orders of
 magnitude,  say to  277 kg (611 pounds)  per year  (Case No.  7 of TABLE 20), it
 would  be necessary  to upgrade interceptor capacity  to 7 m /sec  (161 mgd) or
 to about 18 percent  of the peak 5-year  synthetic storm  runoff estimated for
 District  A.  The same  amount  of  SS  reduction  can be accomplished if 50,300
 m  (13.3  million  gallons)  of  storage is provided and the  interceptor
 capacity is  equal  to  about  0.9  m /sec (20 mgd).   To  reduce  SS in the
 overflow  by one order  of  magnitude,  an interceptor capacity of  about 2.7
 m /sec  (62 mgd) would be required.   Alternatively,  the same  reduction
 should  result from upstream storage  of 36,300  m  (8.0 million gallons)  with
 interceptor capacity  (Case No. 22 of TABLE  20) equal to  the peak dry-weather
 flow.   Hence, combinations  of  storage  and interceptor capacity could be used
 to advantage in meeting pollution control objectives.

     Data in TABLE  20 permit  a quantitative evaluation of the effectiveness
 of various pollution control measures.

 EFFECT OF STREET  SWEEPING PRACTICE

     Dust  and  dirt accumulated  on  streets  during ,dry  days  contributes  to
 water pollution.  A source control alternative is more frequent and effective
 street  sweeping.   Computer  runs,  summarized in TABLE  20, assume a street
 sweeping  interval  of seven  days  and  a  sweeping efficiency of  75 percent.
 The  reported removal efficiency  of  the dust  and dirt averages about  50
 percent and improvement to  70 percent  and possibly as high as 90 percent may
 be feasible under  suitable conditions  if  the  parked  car problem can  be
 surmounted  (19).

     TABLE  21  presents  the simulation  results, using  STORM,   for  various
 street  sweeping  efficiencies   and  intervals.   The  average  quantity of  SS
 in street  washout  is  plotted  in Figure  33 for various  cleaning  intervals
and appears almost  linearly  proportional  to  the street sweeping interval.  If
 the sweeping efficiency is reduced to  0.5, the amount of pollutants expected
would increase by  about 35 percent (Case Nos.  3 and  5  of TABLE  21).   Case
Nos.  6  and  7 present  the effect  of  street  sweeping efficiency  on combined
sewage  overflow  quality.   The numerical  difference  in  pollutant  loadings
between these two  cases  is  about the  same  as  that  between Case Nos. 3 and
5.                    "

     Simulation analysis  by  others  (47) using STORM indicates  the amounts  of
                                    111

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pollutant  contained  in urban  runoff increases  rapidly as  the interval
between successive street sweepings increase until the interval exceeds  about
20 days.   Beyond this interval,  the amount  of  pollutants  in the urban
runoff becomes essentially  constant,  and  the entire  cost  of  street  sweeping
may  be attributed  to  aesthetics.   At  lesser  sweeping intervals,  part  of
the cost may be attributed to reducing pollution.
                                   114

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                                SECTION XI  .

                    INTERCEPTORS FOR POLLUTION CONTROL
     For effective .combined sewage overflow  pollution abatement,  the "first
flush", which  usually occurs early  in a storm runoff  event,  should be cap-
tured  for  treatment.   The  interceptor capacities  required to  contain the
"first  flush"  for  the  alternative  collection  sewer systems  considered  in
District A are  defined  herein.   These  interceptor capacities  are further
considered in  Section  XII  to develop  and compare alternative combined sewage
overflow pollution control programs for the City of Elizabeth.

THE "FIRST FLUSH" PHENOMENA

     As previously  discussed,  the outflow  mass  rate pollutograph in  a com-
bined system exhibits two peaks.  The first peak results from the flushing of
dry-weather flow solids  deposited  in the  sewer  and the  second  from street
washout. The first  peak  is of low volume but with a high concentration and,
perhaps, the  larger mass of  pollutants,  while the  second  is  of  high volume
but with much  lower concentrations as well as less  mass of pollutants.  The
outflow concentration  pollutograph exhibits only  one peak which occurs early
in the  storm when the flow  rates are  small.   The peak concentrations may be
an order of magnitude  higher than  that found  in dry-weather flow.  In consi-
dering the impact on  a free-flowing  stream,  the peak of the overflow concen-
tration pollutograph may be  of primary concern.   The characteristics of this
peak are tabulated as follows:
Synthetic
Storm
Return
Frequency
5-year


1-year


1.3-month
Peak
Overflow
Concentrate
SS	

  (mg/1)

     20
     25

     20
     22

     92
     20
Time to
Peak Overflow
Concentration

(minutes)	

     56
     50

     70
     60

     60
     84
Runoff Volume*
To Time of
Peak Overflow
Concentration

 (mm) (inches)
            Maximum
            Flow Rate
            to Inter—
            ceptor
                                                             (m /sec) (cfs)
2.50
1.60

3.16
1.40

0.30
2.62
0.098
0.063

0.144
0.055

0.012
0.103
 7.05
 5.86

15.55
 4.33

 0.99
 6.09
249
207

449
153

 35
215
*  Expressed in terms of area of District A (265 hectares or 655.1 acres)

                                     115

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     A significant finding  of  the above tabulation is the need  to  control  a
greater volume of combined  sewage for a 1.3-month synthetic  storm than for  a
5-year synthetic storm to achieve equal pollution abatement.

     The  estimated  storage  required  to contain  the  critical first  flushes
from  the  entire  City  is  less  than  80,000  m   (21  million  gallons),  which
is equivalent  to about  4.6  mm (0.18 inches) over  the  drainage area.   This
storage capacity is  being  developed  by the  U.S.  Army  Corps  of  Engineers
along the Elizabeth River near the Joint Meeting Treatment Plant.

     Interceptor  capacities  required  for  containment  of  the  first  flush
from  District  A  are  presented  in  TABLE 22  for storage  basins of  varying
size.   The location and  operating  mode  of storage basins  influence  the
amount of interceptor capacity required to limit  the  pollutants  in overflows
             TABLE 22.  INTERCEPTOR CAPACITY REQUIRED TO CONTAIN
                         FIRST FLUSH FROM DISTRICT A
                                                      „>
                         Interceptor Capacity *** (cfs)
              Storage*     	Synthetic Storm Return Frequency
              Capacity	5-Year	1-Year	1. 3-Month
                 0

                 9.4

                 17.0

                 41.3
                   249

                   218

                   218

                    20
549****

358

361

137
215

127

128**

 49**
 ***
****
expressed percent of runoff  determined  using  SWMM and the synthetic,
intermediate pattern,  5-year return period hyetograph.   The  storage
basins are located as defined in Figure 22.

with storage located at  the  confluence  of  the trunk and interceptor,
the entire storm volume would be stored.

assumes  intermediate pattern storms and suspended  solids concentra-
tion of less than 20 mg/1 in any overflow.

reduces  to  153  cfs  if  the  maximum allowable  concentration in  the
overflow is 22 mg/1.
        Note:   1 cfs = 0.0283 m /sec.
                                     116

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to a  specified  value.   The operating mode has  a  greater effect upon storage
located  close  to or  at  the confluence  of  the  trunk and  interceptor  sewers
than  if  located  upstream.   If  storage  is  operated so  that there is  zero
discharge from  the basin  until  it  is  full,  the interceptor  capacities  re-
quired for  upstream and downstream  storage  locations for storms  of  various
return intervals  are  tabulated below.   This  tabulation  assumes intermediate
pattern storms and  a maximum permissible concentration of  SS in the overflow
of 20 mg/1 using STORM default values.
                                          Interceptor Capacity
Storage
Location
Upstream*
Downstream
Storage*
   17
   41.3

   17
   41.3
       Synthetic Storm Return Frequency
     5-year       	1-year  	1. 3-month
                            m /sec  cfs
                                 3             3
                                m /sec  cfs   m /sec
                                           cfs
 6.17    218      10.22   361    3.62    128
 0.57     20       3.88   137    1.39     49

39.85   1407      15.52   548  No Discharge
25.20    890       0.28   108  No Discharge
*  In percent of runoff computed using synthetic, intermediate pattern,
   5-year return interval storm hyetograph.

** Located where defined in Figure 22.

     Runoff  from the  frequent  storm  (1.3-month  return frequency) would  be
completely contained  within the downstream  storage  volume.   The  rare  storm
(5-year  return  frequency)  would  require  interceptor  capacity  equal to  the
peak runoff rate with 17 percent downstream storage volume and equal to  about
63  percent  of  the peak  runoff  rate with  41.3 percent downstream  storage
volume.   Less  rare,  but  still severe,  storms  (1-year return frequency)
would require about  52 percent greater  capacity with  17 percent  downstream
storage volume,  but  about  21 percent less capacity with 41.3  percent  down-
stream storage  volume than  those with upstream storage.   This reversal  in
trend basically  results  from less dilution  of the  first flush with  smaller
amounts  of  storage.    Where the  interceptor  capacities indicated  above  for
downstream storage  are in  excess of  those  shown for  upstrem  storage,  they
could be reduced by changing the operating mode to permit discharges equal to
the interceptor capacity during the storage fill period.
                                    117

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                                SECTION  XII

                  ALTERNATIVE POLLUTION  CONTROL  PROGRAMS
     While  removing  almost  all pollutants  from  a 5-year  synthetic storm
might  be  desirable  in areas  draining to  environmentally  sensitive waters
demanding very high quality effluent discharges, it is not normally  required
to protect  the environment.   In the  development  of a  feasible program for
acceptable pollution control in Elizabeth,  a maximum treatment  rate of
1.75  m /sec  (40  mgd)  (as  is  available  to the City at the Joint  Meeting
Plant), and a storage  capacity of  about 80,000 m   (21 million  gallons) near
the treatment plant  (as  is  being  developed by the Corps  of Engineers)  are
assumed to be an integral part of the cost-effective program.

     The alternatives compared are shown in TABLE  23.  The variables include
(a) ratio of  interceptor  capacity  to the peak  5-year synthetic storm runoff
rate  and  (b)  amount and  location  of  in-system   storage.    The  interceptor
capacities  investigated  ranged from 1.4  to 100 percent of  the peak 5-year
storm runoff  rate as computed  from the intermediate pattern  synthetic hyeto-
graph. The  overflow  concentrations  for  the selected standard, intermediate
pattern storms of 5—year, 1-year and 1.3-month  return intervals  were  obtained
using  SWMM.   The annual  overflow  frequencies  and  mass pollutant  discharges
were obtained using STORM and  are based on  analysis of a 12-year,  continuous
real  rainfall record.   The annual  overflow characteristics  are the  primary
influence in determining  the "cost-effective"  alternative.   Hence,  the
findings are  based  on real rainfall events rather than on  synthetic hydro-
logic phenomena.

     For  each alternative,  interceptor sewers were  selected  and the cost
estimated.   The ratios  of regulated flow  to the peak  5-year  synthetic
storm  runoff  obtained from District A were used  to  modify the  unregulated
5-year  synthetic  storm  hydrographs  of the  remaining  drainage districts to
obtain  the regulated  outflow  hydrographs  required to  size the  interceptor
sewer.  Downstream storage  of  80,000  m  (21 million gallons)  is more than
adequate for  containment of the environmentally significant  portion of runoff
except for Case Nos.  6 and 7 where additional storage would  be  required.  The
cost  of downstream  storage included  only  the pumping  station required to
lift  interceptor  flow to the  storage  basins  for   later treatment.   The unit
cost  of satellite and  off-line storage of  $0.08 per liter  ($0.30  per gallon)
was used in the comparison.

CONVENTIONAL  COMBINED SYSTEM

      Case  Nos. 1 to  7 of  TABLE 23 apply  to   conventional  combined systems
                                     118

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M

S3.
                         CO 01 O irt O  i-l CM     mvDu-tmiHOONiHC
                         co co [-* 1-1 o  \o       o\ CM     co co CM    CM
                         rH i-H CM t-t iH                                ,-|
                         CO CO vO CO u") CO CM    COt
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3
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                               cji o m co o

                         ^ooor-*\oio-a-co^
                                                           119

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with various rates of flow intercepted for treatment.  The effect of increas-
ing interceptor capacity on pollution  control  and  costs  are evident.   Figure
34  presents  for various  ratios of  interceptor  capacity to the  peak runoff
rate of  the  adoped 5-year synthetic storm the estimated (a)  combined sewage
SS  concentrations discharged to receiving  waters, (b)  annual number  of
overflow  events from  District A  and  (c) cost,  assuming  new  sewers.   The
difference  in cost  between  the  systems  results  from the alternatives  for
interceptor  sewer  and  pumping  station capacity.   The cost  of  the collection
system is the same for all alternatives.
     The findings in TABLE 23 are summarized as follows:
 1
 2
 3
 4
 5
 6
 7
Pollutants*
Captured for
Treatment (%)

    58
    95
    98
    98
    99
    99.9
   100
    Number of
Overflows per year
(1 hour or more)

     40.3
      6.6
      3.8
      3.5
      2.3
      0.2
      0
  Overflow in
1-i 3-month Storm
Duration (Min.)

      26
      18
       4
       0
       0
       0
       0
 *  % of  annual  SS overflow for Case No. A  (TABLE 23) captured and '
 treated.

     In  terms  of  pollution  control,  there appears  to be  little  reason to
 provide  facilities better than those included in Case Nos. 3 and 4.  Based on
 the  estimates developed herein,  it appears  the  maximum justifiable cost for
 combined sewage  pollution  control  is less  than  $96,000  per  hectare  ($25
 million  per square  mile)  and is  about 21 percent greater than for Case No. 1
 which  would only capture for treatment about two-thirds  of the pollutants.
 By utilizing the storage available in the combined system through devices to
 control  routing as previously discussed,  pollution control  better than  that
 offered  by Case No.  4 might be achieved  for  somewhat  more  than $89,000 per
 hectare  ($23 million  per square mile)  (Case No.  11  with a conventional  system
 plus storage regulators).

 ADVANCED COMBINED SYSTEM

     An  advanced system differs  from a conventional system in that storage
 capacity and controlled routing is built  into the system.  The conventional
 combined system, designed to convey flows determined using  the  5-year  return
 frequency,  synthetic, intermediate-pattern hyetograph,  has  sufficient  volume
 to  prevent overflow from storms  with a return frequency of  1.3-month if  flow
 routing  devices are installed.

     A storage  facility  may be  operated  to permit  either  (a)  no diversion
 to  storage until downstream sewer capacity is reached  (to minimize operating
 cost), or  (b)  diversion to storage with  controlled,  low rate  outflow until
 storage  is  full (to maximize pollution  control benefits).   With the first
                                     120

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400 i-
                                                               -.200
                         NO STORAGE  PROVIDED
                     NUMBER OF OVERFLOW EVENTS
                                                                         60
                                                                         50
                                                                         40
CO
I-
z
LU

Ld


5?
o

li-
ce
Ld
                                                                         30
                                                                            cr
                                                                            Ld
                                                                            m
                                                                         20
                                                                            <

                                                                            z
                                                                            z
                                                                            <
                                                                          10
                                                                  120
                   O.I             0.2             0.3             0.4

                INTERCEPTED  FLOW/PEAK 5-YEAR STORM  RUNOFF


       Figure  34.   Pollution Control Costs - Conventional Systems
                                     121

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operating mode,  the peak  flow to be  accepted  for pollution control  is
a~bout 15  percent or  less  of  the  peak runoff  from the synthetic  storm  of
5_year return  interval  used herein.  This  amount is less  than the reduced
peak flow from the 5-year synthetic  storm for the  amounts of upstream, storage
investigated (up  to  41.3 percent of the 5-year  synthetic  storm runoff vol-
ume). Hence,  upstream  storage  would not  reduce  the  size  of  intercepting
sewers required for pollution control under  this operating mode.

     With  the  second  operating mode,  the highly polluted  initial  runoff
is mixed  in the  basin  with  the  less  polluted later  runoff.   Case Nos.  8
to 14 of TABLE 23 compare alternative advanced combined systems with upstream
in—system storage.  The  findings are summarized as  follows:
           Pollutants
Case       Captured for
No.        Treatment (%)

  8            98
  9            99+
 10           100-
 11            99+
 12            99+
 13           100-
 14          .100-
    Number of
Overflows per year
(1 hour or more)

      1.8
      1.1
      0.5
      2.7
      1.4
      1.1
      0.6
  Overflow in
1.3-month Storm
Duration (Min.)

    26
     0
     0
     0
     0
     0
     0
There  appears little justification in providing facilities better  than
those  provided  in Case  No.  8.   This  alternative  costs about  $81,000 per
hectare  ($21  million per square  mile)  but is predicated on  a large, volume
of upstream  storage.  Case Nos. 11 and  12,  and 13 and  14 compare  costs
for  lesser amounts  of  storage  with equal  interceptor  capacity.    In  both
instances, increased  storage reduces costs by about $3,900  per  hectare ($1
million per square mile).  All  the alternatives provided  for a high degree of
solids capture at a  cost ranging  from six  percent to 28  percent greater than
a conventinal combined system.   The upper  permissible  limit of expenditures
would.be  fixed  by  that  system which  exploits  the storage  available  with
the  conventional combined system most effectively (similar to Case No.
11).  This  system  cost is estimated  at about  $89,000 per  hectare ($23 million
per square mile)  and is  about  19 percent greater than  the cost of a conven-
tional combined system.

     The  effect of upstream versus  downsteam locations  for satellite storage
facilities is  shown  as Case Nos. 15 and  16.    Relatively  small  amounts of
storage  (Case Nos.  11 and 15)  are more  advantageously  located upstream
for pollution control if the capital costs are to be maintained about equal.
Large amounts of  storage in the upstream collection system (Case Nos. 10 and
16) result in lower  costs than those at  the  confluence with  the interceptor,
since the  size of the trunk  sewers can be reduced.

     The  relation between mass  pollutant  capture and  system cost  for the
indicated  range of interceptor  capacity  is  presented in Figure  35.
                                    122

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                                                                        175
                                NOTE:
    84 i-
                          STORAGE LOCATIONS ARE

                          DEFINED IN FIGURE 40.
   86  -
    88
 CO
 co
   90
                                          NO STORAGE
 O
 o.

 co
 CO
   92  •
 UJ
 QL
 O.
 <
 O
UJ
•o
cc
   94 -
   96 -
   98 -
   100
                                                                       170
                                                                       165
                                                               (O

                                                            160 —
                                                                UJ
                                                                I-
                                                                co

                                                                CO
                                                            155
% CAPTURE



COST
                                           ASSUMED  STORAGE  COST

                                             0.30 PER GALLON
                                                                       150
                                                                a:
                                                                ui
                                                                S
                                                                UJ
                                                                CO

                                                                u_
                                                                o
                                                                CO
                                                                O
                                                                o
                                                                       145
                                                                       140
                                                                       135
         0.05             0.10             0.15

  INTERCEPTED  FLOW/PEAK 5-YEAR  STORM RUNOFF



Figure 35.   Pollution Control Costs - Advanced System



                            123
                                                                    0.20

-------
     Interpretation  of  this  figure  indicates  the  following for  a  capture
rate of 96 percent of the suspended solids:
In-System**
  Storage

    0

    9.4

   17.0

   41.3
Ratio:
Interceptor Capacity
to 5-year Peak* Storm
	Runoff	

   0.124

   0.057

   0.031

   0.006
Capital
Cost,
($iob)

 164.4

 151.2

 136.0

 138.5
    *  Based on intermediate pattern synthetic hyetograph
       adopted for this report.

   **  In percent of volume determined from intermediate pattern,  5-year
       synthetic storm hyetograph.

    For  lesser capture  rates,  there  is  almost  no cost  reduction if  41.3
percent storage  can be  provided, but  the cost  reduction  increases with
decreased capture as  the  amount  of  storage  reduces.   The minimum cost still
occurs at about 17 percent storage.

    For  greater capture  rates,   the  greater  the  amount  of  storage  within
the  range tested,  the lower  the increase in  costs.   At  about  98 or more
percent  capture,   it  becomes  economical  to  provide  41.3 percent  storage.

DESIGN STORM CONSIDERATIONS FOR  SEPARATE AND COMBINED SYSTEMS

    In  design  of  a separate storm  system,  the  pollution control  aspects are
less  controlling  than the  flood damage aspects.   Hence,  cost-effectiveness
is  largely determined by  benefits to  be gained  from relief of  flooding.
In design of  a combined  system,  the pollutional control aspects are predomi-
nant  and  cost-effectiveness   is  determined by  the facilities necessary  to
achieve  appropriate pollution abatement.  These conflicting standards  affect
the selection  of the  design storm.

    As  the sewered  area contributing to a  single outlet  increases,  the
cost  of sewers increases,  and at a more  rapid irate than  the drainage area.
This  results  since the  relative lengths   of  larger  size pipe required in-
creases  and the unit  cost  for pipe greater than about  2.1 m (84 inches)  in
diameter increases  faster than the carrying capacity.   Hence, for protection
of  a fixed property  value  from  flood damage,  the justifiable investment  in
storm drains  would remain  essentially  fixed,  and as  the  drainage area^in-
creases, the  storm return frequency  for   which  protection  can  be provided
reduces•

     In  considering pollution abatement,   however,  in-pipe  storage  can  be
                                     124

-------
justified as  a significant  element  of a  cost-effective program.   As  pre-
viously  discussed,  the conventional combined system  has about  the  same
total pipe volume  as the advanced combined  system  with  8.3 percent in-pipe
storage,  and  can  provide storage  for  about  3.8 mm  (0.15  inches)  of runoff
with appropriate flow control devices  (TABLE  10).

    If a 2-year synthetic storm is  used, the  total volume in the sewer system
would be reduced by about 5.1 mm (0.20  inches)  or the potential for  in-system
storage would be significantly reduced.  However, the cost of the collection
system would  be reduced by  more than  20  percent,  or more  than  $13,900 per
hectare ($3.7 million per square mile).  At  a  cost  of $0.08 pej: liter ($0.30
per  gallon),  this  saving   could  build more  than  45,000 m  (12 million
gallons)  of  storage or  more than  13,600 m   of storage at  $0.26 per liter
(3.7 million  gallons at $1.0 per  gallon).   These  volumes  are equivalent to
more than 17.5  and  5.3 mm (0.69 and 0.21 inches) of  storage respectively, or
37  percent  and 12  percent   of  the runoff volume  from  the  selected 5-year
return interval storm hyetograph respectively.   Hence, if sites are  available
for  construction,  satellite  storage  is more  economical than using sewers
sized for a  larger  return interval storm  for  pollution control.    Designing
sewers to provide flood  control protection for  less frequent  return interval
storms on  the basis of  pollution  control  is even less  justified.   The in-
creased  cost  per hectare  for a  sewer system  designed  based on  a 10-year
return period storm is more  than $17,400 per  hectare ($4.5 million per square
mile).   The   system  would  provide  a potential  storage  volume for  pollution
control  of about  7.1 mm (.28 inches) of  runoff or about  18,500 m  (4.9
million gallons) of storage.   Such  design  is  not cost-effective for  pollution
control  because of  the  high  cost  of  such  storage.  Hence,  selection  of  a
5-year return interval  storm design  criteria can be justified for  pollution
control if there is no other alternative for  obtaining storage.  If  there are
alternatives  for providing storage, a  2-year design storm for flood control
could  be ample except  in high  risk  areas  where  the potential  for damage
justifies greater protection and investment.  With  protection  based on
a  design  storm with a  2-year return  interval, flooding of perhaps  one-half
hour duration would  be expected every five years and lesser flooding at more
frequent intervals.
                                    125

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                                SECTION XIII

                                 APPENDICES

                                                                   Page
A.  ALTERNATIVE MODEL EVALUATION	127
        EQUATIONS OF MOTION	127
        COMPARISON WITH MANNING'S EQUATION	131
        COST OF SOLUTIONS	136
        FINDINGS	..137
        MODEL OPERATING CHARACTERISTICS	137
        MODELS EVALUATED	 138
             Corps of Engineers' STORM	139
             EPA - Storm Water Management Model (SWMM)	141
             University of Illinois - Storm Sewer Simulation
                Model	142
        COMPARATIVE EVALUATION	142
        THE RATIONAL METHOD	143
        METHODOLOGY	 .145
B.  MODIFICATION OF SWMM AND STORM PROGRAMS	147
        SWMM	147
        STORM	148
C.  QUANTITY AND QUALITY CONSIDERATIONS, SWMM VS STORM..	150
        QUANTITY	150
        QUALITY	151
D.  MODEL INPUT DATA	 .154
        LONG-TERM METEOROLOGICAL DATA	154
        FIVE-YEAR SYNTHETIC STORM HYETOGRAPH	159
        HYETOGRAPHS OF LESS INTENSE STORMS	161
        DEFINITION OF DISCRETE ELEMENTS	165
        HYDRAULIC PROPERTIES AND LAND USE	 .172
        DISTRICT A DATA FOR STORM.	 .172
        AREA AND LAND USE FOR OTHER DISTRICTS	184
        DRY-WEATHER FLOW QUANTITY AND QUALITY	185
        UNIT COST DATA	..192
             Sewer Costs	 .192
             Storage Costs	192
             Pumping Station Costs	195
             Treatment Costs	195
E.  CALIBRATION OF STORM RUNOFF COEFFICIENTS	..197
                                  126

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                                APPENDIX A

                       ALTERNATIVE MODEL EVALUATION
    There  are  at  least  24 models  available  for  the  assessment,  planning',
design  and control of  sewer systems  (20).   These models compute  time-vary-
ing  runoff as  opposed to  steady state  analysis.   However,  they differ  in
scope  and purpose  and in  the mathematical  detail of  routing flow  through
sewers.   In essence,  the difference  is  in  the approximations made to  model
the complete  momentum equation.   The  simplest models  use Manning's equation
or  similar formulae.  Simplification  of  the  momentum  equation  affects  the
sizing  of  collection sewers  and downstream interceptor,  storage and treatment
facilities  (17).   As  part of  the study,  Resource  Analysis,  Inc.   (RAI),
Cambridge, Massachusetts  made an  evaluation  of sewer design equations.   In
addition,  RAI  evaluated the applicability of  available  stormwater  management
models.

    Stormwater  simulation models  use the governing  equations  of  motion
-  continuity  and momentum  - to  numerically   predict the  flow in  stormwater
systems. Fo.llowing  is an analysis of  the momentum equation, evaluating  the
relative importance of the various terms  in  this  equation.   A qualitative
analysis of the effect of  eliminating some  of these terms was investigated,
focusing on the accuracy  of the simulation predictions,  the  cost of unproved
accuracy, and the potential mis-design of  the  resulting  structure.

EQUATIONS OF MOTION

    The  governing  equations  of   motion for  one-dimensional  unsteady open
channel flow (21,22) are:

Continuity Equation:
                          A-
                            (a)    (b)   (c)   (d)
                                                            (A-l)
Momentum Equation:
                     (e)  (f)    (g)
 dx   
-------
Where:


     A  s  the cross-sectional area of the channel,



     v  s  the mean flow velocity,



     x  =  the downstream distance along the channel,



     B  -  the surface width  of  the channel,



      S  =  the friction  slope,  ,



      S  =  the bed slope,
      o


      y  =  the water depth,



      t  =   the  time,



      g  s   the  gravitational constant, and



      q   =  the  lateral inflow.


 Figure A-l presents a definition sketch for the equations of motion.
            Figure A-l.  Definition sketch for equations of motion






  The assumptions made to arrive at these equations are:


       1.  The  flow  is  one  dimensional,  i.e.  uniform velocity  distribution
                                       128

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         across each cross section,  and  the  free surface is horizontal across
         the section,

     2.  pressure is hydrostatic, i.e.,  vertical  acceleration is neglected,
         and

     3.  boundary friction  and/or  turbulence may  be accounted  for  through
         Manning's equation.

These  equations  can  also be applied to cases  of flow  in partially  full
pipes,  with the  proper  definition of  area  and friction terms.  The terms in
Equations A-l and A-2  can be described as:

    (a)   prism  storage  term due  to  variations  in velocity with space,

    (b)   wedge storage  term due to  variations in cross-sectional area  with
          space,

    (c)   rate-of-rise  term  that describes  the  changes  in storage due to
          water surface elevation variations over time,

    (d)   lateral inflow  term that  represents the net inflow  from  lateral
          sources,

    (e)   bottom slope term,

    (f)   friction slope term,

    (g)   water surface slope term (pressure force),

    (h)   convective  acceleration  due to  spatial variation in velocity,

    (i)   local  acceleration due  to temporal variation in velocity,  and

    (j)   term indicating momentum change due  to lateral inflow.

     Various  mathematical  models for  flow  routing have  been  proposed  in
the literature.   These  models can be classified  according to which terms of
the governing equations they include  in  their  solution.  Some general classi-
fications are (neglecting lateral inflow):

     1.  Storage  Routing Models - use continuity equation only,

     2.  Kinematic Wave  Models - use continuity equation,  and  friction (f)
         and bottom slope (eX terms  of momentum equation,

     3.  Diffusion Wave Models - also include pressure  term (g)  of momentum
         equation,

     4.  Dynamic  Wave  models - use all terms in momentum equation.
                                    129

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     Only the Dynamic  Wave  Models  can describe exactly all  of  the effects
present in  a  flow motion since  these  are  the only models  that  retain all
of the terms  in  the momentum equation.   For many practical situations,
some of  these terms may  be  ignored resulting in a significant reduction in
the cost  of simulation runs.   An order of magnitude  analysis of  the terms
in the momentum  equation can give some  indication  as  to the importance
of each of  these  terms.   A compilation of the  range  of  typical  values for
these  terms is  presented in  TABLE  A-l.    These values were  obtained  from
Schaake (23), Henderson (21),  Eagleson  (24)  and experience with these
models.

   TABLE A-l.  RANGE OF TYPICAL VALUES FOR EACH TERM IN THE MOMENTUM EQUATION
    Term
Overland Flow
  (ft/sec2)
Pipe & Gutter Flow
    (ft/sec2)
Streamflow
 (ft/sec2)
          (e)
 0 - 3.20
    0 - 1.60
  0 - 0.30
    gSf   (f)       0 -  3.20
      3x
          (g;
    vl*  (h)
      ox

      £  <Ğ

      *  Ğ)
 0 - 0.10
 0 - 0.01
 0 - 0.01
 0 - 0.001
                       0 - 1.60
    0 - 0.60
    0 - 0.30
    0 - 0.30
    0 - 0.05
                         0 - 0.30
  0 - 0.005
  0 - 0.002
  0 - 0.0005
  0 - 0.005
          Note:  1 ft/sec2  =  0.305 m/sec2
     The local acceleration (i) and  lateral inflow (j) terms appear to
be  relatively  small for all  cases.   For overland  flow  and  steep  streams,
the water surface  slope (g) and convective acceleration (h) terms  also
appear to be of small magnitude when compared to  the bottom (e) and friction
(f) slope  terms.   Henderson  (21) has  shown that for  most streams  and for
Froude numbers  less  than 1,  the acceleration terms  due  to spatial  (h) and
temporal variations  (i)  in  velocity  are  much smaller than the acceleration
due to the water surface slopes (g).   For Froude numbers higher  than 1
                                   130

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all  three terms  (g),  (h) and  (i)  are  of  the same  order of magnitude  but
these cases  only  occur in mountain torrents where  the  bottom slopes  (e)  are
much  larger.   Flows with high  Froude  numbers  may also occur  in  urban  storm
drainage  systems.   But in these systems, the  effects  of  control  structures,
e.g., weirs,  flow dividers,  etc.,  produce more noticeable flow changes  than
the additional terms (g), (h) and (i)  in the momentum equation.

     For  flow  in  pipes,  the  water surface slope  (g)  and  convective accelea-
tion  Ch)  terms  may be large enough to be significant  relative to the bottom
(e) and friction  (f) slope terms.   Terms (g)  and  (h)  are  the key  to*modeling
the dynamic  (e.g.,  backwater, subsidence) effects  that  are sometimes  present
in pipe flows.  The major difference between  a pipe system and stream system
is that pipe systems are usually surrounded by highly  urbanized  catchments.
These catchments  respond much  more  quickly and  with  higher  lateral  inflow
rates  than  non-urban  catchments.  Therefore,  terms (g)  through  (j)  are
relatively larger for pipes  than for streams.

     An order  of  magnitude  analysis  can only give an indication as to  the
relative  importance of the different  terms.   But  it is unlikely that  a
very small term in the momentum equation could have any significant effect on
the  solution to  the equations  of  motion.    With this condition,  only  the
bottom (e) and  friction  (f)  slopes appear significant  for overland flow  and
steep sloped streams.  For mild sloped streams and  for pipe  flows,  the water
surface slope (g)  may be significant.  In addition, for pipes the convective
acceleration term (h) may also be significant.

COMPARISON WITH MANNING'S EQUATION

     If Manning's  equation is used  as  the basis  to establish  a relationship
between depth  of  flow and  discharge,   the  influence  of   the smaller terms
in the  momentum  equation  is  of  interest.    Manning's equation  provides  a
relationship among  the flow  velocity,  v,  depth  of  flow and shape  of  the
channel cross section  as  expressed  through  the hydraulic  radius,  R,  and  the
friction or energy grade line slope,  Sf.   The  relationship is:
                                                         (A-3)
In which "n" is Manning's resistance  coefficient.   Equation A-3 may be
solved for the friction slope,  Sf,  to  yield:
                                 (l.49)2R
(A-4)
                                   131

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which  may then be substituted into the  complete momentum Equation A-2.
The latter is solved for the flow velocity,  v,  giving:
   1.49 ^2/5,
v =	R    '
a y   v
>x   g
                                           '
                                           g
                                                  (A-5)
If  the  flow is steady, (^=0),  uniform,  (y^=0),  and there is no  lateral
inflow, (q = 0), all but the first 'of the terms in parentheses  disappears  and
Equation  A-5 is  reduced  to  the  familiar  form of  Manning's  equation that
is:
                              1.49 D2/3C
                           v=—R    S0
                                 (A-6)
     The  significant difference between  Equations A-3 and A-6  must  be noted.
In  Equation A-6 the term S  ,  is  a known geometric property of  the channel,
hence  a unique, known relation exists between velocity  and  hydraulic radius
 (or,  as  more  commonly  expressed,  between  stage  and discharge).    But,  in
Equation  A-3  the  slope,  Sf,  is  in  general not known,  and,  from Equation
A-5, the  friction  slope  depends  on the rates at which the depth and velocity
are changing.

     Equations A-5 and A-6  may  both be considered to be forms  of  Manning's
 equation.  However, the  latter is  a special  case  and  thus  limited  in  its
 application.   The effect of the  extra terms  in  Equation A-5 is  readily
 demonstrated for the case of a prismatic channel of constant bottom slope and
 having no lateral  inflow.  For this case, the two equations provide relations
 between stage and  discharge which may be plotted in Figure A-2.
        ui
        o
        <
        t-
        V)
                         EQUATION A-5

                         EQUATION  A-6
                                           DISCHARGE, Q

          Figure A-2.  Uniform flow rating curve and loop  rating  curve
                                     132

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Equation A-6  gives  a single-valued  relation,  while Equation A-5  is  multi-
valued  according  to whether  the stage is rising or falling with  time.
The latter describes a loop—type  rating  curve.

     The relation  between stage  and discharge at  a given  channel  section
depends on whether  one  is on the rising or  falling limb  of  the hydrograph.
Although not  shown  in Figure A-2,  the  shape  the  loop rating  curve  is not
unique, but  is directly  dependent  on  the  shape  of the  inflow hydrograph.

     Three points on  the  loop  rating curve, A, B,  and  C,  are of particular
interest.    At point  A,  the instantaneous  gradient of depth  with distance
is  identically zero and Manning's  equation  in  the form of Equation A-6
is  applicable.  However, neither  the peak discharge nor  the peak  stage
occur at  this point.   The peak  discharge  occurs  at  point  C  prior  to the
occurrence of the peak stage which is  at point B.   Thus,  the peak stage and
discharge develop a phase shift  which  makes it difficult to  determine the
peak stage from the  peak discharge.

     If by routing  an accurate  value for the  peak  discharge,  Q ,  is  deter-
mined,  the  peak stage at  point  B must  still  be determined.   Substitution
of  the  peak  discharge,  Q , into Manning's Equation A-6 would  yield  a stage
at point D which is too tiigh.  In this  sense, use of Manning's equation will
in general lead to  conservative predictions of peak  stage.

     This tendency  to overestimate  the  peak stage  is  reinforced  since the
peak  discharge  and  peak  stage  do tend  to   subside with  distance down the
channel. This effect would not be'predicted without  the higher order terms of
the momentum  equation.   Hence,  any procedure  such  as  direct translation of
the inflow hydrograph to downstream locations or the kinematic routing model,
both  of which fail to  reduce the peak discharge, will  overestimate the
discharge and thus  add to  overestimation  of the peak stage.

     The problem  may also  be  reversed.   Substitution of the  peak  stage,
YB,  into  Equation  A-6  will  yield a  discharge, Q ,  which  is clearly
smaller than the true  peak, Q  .  Hence, Manning's equation can tend to
underestimate the  peak discharge.

     A  similar  situation  occurs  when  one  uses the  Manning's  equation to
estimate the discharge capacity  of a  structure.  The geometric properties of
the  structure together with  the given  bed slope,  S  ,  can be substituted
into  Equation A-6   to yield the  capacity  of the  structure.    However,  the
friction slope,  S  ,  observed in  the neighborhood  of  such control is  fre-
quently less  than   the bed slope, S  ,  and   the true discharge  capacity as
yielded by Equation A-3 will be  less than  that obtained using the bed slope
directly.   In this sense,  use (or misuse) of the Manning's equation can lead
to overprediction  of the discharge capacity of a structure.

     In summary,  the use  of Manning's  equation,   without  the  other  terms
in  the  momentum equation,  is  deficient in at  least the following respects:

     1.  It fails  to produce the  loop-type rating relation.
                                    133

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    2.   It fails  to  produce a reduction of the peak discharge.

The magnitude and importance of  these effects  depend on the  particular
problem under study  and  may  often be negligibly small.   In some classes of
problems,  the need to include these effects is obvious.   For example, in long
natural channels with extensive flood plain storage or in river  systems which
include ponding areas and reservoirs, these effects may be  very  pronounced.
On  the  other hand,  urban  drainage systems  typically  involve  short,  steep
channels with well defined  boundaries;   in these cases  the  indicated effects
may be secondary and  are  often negligible.

     Simple  criteria for  determining  when these  effects may  reasonably
be  neglected  are  not readily  available.   Until  these  criteria  are forth-
coming,  considerable  reliance will continue  to  be  placed  on the judgment and
experience of  the design engineer.   Hopefully,  the  existence of computer
models  which  allow  retention  of all  terms  in the  momentum  equation will
permit  the development of  sounder judgment  and the eventual preparation of
precise criteria.

     Other factors affect  the  accuracy  of  results  from simulation models.
For example,  inaccuracies in rainfall measurements and/or,the simplifications
used  to model a  prototype  system within  a  limited set  of model elements
(i.e.,  catchments,  pipes,  flow  dividers,  etc.)  may introduce  significant
errors.    In  fact, these errors  will in general  be  much larger  than those
resulting from neglecting some terms in the momentum equation.   It is usually
more important to  model the effects of a flow diversion structure accurately
than  to model the subsidence  of a  flood  wave in  the  input  pipe exactly.

     The preceding conclusions  apply only  to  the  case of  open-channel flow
in which  downstream conditions  do  not have  a significant effect  on the
upstream stages.   This idealized  situation  frequently is  not applicable.  If
a channel is terminated by  a control structure such  as  a weir,  constriction,
culvert, etc., with  discharge  characteristics  such  that  the  stage  in the
channel immediately upstream of  the structure  must  build up  to a level
greater than normal,  a backwater profile will form for some  distance upstream
where the stage will  be above normal.  The actual values of  stage  will exceed
those calculated  by  a simple  application  of  Manning's  equation with  Sf =
S .   Manning's equation will  then yield  stage values which  are  too low,
rather  than too  high as in the  preceding discussion.  The  same type of
behavior can arise when anlyzing  flows in sewer' systems.   When the flow rates
and/or downstream  boundary conditions are such that the  sewer pipes  flow full
and surcharinging occurs,  the  relationships  defined by  the normal flow
condition, Sf =  S , are no longer  applicable.  The  friction  slope,  Sf,
in  these  cases  is related to differences  in  water  level  in the  surcharged
sewers  which,  as  in   the backwater example, will  be higher than the levels
given by Manning's  equation with S_=S  .   The  difficulty lies  not with
Manning's  equation per  se.  Rather, the  difficulty  stems  from  the inappro-
priate  use of the assumption  that the  channel (or  pipe) slope and the
friction  slope are  equal,  i.e.  Sf  = S  .   Manning's  equation  is  valid
where written in terms  of an appropriate friction slope.   However,  the
                                    134

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 friction  slope depends  on  the flow conditions.  Thus,  in general,  the true
 friction  slope is a  dependent  variable  of the problem and  is  not  known in
 advance.   The assumption of  S  = S  can  be  made only when the validity of
 the  assumption is known.  If this assumption is indiscriminately built into a
 sewer  design program (for example), considerable  caution  should  be used in
 interpreting  the  model's results, especially  if  the  results are  to include
 predictions of stage or piezometric grade line elevation.

     Figure A-3  presents a  surcharged  simple pipe  system consisting of
 three links and manholes at each of the  two nodes.
M.H*2 M.H.*




!>
v




El. Z
3




V





El. Z
2

               LINK 3
                                  LINK 2
                                                                  El. Z.
                                    LINK I
                   Figure A-3.   Surcharged simple pipe system

The  inflow  to the  system  is  a discharge from  upstream sources and  is  de-
signated as  QL.   The  outflow,  QQ, is  into  a reservoir whose  free  surface
is at  elevation  Z .  The instantaneous water levels in  the manholes  are at
elevations  Z2 and  Z^  as indicated.   If the reservoir elevation, Z ,  is
known  as a  function of time  (e.g.,  constant,  as in the case of a large
reservoir),  a mathematical  relationship  can be derived  which  expresses  the
manhole water surface  elevations as  a function of  the inflow,  Q .    A
particularly simple  form of  the  relationship is obtained if a  linear relation
is assumed between  discharge and head and the  inertial  effects  of  the water
columns can be neglected.   In  this simplest  representation the relationship
between Q and ZĞ takes  the  form:
d2Z3
   -
                        dZ3
                                                                (A-7)
                                    135

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in  which  the  coefficients, a,,  aĞ  and a^,  depend on the  geometry
and hydraulic resistance of  the system.   The left-hand side of the equation
is analogous to a simple spring-mass-dashpot system.  The right-hand side is
a  function  of the  boundary  conditions  which  serve as a  forcing  function.

     One property of the solution  of  this equation is a phase shift between
the forcing function and the response,,  Z^.   Among other things this implies
that  in general  the peak inflow, (Q1>max.'  and the  Peak water level in
the manhole, (Z_)     , do  not occur at the  same time.   Thus, it  is  not
possible to relate "th'e' peak  flow  and  stage (i.e., manhole water level)  in a
simple manner.  This behavior is analogous to that attributed earlier to the
effects of channel storage  in the  open channel case, and again points out the
problem of  any  routing procedure  which  fails  to  take these storage effects
into account.

COST OF SOLUTIONS

     Cost  reductions  for  simulation runs  may be attained by neglecting
terms from the momentum equation.   These  reductions in  cost  are indirectly a
result of solving a simpler set of equations.  Such  an action would allow the
models to:

     1.  use  larger At  and  Ax grids in the  finite  different formulations
         or

     2.  step-down  to  a less  numerically complex solution  of the equations
         (e.g.,  from the  method  of  characteristics  to  a finite difference
         scheme).

Any of these two steps would result in significant cost  reductions in simula-
tion models.

     From  a qualitative point  of view,  some  estimates  of  the   effect of
each  term  can be made.  Schaake  (23) has shown that  neglecting the temporal
variation in  velocity  term (i) can reduce the cost of  simulation runs by at
least  a factor  of 2.  This is a result of the larger time steps that can be
used  for  the finite difference schemes when Av/At is not in the equations.
A similar reduction  in cost can be  obtained when  the spatial variation
in  velocity  term (h)  is eliminated.    In this  case  larger  Ax.steps  can be
used.  Neglecting the water  surface slope term  (g')  may  not  have as large an
effect  on the cost  of solutions as the previous two terms.   But  this term can
cause  stability  problems.    In  some  cases,  neglecting it may allow for  much
larger  At and Ax grids  and  therefore  result in significant  cost reductions.
The final term  (j), the acceleration  imparted  on the  lateral  inflow, would
have  no significant effect on the cost of simulations since it  only involves
one additional operation.

     In summary, if  the variation in  velocity  terms  (h)  and  (i)  could be
neglected,  significant  reductions in  simulation costs  could  be obtained.

     No detailed  comparison of  cost reductions versus  number  of terms
                                    136

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modeled for  the  small  errors  introduced  by  using  a  simple model  such  as the
         Kinematic Wave Model.

     6.  In cases where backwater effects or surcharging of pipes  is present,
         it is inappropriate to  use the  assumption that  the channel (or pipe)
         slope and  the  friction  slope are  equal,  i.e.,   S    = S   .
         Manning's equation can  only be  used  in these cases if   the  appro-
         priate friction slope is computed.  But in these cases the friction
         slope is a dependent  variable and is not known  in advance.

MODEL OPERATING CHARACTERISTICS

     The desired  operating characteristics  of the chosen  simulation  model
(or models) are:

     1.  Ability to simulate   •

         (a) the surface runoff  quantity,
                                    137

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         (b)  the  operation of  the trunk sewers,  and

         (c)  any  storage (in-pipe or  satellite).

     2.   Ability  to run on  continuous  records  to check the  overflow  charac-
         teristics  of  the  system over a period  of record.

     3.   Ability  to simulate quantity based on  physical parameters.

     4.   Capability to be  transferable from one area to another within a city
         and its  environs  without extensive calibration exercises.

     5.   Ability  to predict the  quality  of  surface  runoff  during wet-weather
         conditions.

     6.   Capability of  handling  the  sanitary and dry-weather quality  aspects
         of the system.

     7.   Ability  to handle the  pollutant  transport in  the trunk  system on
         a conservative (i.e., no  time decay)  basis due to the small size of
         the drainage systems and hence short in-system time.

     8.   Ability  to simulate directly the quality of overflows.

     In the above synopsis "quality" has been used in the generic sense.  For
urban purposes it  appears  that  the following  constituents  are of importance.

              a)   Biochemical oxygen demand (BOD)
              b)   Chemical oxygen demand (COD)
              c)   Suspended solids (SS)
              d)   Settleable solids
              e)   Nitrogen/nitrates
              f)   Phosphates
              g)   Grease
              h)   Coliforms
              i)   Heavy metals

The  ability  to simulate the pick-up, transport, etc. of the above  pollutants
is  relatively crude at present.   In  particular, little  or no capability to
simulate heavy metal  pollutants exists.  However, the models discussed below
are  evaluated on their ability  to handle  pollutants in terms of the  "ideal"
set  presented here.

MODELS EVALUATED

     Following an  initial survey, attention was focused  on three  models for
a detailed review.  These models were:

         Corps of Engineers Storage,  Treatment,  Overflow, Runoff  Model  (STORM)
                                     138

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         Environmental Protection Agency  Storm  Water Management Model  (SWMM)

         University of Illinois  Storm Sewer  Simulation Model

 The thorough analysis of urban  models  by Brandstetter (25)  has been used as
 a, general  reference in much  of  the discussion on models which  follows.
 Recently,  the same author prepared  a more  comprehensive comparison of urban
 runoff  models (26).  The following sections review each of  the above models,
 and recommend that both  STORM and  SWMM be used  to provide adequate simulation
 capability.

 Corps of Engineers'" STORM

     STORM  was developed  in early  1974  by Water Resources Engineers, Inc.
 (WRE) of Walnut  Creek, California  under contract to the Hydrologic Engineer-
 ing Center  (HEC)  of  the U.S.  Army Corps  of  Engineers.   The  program  is an
 outgrowth  of work  performed by WRE for  the  Environmental  Protection Agency
 and the City  of  San  Francisco.   The following comments on the  program are
 based  primarily  on the  User's  Manual  (27)  and discussion  with WRE  and HEC
 personnel.   The program  is  intended primarily  for  the evaluation of storm-
 water  storage and treatment capacity  required to  reduce   overflows  to  the
 receiving waters  to  acceptable  (defined externally) levels.   The  model
 recognizes that  the intense  short-duration  storms,  so  often used  as "design"
 storms,  may  well  be completely  contained through  natural and  artificial
 storage  mechanisms so that  no  untreated  overflows occur.   Alternatively,  a
 series  of  moderately  sized  storms  may  load the  system  to the  point  where
 untreated  releases occur. The  program  is  thus designed to account  for  the
 characteristics  of the  area.   Lumped  storage  and treatment capacities  are
 also considered.   The model considers the  interaction  of  eight variables in
 determining  the operation of the system:

     1.  Precipitation
     2.  Air  temperature  (for snowmelt computations)
     3.  Runoff
     4.  Pollutant  accumulation on the land surface
     5.  Land surface erosion
     6.  Treatment  rate
     7.  Storage
             — tj
     8.  Overflows from the storage/treatment systems
The model operates on  land uses,  including  single  family  residential,  multi-
ple family residential,  commercial,  industrial,  parks  and undeveloped  areas.
The program is designed  to simulate  hourly  stormwater  runoff  and quality  for
a single catchment.  It  is a  continuous  simulation model  with the capability
of simulating a  number of years of record but can  also be  used  for  selected
single events.  The model, as prepared by WRE,  does not  simulate dry-weather
flow and  its  associated quality  components.   Modifications to  include dry-
weather flow simulation  and up  to 20 land uses have been made in the  latest
version of STORM (28).
                                    139

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    The runoff from  the  catchment  is computed using runoff coefficients and
hourly precipitation data  for  a single rain gauge in the basin.  Depression
storage is simulated as the prime mechanism of reducing  rainfall  to effective
rainfall.   This  depression storage is allowed to recover at a constant rate
to  account  for  evapotranspiration.   The  runoff  from  the  area  is  computed
by  applying  a simple  runoff  coefficient  to the effective  rainfall.   This
coefficient is  a weighted  average  of  the coefficients for pervious and
impervious areas  and does represent  losses  due  to  infiltration.  A similar
coefficient is used  to simulate runoff  during  periods  of no precipitation.
Runoff from snowmelt is computed using a degree-day  technique.

     Six  water  quality  constituents  are computed  for  different land uses.
These constituents are:
     1.
     2.
     3.
     4.
     5.
     6.
Suspended solids
Settleable solids
Biochemical oxygen demand (BOD)
Nitrogen (N)
Orthophosphates (PO,)
Coliforms
These  quality  components  are computed from non-linear  functions  considering
the daily  rate of dust and dirt accumulation,  the percent  of  each  pollutant
contained  in  the dust and  dirt,  street  sweeping practices and days  between
runoff  events.   Erosion is computed using the  universal  soil  loss  equation.
The BOD, N and PO, runoff  rates depend on the  pickup rates of  the  suspended
and settleable solids.

     The model is very much a "black-box", type model.   It  does  not  route
the runoff quantity  or quality in  a sewer or channel network.   The  routing
aspects have to be reflected in the runoff coefficients.  The  computations  of
the  treatment, storage and overflow processes  at the  single outflow  from
the system are performed  by volume and pollutant mass  balance  only.  A very
simple  logic is employed as follows:  if the hourly runoff volume  exceeds the
treatment  capacity,  the  excess runoff  is diverted to storage;  once  the
storage  capacity  is  exceeded, the  excess  runoff becomes  untreated  overflow.
During  dry-weather conditions,  the treatment capacity  is used to  draw down
the volume in  the  storage element.  The quality of the runoff  is not modified
in storage.   Simple  plug  flow routing is  used.   Similarly,  the simulation of
the  treatment facility does  not  include  the  quality improvement  to be ex-
pected.

     The  model  is completely based  on  the  use  of  empirical  coefficients
for  both  stormwater  runoff  and  quality  computations.   These  coefficients
were  provided by the  user for the  runoff case,  and are internal to  the
program in the quality  aspects.   Verification  of  the various equations
appears to be limited to date, and the dependence  of the runoff  and  quality
coefficients  on the catchment characteristics  does  not appear to  have been
fully  established.

     The model is  useful primarily  as a planning tool to estimate  the  approx-
imate  number  and magnitude of overflows for various  combinations of  storage
                                     140

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and
treatment.  It is a useful screening tool in these aspects.
EPA - Storm Water Management Model (SWMM)  (6,29)

     This  is probably  the  most comprehensive  mathematical model  for  the
simulation of storm and combined  sewer  systems.   It  computes runoff  quantity
and quality  from the watershed  by  using  a number of overland  flow  elements
to simulate  the initial  collection process,  and  a  converging branch  sewer
network to simulate  the  trunk sewer system.  It  can also handle  up  to  three
storage basins  and  one treatment plant,  together with the  appropriate  flow
diversion structures.

     The model,  as  initially developed  and used  in this work,  was primarily
an event simulator -  its  complexity and  cost  effectively  limiting  its
use to  a  single storm at a  time.   However, the  latest  version  has incorpor-
ated  continuous simulation  capability.   Spatial rainfall variations over  a
basin  can  be taken  into  effect since  independent  inputs  can be  applied to
each  subcatchment.   The  runoff  from  the overland  flow  areas is simulated
using  the  kinematic wave  equations.   Depression storage  is accounted  for,
and  infiltration from pervious  areas   is  computed using Horton's equation.

     The  stormwater quality is  computed  using  non-linear  functions  which
are a  function  of  land uses, street cleaning practices, pollutant accumula-
tion and rate of runoff.   The pollutants considered are of  a  wider range than
considered in  STORM and include  suspended  and  settleable solids, BOD,  COD,
coliform  bacteria,  nitrogen,  orthophosphates,   oil  and grease.  • Daily  and
diurnal variations in the  dry-weather flow  and quality  are accounted for and
are  estimated   from  land  use  characteristics  or  directly  from  input  data.

     The flow  in the sewer  network, as included initially  in  the model and
used  in this work, was  simulated using the kinematic wave  equations.   Com-
plete  continuity and momentum  equations  are included  in  the  current  model
version (30).   The  elements  in the  network can  include manholes and  conduits
from the selection of 12 internally stored geometric shapes,  as well  as  three
additional arbitrary  shapes.   Other  elements in the  network  are diversion
structures and  up to two satellite storage facilities.   Pumping stations with
constant pumping rates can be included. Surcharging  can be handled by assum-
ing  all flow  in excess  of  full pipe  flow is  stored  in  the  next  upstream
manhole.   The   model also  allows the  option of  letting the  program  size the
sewer  to eliminate such surcharging.

     Quality routing  through the trunk sewer system is  primarily based
on an approach of pure  mixing in  each pipe  element.   Decay  is  allowed for
the  BOD,  and scour and  deposition  of  suspended  solids is simulated.   Other
quality reactions and interactions are not considered.

     Unlike  STORM,  SWMM  can simulate the  operation of  up  to  nine unit treat-
ment  processes  which can be  inserted in  series  for  a  single overflow treat-
ment  facility.    It thus  allows more  accurate  estimation  of  the pollutant
mass loads on the receiving  waters.
                                    141

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     The model  also has  the ability  to  simulate both  quantity  and quality
behavior in the receiving water system.

     The model has been applied to a large number of watersheds.  In general,
it  has been  found  that  the  accuracy of  the  runoff  quantity computations
for basins ranging from 4—2000 hectares  (10-5000 acres)  was relatively good.
If  adequate  segmentation rules  are applied, the  model can  be successfully
used for  runoff prediction  in  most urban areas.   On the  other  hand,  as in
similar models,  significant  doubts still  exist as  to  the adequacy  of  the
runoff  quality  prediction  mechanisms.    It  is  not  yet known  how generally
applicable are  the regression equations relating runoff  quality to land use.
Although they  can be calibrated  for  individual basins, they can hot  yet be
used with complete confidence for prediction purposes.

University of Illinois — Storm Sewer System Simulation Model (7)

    "This model  basically computes nonsteady flows  in  a converging sewerage
network using a solution of  the dynamic wave equations.   The routing is based
on  a  first-order explicit  finite difference solution  to  the characteristic
equations of  the dynamic wave equation.    It can consequently  consider  up-
stream  and  downstream flow  controls,  backwater effects and  flow reversals.
It  does not, however,  include, surcharging  and pressure  flows.    A certain
number  of  controls, diversions  and pumps  can  be included but only  at  the
outlet  from  the  system.   The  model  does not  include  any  quality effects.
Similarly, overland  runoff  from precipitation is not computed.   Rather,  the
required .flows  must  be entered  as  separate hydrographs.   Dry-weather flows
must be handled in a similar fashion.

     The model  includes  a  comprehensive formulation  of  open channel  flow
routing in circular sewers.   It includes a feature for the sizing of circular
pipes  to accommodate peak flows.   However,  its lack of overland runoff  and
quality simulation capabilities  limits its  usefulness for  the present  study.
In  a  recent  study  by Chow and  Yen  (31) for  EPA,   these  capabilities  have
been incorporated into the model.

COMPARATIVE EVALUATION

     The work under this  project mandated  use of  a model or models  which
would be capable of being used in:

     a)  Planning of required facility locations and sizes, and

     b)  Evaluating alternative designs.

In  addition,  the models  must  be readily transferable  from basin  to  basin
within the urban area.

     In light of the above discussion it appeared:

     1.  The University of Illinois model was of no advantage.
                                    142

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     2.  STORM included  the  storage/treatment capabilities  required  and,  in
         particular, allowed comparison of a wider range of treatment/storage
         alternatives than could  be economically considered using  SWMM.   It
         suffers from calibration problems.

     3.  SWMM  was   the  most  suitable  model  for  the design  aspects of  the
         current study.   Its RUNOFF and  TRANSPORT  Blocks have  the required
         capability  to  simulate the stormwater  quantities involved.   Addi-
         tionally,   it  considered  a wide  range  of pollutants.    However,  the
         pollutant  pick-up  simulation mechanism  must  still  be regarded  as
         suspect and subject to calibration.

THE RATIONAL METHOD  (32)

     This method  has been widely  used for  the determination of peak  rates
of  stormwater  runoff.    It  relates  peak  runoff  rate to  rainfall  intensity
by the formula,
                                Q =  Cia
(A-8)
where  Q,  the peak flow,  is  dependent  upon rainfall intensity, i, and  a
runoff  coefficient  C which attempts  to weight  all the variables  affecting
runoff  rates, and  the  tributary area, a.  When  applying  the Rational Method
the intensity is the average rainfall intensity for a storm having a duration
equal  to'the longest time  of  travel in the system being  designed (overland
+ pipe) and  the runoff  coefficient is a composite  of  published coefficients
as weighted  by  land  use characteristics.    In  this  study,  the  maximum  and
minimum values  of  the composite  runoff  coefficient were obtained  using  the
runoff coefficients published on page 51 of Reference 32.

     To compare runoff  rates  determined  by the  Rational  Method  with  those
using SWMM, flows,  developed using SWMM Model and the synthetic, intermediate
pattern, hyetograph  shown in  Figure  D-5,  were  used in the  Rational Method
formula.  A  corresponding runoff  coefficient was  obtained  using the rainfall
intensity determined from  the  appropriate  intensity-duration frequency  curve
with the estimated time of  concentration.  The  time  of  concentration includes
the suggested  inlet  time of five minutes  (32)  and time  of travel  in  trunk
sewers, which is estimated  from SWMM  output  assuming pipes  are flowing full.
TABLE  A-2  summarizes the  SWMM "C"  values calculated  at  various  points  in
District A and  compares the peak  5-year  synthetic storm flows obtained using
the Rational Method  with  peak  flows using SWMM.  The Rational Method results
in runoff  rates from  30 to 60 percent lower  than runoff  rates determined
using SWMM.
                                    143

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      TABLE A-2 PEAK FLOW  COMPARISON BETWEEN RATIONAL METHOD AND SWMM

Area
(acres)
353
366
599
655
SWMM
Flow
(cfs)
898
909
1370
1406

Intensity
(in/hr)
3.5
3.4
2.7
2.5

SWMM
npii
.726
.730
.847
.859

Rational
"C" Range
.507-. 311
.519-. 321
.549-. 356
.562-. 372
Time of
Concentration
(Minutes)
15.2
16.0
22. '5
25.2

Rational
Flow Range
626-384
646-399
887-576
920-609


(cfs)




 Note:  1 in/hr - 25.4 mm/hr; 1 acre
       1 cfs = 0.283  m3/sec
                        0.405 hectares;
     Assuming the  "C"  values calculated using  SWMM flows are  correct,  the
peak rainfall intensities would have to be reduced to obtain the peak runoff
rates generated using the Rational Method as  follows:
Rational Method
  Flow Range (cfs)
                           Rainfall
                           Intensity
                          Range  (in/hr)
  626
  646
  887
  920
384
399
576
609
2.44
2.41
1.75
1.64
1.50
1.50
1.14
1.08
   Time of
Concentration
 (minutes)

      15.2
      16.0
      22.5
      25.2
     Extrapolating  the  above,   using  the   appropriate  intensity-duration-
frequency curves  indicates  that use  of the Rational  formula results in.
protection from storms having a return frequency of  about two  years if
maximum "C" values are used,  to  eight months  if minimum  "C" values  are used.
Hence, drainage  systems  designed by  the Rational  Method may not provide the
anticipated degree of protection.

     The magnitude by  which  the pipes are undersized can be estimated since
the  pipe  diameter  for  a  given  rainfall intensity  is  directly  related to-
the  3/8  power  of  the associated  "C"  if the slopes  are  maintained equal.

     The  following  summary  indicates  the  actual pipe diameter  changes:
               Rational
              "C" Range

              .507-.311
              .519-.321
              .549-. 356
              .562-.372
                             SWMM
                         Diameter (ft)

                             8.0
                             8.0
                            11.5
                            11.5
                      Rational Diameter
                         Range  (ft)

                      7.0 - 5.8
                      7.0 - 5.9
                      9.8 - 8.2
                      9.8 - 8.4
This demonstrates a pipe diameter underestimation of  from 12.5  to  29 percent.

     This  undersizing of pipes can result in  reduced capital costs but
                                    144

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offers less  protection  against flooding.   The following summary  of  typical
costs for sewers  installed  in 18 to  20  foot  trenches  illustrates  this appa-
rent  savings.  The diameters are based  on flows as calculated  above  and the
costs are estimated using TABLE D-17.
    SWMM
Diameter (ft)

   8.0
   8.0
  11.5
  11.5
SWMM
$/LF

420.
420.
800.
800.
 Rational
Diameter (ft)
                Rational
                 $/LF
                Percent
                Savings
 7.0 •
 7.0 -
10.0.-
10.0 •
6.0
6.0
8.5
8.5
350
350
612
612
298
298
452
452
17
17
 3
 3
29
29
44
44
     The inclination to use-this method  can be great since initial costs may
be up  to  44 percent lower.  But/use of  the Rational Method  to design storm
sewers  proposed  to provide  protection  for the  5-year  storm  can  result in'
flooding with storms  having  as short  a  return  frequency as  eight  months.

     As a  further  indication of the  underestimation of  flows  generated
by the Rational Method, reference is drawn  to a drainage study in Louisville,
Kentucky by  the  U.S.   Army  Corps  of Engineers  in 1949 (33).   In this study
report, a  series  of pumping station inflows were calculated,  using both the
Rational and  the Unit  Hydrograph approaches.   The results  of this comparison
are summarized below:
     Pumping Station

     Seventeenth St.
     Shawnee Park
     State Fair Grounds
     Lower Paddy Run
                 Rational
                Flow (cfs)

                  99.9
                 939
                1700
                1495
                             Unit Hydrograph
                                Flow  (cfs)

                                    126
                                   1359
                                   2520
                                   2630
     The  Rational flows are  lower  by 20  to  43 percent and  the results are
comparable to that predicted using the Elizabeth data.

METHODOLOGY

     SWMM,  as  used  in this work represents  the state-of-the-art, hydrauli-
cally  and hydrologically  sophisticated,   single  storm event  simulator.   It
uses a "micro"  approach in that  the  rainfall-runoff process is divided into
its basic elements.   It simulates the process, spatially and  temporally, and
routes  storm runoff  and combined sewage quantity and quality from individual
catchments  and subcatchments  through a  sewer network,  interceptor system,
storage and treatment facilities,  and  finally \to  receiving waters.   SWMM
analyzes  or designs a sewer  system for an actual  or synthetic storm event.
It requires  detailed delineation  of the subcatchments and sewer  layout and is
an expensive procedure.

     STORM is  a  continuous  simulation model  for overall  planning.   It ana-
lyzes  hourly runoff quantity  and quality  for long-term hourly  precipitation
                                     145

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records, based on such parameters as percent imperviousness and land use and
evaluates the  effectiveness  of  storage and interceptor/treatment facilities
for overflow pollution control. Typical to all continuous simulation modelsj
STORM uses a  "macro"  approach by combining and averaging the effects of the
basic elements.  That is,  rainfall-runoff  processes are simulated for areas
of finite size and for coarse time intervals.   It  emphasizes the  gross
pollution effect  (total  pounds) of  pollutants  discharged in  a  given storm
rather  than  the detailed  time and  spatial  characteristics.  To  operate 0n
precipitation  data  over  long  time periods, the  model  contains  a  feedback
mechanism which does  continuous accounting of  water inputs (rainfall and/or
snowmelt)  to  and  losses  (depression storage and  infiltration)  from the
drainage basin.  In dealing with' long-term real rainfall events, STORM was a
necessary tool in the project study.

     The methodology used follows:

     1.   SWMM developed the alternative designs in District A for runoff from
         a synthetic,  intermediate  pattern,  5-year return interval hyetograph
         shown in  Figure D-5.   Quantity  and  quality  characteristics,  with
         respect to  combined  sewage and storm runoff,  were also determined
         for smaller rainfalls.

     2.   STORM evaluated  the  effectiveness  of storage  and interceptor/
         treatment facilities for  storm  runoff  and combined sewage overflow
         pollution control using continuous real  rainfall events.

     3.   Calibration of the quantity parameters contained in STORM used SWMM
         data generated from the detailed simulation of District A.

     4.   Quantity and quality and  cost data, obtained  from District A,  were
         projected to  the entire  City for the  evaluation of  sewer  system
         alternatives for both flood and pollution control.
                                    146

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                                APPENDIX B

                   MODIFICATION OF SWMM AND STORM PROGRAMS
      In addition  to  continuously  updating  the models  as revisions  became
 available,  both models were modified  to meet the project  requirements.   The
 modifications  made  to  SWMM and  STORM and the  necessity  of making them  are
 described.

 SWMM

      Both  the  RUNOFF and  TRANSPORT Blocks in  SWMM  consider flow routing  in
 sewer pipes.   The RUNOFF Block employs a  simple  storage  routing  scheme using
 the  continuity equation of flow in the gutters/pipes and Manning's  equation.
 This  technique is  sufficient as  the RUNOFF Block considers  runoff in overland
 and  gutter/pipes  where sewer sizes are  generally small and slopes  are rela-
 tively  steep.  The  RUNOFF Block can  handle  up  to  200 pipe  elements.

      The sewer routing in the TRANSPORT Block  uses  a more  complicated' tech-
 nique of  a  modified kinematic  wave  approach  in accordance  with 'Manning's
 and  continuity equations.  Backwater effects  within individual sewer segments
 are  considered.   The TRANSPORT  Block  can  handle up  to a total  of  160 sewer
 elements  (conduit  and non-conduit),  of  which  about  half  are   non-conduit
 elements.  The TRANSPORT Block uses better  routing techniques and  has a sewer
 design  option   that  the RUNOFF  Block  lacks.    In the design  version,  small
 diameters are  first  assumed  for  the sewers that would ensure full pipe flow.
 The size of the sewer is then increased and the computation  is repeated until
 free-surface flow  occurs.    In  the  previously available  RUNOFF  Block,  pipes
 are permitted  to surcharge when  full.  The  surcharged volume is assumed to be
 temporarily  stored  at  the  upstream   junction  until  sewer  capacity becomes
 available to  drain  it.   Use of  the RUNOFF Block for  design  requires  trial
 assumption of  sewer  sizes until stored surcharges are eliminated.

     Because the  SWMM  RUNOFF  Block (a) can  handle  more pipe  elements than
 the  TRANSPORT  Block;  and  (b)  has an acceptable flow  routing  routine,  it
 appeared advantageous to use the  RUNOFF  Block for design of upstream lateral
 sewers. Consequently, SWMM was modified to allow design capability with pipes
 surcharged.   As the  capacity of  the initially assumed pipe size is exceeded,
 the pipe size  is  automatically increased  to  the  next larger commercial size
until  free-surface flow is  attained.    When  a  pipe  is  resized,   the  runoff
computations are repeated  for  the new (larger)  conduit for the  current time
step only.   The runoff  hydrograph up to  the time when surcharging would have
occurred in the particular pipe  is  not recomputed since this would require a
                                     147

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basic change  of  the internal computational sequence.  The design version of
the TRANSPORT  Block also does not  recompute  the previously computed hydro-
graph  and pollutograph.   The subroutines  involved in  the  program  changes
include RHYDRO, and GUTTER.

STORM

     The  available  version  of STORM was developed  for  simulation of  urban
stormwater runoff quantity and  quality.   It did not model  dry-weather
flow  and  consequently  could not be used  for simulation of combined sewage
overflows.  Combined sewer overflow problems and their  extent,  and  corrective
measures,  and their  effectiveness,  were an  essential  part  of  the  project
study.   Hence,  STORM  was  modified in this study to add the  dry-weather
flow simulation capability.

     Dry-weather  flow input data provides for  diurnal variation of  quantity
and  quality  for various  land  uses.   Dry-weather flow can  include  domestic,
commercial and industrial wastes and infiltration.  Four options  are provided
for computation of  average daily dry-weather flpw quantity:


      1.   inputs  of the total dry weather flow,

*      2.   inputs  of flow for each land use separately,

      3.   inputs  of the coefficients to be applied to populations or
          areas to  estimate  each component of the dry—weather flow.
          Domestic flow is assumed to be linearly proportional to  popu-
          lation.   Other component flows  are  linearly proportional to  the
          area, and

      4.   use of  default values  provided in the program.

      The  daily  flow may  also  be  varied  for  weekdays, Saturdays,  Sundays
 and  Holidays  and for  hourly flow during the day by input  of user-specified
 ratios  or by default values in  the program.   This option allows computation
 of the diurnal flow variations.

      For  computation of dry-weather flow quality, coliform counts  were added
 to the five  pollutants  considered  in  the available STORM program.   Compu-
 tation of coliform organisms  washoff  is assumed similar  to  the computation
 for  other pollutants  except that  no  contribution is assumed from the sus-
 pended and settleable solids.  The default values for the coliform counts in
 dust and dirt  are programmed.   These  default values,  like  those  for  other
 pollutants,  are used to compute the amount of pollutant washout in relation
 to the amount of dust  and dirt  washout in a storm event.   The  options pro-
 vided to  compute average daily dry-weather  flow pollutant loading for all six
 constituents  are similar to that  provided  for  the dry-weather flow quantity
 computation.   Variations of pollutant  load for the day of the week and hour
 of the day are also incorporated.
                                    148

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     Changes to  the STORM  program include  (a)  the addition  of  Subroutine
DWFLOW  which carries  out most  of the dry-weather flow  computation,  (b)
substantial modification' of the  MAIN program  and Subroutine OUTPUT  which
reads input data and prints out computed results respectively,  and (c)  minor
modifications  to Subroutines DEFINE,  DIRT,  EVENT,  and ZERO.   A copy of  the
program changes  was forwarded  to  the Hydrologic Engineering  Center, of  the
Army Corps  of  Engineers  and was incorporated in  the  new version of  STORM
released in July, 1976  (28).

     In the original  version of  STORM, a  storm event  is.defined by  the
properties of  the individual rainfall  events, such as duration and. intensity,
storm  spacing,  and time to empty any storage facilities.   An event  was
defined as beginning when storage was first required and continued until  the
storage basin  was   emptied.   Any  number  of  overflows occurring  during  the
duration  of the event was considered as the  same overflow  event.  If  a
rainfall  event  produces  runoff  that  does  not  exceed  the  sewer  capacity,
storage would  not  be  utilized,  and  the rainfall  would  not register  as  an
event.    In the  case of zero storage, runoff from  watershed would  directly
drain to  the  interceptor sewer, and  the  number of events  as  defined  above
would be the same as the number of  overflow events.

     With  the  inclusion of dry-weather flows, the  treatment or  interceptor
capacity should be  at least adequate to handle peak dry-weather flows.   Flows
exceeding this  value would require  additional control measures.
                                   149

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                              APPENDIX C

           QUANTITY AND QUALITY CONSIDERATIONS,  SWMM VS. STORM
     Difference between SWMM and  STORM  regarding storm runoff  quantity
and quality are worth noting.  Recognition of these differences is necessary
for interpretation  and  interchange  of results generated by  the  two models.

QUANTITY

     STORM accounts  for losses  of  rainfall  and/or  snowmelt volume  due  to
infiltration in the watershed by  the use  of a  runoff coefficient.  The runoff
computation during a given hour is expressed as:
                           R = C;(P - f)
(C-l)
where R is  runoff  volume,  P the rainfall volume, f the available depression
storage and C  the  composite runoff  coefficient  depending upon  urban land
use.   C -is derived from  two basic  coefficients,  C, and  C?.  C,  repre-
sents  the  runoff  coefficient for pervious areas  and  C,,  for impervious
areas.  For  a  given watershed,  knowing  the area  for  each T.and  use  and the
associated percent  of  imperviousness,  C  can be calculated  arithmetically from
C^ and  C2.   In the STORM Program,  the default values of  C^ and  C^ are
respectively  0.15 and  0.90.   These coefficients  are  a function of rainfall
characteristics  (depth,  duration,  intensity)  and  antecedent  dry conditions
and calibration is  required.   The parameter  "f"  represents  the antecedent
conditions.  There is no runoff from  the watershed until  depression storage,
which is uniformly  applied  to the  entire watershed, is  filled.

     In SWMM,  runoff volume over a short time interval, measured in minutes,
is determined  by using  a  number  of  overland flow elements  to  simulate the
initial collection processes.  The amount of runoff from  pervious and imper-
vious areas is  separately  considered.   Rainfall on certain impervious areas
results in  immediate runoff without loss to depression storage.   This is the
case in Elizabeth, since most  dwellings have  roof drains  directly connected
to a street gutter.

     SWMM uses  a more  detailed  concept  of  the hydraulics  of rainfall runoff
process  than  STORM.    Parameters required can be reasonably estimated.
Consequently,  in the absence of  real time runoff data in the study area, data
generated by  SWMM  in District  A  were used to  calibrate  the  runoff  coeffi-
cients  C, and C? in STORM.
                                     150

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QUALITY

     Neglecting  land  surface  erosion  and dry-weather  flow,  both  SWMM and
STORM compute  pollutant street washout in runoff  according  to the amount of
dust and dirt  (DD)  accumulated along the street curbs prior to occurrence of
a  storm.   From  the  total pounds of  dust  and dirt washout,  the loadings of
pollutant components  such as SS and  BOD are  computed either from the avail-
able local data  or  from specified  default  values.   Where quality data is not
available for  evaluating pollutant  parameters,  default values  specified in
either program could be used.  TABLE  C-l shows  the default values internally
specified in SWMM and STORM for computation  of  SS,  BOD and coliform loading
from mass of dust and dirt  in  the  street  washout.  Also  shown  in the table
are the  rates  of dust  and  dirt  accumulation  in each land use.   These rates
were obtained  from  an APWA  study in the Chicago urban area (34)  and are used
in both programs as default values.

          TABLE C-l.  POLLUTANT DEFAULT VALUES FOR SWMM AND STORM
Land Use
Dust and Dirt (DD)*
lb/day/100 ft. of
curb
mg Pollutant/
gram of DD
SS BOD* Coliforms
SWMM STORM (MPN/gram)
Single Family
Multiple Family
Commercial
Industrial
Park
0.7
2.3
3.3
4.6
1.5
1000.
1000.
1000.
1000.
1000.
111.
 80.
170.
 67.
111.
5.0

3.6
7.7
3.0
5.0
1.3 x 10"
f.
2. 7 x 10°
1.7 x 10b
1.0 x 10b
0
                * For both SWMM and STORM to compute soluble BOD

                  1 lb/day/100 ft = 1.486 kg/day/lOOm

     The  SWMM TRANSPORT  Block only  routes  three  pollutants;  SS,  BOD  and
total coliforms.   These  are commonly used  as indicators of  effluent  water
quality.  In this study, only SS' and BOD were used.

     SWMM and STORM use the  same  default  values  for pollutant loading calcu-
lations except for SS and BOD.   SWMM assumes the quantity of SS as about ten
times  greater than STORM.   Both SWMM  and STORM  use the  same values  for
computing pounds  of  soluble BOD  from pounds of dust  and dirt.   However in
the programmed calculations,  SWMM adds five percent  of the SS  and  STORM 10
percent to allow  for  the  non-soluble BOD contribution.   This  results  in BOD
loadings  (or  concentrations)  computed using  SWMM default  values  equal  to
about five  times  that computed using  STORM default values.   The  SS factors
used by  STORM are based  on  calibrations from the  Selby  Street data in  San
Francisco (35) rather than on physical  analysis on dust  and dirt.   The SS
factors used by SWMM appear to be based on convenient  choice.
                                    151

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     Test runs  made by  Huber  (35) with  Lancaster,  Pennsylvania data,  show
that use of the SWMM SS  default.values  and availability factor could produce
SS  concentration  levels  corresponding  roughly  to that  obtained using  the
STORM default values.   The availability  factor varies  with the rate of runoff
and measures  the  portion of the dust and  dirt available  in  a given rainfall
event for the production of SS  (6).   Recently,  Ganczarczyk  (36)  studied  99
hectares (245 acres) of  catchment  in  Canada under  developed  conditions using
the STORM program and STORM default  values.  The  predicted BOD was  of  the
same order of magnitude as reported in the literature  for several cities both
in  and  out  of the  United States while  predicted  SS were  underestimated.

     As SWMM  is an event simulator and  STORM a tool for runoff simulation of
long-term precipitation  records,  the computations of  street dust  and dirt
accumulation with varying numbers  of  antecedent  dry days  and street sweeping
intervals are  different.  These  differences  are best  illustrated  by  an
example.   Figure C-l, developed for District A,  compares  the  predicted  SS
accumulation  in streets  using  the  SWMM  and STORM programs with both SWMM and
STORM default values for an assumed seven-day street  sweeping interval and a
75  percent  sweeping efficiency.    The  daily  SS  accumulation in  streets  of
District A computed with the  SWMM  default  values  is  1,195 kg (2,638 pounds)
and with the  STORM default values,  131  kg (290 pounds).   The  SS accumu-
lation computed in SWMM  increases monotonically with the number of antecedent
dry days. Those calculated with STORM  indicate  periodical fluctuation of  SS
accumulation  at the street curb  reflecting the  effect  of   street  cleaning
frequency and the number  of  dry  days  since  the  last street cleaning.   In
SWMM, the additional  accumulation of dust  and dirt,  consequently SS, on the
street curb is assumed to be equal  to the maximum accumulation for the period
between successive street sweepings.  It does not credit the cleaning effects
of  street sweeping.   Recognition of  this  difference  is  significant when
comparing runoff quality from a single storm event with two models.

     In  computing pounds of pollutants  washed off  streets in any given time
interval, both  SWMM and  STORM assume the  washoff  rate to be proportional to
pounds  remaining  on the  ground and to  the runoff  rate.  In SWMM, the rate is
the average from  both  pervious and impervious areas.   STORM uses runoff from
impervious areas  alone.    For  a given  storm event,  the runoff  rate from an
impervious area is greater  than the average  rate from both the impervious and
pervious  areas.  A higher runoff rate means higher  washoff and  a greater
availability  factor.     Consequently,  for  the  same  storm  event,  pollutant
washout  computed by  STORM could  be greater  than that  computed  with SWMM.

     Since STORM  does  not model sewers, it can not model  solid deposition in
sewers  during  dry  days   or  their  resuspension  during wet  days.    For this
reason,  STORM can  not simulate the  "first flush" phenomenon in a  combined
sewer system.
                                     152

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   DRAINAGE  AREA = 655 ACRES (DISTRICT A)
   STREET SWEEPING INTERVAL = 7 DAYS
   SWEEPING  EFFICIENCY = 0.75
CURVE I  - SWMM USING SWMM DEFAULT VALUES
CURVE 2 - STORM USING SWMM DEFAULT VALUES
CURVE 3 - SWMM USING STORM DEFAULT VALUES
CURVE 4 - STORM USING STORM DEFAULT VALUES
          10           15           20

            NUMBER  OF DRY DAYS
                                                                    25
                                                                                30
           Figure C-l.   Street, SS  accumulation,  SWMM vs.  STORM
                                        153

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                                APPENDIX D

                             MODEL INPUT DATA
     Input data to computer models  utilized  in  the study includes (a) meteor-
ological data for long-term rainfall-runoff simulation, (b) a 5-year synthe-
tic  storm hyetograph for runoff  determination, (c) hyetographs  of  less
intense storms  for planning  a pollution control  system,   (d)  the discrete
elements of  the drainage  system,  (e)  hydraulic properties and  land use of
discrete elements,  (f) area and  land use of other drainage districts in the
urban area, and  (g)  unit  cost data for sewers of varying size and depth and
other elements of the sewerage system.

LONG-TERM METEOROLOGICAL DATA

     To use the  STORM program to account for the rainfall-runoff  character-
istics of  the  study area,  the continuous record of the hourly precipitation
data at Newark International Airport  over  the  12-year period  from 1963 to
1974 was used without modification.  Rainfall was assumed  to be uniform over
the seven-square mile study area.

     Average  daily  air  temperature  data  at  Newark  International Airport
over the same  12-year period  was also used for  snowfall and snowmelt compu-
tation.   Precipitation occurring  on  the days with air  temperatures at and
below  freezing  (°C or  32°F)  were considered  to be snowfall and  no runoff
was  assumed.   Snow pack  on  the ground  was  assumed  to  start melting  as
the  recorded air temperature rose above  freezing.  TABLE D-l  shows the
amount of annual precipitation, the number of  annual precipitation  events and
the  estimated number  of  runoff events.  A precipitation event is  defined as
a period of  continuous  non-zero  precipitation.   Traces (rainfall  or equiva-
lent water depth less than 0.25 mm/hour or 0.01 inches/hour are considered to
be non-zero  precipitation.   Precipitations  interrupted  by a period of one
hour or longer  are separate events.   To  eliminate  many inconsequential
precipitation  events,  those  events  with a total less  than 0.76 mm  (0.03
inches) are deleted and become part  of  the  dry period.  The estimated number
of runoff  events  is  based on  the depression  storage capacity of  3.94 mm
(0.155  inches)  computed for  District  A.   No  runoff  occurs until  the  total
precipitation exceeds  the depression  storage  capacity.   The 12-year period
selected for  evaluation of stormwater  runoff  and combined sewage  overflows
included the severe drought years  of the  early 1960's  and  the very wet years
of the  early  1970's.   The analysis made with .the data collected during this
period, therefore,  should  be representative of  the range  to be expected in
future years.
                                     154

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       TABLE D-l.   ANNUAL  PRECIPITATION AND RUNOFF EVENTS
Year
Precipitation
  (inches)
 Number of
Precipitation
   Events
Number of
  Runoff
  Events
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
  29.48
  33.45
  26.02
  37.86
  44.09
  36.89
  40.74
  34.38
  49.78
  48.30
  46.29
  39.86
    96
   118
   108
    94
   132
    89
   132
   113
   130
   135
   125
   111
Annual Average  38.89                   115
Annual Average (1941-1970)=41.45 inches
        Note:   1 inch  =  25.4 mm
    56
    76
    59
    51
    84
    53
    77
    74
    79
    83
    72
    70

    70
     There  are,  on the  average, about 115 annual precipitation events.
About 40  percent  of these precipitation events have  a  total less than the
depression  storage  capacity  for  District A and would not result in runoff
using  STORM.   About  70 annual storm runoff events  are  estimated for
District A.

     Figures D-l, D-2  and D-3 present a statistical  analysis of  the amount
and  duration of each  precipitation event, and  the antecedent  dry hours
for the 12—year period.  Precipitation events  can  be expected on the  average
of about every three  days  with  an average duration of about 4.5  hours.
The median  value of antecedent dry  hours is  36, and precipitation duration,
three  hours.   Similar  analysis was  made for cumulative  precipitations
exceeding 3.94 mm  (0.155 inches)  or  greater than  the assumed value of
depression  storage.   The average' interval  between  consecutive runoff events
is about  six days with a median  of  four days.  The average duration  of each
runoff event is seven  hours  and  the median duration is six hours.  About 75
percent of  the precipitation events with a cumulative rainfall  of less than
3.94 mm  (0.155  inches) were  of. three  hours or less duration,  and about 90
percent were of four hours or  less.   During  the 12-year  period, the  longest
duration rainfall was  34 hours (September,  1969),  with a  cumulative total of
126 mm  (4.97 inches).  The largest  amount  of  precipitation was  143 mm  (5.62
inches)  over 15  hours  recorded  on  August  29,  1971.   In October, 1973, 26
consecutive dry days  were recorded, the longest in the 12-year period.

     Previous study (8)  of rainfalls  in the Elizabeth River drainage  basin
indicated about  35  percent   of  the  rainfalls  were of the advanced  pattern
                                    155

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in  which  the most  intense rainfalls occurred  in  the first quarter  of  the
storm  period,   about  45  percent were of the  intermediate  pattern  in which
the peak  rainfalls  occurred  in the middle half of the storm, and 20 percent
were  of  the delayed  pattern in which  peak  rainfalls occurred  in  the last
quarter of  the  storm  period.   The 12-year data  generally  conforms  to this
rainfall pattern.   Peak runoff  from  an  advanced  pattern  storm is less than
that  from an intermediate  or delayed  pattern storm since the rainfall-
producing runoff,  or  rainfall excess at  the  time of the peak  rate  of pre-
cipitation is  less due  to depression storage  and greater  infiltration
losses.  In this study, both the advanced and  intermediate pattern storms are
considered in evaluating control of wet-weather  overflows.

FIVE-YEAR SYNTHETIC STORM HYETOGRAPH

     The  sewer  system was  designed to  accept  runoff from  an intermediate
pattern synthetic  storm  hyetograph.   The hyetograph  of  the.synthetic storm
was developed using the  intensity-duration curves  shown  in  the U.S.  Weather
Bureau Technical Paper No.  25 (37) for  Sandy Hook,  New  Jersey.   The inten-
sity-duration curves shown in Figure D-4 were considered  to be  applicable to
the study  area.    Twelve-year  data at the Newark  International  Airport  was
analyzed.  The  peak hourly  rainfall  with 5-year return  interval was  in
excellent agreement with that obtained  from the  Sandy Hook intensity-duration
curves. The rainfall intensity-duration curves at  Sandy Hook were 'updated in
a more recent U.S.  Weather Bureau  publication,  Technical  Paper No.  40 (38).
Intensities obtained from  this later publication  were found to  be  about 10
percent greater  than  that obtained  from the older  Technical  Paper  No.  25.

     The  synthetic  storm hyetograph was  computed for the  assumed  duration
of three hours, with peak  rainfall intensity  assumed to  occur  at the begin-
ning of the middle  third of the storm duration.  This duration is long enough
to cover the time of travel from headwater to outlet in the largest district
in Elizabeth.

     In developing  the shape  of  the  storm  hyetograph,   it was  recognized
that real storm  events can produce rainfall  intensities  equal  to different
return frequencies  during  their history.   In  the  storm of  July 20,  1961
at the Newark International  Airport  Weather  Station,  the  frequency  approxi-
mated  a  15-year return  period  storm  at ten  minutes duration,  a. two-year
return period  at one  hour duration and  less  than  this  return  period  for
three hours duration.   The measured data is  shown in Figure D-4.   Because
each  reach  of  a sewer conveying  urban  drainage   is  tested by  a different
duration  storm  for a  given  return  frequency,  the  concept of  an  envelope
hyetograph has  been developed and successfully applied.   The intensity-dura-
tion relationships  of  this hyetograph  matches  the  Weather Bureau intensity-
duration  curves at all time  intervals.  This hyetograph can be used  to
determine  the design flows which test  the  entire  system,  and eliminates  the
heed  of using more than one  hyetograph of  varying durations in design.

     Figure D-5 shows the  5-year synthetic  storm hyetograph developed
for 2-minute  intervals.    The  storm  hyetograph was  developed as  follows.
The intensities were  read from the intensity-duration curve for 5-year
                                    159

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                            SYMBOLS REPRESENT MEASURED RAINFALL!
                            AT NEWARK AIRPORT ON JULY 20, 1961
                    RETURN PERIOD(YEARS)
	 1 	 1 	
1 1 1 1 — 1
                        34       5

                        DURATION (hours)
Figure D-4.  Rainfall intensity-duration frequency curves
                             160

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return frequency at durations which are multiples  of two minutes.   The
rainfall amounts for incremental duration were obtained by multiplying
the intensity and duration.  The rainfall amount  differential of a successive
duration  represents a  possible  2-minute  interval  rainfall  in  the  hyeto-
graph.  After all possible  two-minute rainfalls have been obtained, they are
recorded  in sequence beginning  with the  largest  two-minute  interval rain^-
fall.   The most  intense  rainfall rate  was  placed at  the  beginning  of the
second hour of  the  hyetograph,  the second most intense rainfall at the next
later  time  interval and  the third most intense rainfall at the next earlier
time interval.  The remaining hyetograph was developed  in a similar fashion.

     From  the  intensity-duration  relation  used  to develop the  5-year  syn-
thetic  storm  hyetograph,  the  average 1-hour, 2-hour,  and  3-hour rainfalls
have intensities  of 40.6,  26.7 and 20.6 mm  (1.6,  1.05 and  0.81 inches) per
hour respectively.

     For input to calibrate the STORM program, which accepts hourly rainfall
data  only, the  5-year synthetic storm hyetograph with  hourly intervals
(Figure D-5) was  used.   The hourly  intensities  of the hyetograph are 12.7,
40.6 and  8.4  mm  (0.50, 1.60 and  0.33  inches)  per  hour respectively.   These
intensities were computed  so   as to  conform to  intensity-duration  curve.

     Storms of advanced pattern were  considered in  relation with the contain-
ment or  interception of storm  runoff for pollution control.   The advanced
pattern storm was assumed to start with the most  intense rainfall and then to
decrease monotonically as  the  storm  progressed.   The 5-year synthetic storm
of advanced pattern is shown in Figure D-5.

HYETOGRAPHS OF LESS INTENSE STORMS

     The  5-year  synthetic storm hyetograph was  used for  the design  of
collection systems for flood relief.   Optimum sizing of  the pollution control
system components,  such  as interceptors,  storage  and   treatment facilities,
are defined here by  less intense  but more  frequent rainfalls.  Consequently,
1—year and 1.3—month synthetic storms were developed and  used as input
to SWMM  to  determine the character of runoff  quantity and  quality required
to  develop  pollution  control   strategy.    The hourly  rainfall  intensities
of these  1-year and 1.3-month  synthetic storms  and storms of  other  return
intervals are shown in TABLE D-2.

     The  data were prepared from a partial duration series analysis  of
hourly data for the 12-year period  assuming hourly intense  rainfalls  were
independent of  others  regardless  of  whether they  occurred  in  the same  pre-
cipitation event  or in a separate event.   Monthly exceedance  values  of the
rainfall data were  arranged according to magnitude.   The values are plotted
using  the Weilbull  formula  (39)  on semilog paper with   the rectangular scale
representing hourly rainfall  intensities  and  the  logarithmic  scale  repre-
senting the return  interval in months.   Figure D-6 shows such a  plot.   The
plotted values lie approximately on a  straight  line up  to the return interval
                                    162

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163

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of two years.   To check the hourly rainfall of  40.6  mm (1.6, inches) of the
5_year  return  interval storm,  an annual .exceedance  series was  prepared
and plotted  on a Gumbel's  extreme probability  paper.   The hourly  rainfall
value corresponding  to  the 5-year return interval  agreed  well with 40.6 mm
(1.6 inches).

             TABLE D-2.   HOURLY RAINFALL VERSUS RETURN INTERVAL
            Return Interval

             6 - Month
             3 - Month
           1.3 - Month
             1 - Month
Hourly Rainfall
	(inches)

    0.74
    0.60
    0.40
    0.34
                 Note:  1 inch = 25.4 mm
     The  advanced  and intermediate  rainfall  hyetographs  of  1-year and
1.3-month storms were synthesized in the same manner  as  the 5-year  synthetic
storm. The magnitude of these  storm hyetographs were  derived  from the  5-year
synthetic storm  hyetograph by multiplying the  latter by the ratios of  0.58
(0.92/ 1.60) and 0.25 (0.40/1.60) (TABLE D-2)  respectively for the 1-year and
1.3-month synthetic  storms.   TABLE D-3 summarizes  the gross  characteristics
of  5-year,  1-year  and  1.3-month synthetic storms.  The  1-year  and  1.3-month
synthetic storms as  developed  represent one of  many possible  storm  patterns.
However, they provide a consistent tool for the derivation of  runoff quantity
and  quality information  for  planning level  decisions  of pollution control
strategy..
                TABLE D-3.  SYNTHETIC STORM CHARACTERISTICS

                       Average Rainfall Intensity (in/hr)
Return Interval        1-hour        2 hour        3-hour
             Total Rainfall
                 (inches)
5-Year
1-Year
1.3-Month
1.6
0.92
0.40
1.08
0.63
0.27
0.81
0.47
0.20
2.43
1.41
0.60
 Note:  1 in/hr  =  25.4 mm/hr
                                    164

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DEFINITION OF DISCRETE ELEMENTS

     For use of  SWMM,  District A was divided into five major  subareas,  each
having  relatively  homogeneous  land use.   These  five  subareas are shown  j^n
Figure D-7.  Subareas  I and  II are  almost  entirely  single family  residential
housing, which contain approximately 43 percent  of impervious  surface.  About:
half of  Subarea  III  consists of commercial and industrial  development which
contains about 80  percent  impervious  area.  Subarea IV includes  a  park  with
about 19 percent  impervious  area,  while Subarea V is  generally high-density
residential with  50  percent  impervious  area.   TABLE D-4  summarizes the  land
use distribution for each subarea as well as for all  of District A.

  TABLE D-4.  AREA OF LAND USE DISTRIBUTION IN EACH SUBAREA (ACRES)

                                                               Percent
           Single  Multiple                               Total Imper-
  Subarea  Family  Family  Commercial  Industrial  Parks   Area viousness
I 175.73
II 164.59
III 9.18
IV 115.36
V 5.33
Total 470.19
-
11.60
43.03
17.76
46 .,83
119.22
-
0.33
27. 07
4.67
2.63
34.70
- - 175.73
- 176.52
18.0.2 - 97.29
13.03 150.83
54.79
18.02 13.03 655.16
43.0
43.5
63.2
42.9
50.8
46.8
    Note:  1 acre = 0.405 hectares ,
    The  five subareas were  further subdivided  into  279 subcatchments
areas ranging  from 0.08 to 4.05 hectares  (0.2  to 10 acres) with  an  average
of  0.93  hectares (2.3 acres).   Overland drainage was routed to the  nearest
street.   The  surface runoff drained  to 139  lateral sewers (analyzed  w|th
the  SWMM RUNOFF Block)  and  subsequently to  31 trunk sewers (analyzed  with
the  SWMM TRANSPORT  Block).   The  downstream  end of  the sewer  system  in
District "A  connects  to the Westerly Interceptor.  Flows  exceeding the  capa-
city of the interceptor discharge to the Elizabeth River. .

    The  schematics  of the combined  sewer  layout for each subarea are  shpwr)i
separately  |_n  Figures D-8 to D-12.   The combined sewer system was extended
from  the separate storm sewer  system  shown in  Figure  D-13.   It  includes  a
pipe in  every  street  but excludes drainage  at  the upstream end  of  each  sewer
branch.   The separation  of sewers in District  A was  studied  previously  (J.1-)
in  an effort  to alleviate  frequent street and  cellar flooding.  In the
separate  system,  overland  flow  was  allowed to  the maximum  extent  practical,
TABLE D-5 compares  the total  length  of  separate sanitary,  separate storm and'
the combined systems.
                                     165

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Figure D-7.  Subareas of drainage District A





                              166

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     LEGEND
    JUNCTION MANHOLE
    TRUNK INLET (ELEMENT  NUMBERS ASSIGNED)
	  PIPE WJTH COMBINED FLOW (ELEMENT NUMBERS ASSIGNED)"
 —  PIPE WITH SANITARY FLOW ONLY

  Figure D-8.  Combined sewer system layout,  subarea I
                            167

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SUBAREA HL
  SEE FIGURE D-8 FOR LEGEND
                                       341
      Figure D-9.  Combined sewer system layout,  subarea II
                               168

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                  SUBAREA
     •	.201
                                                                346
 SEE FIGURE D-8 FOR LEGEND
                                                   SUBAREA XZ
        Figure D—10.  Combined sewer system Xayout, subarea III




                           /
   SUBAREA 33C
     356
SEE FIGURE D-8 FOR LEGEND



      Figure D—11.   Combined sewer system layout, subarea V




                                 169

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      Figure D-12.  Combined  sewer system layout, subarea IV
                             170

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   LEGEND
JUNCTION  MANHOLE
PIPE  ELEMENT-(ASSIGNED NUMBER SHOWN)
 Figure D-13.   Separate storm sewer system layout

                           171

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                TABLE D-5.   TOTAL SEWER LENGTH COMPARISON
                System
Length (ft)
                Separate Sanitary

                Separate Storm

                Combined
106,000

 29,000

 63,640*
                * Length of sewers carrying combined
                  sewage only.  The total length of
                  the combined sewer system, including
                  extensions at extremities, is
                  106,000 feet.

                Note:  1 foot = 0.3048 meters

HYDRAULIC PROPERTIES AND LAND USE

     Delineation of  subcatchment  boundaries were prepared from a  street  map
of scale  1:4,800 and field  checked.   Subcatchment areas were  planimetered.
Data prepared  for each  subcatchment  included catchment width, area,  imper-
viousness, slope, overland  resistance  factors,  surface  storage  and infiltra-
tion factors.  The subcatchment data are shown in TABLE  D-6.

     Definition  of   pipe elements  includes length,  slope,  tributary  area,
upstream  and  downstream connecting pipes and  roughness  coefficients.   TABLE
D-7 lists the pipe element  and its corresponding slope,  length  and tributary
drainage  area.    The trunk sewer  elements were  assigned  numbers  starting
at 300 and the lateral sewer elements, numbers below 300.

     Since  the  SWMM RUNOFF  (modified) and  TRANSPORT Blocks  have  sewer
design  capability,   the  sewer  diameters  required  as  input  to the  program
were generally assigned  as  0.457  m (18 inches),  the minimum diameter used in
practice for combined sewers.  The Manning "n" was assumed equal to 0.013  for
diameters less than  0.762 m (30  inches)  and  0.011 for  diameters  equal to or
greater than 0.762 m (30 inches), respectively.   The modified version of  the
SWMM  RUNOFF program has  incorporated  these  changes  of roughness  coeffi-
cient with  pipe  sizes.    Data on  the  land  use and curb  length in each sub-
catchment was  prepared  and is presented in  TABLE  D-8.  Dry-weather flows
were entered at designated  inlet manholes to trunk sewers.

DISTRICT A DATA FOR  STORM

     STORM  is  a  "macro" model and is intended  to  consider  a large drainage
basin.   It  processes the composited information of  all subcatchments rather
                                     172

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TABLE D-7,  PIPE ELEMENT DATA FOR COMBINED SEWER SYSTEM



  SUBAREA III                                    SUBAREA V
Pipe
Number
201
202
203
204
205
206
207
208
212
213
214
215
216
209
210
211
219

220
221
227
226
225
228
229
230
233
222
232
235
234
231
224
223
236
238
246
249
251
253
252
250
248
247
245
244
243
242
241
240
239
237
Slope
.0050
.0013
.0043
.0043
.0054
.0054
.0290
.0025
.0100
.0100
.0100
.0025
.0025
.0193
.0092
.0248
.0025

.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0070
.0030
.0025
.0040
.0020
.0025
.0025
.0025
.0025
.0025
.0012
.0010
.0010
.0020
.0010
.0042
.0050
.0050
.0050
.0040
Length
(Ft)
220
440
200
250
300
230
320
480
850
450
470
300
750
350
250
300
1250
SUBAREA
400
350
650
280
330
350
280
260
290
165
500
320
300
580
180
400
540
250
250
340
300
300
250
250
250
360
320
250
320
320
300
300
300
400
Tributary
Area
(Acres)
8.88
4.00
13.31
1.28
5.17
2.20
1.61
5.28
16.52
2.39
8.99
5.10
5.10
2.09
1.84
1.36
9.69
IV
6.02
8.70
2.90
3.08
4.59
3.22
5.22
1.14
5.94
4.20
4.95
2.72
1.06
10.50
0
2.86
4.51
5.84
2.20
3.66
3.63
3.53
3.27
1.43
0.59
3.60
3.38
2.13
3.78
4.63
4.88
5.22
2.02
5.43
Surface
Elevation
(ft. MSL)
56.80
52.00
53.00
53.50
51.00
49.00
38.50
38.50
42.00
33.00
28.00
40.00
38.50
32.80
30.00
28.00
37.50

31.20
31.20
32.80
31.00
29.0Q
30.50
30.50
30.00
31.00
30.50
30.00
34.00
33.00
30.00
29.00
28.00
33.00
35.00
36.40
33.20
34.00 '
35.00
34.00
32.00
33.20
36.40
38.00
38.00
36.00
34.00
32.00
33.00
35.00
33.00
Pipe
Number
260
261
262
263
264

301
303
305
307
309
311
313
315
317
319
321
323
325
327
329
331
333
335
337
339
341
343
345
347
349
351
353
357
359
361
363
Slope
.0025
.0025
.0025
.0025
.0025

.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0090
.0031
.0017
.0020
.0099
.0048
.0019
.0133
.0089
.0091
.0034
.0019
.0019
.0019
.0004
.0004
.0004
.0013
.0030
.0030
.0030
.0030
Length
(Ft)
480
540
490
350
360
TRUNK
130.0
250.0
250.0
270.0
290.0
300.0
800.0
420.0
390.0
330.0
240.0
250.0
260.0
320.0
320.0
390.0
390.0
350.0
340.0
340.0
220.0
430.0
320.0
870.0
430.0
220.0
710.0
340.0
470.0
900.0
750.0
Tributary
Area
(Acres)
8.63
7.78
6.42
2.09
7.63
SEWER
0
1.87
0
0.66
0.81
0.99
1.10
4.07
1.69
6.49
1.76
1.84
0
0
1.28
4.40
9.42
1.69
5.65
1.50
2.24
8.20
4.10
2.83
2.20
1.50
0.77
3.38
8.70
0
13.54
Surface
Elevation
(ft. MSL)
38.00
38.00
37.50
37.50
32.00

71.69
70.55
69.89
69.09
69.44
67,95
61.30
62.20
59.00
57.20
56.00
56.50
54.50
51.80
49.50
46.80
44.10
42.00
39.60
38.10
36.50
36.00
32.00
31.20
37.00
37.50
38.00
30.50
37.50
32.00
30.00
                         177

-------
               TABLE D-7.  (continued)
SUBAREA I
                                             SUBAREA II

Pipe
Number
1
3
4
7
8
10
13
14
15
20
19
24
25
29
30
33
31
35
42
40
38
36
47
49
56
52
54
55
114
117
59
72
74
75
67
105
109
129
77
76
71
69
64
62
60
58


Slope
.0025
.0032
.0025
.0098
.0098
.0098
.0025
.0025
.0092
.0018
.0025
.0025
.0053
.0025
.0025
.0025
.0025
.0212
.0071
.0071
.0071
.0013
.0091
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0025
.0065
.0065
.0065
.0065
.0038
.0036
.0063
.0184

Length
(Ft)
280
240
280
220
420
300
240
570
310
310
570
570
310
230
300
220
235
300
275
260
280
620
480
600
360
400
280
240
220
370
680
420
260
540
290
150
150
690
690
220
300
300
650
290
290
270
Tributary
Area
(Acres)
3.71
3.60
4.66
1.65
3.05
3.78
3.23
3.38
3.05
3.01
6.42
6.79
2.86
2.75
5.65
3.56
3.45
0
2.82
3.12
3.08
5.14
4.58
3.56
4.15
6.26
1.87
2.02
0
4.11
4.15
4.95
4.98
3.12
3.47
0
0
1.60
0
1.36
1.14
5.50
7.16
2.28
4.44
1.28
Surface
Elevation
(ft. MSL)
73.24
72.49
72.49
77.62
73.30
71.69
77.00
70.55
70.55
69.89
69.89
69.09
69.09
76.00
74.81
76.00
74.81
68.44
72.52
70.63
68.95
68.44
67.95
63.50
62.00
64.00
63.00
62.00
61.30
63.00
62.00
71.00
72.00
71.00
68.50
62.00
61.30
73.00
72.00
71.00
69.00
68.50
68.00
65.00
62.00
62.00

Pipe
Number
82
101
99
98
95
94
92
91
189
187
85
104
103
108
112
119
78
80
83
121
123
125
126
84
128
148
149
147
146
143
141
139
138
135
87
89
133











Slope
.0025
.0025
.0075
.0025
.0062
.0025
.0141
.0025
.0104
.0425
.0025
.0217
.0025
.0025
.0025
.0025
.0025
.0025
.0055
.0025
.0025
.0025
.0054
.0059
.0233
.0025
.0388
.0413
.0118
.0025
.0058
.0026
.0025
.0085
.0085
.0051
.0051










Length
(Ft)
170
550
280
320
250
860
230
860
230
150
660
270
610
640
570
390
270
300
160
350
250
450
200
200
580
650
250
250
380
360
350
310
250.
150
150
220
310









Tributary
Area
(Acres)
4.51
.6.69
3.26
4.26
0.92
6.83
2.49
6.79
2.31
4.36
7.56
3.63
4.55
7.68
6.68
5.02
1.36
2.54
0
4.18
2.17
3.52
0
4.44
8.55
3.27
0.88
2.83
7.68
6.35
7.07
5.98
1.46
2.39
0.73
3.01
1.39









Surface
Elevation
(ft. MSL)
57.70
64.30
62.00
62.00
61.00
62.00
59.40
59.40
56.70
56.50
56.50
54.50
54.50
51.80
49.50
56.00
55.00
54.60"
55.00
56.00
55.00
55.00
54.90
54.80
44.10
69.00
60.10
50.50
48.30
46.20
44.10
43.10
43.10
42.80
42.20
41.00
39.60









                        178

-------
TABLE D-8. SUBCATCHMENT WATER QUALITY INPUT DATA FOR SWMM
SUBAREA LAND USE
NUMBER CUASS.
•1
2
3
4
5
I
8
9

11
12
13
14
IS
i ^
18
19
20
21

23
24
25
'26
27
28
29
i?
i2
33
I?
38
39
1

II
55
56

59
60
14
63
64
II
165
164
163
162
161
160
- 159
15ft
157
156
155
15*
153
152

150
149
148
147
146
145
144
143
148
141
171
35
36
45
46
47
46
49
50
51

53
66
2
2
2
2
2
2
J
J^
1
1

J
J_
1
J
J_
|

1
J_
J_
J
X
^
^
^
1
J^
J^
1
J
^
1
i
i

1
|
j^
^
i

1

i
i
I

1
1

^
^
i
i
i
i

i
i
i
^
i

j
^
1

^
i

i
TOTAL GUTTER MUHBER OF
UEN6TH*10**2 FT. CATCHBASINS
10.00
4.00
5.00
8.00
5.00
8.00
4.00
8.00
4.00
5.00
3.00
8.00
15.00
12.00
8.00
7.00
7.00
7.00
8.00
11.00
a. oo
11.00
8.00
6.00
11.00
14400
6.00
13.00
6.00
10.00
6.00
lO'.OO
7. -00
16400
20.00
16.00
14.00
3. .00
5.0.0
t. 00
.00
.5.30
13.00
4.00
7.00
4.50
27.00
27.00
15.00
6.00
5.00
8.00
6.00
7.30
6.50
8.00
4.00
5.00
s.oo
3.50
13.00
3.00
7*00
3.00
5.00
17.00
6.50
9.00
7.00
8.00
7.50
5.50
7.50
15.00
7.50
8.00
5.00
•9.00
5.00
13.50
11.00
6.00
8.00
9.00
5.00
3.00
6.00
4.50
,9.50
'8.00
7.50
12.00
8.00
0.0
0*0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
oTo1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
8.0
.0
§:§
O.G
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
o.c
0.0
0.0
0.0
0.0
0.0
0.0
040
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
o.o
0.0
0.0
0.0
0.0
0.0
S.o
.0
0.0
?Ğ0
.0
0.0
g.o
0.0
0.0
o.c
                           179

-------
TABLE  D-8.   (continued)
SUBAREA
NUMBER
67
68
69
7P
71
72
73
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97,
98
99
100
101
102
103
104
105
106
107
10B
109
110
111
112
113
114
115
116
in
119
120
121
122
123
124
125
126
127
128
III
131
132
133
134
135
136
137
138
139
140
172
166
170.
310
309
306
283
284
282
286
285
294
295
296
300
298
299

§97
93
LAND USE
CLASS.
1
1
1

1
1
1
1

. 1
1
1
I
1
1
1
1
1

1
1
1
1
1
1
1
1
1
1 ,
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
\
1
1
1
1
1
1
1
1
1
i
1
1
1
1
1
1
1
1
1
1
1
1
1.
3
3
3
1
1
1
2
2
4
2
2
2
2
2
2
2
2
         TOTAL  GUTTER
        LENGTHĞ10ğ*2 FT.

              6.50
              6.00
              6.00
             10.50
             11.50
             14.00
             13.50
             11.00
             17.00
              5.00
              7.00
              7.00
              7.00
              6.00
              6.00
              6.00
               §. 00
               .00
             11.00
             24.00
              6.00
             11.50
              9.00
              5.00
             15.50
             25.00
              6.50
              9.50
             10.00
             11.00
              4.50
              5.00
              6.00
              9.50
              5.00
              7.00
 NUMBER  OF
CATCH6ASINS

    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    o.o •
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    O.D
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    0.0
    o.o
    0.0
    0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
           180

-------
TABLE D-8.   (continued)
SUB AREA :
NUMBER
274
287
288
302
303
304
305
291
292
201
202
203
204
205
206
207
208
209
218
219
220
III
223
224
225
226
227
228
229
230
231
232
233
^34
235
236
237
244
245
246
247
248
249
250
251
252 •
253
254
255
256
257
258
259
260
262
264
268
269
270
271
m
275
276
277
278
279
260
281
261
289
307
308
266
210
211
212
213
214
215
216
217
238
239
240
241
242
243
263
265
290
267
Lcf5i
3
2
: T
3
4
4
4
4
3
1
1
1
1
1
1
i
5
5
5
5
1
1
1
1
1
1
1
1
1
1
1
1
5
5
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
1
2
1
1
1
1
3
f
1
1
1
1
1
1
1
1
2
2
1
2
2
2
2
2
2
2
2
2
2
2
2
2
3
2
T.OTA
LENGT














































































L ,GUXT£R.
H*la**2 Ft.
6.00
20.00
9.00
9.00
17.00
17.00
6.00
17.00
1:88
9.00
9.00
9.00
9.00
10.00
10.00
10.00
15.00
10.00
6.00
6.00
6.00
7.00
10.00
!:88
6. DO
2.00
6.00
£.00
9.00
4.00
6.00
7. 00
7.00
13.00
12.00
11.00
11.00
5.00
13.00
11.00
11.00
11.00
6.00
6.00
9.00
12.00
5.00
9.00
5. CO
7.00
5.00
10.00
3.00
25.00
*:H-
8.00
6.00
9.00
8.00
9.90
6.00
13.00
12.00
11.00
12.00
.4 ..0.0
13.00
5.00
9.00
6.00
6.00
17.00
16.00
§.00
.00
12.00
18.00
8.00
9.00
7.00
11.00
10,00
9.00
10.00
10.00
9.00
8.00
9.00
3.00
16.00














































































                           jyaBnfi
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               p. o
                               6*0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                                 0
                                 p
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               o.o
                               0.0
                               0.0

                               1:1
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               .0.0.
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0

                               8:8
                               0.0
                               0.0
                               0.0
                               0.0
                                8.0
                                .0
                               O.Q
                               0.8
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0
                               0.0

                               2 '2
                               0.0
                               O.Q
                               0.0
                               .0.0
                               0.0
                               0.0
                               0.0
                               0,0
                               0.0
                               0.0
                               O.Q
                                S.Q
                                .8
                               0.0
                               0.0
                               0.0
           181

-------
than  each  separately.   The pervious  and impervious areas  of each subarea
in District A were computed.  The data  on curb  length to  develop  criteria as
to dust and dirt   accumulation is included in TABLE D-9 for  each  major
subarea. The data were developed from an  integration  of subcatchment quality
input parameters shown  in TABLE D-8.   TABLE D-10 summarizes the District A
land use data which are used as  direct  input to  the  STORM program.  The curb
length  in single family  residential  is the greatest among all types of land
uses because, in Elizabeth, each single family lot is quite  small,  generally
0.08 hectares  (0.20  acres) or less, and  the street arrangement  is compact.
      TABLE D-9.  SUBAREA CURB LENGTH (FEET)  VERSUS  LAND  USE, DISTRICT A
Subarea
I
II
III
IV
V
Total
Single
Family
77,000
67,300
3,100
44,385
1,795
193,680
Multiple
Family
r-
2,480 •;
11,920 .
5,540
15,585
35,5-25
Commercial
-
120
6,980
1,810
920
9,830 '
Industrial Parks
_
;
3,900
3,685
_ • _
3,900 3,685
Note:  1 foot = 0.3048 meters
            TABLE D-10.  SUMMARY OF DRAINAGE DISTRICT  A LAND  USE DATA
Land
Use
Single Family
Multiple Family
Commercial
Industrial
Open Space
% of
Area
71.7
18.2
5.3 :
2.8
2.0
% Imper-
vious
43
50
80
80
19
Curb Length
(ft/acre)
413.
298. '
283.
216.
296.
1 ft/acre = .753 m/hectare
                                   ; 182

-------
     The  depression storage  capacity  as required  by the  STORM program  is
a  single  parameter  average over the entire drainage basin  being  considered.
With 47 percent  impervious area,  1.59 mm (0.0625 inches) depression  storage
capacity  for  impervious  areas and 6.35 mm  (0.25 inches)  for  pervious  areas,
the  average  depression storage capacity for  District  A is computed as  3.94
mm (0.155 inches).   In  STORM,  no runoff  from a  watershed  takes place  if
the  total  rainfall  is  less than available  depression storage.   STORM  allows
depression storage  to  recover to  its  maximum capacity at a constant rate  to
account for evaporation.  The recovery rates are assumed  constant  for a given
month but  may vary  from month to month.  The recovery of depression storage
is  the mechanism in STORM to account  for antecedent  dry  conditions and
enables the model to process continuous rainfall data.

     The  recovery  rates are computed  using the  Meyer formula (40) with
the following expression:
                         E = C(e  - e )
                                s    a
(D-l)
                                            10
where:

     E  = the rate of evaporation in inches  per  month,

     eg = the saturation vapor pressure in inches of mercury  (Hg) corresond-
          ing to monthly mean air temperature,

     e  = the vapor pressure of air in  inches of Hg, based upon monthly mean
          air temperature and relative humidity,

     W  = the monthly mean  wind  speed in miles  per hour obtained at 30 feet
          above general level of  surrounding  roofs of building,

     C  = a  coefficient depending on  various  factors  affecting evaporation
          and a value of 0.15 is  suggested for small bodies of shallow waters
          such as wet soil surfaces  and small puddles.

   .  The monthly  variation  in  evaporation  rates  for  the  study area  were
computed and are  shown in  TABLE D-ll.  The  inputs  to  the Meyer  formula
for  computing  the rate of  evaporation  are also shown.   The inputs  were
prepared using  the  climatological  data recorded  at  Newark International
Airport during the period of 1963-1974.   The  computed evaporation rates agree
with the average  annual lake evaporation in the New York  area  (41).  Since
the  evaporation rates  affect  the available depression  storage prior  to  a
rainfall event, they have a more pronounced effect on  runoff from low inten-
sity rainfall than from high intensity rainfall  of the  same duration.
                                    183

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                 TABLE D-ll.  MONTHLY EVAPORATION RATE
Mean Air
Temperature
Month (°F)
January
February
March
April
May
June
July
August
September
October
November
December
31.4
31.1
41.5
51.9
61.9
71.9
77.0
76.0
68.5
57.4
46.9
36.6
Mean
Relative
Humidity
(%)
65.3
59.3
63.3
57.0
.60.7
61.5
61.1
66.7
66.9
66.2
66.9
68.0
Mean
Wind
Speed
(mph)
11.3
12.2
12.1
11.6
10.5
9.6
9.2
9.2
9.6
9.6
10.5
11.1
Evaporation
Rate
(inches /day)
.065
.078
.105
.186
.232
.302
.322
.288
.233
.159
.112
.078
Note:  1 mph= 1.61 km per hour
       1 inch/day - 25.4 mm/day

     Pollutant washoff coefficient K is determined by the equation:
                      - P = Po(l-e-krAt)
                                        (D-2)
where:
     P  - P
     P°
     P°
     At
     r
pounds of washoff in a time interval,  At,
pounds of pollutant in the street at the start of  rainfall,
pounds of pollutant remaining at the end of  the time interval,
the time interval, and
runoff rate in inches per hour.
In SWMM, K is internally set equal to a value of 4.6, based on the assumption
that  a uniform runoff rate of 12.7  mm (0.5  inches)  per hour  would wash
away 90 percent  of  the  pollutant  in  one hour.   For consistent comparision of
the results  obtained with  STORM  and  SWMM,  the same washoff  coefficient  is
used  for  the  STORM.    There are  studies  in which  other  K values are  used
(42).

     Data for  dry-weather  flow quantity and quality  required  for simulation
of combined sewage overflow are discussed elsewhere.

AREA AND LAND USES FOR OTHER DISTRICTS

     The City has been  divided into  25 drainage districts.   These districts,
                                    184

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lettered A through Y,  are shown in Figure D-14,  which also  shows  the  Easterly
and Westerly Interceptors  and their  corresponding inlet and sewer pipe
elements.                                               *

     Only  composite  data  were required  for drainage  districts other  than
District A.   TABLE D-12 presents for  each district  the  area,  the  various
kinds of land use, and  the percent imperviousness.   The areas  of the planned
land  use were  taken  from the approved master plan (43).   Where  planned
ultimate land use differed from  the  existing  use,  the use resulting  in  the
greater population was adopted.   The  percent imperviousness in each  district
was the weighted average based on the percent imperviousness for  various  land
uses  as  shown  in TABLE  D-10.   Two-family houses were considered as  part  of
the multiple family residential area.   District  A is the  largest district  in
the  City and includes  all  land uses  and, therefore, permits developing
relevant parameters for City—wide application.

     The  developed population  of each district are shown in  TABLE D-13.
The populations  estimated are based  on densities  of 55.8 and 121.3 persons
per hectare  (22.6  and  49.1 persons per  acres)  respectively for single-family
and multiple-family  residential  areas.   These densities were obtained  from
census data  at presently  developed areas  for each land use.  These estimated
populations  were  used  to compute dry-weather flow.    The  estimated developed
population for  District A is  about  16,500 and  for  the City,  124,000.   The
present population of the City is about 115,000.

     The  curb  lengths  for  the various land uses were developed from  data
presented in TABLE D-10  for  District  A.  The curb  length is used to  estimate
the  accumulation  of  dust and  dirt  on  the  streets and to define the amount
of pollutant washoff.                              '   "  .    *

DRY-WEATHER  FLOW QUANTITY AND QUALITY

     Use of  SWMM  and  STORM as modified,  for the analysis  of combined sewage
quantity and quality requires ' input  of  dry—weather.flows,  including  domestic
sewage,  commercial and   industrial  discharges  and  infiltration.    Domestic
sewage  flows were estimated from daily per capita  water  use  and commercial
and industrial flows from average contributions  per  area.  unit.  Both commer-
cial  and industrial wastewater quantities vary widely depending upon  the  type
and size- of  the commercial and industrial  development  (44).   Quality compo-
nents in the commercial  and  industrial  wastewaters also vary widely  (45,46).
Both  the  quantity and  quality of dry-weather flow vary with the hour of the
day  and the . day  of  the  week.    While  dry-weather  flows make a significant
contribution to  the quality  of  combined  sewage,  their average  quantity  is
small,  generally  less  than  0.2  percent  of the sewer design  flow computed,
using SWMM,  with  the  5-year  return interval,  intermediate pattern, synthetic
storm hyetograph  (Figure  D-5).

      With  the  assumed per  capita contribution  of  379 liters (100  gallons)
per day from all  sources, the average daily wastewater quantity from  District
A  is 6,245  m   (1.65  million  gallons).    The  average daily  concentrations
of pollutants in  the wastewaters  adopted are shown in TABLE D-14.
                                    185

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    BOROUGH V,
      OF
    ROSELLE  \>
     PARK   II
    BOROUGH
       OF
    ROSELLE
         WESTERLY  '
        INTERCEPTOR
                                                                         EASTERLY
                                                                       INTERCEPTOR
      LINDEN
              TO
        JOINT MEETING
          TREATMENT
            PLANT
                                                   NOTES;
                                                    I. LETTERS DESIGNATE
                                                      DRAINAGE DISTRICTS.
                                                    2. NUMBERS ARE
                                                      INTERCEPTOR SEWER
                                                      ELEMENTS.
Figure D-14.
Definition  of drainage, districts  and interceptor  system in
Elizabeth                                '
                                          186

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           TABLE D-12.   SUMMARY OF LAND  USE  IN  THE  CITY  OF ELIZABETH
Land Use (%)
District
A
B
C
D
E
F
G
H
I
J
K
L
M
N
0
P
Q
R
S
T
U
V
W
X
Y
Area
(acres)
655
112
111
117
229
88
34
122
70
420
65
66
67
79
103
37
83
303
207
62
331
440
415
138
56
Single
Family
72
90
20
10
35
0
0
0
0
10
0
0
0
0
5
0
10
0
0
0
0
0
0
15
0
Multiple
Family
18
10
55
60
35
70
0
25
85
70
60
50
90
100
0
50
40
0
75
50
50
40
90
65
100
Commercial
5
0
25
30
30
30
100
75
15
15
40
10
5
0
0
50
25
0
5
0
25
27
10
0
0
Industrial
3
0
0
0
0
0
0
0
0
5
0
40
0
0
50
0
25
100
15
50
25
30
0
0
0
Park
2
0
0
0
0
0
0
0
0
0
0
0
5
0
45
0
0
0
5
0
0
3
0
20
0
District
Percent
Impervi-
ousness
47
44
56
58
57
59
80
73
55
55
62
65
50
50
49
65
64
80
54
65
65
66
53
43
50
City
4410
17.3
47.5
16.3
16.3
2.6
58
NOTE:  1 acre = 0.405 hectares

       Acres of Land Use indicated are based on approved Master Plan of the
       City (43)
                                     187

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          TABLE D-13.  POPULATION AT SATURATION DEVELOPMENT
District
A
B
C
D
E
P
G
H
I
J
K
L
M
N
0
P
Q
R
S
T
U
V
W
X
Y
Area
(Acres)
655
112
111
117
229
88
34
122
70
420
65
66
67
79
103
37
83
303
207
62
331
440
415
138
56
Single*
family
10,658
2,278
502
264
1,811
0
0
0
0
949
0
0
0
0
116
0
188
0
0
0
0
0
0
468
0
Multiple**
Family
5,789
550
2,998
3,447
3,935
3,025
0
1,498
2,921
18,560
1,915
1,620
2,961
3,879
0
908
750
0
7,623
1,522
8,126
8,642
18,339
4,404
2,750
Total
16,447
2,828
3,500
3,711
5,746
3,025
0
1,498
2,921
19,509
1,915
1,620
2,961
3,879
116
908
938
0
7,623
1,522
8,126
8,642
18,339
4,872
2,750
Total
4,410
17,234   106,162
123,396
*  Based on 22.6  persons per acre  (55.8 persons per  hectare)

** Based on 49.1  persons per acre(121.3 persons per  hectare)

   Population Densities  for indicated land uses are  derived
   using census data from presently developed areas.
                             188

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TABLE D-14.  AVERAGE DAILY POLLUTANT CONCENTRATION OF DOMESTIC WASTEWATER

                   Pollutant              	Concentration
                   Suspended solids

                   BOD

                   Settleable solid

                   Total nitrogen

                   Total phosphate

                   Total coliform
   240 mg/1

   200 mg/1

     6 mg/1

    30 mg/1

    10 mg/1

5.27 x 107 MPN/100ml
 These  pollutant  concentrations are classified as "medium" according to an EPA
 study  report (45).   Diurnal  variations of sanitary  wastewater  quantity and
 quality  are  shown  in  TABLE D-15.  These variations are based on experience in
 cities with population and urbanization  comparable to Elizabeth.   The peak
 hourly rate occurs at  10 a.m.  and equals  1.45 times  the  daily  average flow
 rate.   For District  A, the peak hourly wastewater flow rate is  0.105 m /sec
 (2.4 mgd).   Possible variations  in  quality and quantity  of wastes by day of
 the week were not  considered.

      The hourly DWF pollutant  loadings  for  SS, BOD, and total  coliform
 in TABLE D-15 are based  on the  daily  average  concentrations  shown in TABLE
 D-14.   It  was assumed that the same concentration ratio variation applies to
 all pollutants.    During  the preparation  of input data  to STORMS pollutant
 concentration ratios  in TABLE D-15 were used as pollutant mass loading.  This
 artifically  increased the pollutant  mass  loading in  the  early  hours of the
 day and decreased it in  the  later  hours.  As  a result,  the amount of un-
 treated sanitary sewage in the  overflow may either increase or decrease for
 individual   storm  events,  depending  upon  the  time  of the  day  the  rainfall
 starts.    On the  average,  it may  increase the  computed  amounts  of annual
 pollutants   discharged  by about  10  percent.   This  deviation  in computing
.annual amount of pollutants in the overflow would be the same for all alter-
 natives tested  and would not change the  relative proportions  of pollutants
 discharged  which- were  used  as a  measure for  determining  the desirable
 systems.  Based  on the  assumed  SS contribution  from commercial and industrial
 areas to be 0.06 and 0.08 kg per hectare  (0.33 and 0.44 pounds per acre) per
 day respectively,  the  total  non-domestic  portion of SS  in the  dry-weather
 flow would be about 9 kg  (20  pounds), or less than one percent of  the assumed
 wastewater loading.  The  diurnal variations shown  in  TABLE  D-15 are DWF input
 data to STORM.

      In SWMM, consideration  of DWF  is  made in the  TRANSPORT  Block.  Thus,
 for District  A,  DWF enters  the  trunk sewers directly.    The  district was
 divided into 25 sub.areas.  TABLE D-16 presents,  for each  subarea, the  inlet
 manhole,  area, predominant land use, population  density,  average daily
 flow  and  daily  SS  and  BOD loading.   Other than daily  pollutant  loadings,
                                     189

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              TABLE D-15.   DIURNAL VARIATION OF DOMESTIC WASTEWATER
                          QUANTITY AND  QUALITY FOR DISTRICT A
Hour of
the day
Flow
Ratio*
         Flow
         Rate
         (mgd)
         Concen-
         tration
         Ratio*
           SS
           (lbs/hr)
         BOD
         (lbs/hr)
          Total
          Colifortn
          MPN x 1015/hr
   1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
 .9
 .7
 .5
 .35
 .30
 .30
 .40
 .85
1.35
1.45
1.35
1.30
1.25
1.20
1.15
1.05
1.05
1.15
         1.49
         •1.16
          .83
          .58
          .50
          .50
          .66
         1.40
         2.23
         2.40
         2.23
         2.15
         2.
         1.
         1.
1.
1.
  ,25
  ,35
1.35
1.25
1.15
1.05
  .06
  .98
  .90
1.73
1.73
1.90
2.06
2.23
2.23
2.06
1.90
1.73
 .90
 .70
 .60
 .50
 .45
 .40
 .45
 .50
 .60
 .70
 .85
1.15
1.25
1.50
1.55
1.55
1.50
1.40
1.35
1.30
1.25
1.20
1.20
1.15
123
 96
 82
 69
 62
 55
 62
 69
 82
 96
116
158
171
206
212
212
206
172
185
178
171
164
164
158
   Daily Average =  1.65  Daily Total =3289
 103
  80
  68
 .57
  51
  46
  51
  57
  68
  80
  97
 131
 143
 171
 177
 177
 171
 160
 154
 148
 143
 137
 137
 131

2738
 .124
 .096
 .083
 .069
 .062
 .055
 .062
 .069
 .083
 .096
 .117
 .158
 .172
 .206
 .213
 .213
 .206
 .193
 .186
 .179
 .172
 .165
 .165
 .158

3.3
 * Ratios are with respect to the corresponding average  values.

   Note:  1 mgd = 0.0438 m3/sec
          1 Ib = 0.453 kg
                                 190

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    TABLE D-16.
SWMM INPUT DATA FOR DOMESTIC WASTEWATER COMPUTATION,
                DISTRICT A
Subarea
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Inlet
Manhole
360
358
356
352
352
353
350
244
342
338
334
330
328
326
324
316
316
314
312
310
308
306
304 ,
302
300
Area
(Acres)
14.53
31.56
8.70
67.10
135.35
10.46
21.32
4.10
8.20
46.78
37.32
17.75
10.46
11.48
39.14
17.64
54.08
24.35
8.65
32.69
10.64
10.24
10.32
10.35
11.97
Land*
Use
2
2
2
1
1
1
1
3
3
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Population
Density
(persons
per acre)
37.0
47.8
43.1
22.6
23.4
22.6
30.7
15.7
22.6
22.6
30.6
22.6
22.6
22.6
22.6
22.6
22.6
22.6
22.6
22.6
22.6
22.6
22.6
22.6
22.6
Average Average
Daily Daily Loading
Flow
(cfs)
.083
.233
.058
.237
.469
.036
.101
.010
.028
.164
.177
.062
.037
.040
.137
.062
.181
.085
.030
.115
.037
.036
.036
.036
.043
ss
(Ibs/day)
107.4
301.5
75.0
306.6
641.8
46.6
130.7
12.9
36.2
212.2
229.0
80.2
47.8
51.8
177.3
80.2
234.2
110.0
38.8
148.8
42.9
46.6
46.6
46.6
55.6
BOD
(Ibs /day)
89.5
251.2
62.5
255.5
534.8
38.8
108.9
10.8
30.2
176.8
190.8
66.8
39.9
43.1
147.7
66.8
195.2
91.6
32.3
124.0
39.9
38.8
38.8
38.8
46.4
                                            2.56
                                      3307.3
2760.
Predominant Land Use
1 - Single Family Residential
2 - Multiple Family Residential
3 - Commercial

Note:  1 person/acre = 2.471 persons/hectare
       1 cfs = 0.0283 m3/sec
       1 Ib/day = 0.453 kg/day
                               191

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which  are computed internally in  the  program,  additional data  are  required
for  the  computation of  combined  sewage.   The slight differences  for  daily SS
and  BOD  loadings between TABLE D-15 (for STORM)  and TABLE D-16 (for SWMM)  are
due  mainly  to  the  significant  number contained  in the SWMM print out and  are
inconsequential. The  same diurnal  quantity  and quality variations  shown in
TABLE  D-15  were  applied to SWMM.   In  SWMM computations,  the simulations were
assumed to begin  at 10  a.m.  when the  hourly DWF quantity was greatest.

UNIT COST DATA

     To  compare the  cost—effectiveness  of  the  alternative sewer  systems,
cost data were  developed for sewers,  storage  facilities,  pumping  stations
and  treatment  works.    These costs are  affected  by variables such  as  land,
weather,  subsurface  conditions,  groundwater,  access,  size of   facilities,
process involved, etc.   The cost data used  are applicable  to  work  in
Elizabeth,  New Jersey  and  consolidate  many  factors that  affect cost into
a single parameter (such as costs per  foot for each size of sewer for various
depths  of excavation,  per  gallon  of  storage capacity,  per mgd  of  pumping
capacity, etc.).   These parameters  are adequate for comparative  purposes  but
would  require refinement for definitive projects at specific sites.

Sewer  Costs

     Figure D-15 and TABLE D-17 present pipe cost  per linear foot for various
depths  of  trench  developed  from actual  cost data.   The unit cost  includes
the  cost of pipe, pipe  laying, excavation, dewatering,  temporary tight
sheeting  and  backfill,  and  is based  on  the  ENR  construction cost  index  of
1,800.   Pipe  sizes smaller  than 0.457 m  (18 inches) are  used only for  sani-
tary sewers.   Circular pipe sewers were assumed.  The unit  price increases
substantially at about  a 6.1 m  (20 fe,et) trench  depth due  to the additional
bracing and sheeting required and greater excavation costs.

Storage Costs

     Costs  of storage facilities presently in operation have been summarized
(18, 19).   The  cost of  in-pipe storage,  as used  in  Seattle,   Washington,
was  estimated at about  $0.06 per liter- ($0.23 per gallon)  of storage, mostly
for  control and  monitoring  systems  and  automated  regulating  stations   in
existing pipes.  The  cost of off-line storage depends upon  the  type  and  can
include open lagoons, concrete covered reservoirs or deep  tunnels.   The open
lagoon,  such as  the  one used in Chippewa Falls,  Wisconsin,  costs  about $.07
per  liter ($0.26 per gallon)  of storage.   The cost range  for covered  concrete
storage  is  from $0.13  per  liter   ($0.50  per gallon)  for Humboldt  Avenue,
Milwaukee to  $0.56 per  liter  ($2.12  per gallon)  for  a more recently built
storage  basin  at Jamaica Bay, New  York  City.  For the  deep tunnel  storage
system  in  the City of  Chicago,  the cost was estimated  as  $0.06 per  liter
($0.24 per  gallon).   The above costs  are based on  the ENR  construction cost
index of 2,000.  In a sewerage improvement program recently developed for  the
City of  Trenton, New Jersey (16),  the cost  of  a  sewage detention basin  and
appurtenances  was  estimated  at  about  $0.07 per  liter   ($0Ğ25  per   gallon)
                                    192

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  3000
  2000
  1000
   900

   800

   700

   600

x- 500
 in
 t_
 o
= 400
 o
•o

I- 300
O
O
u.


< 200
b
o
   100
    90
    80

    70

    60

    50


    40



    30
    20
I. COST INCLUDES  TRAFFIC, EXCAVATION,
  OEWATERING, MAINTENANCE, UTILITIES,
  TEMPORARY SHEETING, PIPE, BACKFILL,
  TESTING AND RESTORATION.
  (BASED ON ENR CONSTRUCTION COST
   INDEX 1800)

2. NUMBERS ARE SEWER DIAMETERS IN INCHES.
     6-8    8-10   10-12   12-14   14-16   16-18   18-20 20-22  22-24  24-26  26-28  28-30
                             EXCAVATION  DEPTH  (ft.)
                     Figure D-15.   Unit  cost  of sewers
                                      193

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of storage, based  on the ENR  construction  cost index of  2,800.   This cost
included  an improvement of the existing  64,345 m   (17 million  gallons)
detention basin, a 8.3 m /sec  (190 mgd) capacity pumping station  and over
610 m (2,000 feet)  of inlet  and outlet sewers.

     For the purpose of this study  it  appears reasonable  to assume, from the
above data, a  cost of  $0.08 per liter ($0.30 per gallon)  of storage. Higher
storage costs,  up to $0.26 per  liter ($1.00  per  gallon), were also considered
to analyze  the tradeoff between  various amounts of  storage  facilities and
varying collection sewer,   interceptor,  and treatment plant  capacities for
joint  flood  and pollution  control where local conditions would  result  in
higher storage construction  costs.

Pumping Station Costs

     Pumping is  generally  required to  deliver to  or return  from storage
wet weather flows.   In very steep terrain,  gravity flow into and out of the
storage facility may be  possible.   The cost of the pumping station proposed
for Tnenton is estimated at about  $1,710,000 or an average of about $206,000
per m /sec  ($9,000 per  mgd)  based  on the  ENR construction cost  index  of
2,800.  This  cost  has  been  used in this study without  adjustment  for cost
index difference.

Treatment Costs

     The alternative treatment  processes for stormwater runoff and combined
sewage  and their  associated  treatment  costs  were  presented  in Lager and
Smith  (18)  and  later  summarized  by  Field  and Lager (19).    The  cost data
plotted in  Figure  D-16 are taken  from this latter reference.   Capital cost
per mgd of treatment capacity appears  to increase nearly linearly with
BOD removal  efficiency.   The  microstrainer, which is relatively economical
but relatively inefficient  in  removing BOD, is effective  in SS removal with
a  removal rate  of 70 percent (19).  Biological treatment processes are
impractical for  satellite plants  because of the problem of  maintaining  an
effective biomass  with intermittent flows.  However,  it is practical and may
offer  benefit  to treat combined sewage  or  urban  runoff  at a central plant.
                                                                   3
     Elizabeth has been  allocated a peak treatment  rate  of 1.75 m /sec (40
mgd)  at  the Joint Meeting  Plant  (about  two times  average flow).   The  plant
is being upgraded to provide secondary treatment.   Hence, one  approach
investigated provided  external  storage  near  the  treatment plant  for flow
equalization to make effective use of the allocated capacity and as a result,
the treatment  costs for the alternative  sewer  systems were practically the
same.   A second  approach assumed varying  peak treatment  rates  (up to 17.5
m  /sec  or  400 mgd)  and  appropriately modified storage  quantities  for flow
modulation. The SWMM STORAGE/TREATMENT Block was used  to estimate costs  under
this  approach.   All costs  were adjusted to the ENR  construction cost  index
of 1,800.
                                    195

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       I.  DISSOLVED AIR FLOTATION
       2. MICROSTRAINER

       3. ULTRAFINE SCREEN

       4. CHEMICAL CLARIFICATION
          USING  WASTE LIME SLUDGE
       5. CONTACT STABILIZATION
          MODIFICATION  OF
          SECONDARY PLANT

       6. HIGH RATE TRICKLING  FILTER
          MODIFICATION OF SECONDARY
          PLANT

       X   DATA  OBTAINED FROM
           REFERENCE 19  (BASED  ON ENR
           CONSTRUCTION COST INDEX OF 2000)
           10    20   30   40    50   60   70    80   90    100

                       % REMOVAL OF BOD
            Figure D-16.   Cost of treatment vs.  % of BOD removal

                                     196

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                             APPENDIX E

                CALIBRATION OF STORM RUNOFF COEFFICIENTS
     Two runoff  coefficients  are  specified in  STORM:   C,  and  C~,  respec-
tively,  for pervious and impervious areas.   Infiltration Tosses are limited
to pervious  areas.   Consequently,  C,  is variable while  C~ is essentially
constant.
     Infiltration in  pervious areas  is generally the  most significant
rainfall loss. Infiltration rates may vary  from several  inches per hour in
extremely pervious  deep  sands  to  zero  on  tight clays.    The infiltration
rate is  dependent on  soil  characteristics,  the  terrain,  the rainfall rate,
pattern and  duration,  and on the water content of the soil.

     Because of  the  variability in  the  factors affecting the infiltration
rate for a  given area,  C,  is not susceptible  to  precise determination.
It  is  higher for less  frequent,  more intense  storms  because infiltration
and other losses  have  a proportionally smaller effect on runoff.

     Runoff  coefficients  for STORM were  calibrated using  runoff data gener-
ated by SWMM in  District A.   These coefficients were  applied  to  other
drainage districts in  the  City to obtain  the runoff volumes for  synthetic
or real storms.   The following assumptions were made:

     1.   C~ was set equal to  1.0,  since there is no infiltration loss in
          impervious  areas and the depression  storage is accounted for
          separately.

     2.   Surface  runoff  data  were generated by  adapting  the  quantity
          portion  of the  SWMM RUNOFF  Block  to exclude sewer  routing.
          This  is  consistent  with  STORM,  in which  the effect  of  sewer
          routing  is not  considered.   All subcatchments in District A
          were used.

     3.   The depression  storage  capacities  for pervious  and  impervious
          areas  used  in SWMM were 6.35  and ,1.57 mm  (0.25  and  0.062 inches)
          respectively.   Twenty  five  percent  of the impervious  area was
          assumed to  have  no  depression  storage.   The  equivalent depression
          storage for District A  was  3.94 mm  (0.155  inches),  based  on 47
          percent of  the area being  impervious.

     4.   The infiltration capacity  curve shown in Figure  D-5  was  used
          in SWMM  to account for  the  infiltration loss.   Maximum and
                                    197

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     5.
    minimum  infiltration rates  of  76.2 and  7.11 mm  (3.0 and 0.28
    inches)  per hour,  respectively,  and a decay rate  of 0.00138/
    sec was  used.  The antecedent  conditions  for rainfall events
    were such that the infiltration curve specified applied.

    The typical rainfall  event was assumed  to  have a 3-hour  duration
    and an intermediate pattern similar  to the 5-year synthetic  storm
    pattern shown in Figure D-5.
C, was  calibrated  so that the  3-hour  storm runoff volume computed with  the
computer program  adapted from  SWMM  was  the same  as  that computed with  the
STORM program.

     Sensitivity runs were made using the  adapted SWMM program to  investi-
gate the effect on the  runoff  volume  of  (a)  using the hourly hyetograph as
opposed to 2-minute hyetograph,  and (b) the integration interval.   These runs
were made  for  the  5-year  synthetic  storm  in  District A.   The results  are
presented in TABLE E-l.
                 TABLE E-l.  SENSITIVITY OF HYETOGRAPH AND
                  INTEGRATION INTERVAL ON RUNOFF VOLUME
Case
No.
Hyetograph*
Integration
Interval
(min.)	
5-Year   Storm
Rainfall Runoff
(inches) (inches)
              Percent  of
              Rainfall
              Runoff
1

2

3
2 - min

Hourly

Hourly
    2

    2

   60
 2.43

 2.43

 2.43
1.75

1.69

1.72
0.72

0.70

0.71
      * See Figure D-5 for intermediate pattern storm hyetograph

        Note:  1 inch = 25.4 mm
There  is  insignificant difference  in runoff  volume obtained  by  using  the
hourly hyetograph with  a  one-hour integration interval and that obtained by
using  the  2-minute hyetograph with  a 2-minute  integration  interval.   This
finding does  not apply to peak  flow rates,  however,  where the  hyetograph
interval makes  a substantial  difference.   The savings in computer costs in
using hourly intervals  to determine runoff  volume are  substantial  being only
25 percent  of those  using  2-minute intervals.   Hence,  data generated with
the adapted SWMM program  for  calibration purposes use the hourly  hyetograph
and integration interval.

     The calibrated C,  values  are shown both  in TABLE E-2 and  Figure E-l as
                                    198

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a function of 3-hour rainfalls.  C, increases  with rainfall  intensity.

             TABLE E-2.  CALIBRATION OF RUNOFF COEFFICIENT C
Case
No.
1
2
3
4
3-hour
Rainfall
(inches)
4.86
2.43
1.38
0.61
Average
Return Intensity
Interval (In/hour)
> 100-Year
5-Year
1-Year
1.3 -Month
1.62
0.81
0.46
0.20
Runoff
Volume
(inches)
4.15
1.72
0.76
0.27
STORM
Cl
0.78
0.55
0.30
0.25
        Note:   District A  data:   Area =  655.1 A.cres
                        Impervious ness == 47%

                85 percent  of the  rainfalls during the  period
                studied  (1963-1974)  totaled less than  0.6 inches
                1  inch/hour = 25.4  mm/hour
     The effect of storm duration on the runoff coefficient was  also studied.
Computer runs were made with assumed 6-hour storm duration maintaining the
same average  storm intensities as for the 3-hour storm. The increase in storm
duration increases  the total amount  of  infiltration.   Hence,  for the same
average intensity rainfall, coefficients  for longer duration storms are more
affected  than those for  shorter duration  storms.   For instance,  the GI
value for a 3—hour  storm  of average  intensity equal  to 5.08 mm  (0.20 inches;
per hour  is  computed  to be 0.23.   For the same  intensity  storm  with a
6-hour duration,  C.  equalled  0.11.   For  storms  with  average intensity equal
to 20.6 mm (0.81  inches)  per hour  (5-year return frequency  for the 3-hour
storm), the  difference in  runoff  coefficient  C. was insignificant  (0.55
versus  0.58).    However, the  return frequency of  a  6-hour  storm  with an
average intensity  of 20.66 mm  (0.81  inches) per hour is about 100 years or
longer.

     Considering  that  C.   varies  with the  storm severity  (depth, duration)
and STORM assumes  a constant  runoff coefficient for  the entire time span of
                                   199

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records to  be simulated  regardless  of rainfall volume  or  intensity,  a  C,
value of 0.25 was  used  for the simulation of long-term records for evaluation
of overflow pollutional effect.   Reducing C,  to  0.15 would  result  in a nine
percent  reduction  in  the-runoff  volume  from District A.   In addition,
the  amount of  pollutant washout  from streets is independent  of  C,  in
analyses using  STORM  as  previously discussed.   The  selected  C,  value  of
0.25  should provide sufficiently  consistent  results  when  using  STORM  to
permit valid  evaluation of  the  effectiveness  of  pollution  control  measures.
To estimate the 5-year  synthetic storm runoff volume from other districts  in
the City,  however, C, value of 0.55 was used.
                                   201

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                            SECTION XIV

                            REFERENCES
1.   Field,  R.  and E.J. Struzeski,  Jr.,  "Management  and  Control  of  Combined
     Sewer Overflows", J. Water Pollution Control Federation,  Vol.  44, No.
     7,  1972.  pp.  1393-1415.

2.   Bryan,  E.H., "Quality of  Stormwater Drainage from  Urban-Land Areas in
     North Carolina",  Report  No. 37, Water  Resources Research Institute of
     The University of North Carolina, Raleigh, N.C., 1970.

3.   Field,  R.  and A.  N.  Tafuri, "Stormflow Pollution Control  in the U.S.",
     in:  Combined  Sewer Overflow Seminar Papers,  U.S.  EPA Report,
     EPA-670/2-73-007, NTIS-PB-231 836, November 1973.

4-   Nebolsine,  R. and  G. Vercelli, "Is the Separation  of Sewers Desir-
     able?" in:   Proceedings, National Symposium on  Urban  Rainfall and
     Runoff  and Sediment Control,  Lexington,  Kentucky,   July  29-31,   1974.

5.   Tholin, A.L.  and C.J.  Keifer, "Hydrology  of Urban Runoff",  Trans-
     actions of the American  Society of Civil Engineers,   Vol.    125,   1960,
     pp. 1308-1379.

6.   Metcalf &  Eddy,  Inc.,  University  of Florida,  and Water Resources
     Engineers,  Inc.,  "Storm Water  Management Model",  U.S.  EPA Report No.
     11024 DOC 07-10/71, NTIS-PB 203 289-292, Vol. 1-4, 1971.

7.   Sevuk, A.  S.,  B. C. Yen, and G. E.  Peterson, Illinois  Storm Sewer
     System Simulation Model;   User's  Manual,   Water   Resources  Center
     Research Report  No. 73,  University  of  Illinois,  Urbana-Champaign,
     Illinois, October 1973.                     .

8.   Parsons,  Brinckerhoff,  Quade & Douglas, "Sewerage,  Drainage and  Flood
     Control  Improvement Program",  Report prepared  for  the City  of
     Elizabeth, New Jersey, April 1962.

9.   U.S. Weather Bureau, Department of  Commerce,  Technical Paper No. 29,
     "Rainfall  Intensity-Frequency  Regime,  Part  3  -  The  Middle Atlantic
     Region", July, 1958.
                                    202

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10.  Sonnen,  M.B., "Abatement of  Deposition  and Scour  in Sewers", U.S.
    , EPA Report,  Contract No.  68-03-2205, to be published by NTIS.

11.  Clinton Bogert Associates, "Sewerage  and  Drainage  Improvement  Program,
     Districts A-l and A-2",  report prepared for  the  City  of Elizabeth,  New
     Jersey, January 1972.

12.  Harmon,  W.G.,  "Forecasting  Sewage  System Discharge at  Toledo",
     Engineering  News-Record,  1918.

13.  Materials obtained  from  Carl Maegaard, Hydro Storm Sewage Corporation,
     919 Third Avenue,  New York, New York  10022.

14.  Janson,  L.E.,  S.  Bendixen and  A. Harlaut, "Equalization  of Flow
     Variations in Combined Sewers", Journal of the Environmental Engineering
     Division, Proceedings of the American Society of Civil Engineers,  Vol.
     102, No.  EE6, December 1976.

15.  Pisano, W.C.  and  C.S. Queiroz, "Procedures  for  Estimating  Dry  Weather
     Pollutant Deposition  in  Sewerage Systems",  U.S.  EPA Report,  EPA-600/
     2-77-120, NTIS-PB  270 695, July, 1977.

16.  Clinton Bogert Associates,  "Facilities Plan", report prepared  for  the
     City of Trenton, New Jersey, January 1976.

17.  Yen, B.'C.,  and  A.S. Sevuk,  "Design of  Storm Sewer Networks",  Journal
     of   Environmental   Engineering   Division, Proceedings  of the American
     Society of Civil Engineers, Vol. 101, No.  EE4, August 1975.

18.  Lager,  J.A.  and  W.G.  Smith,  "Urban  Stormwater Management and Tech-
     nology, An  Assessment",  U.S.  EPA Report EPA-670/2-74-040,  NTIS-PB  240
     697, October 1974.

19.  Field,  R. and  J.A.  Lager,  "Urban Runoff  Pollution Control  - State-of-
     the-Art",  Journal  of the .Environmental Engineering Division,  Pro-
     ceedings  of the American Society of Civil  Engineers,   Vol.   101,   No.
     EE1, February 1975.

20.  Brandstetter, A.,  R. Field and H.C. Torno, "Evaluation  of Mathematical
     Models  for  the Simulation of  Time-varying  Runoff and Water Quality in
     Storm and Combined  Sewerage  Systems",  Proceedings  of  the Conference on
     Environmental Modeling  and Simulation,   Cincinnati,  Ohio,  April   19-22,
     1976.

21.  Henderson,   F.M.,  Open Channel  Flow,  The  MacMillan  Company, New York,
     1966.

22.  Chow,  V.T.  Open Channel Hydraulics,  McGraw-Hill Book  Company,  New
     York, 1959.
                                   203

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23.  Schaake,  J.C., Jr.,  "Synthesis  of  the Inlet Hydrograph",  Ph.D.  Thesis,
     The Johns Hopkins University,  Baltimore, Maryland, 1965.

24.  Eagleson, P.S., Dynamic Hydrology, McGraw-Hill Book  Company,  New York,
     1970.

25.  Brandstetter,  A.,  "Comparative Analysis  of Urban  Stormwater Models",
     in:   "Short Course  Proceedings,  Application of  Stormwater  Management
     Models",  U.S. EPA Report, EPA-670/2-75-065,  NTIS-PB  247  163,  June
     1975.

26.  Brandstetter,   A.,  "Assessment  of Mathematical  Models  for   Storm  and
     Combined  Sewer Management", U.S.  EPA Report, EPA-600/2-76-175a,  August
     1976.

27.  Hydrologic  Engineering  Center, U.S.  Army  Corps  of Engineers,  "Urban
     Storm Water Runoff:   STORM",  Generalized Computer  Program 723-S8-
     L2520, May 1974.

28.  Hydrologic Engineering Center,  U.S.  Army  Corps  of Engineers,  "Storage,
     Treatment,  Overflow,  Runoff Model (STORM)" Generalized  Computer  Program
     723-S8-L7520,  July 1976.

29.  Huber,  W.C.,  J.P.  Heaney,  M.A. Medina, W.A. Peltz, H. Sheikh,  and  G.
     Smith,  "Storm Water Management  Model  User's  Manual,  Version  II",  U..S.
     EPA Report,  EPA-670/2-75-017,.March 1975.

30.  "Modifications to  the EPA  Storm  Water Management  Model  Documentation
     (Version  of March, 1975)," prepared by Water Resources  Engineers,  Inc.,
     September 1975 and updated  by  University of Florida, May 1976.

31.  Chow,  T.  and  Ben  Chie  Yen,  "Urban  Stormwater  Runoff:   Determination
     of Volumes  and  Flow rates",  U.S. EPA Report EPA-600/2-76-116,  NTIS-PB
     252 410,  May 1976.

32.  American Society  of Civil Engineers,  "Design  and  Construction  of
     Sanitary  and  Storm Sewers", Manual and Report on Engineering Practice
     - No.  37, 1970.

33.  U.S.  Army Corps  of Engineers,  Louisville District,  Kentucky, "Supple-
     mental  Report,  Definite  Project  for Local  Flood  Projection,
     Louisville,  Kentucky"  June  1949.

34.  American  Public  Works Association,   "Water  Pollution Aspects of  Urban
     Runoff",  U.S.   EPA Water Pollution  Control  Research Series,  WP-20-15,
     January 1969.

35.  Huber,  W.C.,  "Difference  Between Old  and New Runoff  Quality Models",
     Project  Memo  to  N682 File,  Grant  R802411, University  of Florida,
     Gainesvile,  Florida, May 28, 1974.
                                    204

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36.  Ganczarczyk,   J.J.,   "Storage   for  Stormwater  Ouallty  Control",  Paper
     presented at  the  SWMM Users Group Meeting,  Toronto,  Ontario, April  1,
     1976.

37.  U.S. Weather  Bureau, Department  of  Commerce, Technical  Paper  No.  25,
     "Rainfall  Intensity  -  Duration  -  Frequency Curves",  December  1955.

38.  U.S. Weather  Bureau, Department  of  Commerce, Technical  Paper  No.  40,
     "Rainfall Frequency  Atlas of  the  United States  for  Durations  from  30
     Minutes to 24 Hours  and Return Periods from 1 to  100 Years",  May 1961.

39.  Chow, V.T., "Statistical  and  Probability Analysis  of Hydrologic Data",
     in  Handbook of Applied  Hydrology,  V.T. Chow,  Editor,  McGraw-Hill  Book
     Company, New York, 1964.

40.  Meyer,  A.F.,  "Computing Run-Off from Rainfall  and  Other  Physical Data",
     Transactions of the American Society of Civil Engineers,  Vol.  79,,1915,
     pp. 1056-1155.

41.  Veihmeyer, F.J., "Evapotranspiration",  in Handbook of Applied Hydrology,
     V.T. Chow, Editor, McGraw-Hill Book Company, New York,,1964.

42.  Roesner,  L.A.,   H.M. Nichandros  and  R.P.   Shubinski,  Water  Resources
     Engineers;   A-D.  Feldman and J.W.  Abbott, The  Hydrologic Engineering
     Center;  A.O. Friedland,  Department  of Public Works,  City and County of
     San  Francisco,  "  A Model for  Evaluating Runoff  Quality  in Metropolitan
     Master Planning", ASCE  Urban Water Resources Research Program, Technical
     Memorandum  No.  23,  345  East  47th  Street,  New  York,  New  York,  April
     1974.

43.  Raymond  & May Associates,  "Analysis  &  Plan,  Volume II,  A Master Plan
     Report, City  of Elizabeth, New Jersey", October 1968.

44.  Metcalf  &  Eddy,  Inc., Wastewater  Engineering;  Collection, Treatment,
     Disposal,  McGraw-Hill  Book Company, New York, 1972.

45.  U.S.  Environmental  Protection Agency,  "Water Quality  Studies",  Water
     Program Operations Training Program, ^NTIS-PB 237 586, May  1974.

46.  McGauhey,   P.H.,   Engineering Management of Water Quality,  McGraw-Hill
     Book Company, New York, 1968.

47.  Heaney,  J.P., W.C. Huber, and S.J.  Nix,  "Storm Water Management Model:
     Level  I  -  Perliminary Screening  Procedures", U.S.  EPA  Report,  EPA -
     600/2-76-275, October 1976.
                                     205

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                                  SECTION XV
                      GLOSSARY,  ABBREVIATIONS,  AND  SYMBOLS
 GLOSSARY

 Advanced combined sewer system - A  combined  sewer system which  incorporates
           flow routing and storage as well as flow conveyance in  the design.
           Types of storage  that  could be considered include in-pipe storage
           and satellite storage.

 Advanced pattern storms - Storms  with peak rainfall occurring  in the first
           quarter of  the rainfall  period.

 Base sewage flow - Average  rate  of  dry-weather  flow  in  the  sewer  system
           after subtracting  infiltration.

 Combined sewer - A sewer  receiving  both storm runoff  and  municipal sewage.

 Combined sewer overflow -  Flow from  a combined sewer in excess of the inter-
                           ceptor capacity that is discharged into a receiving
                           water.

 Concentration pollutograph -  A graph  plotting  pollutant  concentration  per
                             unit of time versus time.

 Conventional  combined  sewer  system  -  A  combined  sewer system  without  flow
           control  devices for routing  combined  sewage  flows.    Within  the
           context of this  report, "conventional" implies the design of sewers
           using  flows  derived  from a synthetic hyetograph.

 Conventional  separate  storm  and sanitary sewer system -  A dual  sewer system,
           one conveying  stormwater  only  and  the  second conveying only
           municipal sewage.  Also see storm sewer and sanitary  sewer.

 Depression storage -  Storm water  retained  in  surface depressions' after
           infiltration  capacity has been exceeded.

 District A -  A drainage district  of  about   265 hectares (655 acres) in  the
              City of Elizabeth. A detailed  study was made  for  this  district
              to  develop runoff  quantity and  quality .characteristics using
              SWMM and STORM for application  to the entire City.

Diurnal variation -  Hourly  variation  in the  dry-weather  flow  quantity  and
             quality.

                                     206

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Drainage district  - The area which  is  drained by a  collection system,  and,
          generally, to one outlet to the interceptor.

Dry-weather flow - That flow  in sanitary or combined  sewers that contains no
          direct rainwater runoff.

Evapotranspiration - Water withdrawn from soil by evaporation and plant trans-
          piration.

First  flush  -  The initial  rainwater  runoff flows  which  may be expected
          to  contain high  concentrations  of  the pollutants  that were  de-
          posited  in the sewer  during the period  antecedent to  the rainfall.

5-year synthetic rainfall hyetograph -  A synthetically generated  hyetograph
          which matches  at all  time intervals the intensity-duration curve
          for a 5-year return interval  prepared by the  U.S.  National  Weather
          Service.  In  the report, it  is also called  "5-year  synthetic
          storm".

5-year synthetic storm - See 5-year synthetic rainfall hyetograph.

Froude number - A  numerical  quantity  used  as an index to  characterize  the
type of flow  in a hydraulic structure  that has the force of gravity  (as  the
only force producing motion)  acting  in conjunction with the resisting force
of  inertia.   It  is equal to  the square of  a characteristic  velocity  (the
mean, surface, or  maximum velocity)  of  the  system, divided  by the  product of
a characteristic linear dimension, such as diameter or depth, and the  gravity
constant or acceleration due to  gravity-all expressed in consistent units  so
that the  combinations  will be  dimensionless.   The number  is  used in  open-
channel flow studies or in cases in which the free surface plays an essential
role in influencing motion.

Hydrograph - A graph plotting flow rates versus time.

Hyetograph - A graph plotting rainfall  intensities versus time.

Infiltration  -  The water  entering  a  sewer system and service connections
          from the ground,  through  such  means as,  but not limited to,  de-
          fective  pipes, pipe  joints, connections, or  manholes.   Infiltration
          does not include,  and  is distinguished from, inflow.

In-pipe storage -  Storage in  sewer pipes  to temporarily  contain combined
          sewage  or urban runoff.  In the design  of an  in-pipe  storage
          system,   sewers are increased in size to provide volumetric storage
          in addition to flow  conveyance.  Regulators  are installed to  permit
          use of this  storage  to reduce  peak  flow rates  reaching treatment
          facilities.

In-system - Within the  physical  confines of  the area served by the collection
          system.
                                    207

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Mass rate pollutograph -  A graph  plotting  pollutant mass  loading  per unit
          of time versus  time.

Off-line storage  -  Storage so  situated  as  to  reduce  peak flow  rates  and
          pollutant  concentrations  entering  or  flowing in  interceptor  and
          treatment facilities from the collection systems.  Construction is
          similar to that for  satellite storage.

1.3-month synthetic storm - Derived  from the 5-year  synthetic  storm in the
          same manner as  1-year  synthetic storm except  the  ratio  of hourly
          rainfalls with  1.3 months  and five  years  return intervals  is
          used.

1—year synthetic storm —  Derived  from the  5-year  synthetic  storm by multiply-
          ing the.5-year synthetic hyetograph rainfall rates by the ratio of
          hourly rainfall rates for one year and five year return intervals.

Overflow event  — Overflow  occurs  during a storm event.   A storm event
          is  defined  by   the  properties of the  individual rainfall events,
          such as duration and  intensity, storm spacing,  and  time to empty
          any  storage  facilities.   An  event  was defined  as  beginning when
          storage was  first  required and continued  until  the storage basin
          was emptied. Any number of overflows occurring during the duration
          of  the event was considered as  the same  overflow event.   If a
          rainfall produces runoff  that does  not exceed the sewer capacity,
          storage would not be utilized, and the rainfall would not register
          as  an  event.   In the case of zero storage, runoff from the water-
          shed would directly  drain to the intercepting  sewer, and the number
          of  events as defined  above  would  be the  same  as the  number of
          overflow events.

Pollutograph  - A graph  plotting pollutional  concentrations  or pollutional
          mass per unit of time versus time.

Routing  - Computing  the  downstream outflow  hydrograph of an  open channel
          or  a sewer  from known  values of upstream flow,  and diversions to,
          and withdrawals from storage.

Sanitary sewer - A  sewer  that carries wastewater from residences, commercial
          buildings,  industrial  plants,  and  institutions, together  with a
          relatively low  quantity  of ground,  storm,  and surface waters that
          are not admitted intentionally.

Satellite storage - Storage  in  the collection  sewer system for  peak flow
          rate reduction and flow mixing.  Satellite  storage basins could be
          open, covered or tunneled structures.

STORM default values - Numerical values  assigned  in the STORM computer
          program. These values  are  used  when they are not specified in the
          input  data.    In  this  report,  the  default values  refer,  in par*-
          ticular, to the factors which compute SS, BOD  and the most probable
                                    208

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          number  (MPN)  of  coliforms  from the weight of  dust  and dirt  washed
          off the street.
Storm runoff  - That  stofmWater  Which flows overland  and enters
          a receiving water body*
a sewer  or
Storm sewer  -  A sewer that  carries  intercepted surface runoff, street  wash
          and  other wash  waters  or drainage,  but  excludes domestic  sewage
          and industrial wastes.

Stormwater - The water resulting from a precipitation event which may  stay  on
          the land surface, percolate into the ground,  run  off  into  a  body  of
          watery  enter  a  storm  sewer or  a  combined  sewer,  infiltrate a
          sanitary sewer, or evaporate.

Subarea  -  A subdivision of  a  drainage district based  upon a  single or one
          predominant land use.

Subcatchment -  A  subdivision of  a  subarea  generally by topography and  pipe
          network configuration  and  usually draining  to one reach of pipe.

Surcharge  -  The  flow  condition  occurring  in closed  conduits  when the hy-
          draulic grade line is above the crown of the  sewer.

SWMM default values - Same meaning  as  STORM default values  except that
          the values are specified in the SWMM program*

Trunk sewer  -  A sewer that  receives many  tributary  lateral sewer branches
          and serves a large drainage area.

Weir-orifice regulator  -  A flow-regulating  structure  proposed  for sewer
          installation.  The  structure  consists of a  weir at an angle to the
          main sewer line  and  a  small branch  sewer  pipe  to pass the normal
          dry-weather flow and  to  control the  wet-weather flow rates diverted
          downstream.  The weir provides  a damming effect to store storm flow
          in large trunk  sewers or purposely enlarged lateral sewers.
                                    209

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ABBREVIATIONS


Ac


APWA


BOD


cfs


cfs/acre


cm


DWF


ENR


EPA


ft


ft3


ft. MSL


ft/sec2


in/hr


kg


km


kg/day/lOOm


Ibs


Ibs/day


lbs/day/100 ft


Ibs/min


m


m3

 o
m /min.
acre (s)


American Public Works Assocation


5-day biochemical oxygen demand


cubic feet per second


cubic feet per second per acre


centimeter (s)


Dry-weather flow


Engineering-News Record


U.S. Environmental Protection Agency


feet


cubic feet


feet above mean sea level


feet per second square


inch (es).per hour


kilogram (s)


kilometer (s)


kilograms per day per 100 meters


pounds


pounds per day


pounds per day per 100 feet


pounds per minute


meter (s)


cubic meter (s)


cubic meter (s) per minute
                                     210

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m /sec
mg

MG

mgd

mg/1

min.

mm/hr

N


P04

SS

STORM
 SWMM
cubic meter (s) per second

milligram (s)

million gallons

million gallons per day

milligram (s) per liter

minute (s)

millimeter (s) per hour

nitrogen

orthophosphates

Suspended solids

Storage, Treatment, Overflow,
Runoff Model as released by the
Hydrologic Engineering Center,
U.S. Army Corps of Enginners

Storm Water Management Model as
released by  the U.S. Environmental
Protection Agency
                                     211

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SYMBOLS

%

$

°F

8"
d/dt
percent

dollar

degree (s) Fahrenheit

8 inches

less than

greater than

partial differential

first order differential with respect
to time,  t

second order differential with respect to time, t

degree (s) Centigrade

STORM runoff coefficient for pervious area

STORM runoff coefficient for impervious area
                                 212

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                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
1. REPORT NO.
 EPA-600/2-78-090
                                                           3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND-SUBTITLE
  CONVENTIONAL AND ADVANCED SEWER DESIGN CONCEPTS
  FOR DUAL PURPOSE FLOOD AND POLLUTION CONTROL
  A Preliminary Case Study, Elizabeth,  New Jersey
               5. REPORT DATE
                  May 1978 (Issuing Date)
               6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
                                                           8. PERFORMING ORGANIZATION REPORT NO.
  Herbert L.  Kaufman and Fu-Hsiung  Lai
9. PERFORMING ORGANIZATION NAME AND ADDRESS
  Clinton Bogert Associates
  2125 Center Avenue
  Fort Lee, New Jersey  07024
               10. PROGRAM ELEMENT NO.

                  1BC611
               11. QCXKDEDSKX/GRANT NO.

                  S-802971
12. SPONSORING AGENCY NAME AND ADDRESS
 Municipal Environmental Research  Laboratory—Gin.,OH
 Office of Research and Development
 U.S.  Environmental Protection Agency
 Cincinnati,  Ohio  45268
               13. TYPE OF REPORT AND PERIOD COVERED
                 Final
               14. SPONSORING AGENCY CODE
                  EPA/600/14
15. SUPPLEMENTARY NOTES

  Project Officer:  Anthony N. Tafuri,  Phone:  201-321-6679
16. ABSTRACT
 Alternatives for pollution abatement  from combined sewer overflows  and  stormwater
 discharges were evaluated.  Separate  storm and sanitary, conventional combined, and
 advanced combined systems with varying amounts of in-pipe and/or- satellite storage
 and  controlled flow routing were compared.   Cost-effectiveness assuming a desired
 effluent quality and new sewer system was determined.  The effects  on pollution
 abatement and cost of changing various elements (collection system,  interceptors,
 storage and treatment works) of the system were investigated.  SWMM and STORM were
 employed to design sewers, analyze the quantity and quality of combined sewage and
 stormwater runoff, and analyze a continuous 12-year, real rainfall  record.   The
 overflow frequency, pollutants, and volume for 59 alternatives were determined.  The
 runoff  and overflow characteristics developed for 265 hectares, were used to deter-
 mine the characteristics from the remaining 1785 hectares to plan a citywide sewer
 system.   The study evaluated the effects  of (a) differing rainfall  patterns and
 intensities on pollutant concentrations,  (b)  varying interceptor and treatment
 capacity on pollutants discharged, and (c)  peak flow equalizing for different levels
 of treatment.  The long-term pollutional  loads from combined sewage overflows were
 quantified as well as the effect on overflow control of varying the amount and
 location of storage.
17.
                               KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                             b.IDENTIFIERS/OPEN ENDED TERMS
                            c.  COSATI Field/Group
  *Rainfall,  *Runoff, *Storm sewers, Com-
  bined  sewer,  *Sanitary sewers, ^Overflows,
  *Hydraulics,  Hydrology, *Cost effective-
  ness,  *Mathematical models, Computer
  programs, Methodology, *Surface water
  runoff,  *Water pollution, Water quality,
  Water  storage
  Combined sewer overflow
  management, In-system
  storage, In-pipe  storage,
  Satellite storage,  Off-
  line storage, Hydrographs,
  Pollutographs, Frequency
  analysis
13B
13. DISTRIBUTION STATEMENT
 Release to Public
                                              19. SECURITY CLASS (ThisReport)
                                                   Unclassified
                            21. NO. OF PAGES
                                   229
  20. SECURITY CLASS (This page)
       Unclassified
                                                                        22. PRICE
EPA Form 2220-1 (9-73)
213
                                                                    *U.S. GOVERNMENT PRINTING OFFICE 1978— 757-140/1362

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