&EFK
United States
Environmental Protection
A}ency
Great Lakes National
Program Office
536 South Clark Street
Chicago, Illinois 60605
EPA-905/2-85-001 -B
In-System Storage
Controls For Reduction
Of Combined Sewer
Overflow - Saginaw, Michigan
Technical Report
Do not WEED. This document
should be retained in the EPA
Region 5 Library Collection.
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EPA-905/2-85-001 B
IN-SYSTEM STORAGE CONTROLS FOR REDUCTION OF
COMBINED SEWER OVERFLOW-SAGINAW, MICHIGAN
TECHNICAL REPORT
WILLIAM C. Pisano, P.E.
Daniel J. Connick
Gerald L. Aronson
ENVIRONMENTAL DESIGN & PLANNING, INC.
369 Winter Street
Hanover, Massachusetts 02339
Grant No. S005359
for
DEPARTMENT OF PUBLIC UTILITIES
CITY OF SAGINAW
SAGINAW, MICHIGAN
Ralph G. Christensen Richard Traver
Project Officer o,*»«MtnnAfltftCtf Technical Assistance
U.S« tfiVilviillw"***
Region 5, Ubraiy(fU2J>
77 West Jackson Boulevard,
Chicago, It 6060V3590
GREAT LAKES NATIONAL PROGRAM OFFICE
U.S. Environmental Protection Agency
536 South Clark Street
Chicago, Illinois 60605
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DISCLAIMER
This report has been reviewed by the Great Lakes
National Program Office and the Municipal Environmental Research
Laboratory, U. S. Environmental Protection Agency, and approved
for publication. Approval does not signify that the contents
necessarily reflect the views and policies of the U. S.
Environmental Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or recommendation
for use.
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FOREWORD
The Environmental Protection Agency was created because
of increasing public and government concerns 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 demonstration is that necessary first step
in problem solving and it involves defining the problem,
measuring its impact, and searching for solutions. This
publication is one of the products of that research, a most vital
communications link between the researcher and the user
community.
In the implementation o'f PL92-500 Congress established,
through Section 108, demonstration funds for developing realistic
and innovative management approaches to solve combined and storm
sewer discharges impacting the Great Lakes. This project has
been supported by Section 108 funds through the Great Lakes
National Programs Office, Region V.
The deleterious effects of storm sewer discharges and
combined sewer overflows upon the nation 's waterways have become
of increasing concern in recent times. Efforts to alleviate the
problem depend in part upon the utilization of improved urban
runoff control strategies.
This report presents the results of a five-year
implementation program effort for management of combined sewer
overflows from the City of Saginaw impacting the Saginaw River.
A CSO Facility Plan was prepared entailing advanced system
management concepts for creating in-system transient storage for
later bleedback to a well-operated advanced wastewater treatment
plant coupled with state-of-the-art swirl solids concentrator
complexes for handling residual overflows. A portion of the
system storage management plan was implemented in 1984 and was
field evaluated. Roughly ten percent of total wet weather
related phosphorous loadings to the Saginaw River was reduced by
this program. In addition, total wet weather related suspended
solids and biochemical oxygen demand discharging to the Saginaw
River were reduced by sixteen percent and twenty percent,
respectively, as a direct consequence of this implementation.
Peter Wise, Director
Great Lakes National Program
Office
Chicago, Illinois
111
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ABSTRACT
This report details the results of a recently completed
five-year combined sewer overflow (CSC) control program in
Saginaw, Michigan (10,000 acres, pop. 85,000) funded through the
U.S. EPA 108 Great Lakes Demonstration Program and conducted by
the engineering contractor, Environmental Design and Planning,
Inc. (EDP), Hanover, Mass. The implemented control program
entailed modification of 12 combined sewer regulation chambers
together with construction of one new in-line control chamber to
maximize transient system storage of wet weather combined
sewerage for later bleedback to a well-operatea AWT/WWTP having
phosphorous removal and ample treatment capacity. These
improvements, "the partial BMP plan", represent a partial
completion of the first of two phases of the City's CSO Facility
Plan. The objective of Phase 1 was to maximize WWTP processing
of wet weather combined sewage generated using inexpensive
transient system storage (less than $l/cu.ft.) so as to minimize
the extent, scale and cost of satellite CSO treatment facilities
(Phase II). The swirl concentratcr technology was recommended to
treat residual overflows remaining after Phase I improvements.
Six major Facilities were recommended and adopted as part of the
CSO Facility Plan.
EDP determined that city-wide availability of in-line
storage without threatening basement flooding was extensive, a
total of 3.9 million cu.ft. Regulation chamber internal weirs
were modified in one portion of the City to enhance in-line
storage and the first of fourteen new in-line storage chambers,
(upstream of regulators) was also constructed. New innovative
vortex valve flow throttling devices were used to replace
existing malfunctioning mechanical float-operated control valves
at regulation chambers and another installed at the new in-line
control structure. These devices actualized the notion of using
a battery of system-wide flow controllers within the hostle
environment of a sewer system to reliably and accurately throttle
flows, pass debris, create storage and allow self-scouring on
draindown without mechanical or electric controls or human
interface.
The total cost of the implemented program including
engineering and construction was approximately $516,000. A post
construction evaluation measurement/modeling program was
conducted by EDP in the Fall, 1984 to verify preproject design
conditions. Implementation of the reduced BMP plan is estimated
to have increased the percentage of total annual wet weather flow
directed to the WWTP by 14.6% (from a previous "as is" level of
37.7%) and is estimated to have incrementally reduced (beyond "as
is" levels) suspended solids loadings to the Saginaw River by
IV
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16%, BOD by 20% and total phosphorous by 8.5% (secondary
treatment). During periods of AWT treatment (pickling liquor
addition) at the WWTP, total phosphorous removals are estimated
to increase to 12.6% above pre-implementation levels.
Implementation of the remaining elements of the complete BMP plan
will produce an overall incremental wet weather flow increase of
30% (increasing the total wet weather flow treated at the WWTP to
67.7%).
In sum, expenditures of approximately $516,000 under
the reduced BMP plan for low level sewerage system modifications
(entailing a significant portion of proposed controls for one-
half of the City) resulted in decreasing the system-wide total
phosphorous wet weather loadings to the river by about 10%. No
adverse conditions resulted from the plan. The concept of
inexpensive system controls to maximize transient in-line storage
of combined sewage with bleedback to a high performance WWTP
worked well and is recommended as a management practice.
This project was funded by U.S. EPA in part, to
demonstrate new innovative full scale approaches for mitigating
CSO impacts on the Great Lakes. The primary project justifica-
tion was to develop and document an innovative, inexpensive and
cost-effective management approach for mitigating wet weather
phosphorous loadings to Saginaw Bay (Lake Huron). The results are
currently being used as part of U.S. EPA's joint efforts with
Canada to develop phosphorous limitation management strategies.
In addition, the results of this demonstration project will
provide valuable insights for a number of projects in the
formative preliminary phase investigating in-system storage
management to "clip" or eliminate CSO from small intensity, high
frequency events as a first "stopgap" and inexpensive control
measure.
This report was submitted in partial fulfillment of
Grant No. S005359 by Environmental Design & Planning, Inc.
sponsored by a Section 108 grant from the Great Lakes National
Program Office, Region V, U.S. EPA with funds also from the City
of Saginaw. This report covers a period of September, 1979 to
December, 1984 and work was completed as of April, 1985.
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TABLE OF CONTENTS
Foreword iii
Abstract iv
List of Figures ix
List of Tables xii
Abbreviations and Symbols xiii
Acknowledgments xiv
Chapter 1 Project Description
1.1 Background 1.1
1.2 Chronological Overview of Project 1.1
1.3 Details of the Phase 1 Evaluation 1.10
1.4 Details of the Phase 2 Evaluation 1.16
1.5 Details of the Phase 3 Evaluation 1.17
1.6 Reader's Guide to Report 1.20
Chapter 2 Conclusions
Chapter 3 Recommendations
Chapter 4 Description of City of Saginaw
Sewerage System
4.1 Descriptive Background Material 4.1
4.2 Sewerage System Overview 4.2
4.3 WWTP Details 4.6
4.4 Regulator Chambers 4.8
4.5 Hancock Street Storage/Treatment Facility 4.8
4.6 Dry Weather Flow Characteristics 4.9
4.7 Wet Weather Flow Considerations 4.13
Chapter 5 Screening of Combined Sewer Controls
5.1 Foreword 5.1
5.2 Modifications to Existing System 5.1
5.3 Sources Control Practices 5.19
5.4 Storage and Treatment 5.20
5.5 Selection of Alternative Controls 5.29
Chapter 6 Combined Sewer Modeling
6.1 Foreword 6.1
6.2 Runoff Prediction 6.2
6.3 Regulator Operation 6.4
6.4 In-Line Storage 6.9
6.5 Interceptor Model 6.13
6.6 West Side Interceptor River
Crossing Considerations 6.20
6.7 Runoff Water Quality 6.28
6.8 WWTP Simulation 6.32
6.9 Model Calibration/Verification Efforts 6.33
6.10 Phosphorous Modeling Data 6.45
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Chapter 7 Design of Reduced BMP Plan Modifications
7 .1 foreword 7
7.2 Regulator Chamber Details and Modifications .... 7
7.2 Proposed Weir Alterations 7
7.4 Special Modification of the Adams
Street Type "E" Regulator 7
7.5 Special Modification of the
Weiss Street Regulator Chamber 7
7.C. Weiss Street Fump Station Wet
Well Modification 7
7.7 New Upstream Regulator Chsnber 7
Chapter 8 Reduced EM? Flan Implementation
8
8
8
8
1
1
8
11
14
16
18
8.1 Foreword
8.2 Special Construction Requirements
8.3 Installation
8.4 Chair.ber Modifications
8.5 Construction ard Installation of
Flow Regulators 8.7
6.6 Weiss Street Fun ping Station Wet
Well Modification 8.19
Chapter 9
9
9
9
9
9.5
c
9,
9,
9,
7
8
9
10
Field Monitoring Prograir, - Post BMP
Implementation Data and Analysis
Foreword
Post Implementation Field Prcgrsm
System Eackwatering
Evaluation of Effectiveness of New
In-line Storage Chamber Constructed
at Salt and Vermont Streets
Monitcring and Evaluation at the
Adams Street Regulator
Monitoring of the Weiss Street
Fump St ation
Monitoring of the Wastewater Treatment Plant.
Field Verification of Flow Regulating Devices
Evaluation of the Cronk Ave Regulator ...
Post Construction Chamber Inspection
and Evaluation. „ ,
9.1
9.1
9 .2
9.7
9.14
9.18
9.23
9.23
9.32
9.34
Chapter 10 Assessment cf Pre BMP Conditions and
Evaluation of Proposed Prcgrams
10 .1
10.2
10
10
10,
10,
10.7
Foreword
Overview of Analysis Criteria and
Results Pr e sent at ion ,
Pre BMP CSO Emission Estimates...
Analysis of Weiss Weir Alteration,
Complete BMP Frcgrati Simulation..,
Reduced BMP Program ,
Phosphorous Analysis ,
10.1
10.1
10.2
10.9
10.1C
10.14
10.17
VII
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Chapter 11 Application of Inlet Control Technology
to the City of Saginaw Combined
Sewerage System
11.1 Foreword , 11.1
11.2 Inlet Control Philosophy 11.1
11.3 Overview of Hydrologic Methodology 11.9
11.4 Saginaw Sewerage System 11.13
11.5 Analysis of the Congress Covrt Area 11.15
11.6 City-Wide Implementation of Inlet
Control Technology 11.23
Ref ei er.ces R.I
Vlll
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LIST OF FIGURES
Figure Number Page
1.1 Location of Saginaw, Michigan 1.2
1.2 Proposed Storage Basin and Regulator Modifications 1.3
1. 3 Proposed EDP CSO Plan 1.5
1.4 Layout of Weiss Street Combined Sewer
Overflow Treatment Complex 1.6
1.5 Webber Street Swirl Facility 1.9
1.6 Typical In-Line Storage Device (Regulator) 1.14
1.7 Typical Float Actuated Type Flow Regulator 1.15
1.8 Details of the Reduced BMP Plan 1.18
2.1 Wet Weather Total Phosphorous Loading to
Saginaw River 2.8
4.1 Saginaw Combined Sewer Service Area 4.3
4.2 Saginaw Regulator Chamber Catchment Area 4.4
4.3 General Plan of Interceptor Sewer System 4.5
4.4 Comparison of Storm Events -
Saginaw vs Vassar (1975-1978) 4.16
4.5 Annual Rainfall (accumulated) Cumulative
Frequency Plot 4.19
5.1 Schematic of Typical Dynamic (Semi-Automatic)
Combined Sewer Mechanical Float Operated
Flow Controller 5.3
5.2 Simple Model of Vortex Valve Representation 5.8
5.3 Johannessen Type Conical Vortex Valve
Flow Controller 5.11
5.4 Brombach Type Conical Vortex Valve Flow Controller 5.13
5.5 Flow Coefficient and Discharge Variations for
Brombach Type Conical Vortex Valve 5.15
5.6 Typical Vortex Valve Stage/Discharge Curve 5.17
5.7 Saginaw Study Typical Storage Facility
Process Schematic 5.22
5.8 Saginaw Study Typical CSO Primary Treatment
Process Scheme 5.24
5.9 Helical Bend and Swirl Concentrator 5.28
6.1 Catchment Area Modeling 6.3
6.2 Discharge/Water Depth Curves
Hancock Area Regulators 6.6
6.3 Schematic of Regulator Operation 6.7
6.4 Interceptor Model Overview 6.17
6.5 Interceptor Model Computation 6.18
6.6 West Side River Crossing Model Area 6.19
6.7 Details of River Crossing, Saginaw Area 6.21
6.8 Analysis of Saginaw River Crossing
Discharge Levels 6.23
6.9 Verification of Weiss Street Pump Station Weir
Modification Effects on Crossover Rates 6.26
6.10 Saginaw Suspended Solids Generating Equation
Compared to Other Municipalities 6.31
IX
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6.11 Single Event Comparison of Modeled
and Recorded Events 6.34
6.12 Single Event Time Sequencing 6.36
6.13 Overflow into Weiss Street Pumping 6.37
6.14 Overflow into Hancock Street Pumping Station 6.38
7.1 Type "B" Regulator Chamber Schematics 7.2
7.2 Type "A" Regulator Chamber 7.3
7.3 Type "B" Regulator Chamber Flow Patterns 7.5
7.4 Adarrs Street Regulator Chamber Modifications..... 7.13
7.5 Weiss Street Regulator Chamber - Plan View 7.15
7.6 Weiss Street Regulator Chamber Modification
Section View 7.17
7.7 Weiss Street Pump Station Wet Well
Modification - Plan View 7.19
7.8 Weiss Street Pump Station Wet Well
Modification - Section View 7.20
7.9 New Regulator Chamber at Salt/Vermont
Street - Location and Profile 7.22
7.10 Salt and Vermont Streets Chamber - Plan View 7.23
7.11 Salt and Vermont Streets Chamber - Section View 7.24
8.1 Typical Type "A" Regulator Chamber 8.5
8.2 Typical Type "B" Regulator Chamber 8.6
8.3 Partial Components of Brown and Brown
Regulator Removed from Chamber 8.8
8.4 Typical Type "B" Chamber Influent Area ;.. 8.9
8.5 Type "B" Chamber - Flapgate to River Area 8.10
8.6 Type "B" Chamber - New Cross Weir 8.11
8.7 Chamber Access Manholes and Gate Covers 8.12
8.8 Segmented Vortex Valve Regulator -
Disassembled and Partically Assembled 8.13
8.9 Segmented Vortex Valve Regulator -
Fully Assembled 8.14
8.10 Salt/Vermont Street Charr.ber Vortex Valve 8.15
8.11 Installed Vertex Valve Regulator at the
New Salt/Vermont Streets Storage Chamber 8.16
8.12 Adams Street Chamber Vortex Valve Regulator 8.17
8.13 Installed Adams Street Chamber Vortex
Valve Regulator 8.18
8.14 Typical Installed Conical Type Vortex
Valve Regulator 8.20
8.15 Installed Conical Type Vortex Valve
Regulator with Modified Inlet Sleeve 8.21
8.16 Horizontal Type Vortex Valve Regulator 8.22
8.17 Weiss Street Pump Station - New Weir
and Splash Wall 8.23
9.1 Hancock Street Area Cup Gage Location. 9.4
9.2 Salt/Vermont Streets Area Cup Gage Locations 9.5
9.3 Rain Accumulation vs Time 9.8
9.4 Sewer Flow Depth vs Time 10/18/84 Event 9.8
9.5 Volume of Stored Combined Sewage vs Time
10/18/84 Event 9.10
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9.6 Combined Sewage Inflow Rate vs Time
10/18/84 Event 9.11
9.7 Vortex Valve Discharge Rate vs Time
10/18/84 Event 9.13
9.8 Overflow into Weiss Street Pump Station 9.20
9.9 Weiss Street Pump Station Suspended
Solids Data 9.22
9.10 WWTP Wet Weather Flow vs Rain Accumulation 9.24
9.11 WWTP Mass Loadings Wet Weather Water Quality 9.25
9.12 Hayes Street Vortex Valve Characteristics 9.27
9.13 Adams Street Vortex Valve Characteristics 9.28
9.14 Court Street Vortex Valve Characteristics 9.29
9.15 Throop Street Vortex Valve Characteristics 9.30
9.16 Ames Street Vortex Valve Characteristics 9.31
11.1 Components of the Inlet Control System 11.3
11.2 Asphalt Contoured Speed Hump 11.5
11.3 Surface/Subsurface Storage Components of
Inlet Control for Congested Areas 11.6
11.4 City of Saginaw Areas of Reported Basement
Flooding 11.14
11.5 City of Saginaw Inlet Control Study Area -
Congress Courts .....11.16
11.6 Typical Congress Court Topography 11.17
11.7 Relationship of Storage Volume to CSO Total
Phosphorous Reduction 11. 25
XI
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LIST OF TABLES
TITLE Page
"O Pollution Abatement Effectiveness of
Best Management Practives Program 2.7
4.1 WWTP Flows 1978-1979 4.11
4.2 System Distribution of Dry Weather Flows 4.12
4.3 Simulation Model Dry Weather Flows 4.14
4.4 Comparison of Annual Rainfall Totals 4.17
4.5 Catchment Area Runoff Coefficients 4.20
5.1 Conditions and Demand for an Ideal Collecting
System Flow Controller 5.6
5.2 Lancaster, PA 1980-1981 Summary of Swirl
Regulator/Concentrator Performance 5.26
5.3 Overview of Desirable CSO Controls for Saginaw 5.30
6.1 Typical In-Line Storage Volume Comparative Analysis.... 6.12
6.2 In-Line Storage Potential 6.14
6.3 Comparison of Collection System Daily
Deposition Loadings 6.30
6.4 Predicted Versus Recorded Values at WWTP (1978) 6.39
6.5 Model Calibration Results - Storm Event 7/8/80 6.41
6.6 Pre Reduced BMP Construction Storm Data 6.44
6.7 Post Reduced BMP Construction Storm Data 6.46
6.8 Waste Water Treatment Plant Total
Phosphorous Summary 6.48
6.9 WWTP Phosphorous Removal Results (1984) 6.52
7.1 BMP Program Regulator Chamber Weiss
Modifications 7.6
7.2 Reduced BMP Program Regulator Chamber
and Flow Regulation Data 7.7
7.3 Vortex Valve Stage/Discharge Characteristics 7.9
8 .1 Flow Regulator Details 8.4
9.1 Cup Gage Monitoring of Peak Water Elevations 9.3
9.2 Adams Street Chamber Storm Samples 9.16
10.1A Pre BMP Conditions Simulation 10.3
10.IB Pre BMP Conditions Simulation 10.4
10.2 Flow Summary Data 10.6
10.3 TSS Summary Data 10.7
10.4 BOD Summary Data 10.8
10.5A Complete BMP Plan Simulation 10.12
10.5B Complete BMP Plan Simulation 10.13
10.6A Reduced BMP Plan Simulation 10.15
10.6B Reduced BMP Plan Simulation 10.16
10.7 Total Phosphorous Summary Data 10.18
11.1 Typical Inlet Control Worksheet 11.19
11.2 City of Saginaw Congress Courts Sewer System
Hydraulic Evaluation 11.20
11.3 City of Saginaw Congress Courts Rainfall/Storage
Requirement Summary 11.21
XII
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ABBREVIATIONS AND SYMBOLS
ac acre
cos cos 1 ne
cf cubic feet
cfs cubic feet per second
cm centlmenter
dwf dry weather flow
fpm feet per minute
fps feet per second
ft feet
ft^ square feet
g gram
gal ga I I on
gpm gallon per minute
h. hour
Imp. Imperv I ous
In. I nch
kg k 1 1 ogram
L liter
I b pound
m meter
mg/lmllllgram per liter
ml ml I I I I Iter
MG ml I I I on gal I ons
sq square
SWMM Storm Water Management Model (U.S. EPA)
A Angle of lateral entry at junction
BOD Biochemical Oxygen Demand (5 days)
CBOD Carbonacous Biochemical Oxygen Demand
CSO Combined Sewer Overflow
DO Dissolved Oxygen
Dp Ratio of pipe diameters at junction
h Depth of flow above regulator orifice
g Acceleration of gravity
H Head loss due to junction
I Percent Imperv I ousness
K Energy loss coefficient
NBOD Nitrogenous Biochemical Oxygen Demand
PR Ratio of flows at junction
TSS Total Suspended Solids
WWTP Waste Water Treatment Plant
Z Runoff coefficient
% Percent
xiii
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ACKNOWLEDGEMENTS
The authors would like to commend the EDP staff who worked so hard to make
this program a success. Through the diligent efforts of many, a study has been
prepared assessing the viability of a relatively new technology for solving a
complex combined sewer management problem in the City of Saginaw.
We would like to thank the City of Saginaw Public Utilities Department for
their extreme cooperation and good will, including Robert Dust, Executive Direc-
tor of Public Utilities, Mr. Jim Anderson, Superintendent and Fred Schulz,
Assistant Superintendent, Wastewater Treatment Division.
We would like to also thank Mr. Ralph G. Christensen, U.S. EPA Region V,
Great Lakes National Program Office, for his support and assistance. The Great
Lakes Program provided funds for this project. In addition, Mr. Richard P.
Traver, U.S. EPA, Edison, New Jersey was extremely helpful in coordinating the
early phases of the project along with Mr. Doug Ammon and Mr. John English U.S.
EPA, Cincinnati, Ohio.
Finally, we would like to express our sincerest appreciation to Ms. Eunice
Harris for her patience in typing this report.
Environmental Design and Planning, Inc. was the engineering contractor for
his project. Dr. William C. Pisano, P.E., President, EDP, was the principal
investigator. Mr. Daniel J. Connick, Sr. Design Engineer, was the project
manager. Mr. Gerald L. Aronson, Executive Vice President, EDP, supervised
field monitoring and evaluation efforts.
xiv
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CHAPTER 1
PROJECT DESCRIPTION
1 . 1 Background
In 1979 the City of Saginaw in cooperation with the
108 Great Lakes National Program, Region V, U.S. EPA embarked en
a program to implement and evaluate on a full-scale basis new
innovative low-cost technologies for mitigating combined sewer
overflows (CSO) discharging from the City of Saginaw sewerage
system into the Saginaw River. The Sagiraw Fiver discharges into
Saginaw Bay and ultimately into Lake Huron. See Figure 1.1. The
108 Program and subsequent funding was established when Public
Law 92-500 came into existence for the purpose of demonstrating
on full scale bssis promising technologies for abating CSO and
stormwater pollution impacting the Great Lakes. Approximately
$1.1 million was allocated to the project. Environmental Design &
Planning, Inc. (EDP) was chosen by U.S. EPA and the City to
perform this work.
The project progressed from 1979 until 1984, culminating
with implementation and evaluation of a number of system
improvements. The overall work effort consisted of three
separate phases. Within Phase 1 EDP submitted a report to the
City of Saginaw which presented the results of a feasibility
study in which the most cost effective means of treating CSO in
the City of Saginaw were established. During this phase a CSO
Facility Plan was developed and adopted as well as
recommendations for implementating a demonstration project. In
1983 (Phase 2) a further investigation was prepared due to a
lack of funds to implement the Phase 1 recommended demonstration
program. Phase 2 efforts were directed at optimizing a reduced
scope of work plan for implementation using available funds.
Following implementation cf the Phase 2 proposed improvements, a
Phase 3 evaluation was performed in 1984. This effort generated
a greater data base for system hydraulic model calibration
allowing for improved estimates of the effects of plan elements
completed to date and the effects of additional plan element
implementation .
1 . 2
In the early 70 's the City had adopted a CSO control
program entailing the use of seven sedimentation/detent icn/
chlorination facilities. In the mid 70 's one such facility was
constructed at the Hancock Street Pumping Station and regulators
in the area were modified to enhance flow to this treatment
facility. See Figure 1.2 for the general location of this
1.1
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HILIAUKEE
CM ICACO
ILLINOIS
Figure ] -1 Location of Saginaw, Michigan.
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LEOCNO:
EXISTING PUMPING STATION
EXISTING REGULATION
CHAMBER
EXISTING INTERCEPTOR
_.— CITY LIMITS
LIMITS OF SERVICE AREA
OUTSIDE CITY LIMITS
, PROPOSED
STORAGE BASINS
Elements completed
fin 1977
EXISTING COMBINED SEWER
AND OVERFLOW(TYPICAL)
. HANCOCK ST.
STORAGE BASIN
HANCOCK ST. PUMPING
STATION
WEST 5OE
INTERCEPTOR
WEBBER ST. PUMPING
STATION
WEISS ST. PUMPING
STATION
EMERSON ST. PUMPING
STATION
EAST SIDE
INTERCEPTOR
EXISTING
WASTE WATER
TREATMENT
PLANT
FOURTEENTH ST.
PUMPING STATION
Figure 182 Location of Proposed Storage Basins and Regulator Modifications
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facility, other proposed detention facilities and the five
modified regulators.
The objectives of the Phase 1 (1979-1981) EDP study
were twofold: a) preparation of an alternative overall framework
plan for the management of CSO from the City of Saginaw
considering, but not limited to, the existing concepts of storage/
treatment/ chlorination facilities; and b) preparation of a
detailed preliminary plan for a portion of the envisioned city-
wide plan, entailing implementation of a full-scale demonstration
treatment facility devised in such a way that it would form a
logical element of the overall CSO Facility Plan.
During the course of the Phase 1 planning efforts
(1,2,3) by EDP, the most cost-effective City-wide programs of
CSO abatement alternatives, were developed for varying levels of
system costs. Runoff simulation studies indicated that the two
most singularly effective measures for handling CSO in Saginaw
were increased wet weather loadings to the City's wastewater
treatment plant (WWTP) and inclusion of actions termed, "Best
Management Practices" (BMP). The BMP program consists of
extensive in-line storage and system modifications to increase
hydraulic capacity so that the WWTP can handle more wet weather
combined sewage. Roughly 2 million cubic feet of new in-line
system storage would be generated as a result of this plan.
Estimated cost of BMP plan equalled $2.6 million (1984 ENR=4300).
^ After implementation of the complete BMP plan, residual
CSO would still remain at six locations: Weiss Street Pump
Station, Weiss Street gravity line, Emerson Street Pump Station,
Fourteenth Street Pump Station, Webber Street Pumping Station and
the Fraser Street Regulator. See Figure 1.3 for locations of the
elements of this plan. The Phase 1 investigation recommended the
use of swirl solids concentrating facilities at these locations
as the most cost-effective technology for abating these residual
overflows. Suspended solids removal optimization analysis of
various swirl configurations/sizes at the various overflow points
(after implementing the BMP program ) resulted in pin-pointing
the Weiss Street area as the most significant location for a
major swirl concentrator facility. See Figure 1.4.
Although the proposed BMP program elements were the most
cost-effective means for abating CSO in Saginaw, U. S. EPA
desired at that time to implement and evaluate the effectiveness
of the swirl concentrator technology for reducing CSO pollutant
loadings. The 24-foot diameter swirl concentrator (design flow
- 40 cfs) in Lancaster, Pennsylvania showed significant promise
as a new inexpensive technology in comparison to sedimentation/
detention for reducing CSO settleable solids and floatables.
Although the suspended solids removal results, particularly
* For moderate to heavy intensity storms*
** Pump station and gravity discharge considered as composite CSO.
1.4
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EXISTING INTERCEPTOR
LIMITS or SERVICE AREA
OUTSIDE CITY LIMITS
^/-Existing Hancock St.
< / Storage/Treatment Facility
/{ ,'
~**- ^ '
PROPOSED REGULATOR
MODIFICATIONS •
• TYPE A
A TYPE B
PROPOSED INUNE FLOW
CONTROL/STORAGE DEVlCEl
TYPICAL EXISTING
SEWER LINE
Proposed
Webber St.
Swirl Facility N.
Proposed
Emerson swirl
.14—Weiss St. pumping station
•—i weir increase
Proposed Weiss
swirl facility (swirl degritter)
EXISTING
WASTE WATCH
TREATMENT
PLANT
Proposed Fourteenth St.-*
swirl facility
Figure 1.3 Proposed EDP CSO plan.
-------
PROPERTY LINE
iversion
Cbambe
INTERCEPTOR^ ^
r-f *"7 ^" - -*---*"
RIVER CROSSING
(PROPOSED)
-I- DISIN----
Degntters
Proposed
Future
EXISTING
WAREHOUSE
-• CONTACT--
--CHAMBERS w
-.( FUTURE )•:-:-
LEGEND
SWIRL PUMPED
^E: INFLUENT
--- SWIRL FOUL SEWER
SWIRL DEGRITTER
_._. SUPERNATANT
r-—SWIRL CLEAR WATER
PRIVATE
PROPERTY
Disinfection chemical
SCALE: 1"
mca i
storaqe building
Fiyure 1.4 Layout of Weiss Street combined sewer overflow treatment complex.
40'
-------
during "first flush" conditions, were extremely favorable at the
swirl concentrator facility in Lancaster, the evaluation program
was plagued with numerous flow measurement instrumentation
problems. Since a number of swirl concentrators were being
incorporated into designs throughout the U. S. at that time, U.S.
EPA believed that the proposed evaluation program at Saginaw
would answer any unresolved questions remaining from the
Lancaster experience. Moreover, the Canadian Ministry of the
Environment at the time was seriously considering this technology
for widespread utilization in the Quebec Province (one facility
was constructed in Quebec City in 1984 and more facilities (1985)
are in design). A comprehensive and complete portrayal of swirl
performance was desired for technology transfer. It was also
desired by U.S. EFA at that time to construct and evaluate a
swirl concentrator of larger physical dimensions than the device
at Lancaster to expand the evaluation experience for this
emerging technology.
The Phase 1 study also recommended within the
budgetary limitations (of the demonstration funding) three
alternative swirl concentrator demonstration facilities located
at the Weiss Street gravity overflow, at the Weiss Street Pump
Station discharge and at the gravity discharge at Fourteenth
Street. Estimated Construction costs (1984) including electrical
service contingency and excluding disinfection chemicals for the
three facilities equalled $3.1 ,$2.6, and $2.38 million (ENR=4500) ,
respectively. No land costs were included. The facility at the
Weiss Street gravity overflow was preferred.
Because of the significant cost savings for City-wide CSO
control program reported from the Phase 1 study and as a
mechanism to facilitate Section 201 Construction Grants funding
to partially support the costs of the proposed demonstration
project at Weiss Street, EDP was instructed by the City of
Saginaw and U.S. EPA in mid 1980 to expand the Phase 1 study into
a proposed CSO Facility Plan for the City of Saginaw '2' . In
January, 1981 the proposed EDP CSO Facility Plan was adopted by
the City of Saginaw.
Although the magnitude of the overflow at Weiss Street
greatly exceeded those at other locations, City-owned land space
to construct the proposed facility was extremely limited. Design
of the proposed swirl concentrator facility at Weiss Street was
curtailed due to the envisioned long and protracted period
required to acquire the necessary land.
In mid 1981 ECP was instructed by the City and U.S. EPA to
re-direct efforts for plecetuent of the proposed swirl
concentrator facility at an alternative location within the City.
The alternative facility was nevertheless to be designed and
1.7
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constructed in such a manner as to be a logical and congruent
element of the overall adopted CSO Facility Plan. The Webber
Street Pumping Station area was chosen as the new location tc
place the proposed demonstration facility. An analysis of this
catchment was conducted supported by detailed field measurement
programs (3). In 1981-1982 EDP prepared construction plans, spe-
cifications and bid documents for a new treatment complex consis-
ting of an in-line diversion structure controlled by vortex flow
regulation devices to direct flow to the existing pump station, a
new 80-cfs low lift pumping plant, a 38 foot diameter swirl
concentrator with stainless steel inner assemblies and ancillary
piping and connections. See Figure 1.5. The cost of the facility
was estimated to be approximately $2.0 million (ENR=4500 , 1985 )
Approximately $.75 million was remaining from the 108
grant and additional funding was requested from the 201
Construction Grants Program. Eligibility status for the proposed
project was poor and it was forcasted that the low status would
remain for the next several years. It was finally decided by
U.S. EPA that the proposed demonstration swirl concentrator
project be indefinitely postponed.
In early 1983, U.S. EPA and the International Joint
Commission (IJC) (U.S. and Canada) became interested in
developing phosphorous limitations for the Great Lakes revolving
around a number of promising BMP practices controlling
agricultural and urban runoff phosphorous loadings. Sewerage
system management employing system controls to inexpensively
maximize transient in-line storage with bleedback to WWTP 's with
high performance treatment was identified and viewed by U.S. EPA
as a promising management prospect in view of the continuing low
federal funding profile for the next several years. Since a
number of the major sewerage systems impacting the Great Lakes
are combined, relatively flat and discharge to high performance
WWTPs, the notion of evaluating inexpensive system storage and
hydraulic optimization in Saginaw was attractive, feasible and
logically extendable to other areas within the Great Lakes
region, if proven to work.
On instruction from U.S. EPA and the City in April,
1983, EDP embarked on Phase 2 of the overall program and prepared
a preliminary concept plan to best spend the remaining grant
monies to implement and evaluate a significant portion of the BMP
plan. The aim was to accomplish as much as possible with
remaining monies. Runoff simulation studies were performed to
evaluate numerous schemes varying the proposed modified control
points. Optimization analysis identified a plan for final
selection which included sewerage system modifications on only
one side of the Saginaw River (4). In May, 1983 EDP met with the
City and U.S. EPA to discuss the envisioned plan which would
1.8
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Figure 1.5 Webber Street Swirl Facility
-------
realize about half of the pollution control effectiveness of the
total BMP plan. As a result EDP was instructed by the City and
U.S. EPA to proceed with an implementation program for the
"reduced BMP" Plan.
EDP prepared construction plans and specifications. In
March 1984, the construction contract was awarded to Gary D.
Steadman Inc. of Bay City, Michigan. The construction began in
April, 1984 and was completed in September of 1984.
During Phase 3 EDP directed a detailed pre-construction
and a post-construction field evaluation program performed by
City of Saginaw personnel. Rain event statistics, river
elevations, sewer depths, regulator chamber hydraulics and water
quality parameters were recorded at numerous locations throughout
the City. Pre- construction data was used to calibrate the
simulation model for discrete events. The model was then run for
a full year simulation to estimate base pre-construction
sewerage system overflows during storm conditions. Post-
construction data was evaluated and compared to predicted
overflow quantity and quality values based on the modified model
reflecting the pre-construction measurements. Model simulation
data and field data were comparable such that further model
calibration was not required. Full year model simulations were
then performed to indicate the effectiveness of the implemented
reduced BMP plan followed by simulations predicting the
effectiveness of completing the entire BMP plan.
This report documents the scope of work and the
simulation results for the five year, three Phase project.
1 . 3
The purpose of the Phase 1 evaluation was to develop a
cost effective plan of action that mitigates impacts on water
quality caused by CSO. The Facility Planning Area encompasses
the City of Saginaw land mass including pertinent contingent
township areas tributary to the Saginaw WWTP. The scope of the
plan was limited to overflows within the facility planning area,
as well as to the water quality parameters defined by the
objectives and issues.
The CSO Facility Plan was developed using the parameters
of dissolved oxygen and oxygen demanding materials, coliform
bacteria, and suspended solids and settleable solids as
indicators of CSO impacts and target levels to be attained.
Although CSO has many other associated pollutant parameters,
such as heavy metals, chlorinated organics, pesticides and other
toxics, this study did not qualitatively address them.
lolO
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The scope of the Phase 1 report was limited to an
assessment and evaluation of water quality impacts resulting from
CSO and then the development of a plan to mitigate those impacts
caused by CSO. It was recognized that water quality is impacted
by upstream conditions from areas outside the combined sewer
study area, point source emissions and direct stormwater runoff.
The study made an assessment of the relative impact from these
areas relative to CSO but did not pursue them in the development
of the Recommended Plan.
1.3.1 Project Approach
Phase 1 of the project was developed in the following
manner:
1. Evaluation of existing conditions
2. Simulation modeling of CSO and water quality
impacts
3. Evaluation/optimization of abatement alternatives
4. Development of the recommended plan
Existing facilities were evaluated to generate an accurate
description of the sewerage system including physical and
operating characteristics of the WWTPf the Hancock Street CSO
storage/treatment facility, all pump stations and all regulator
chambers.
Formulation of the basis of design for CSO overflow
control facilities required input of data, with regard to the
quality and quantity of dry weather flows, so that network models
could be calibrated. Efforts were made to determine the quality
of dry weather flows at various points in the City of Saginaw
system and to isolate catchment areas including the Saginaw WWTP.
A field measurement program was performed to enable estimates of
dry weather flows per catchment area.
Analyses were performed to assemble the wet weather
predictive design features including rainfall characterization,
determination of runoff parameters for the catchment areas, and
evaluation of regulator chambers and pumping stations.
A comprehensive mathematical computer simulation program
was developed to help determine overflow discharges and pollutant
concentrations as a result of hypothetical occurrence of various
size design storms. The model provided an accurate representation
of the physical sewerage system, but also provided an opportunity
1.11
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to determine the benefit of proposed pollution abatement
alternatives. The value of modeling lies in the ability to
predict the outcome of dependent variables as a result of
hypothetical modification of the system. These projections
allowed for more efficient evaluation of abatement alternatives
formulated to meet established goals, concepts and criteria.
Through this process the best alternatives were isolated for
further cost-benefit analysis.
The Saginaw Stormwater Management Model, developed by EDP,
provided an inexpensive and flexible tool for preliminary
planning and sizing of Stormwater facilities. The model provided
a means by which the Stormwater problem could be analyzed and
introduced time and probability to the quantity, frequency and
duration of overflow events by using actual rainfall data
collected over a long period of time. It was used to screen
alternatives based on varying storm conditions.
Feasible abatement programs for CSO pollution control
required evaluation to select the most cost-effective
configuration and scale to achieve water quality goals. This
study examined the effectiveness and costs of selected
alternatives, and combined the estimates to develop a recommended
facility CSO pollutional abatement program.
The major components of the Phase 1 recommended CSO
abatement program are as follows:
• BMP program implementation
• Swirl Concentrator Facilities at:
Weiss Street Pump Station 300 cfs
Weiss Street Gravity Line 100 cfs
Emerson Street Pump Station 300 cfs
Fourteenth Street Pump Station * 50 cfs
Webber Street Pump Station 50 cfs
Fraser Street 50 cfs
* Pump Discharge and Gravity Line
CSO handled by single facility.
1.3.2 Description of Complete BMP Program
The BMP program as proposed by EDP and adopted as part
of the Facility Plan, incorporates low-level structural
improvements and management practices that can be implemented at
relatively low cost. The concept of the program is to maximize
the use of existing WWTP facilities before further CSO treatment
1.12
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facilities are implemented. The program maximizes in-line storage
already available in the system conduits and maximizes the
conveyance of storm flows to the WWTP. To actualize this plan,
the existing regulators were to be modified, new flow control
devices were to be installed to increase in-line storage, weir
modifications were to be accomplished at the Weiss Street Pump
Station to increase flow across the river, and the operating
procedure of utilizing the extra aeration basins at the WWTP for
off-line storage implemented. (The City was utilizing this
option at the time it was identified by EDP.)
It was envisioned to alter 24 regulators (See Figure
1.3) to yield a constant discharge during initial storage
filling, with excess flows beyond available storage diverted to
the interceptor rather than the river. In addition, the five
modified Hancock area regulators (modified as part of the Hancock
Street Detention Facility Implementation in 1977) were to be
replaced with constant underflow discharge devices (vortex valve
flow regulators) to increase the "first flush" diversion to the
interceptor and maximize the use of the interceptor throughout
the storm event. Furthermore, six other regulators of smaller
size were to be altered with weirs to divert most £Lowz to the
interceptor. Fourteen upstream structures with vortex valve flow
regulators were to be constructed to yield additional in-line
flew control for storage upstream of the regulator chambers. The
resulting changes to the regulator operations would achieve the
maximum useable in-line storage potential of the system.
Except in extreme flow conditions, the only possible
points of overflow as a result of these potential actions are at
Fraser, Hancock, Weiss (pump and gravity), Webber, Emerson and
Fourteenth Streets. Weir elevations at Webber and Fourteenth
Street overflow points were to be raised slightly to insure that
the high post-rain discharges from upstream in-line storage
devices are totally diverted to the interceptor. The regulator
chamber at Fraser Street will be unaltered although the
regulating device was to be replaced and a flow control chamber
constructed only a short distance upstream. Figure 1.6 and 1.7
detail typical regulator modifications and the original underflow
control device to be removed.
An increased weir elevation of five feet was to be
imposed at the Weiss Street Pumping Station to reduce pumped
overflows at that point and increase the flow across the river
crossing and into the East Side Interceptor. The aeration basins
at the WWTF were to continue to be utilized as additional off-
line storage devices. The lift pumps at the WWTP were to pump
from the interceptor up to maximum hydraulic capacity until the
aeration basins are filled. The aeration tank contents are
returned to the primary treatment tanks at the end of the event.
* Using vortex flow control devices.
**For small to moderate storm events.
1.13
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— F
©
\jjj j'/ 1 / / / j / / / i
. LOWER
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Figure 1.6
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T f Rfl ClW OVFRFI niV
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1AUUATER GATE _
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- • » - v • • x > V • > \v\\\
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cal in-line storage device (regulator).
1.14
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Flap Gate
to River
Figure 1.7 Typical Float Actuated Type Flow Regulator
-------
1.3.3 Swirl Concentrator/Swirl Degritter/Disinfection
Facilities
Swirl concentrator facilities were proposed at each
of the six major overflow points. The facilities were to be
tailored to the particular needs of each site.
Pumping stations to drive the swirls were considered
necesssary at each site. New lift stations were to be included
for the Weiss Street gravity overflow and for the Fraser Street
overflow. A battery of various size fixed speed pumps were
considered for these stations. The existing 100-cfs fixed speed
pumps were to be used (after revamping/turning) for all other
stations as required. New low capacity (25-40 cfs) fixed speed
pumps were to be included in all revamped stations to provide
variable pumping range using the revamped fixed speed 100-cfs
pumps.
A swirl degritter at the Weiss Street complex may be
necessary if the proposed City-wide system of swirl concentrators
were implemented and pending a careful review of WWTP grit
removal capacity under sustained wet weather high flow
conditions. This degritter contingency was proposed to ensure
that the WWTP's solids handling capacity would not be overtaxed.
In addition to disinfection treatment at the Hancock
Street Facility, overflow disinfection was also considered at the
six aforementioned overflow points. Disinfection process is to be
sequential - staged chlorine/chlorine dioxide application (8
ppm/2 ppm) with total of 2 minute detention. Baffled chambers
are to provide necessary detention.
1,4 Details oj£ the Phase 2 Evaluation
The purpose of the Phase 2 evaluation was to determine
the optimum implementation plan for the reduction of CSO impacts
to the Saginaw River based on available money and the elements of
the overall CSO Facility Plan. Optimization included cost
estimation of each plan element followed by a series of model
simulations using various combinations of elements within the
total allotted project budget.
As a first step, additicnal field evaluations of flow
patterns at various regulator chamlers were performed allowing
further calibration of the simulation model. A limited field
investigation was performed including continuous water elevation
recording at several regulators en each side of the Saginaw
River. This data was combined with information routinely
Iol6
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collected by City personnel at the Weiss Street and Hancock
Street Fump Stations and at the WWTP to estimate area wide
hydraulic conditions. Simulations then indicated the optimum
configuration for a reduced BMP implementation plan. This plan
consisted of modifications to the Saginaw sewerage system only on
the West Side of the Saginaw River. See Figure 1.8 for locations
controlled as part of the reduced BMP plan.
Since the entire BMP plan was not to be implemented at
this time, it was important that all elements of the reduced BMP
plan be designed and implemented such that no modifications will
be required in the future. Furthermore, the concept of the total
BMP plan was to control the system such that overflows (except
for extreme events) would occur only at major pumped discharge
points. Since it was not envisioned to modify the Emerson
Street Pumping Station at this time (for automatic "turn-on"),
the reduced BMP plan was designed such that no additional capital
expenditure for pumpage and/or operational problems vrould occur
as a result of the implementation. In short, all elements of the
reduced BMP plan were to be permanent and not subject to
modifications. The entire BMP plan may be accomplished in the
future and all elements of the reduced BMP project were to be
designed so that the conveyance/pumpage characteristics remain
unchanged.
As part of the reduced BMP plan, 12 of 35, of the City
of Saginaw's combined sewer regulators were modified in
accordance with the CSO Facility Plan Concept. One of the 14
upstream in-system type structures was also constructed. The
Weiss Street Pumping Station weir/wet well operation was modified
to increase river crossing discharge so that more of the West
Side "first flush" is transmitted to the WWTP.
1.5 Details of the Phase 3 Eva^luatjLon
The Phase 1 EDP sewerage system simulation model was
used to estimate City-wide emissions pre/post reduced BMP plan
implementation. Flow measurements using automatic equipment were
made at a number of representative regulators as part of the
Phase 2 measurements.
After the reduced BMP plan project was implemented,
Phase 3 flow measurements were conducted to document the
effectiveness of the implemented controls on a representative
basis. Automatic continuous level sensors were installed in
representative regulator chambers to indicate hydraulic
conditions during dry weather and wet weather conditions. A
limited post-implementation water quality sampling program _was
conducted using automatic sampler techniques to obtain composited
1.17
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00
LEGEND
EXISTING INTERCEPTOR
— •— CITY LIMITS
__ LIMITS or SEHVICC *"»E*
OUTSIDE CITY LIMITS
PROPOSED REGULATOR
MOOFICATIONS
TYPE A
• TYPES
• MODIFIED TYPE B
f J <£ PROPOSED INLINE FLOW
I ^ CONTROL/STORAGE DEVICE
TYPICAL EXISTING
SEWER LINE
O ELEMENTS COMPLETED
IN 1984
-------
samples from one major overflow point (Weiss Street Pumping
Station), at one regulator (Adams Street) and at the WWTP.
Samples were analyzed for TSS, BOD and total/soluble phosphorus
by the City of Saginaw.
These documentary measurements were used to adjust the
simulation model as necessary to note the technical effectiveness
of the flow controllers/in-line storage. The simulation model
was then re-applied to the entire system to estimate residual
emissions as a result of the plan. Thus, Phase 2 pre-
implementation flow measurements were used to sharpen the
planning/design phase and to provide a "pre-project"
documentation. Phase 3 post-implementation measurements were
again used for documentation purposes as well as to "fine-tune"
the simulation model to incorporate the actual effectiveness of
the plan elements. The resulting simulation model thus estimates
residual CSO emissions incorporating to a reasonable extent,
actual configuration effectiveness.
Detailed observations were also noted by City of
Saginaw maintenance personnel during routine post storm
inspection of regulator chambers to determine physical
conditions. One aspect of the BMP plan was to include low
maintenance flow regulating devices to replace the existing float
operated type. These existing devices require frequent
maintenance and are subject to failure. The new vortex valve flow
regulating devices performed satisfactorily and have reduced
maintenance problems.
Structural changes to regulator chambers were intended
to improve system storage capacities and flow hydraulics without
causing excessive surcharge or in-system sedimentation. Degree
of backwatering was noted at numerous locations upstream in the
sewerage system. Debris accumulations in all regulator areas and
sedimentation in dry weather flow channels were particularly
noted. These observations served to document the reduction in
maintenance labor provided by reduced BMP plan implementation.
The post implementation documentary effectiveness of
the reduced BMP plan improvements in terms of increased wet
weather pollutant loadings to the WWTP was close to pre
implementation predictions. In sum, expenditures of less than
$516,000 under the reduced BMP plan for low level sewerage system
modifications (entailing a significant portion of proposed
controls for one-half of the City) resulted in decreasing the
system-wide total phosphorous wet weather loadings to the river
by about 10%. No adverse conditions resulted from the plan. The
concept of inexpensive system controls to maximize transient in-
line storage of combined sewage with bleedback to a high
1.19
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performance WWTP worked well and is recommended as a management
practice.
1.6 Readerxs Guide to Report
Report conclusions and recommendations are presented in
Chapters 2 and 3, respectively. A general description of the
Saginaw sewerage system is presented in Chapter 4. A review of
the combined sewer overflow control technologies considered as
part of the Facility Planning effort is presented in Chapter 5.
Details of the modeling approach used throughout the project are
presented in Chapter 6. Design and implementation construction
details for the reduced BMP plan are presented in Chapters 7 and
8, respectively. Details of the post construction measurement
evaluation program are presented in Chapter 9. WWTP phosphorous
removal performance determinations conducted during this period
are reported in Chapter 8. Final modeling results documenting
overall pollutant removal efficiency for the implementated plan
are given in Chapter 10. Details of stormwater management
investigations intended to alleviate basement flooding problems
due to surcharging sewers in upstream areas which also effect the
magnitude of downstream CSO levels are reported in Chapter 11.
1020
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CHAPTER 2
CONCLUSIONS
EDP has completed a five year 3 Phased study of CSO
pollution from the City of Saginaw, Michigan and concludes that
CSO pollution in Saginaw is controllable at reasonable costs and
that water quality improvements in the Saginaw River and public
health gains will be significant. The conclusions are based on
the analyses performed over the past five years, actual data
collected concerning CSO and river quality, previous analyses of
the water quality of the region and partial impletrentation and
evaluation of proposed system modifications. It should be noted
that the conclusions stated below include those developed during
earlier EDP investigations leading to the development and
adoption of a CSO Facility Plan for Saginaw. These earlier
conclusions are presented to depict a perspective framework for
the more relevent and important conclusions resulting from the
implementation/evaluation of the reduced BMP program which is an
integral element of the overall CSO Facility Plan.
Conclusions are detailed in the following order:
PLANNING & DESIGN
A. Combined Sewer System Data Reduction Analysis
B. CSO Management Model
IMPLEMENTATION & EVALUATION
C. Implementation of Reduced BMP Flan
D. Evaluation of Implemented BMP Plan
FUTURE
E. Optimization and the Recommended Facility Plan
F. Cost Analysis of Completed and Proposed Future Work
G. Effects of Facility Plan Implementation on River
Quality
A. Combined Sewer System Data Reduction Ana_ly_s_i.s
(1) Extensive data concerning the Saginaw combined sewer
system, intercepting sewer systems, and storm and sanitary waste
water treatment facilities were collected, reduced and analyzed.
Available data were supplemented by several EDP measurement and
inspection programs.
2.1
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Wastewater Treatment Plant
(2) The secondary WWTP had the capacity to handle combined
sewage volumes greater than generally flowing to the plant. An
analysis of operating records indicated that both hydraulic and
treatment capacity for additional loadings were available without
impairment of overall WWTF treatment efficiency. Increasing the
flow of combined sewage to the WWTP was a primary goal of this
study. Pollutant loads to the river are expected to be
significantly reduced by increasing flow to the WWTP and storing
excesses within the system until throughput capacity becomes
available.
(3) Review of daily operating records (long term ) indicated
that the BOD removal for the WWTP averages approximately 89% for
both wet days and dry days. It was concluded that the WWTP
could handle higher wet weather flows without compromising the
plant's pollutant removal capabilities.
(4) Review of WWTP data indicate wet weather total phosphorous
removal of 50% without AWT . Non- soluble phosphorous removals
are 95% but no soluble phosphorous removal is achieved. The non
soluble fraction averages 54% of the total phosphorous.
(5) Advanced Wastewater Treatment (AWT) (pickling liquor or
FeS04 addition) is used, as required at the WWTP to meet effluent
standards. Phosphorous removals average 75% with AWT and the
entire additional level removed beyond secondary treatment rates
is attributable to a 50% reduction of soluble phosphorous.
(6) A decrease in non-soluble phosphorous removal occurs
during AWT and is apparently due to incomplete settling of the
floculant material generated by the chemical reaction. Soluble
phosphorous tied up in the unsettled floe appears as non-soluble
phosphorous in the laboratory analysis. Part of the soluble
phosphorous removal rate reported is attributable to this
apparent increase in the non-soluble fraction.
(7) The 1984 field investigation indicated influent WWTP
total phosphorous concentrations for all flow conditions
monitored to be 1.55 mg/1. Wet weather samples at the WWTP grit
chamber indicated a weighted average of 1.3 mg/1 although "first
flush" values were as high as 6 mg/1. Wet weather total
phosphorous concentrations noted at the Weiss Street Pump Station
averaged 1.74 mg/1.
2.2
-------
Interceptor Sewer pata
(8) The junction of the West Side Interceptor river crossing
and the East Side Interceptor was identified as a hydraulic
bottleneck. The Weiss Street Pumping Station relieves
backwater/surcharge at the crossing and together with the Weiss
Street gravity overflow constitute the dominant combined sewer
overflow in the system.
(9) The intercepting system's major hydraulic bottleneck is
the river crossing. Application of additional head to the
crossing by raising the weir level at the Weiss Street Pump
station would increase flows across the river. A five foot
weir height increase was estimated to be optimum. Further
increases provide diminishing marginal gains as flows are
increasingly diverted from Weiss Street to other overflow points
rather than to the WWTP.
Regulator fiata
(10) Regulators (earlier modifed as part of the Hancock Street
Detention Facility improvements (mid 1970's)) had been altered to
cause the underflow orifices to close rapidly, limiting flows to
the interceptor and thus committing the "first flush" of a rain
event to in-line storage created at the chamber. EDP considered
it more advisable to maintain higher underflow discharges to the
interceptor, limited only to what the interceptor can maximally
handle. Operation in this manner will commit the "first flush" of
a rain event, generally carrying the highest concentration of
pollutants, to the interceptor, and eventually to the WWTP.
(11) It appeared during the EDP inspection program that the
mechanical float-operated mechanisms used to regulate flow at
the regulation chambers were slow in responding to rising water
levels, and it was speculated that a number of the float
activated underflow orifices do not appreciably close during high
water conditions. The City reported that the devices required
constant surveillance to maintain operation.
(12) New vortex flow throttling devices having no-moving
parts, large aperture openings (in comparison to conventional
orifices) constructed of durable material (stainless steel) and
reported to be nearly clog-free were envisioned to replace the
existing mechanical float operated mechanisms in the regulators.
These new vortex flow throttling devices combine conventional
orifice flow (high discharge with low head) with vortex braking
operation (low discharge with high head), thus replicating and
enhancing the flow characteristic produced by the variable-
orifice opening mechanical float-operated mechanisms.
203
-------
®5! Storage Data
(13) Potential in-line storage capacity in the Saginaw sewer
network is extensive. A total storage volume of 3.93 million
cubic feet (29.4 million gallons) has been estimated as
available witho.ut threatening basement flooding. Regulator
modifications and in-line storage devices recommended to achieve
this in-line storage potential are inexpensive, and will be less
costly to maintain than present float-type regulating devices.
(14) Regulators on the West Side are typified by conditions
where the influent trunk sewers are on a steep incline to the
regulation chambers which then level- off not far upstream. Far
greater storage volumes could be generated for these trunk sewers
if additional flow control structures were located upstream where
the invert slopes are less steeply inclined.
B. CSO Management Model
(15) The Saginaw CSO Management Model, developed by EDP, is an
inexpensive and flexible tool for preliminary planning and sizing
of CSO facilities. The model provided a means by which the CSO
problem could be analyzed and introduced time and probability to
the quantity, frequency and duration of overflow, events by using
actual rainfall data collected over a long period of time.
(16) Modification of the original model developed in 1980
(Phase 1) using extensive field data collected in 1983 (Phase 2)
and 1984 (Phase 3) has resulted in a fine-tuned edition which
produces flow and water quality data closely matching field
observations.
(17) During Phase 1 it was estimated that 25.6 percent of all
wet weather flow would arrive at the WWTP and implementation of
the partial and complete BMP programs would increase this
percentage by factors of 1.31 and 1.93, respectively.
(18) Using the model as calibrated (based on field
investigation performed in 1984) it is currently estimated that
37.7% of wet weather flow would arrive at the WWTP and will
increase by factors of 1.35 and 1.91 for the reduced and complete
BMP plans, respectively.
C. Implementation of Reduced BMP Plan
(19) Partial implementation of the reduced BMP plan including
modifications to 12 of 35 combined sewer regulators, construction
of one upstream in-system storage structure and increasing the
2.4
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effective head at the Weiss Street crossover was
the construction price of $315,000.
completed for
(20) Modification of regulator chambers was accomplished
under ccr-trolled conditions such that no dry weather sewage or
wet weather combined sewage impacted the river during
construction.
(21) Conditions within regulators were controlled such that
r.c debris generated as part of the modification progrBir impacted
the river or interceptor sewer lines.
(22) Existing chambers were modified using concrete fill to
eliminate areas of debris accumulation and resulting odcrs.
(22) Vertex valve flow regulators were constructed and
installed in variable arrangements to confcrm to existing
conditions vvithir. the regulator chambers. The devices were
segmented for ease of installation particularly where access
space is limited.
(24) Modification of regulator chambers was easily
accomplished using standard construction practices particularly
saw- cutting of concrete, core drilling and concrete forming and
pouring.
D. Evaluaticn of_ Irp£l§roent_ed BMP Plan
With the exception of limited pollutant removal at the
Street Facility, all reduction of CSO impact tc the
transient
materials
that on
would
(25)
Hancock
Saginaw River is attributable to increased in-system
storage coupled with increased flow and "first flush"
tc the WWTP. Prior to this program, it is estimated
annual basis, 37.7% of all wet weather related flew
an
be
handled by the WWTP<
(26) Implementation of the reduced BMP plan is estimated to
have increased the percentage of total annual wet weather flow
directed to the WWTP by 14.6% (from a previous "as is" level of
37.7%). Implementation of the remaining elements of the
complete BMP plan could produce an overall incremental increase
of 30% (increasing the total wet weather flov treated at the WWTP
to 67.7%). For "Low Rainfall" events (less than 0.5 inches rain),
the percentages cf increase flow to the WWTP due tc iirplementa-
2.5
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tion of the reduced BMP plan and tre complete BMP plan are esti-
mated as 19% and 34.6%, respectively. For "High Rainfall" events
(greater than 0.5 rainfall), the respective percentage increases
are 10.5% and 21.8%. Table 2.1 presents estimated related
increase of total systemwide wet weather discharge to the WWTP
for different rainfall conditions as a result of the reduced and
complete BMP plans.
(27) Implementation of the reduced BMP plan is estimated to
have incrementally reduced (beyond "as is" levels) suspended
solids loadings tc the Saginaw River by 16%, BOD by 20% and total
phosphorous by 8.5%. During periods of AWT (pickling liquor
addition) at the WWTP, total phosphorous removals will increase
12.6% above pre-implementation levels. The rain
intensity/percentage increase relationship noted for flow to the
WWTP is consistent for suspended solids, BOD and phosphorous
reductions for the Saginaw River. The greatest increase in
reductions occurs during low intensity events with relatively
lesser reductions udner high intensity conditions. Table 2.1
indicates the annual percentage reduction of total systemwide
suspended solids and BOD leadings to the Saginaw River.
(28) Or. a weight basis, the reduced BMP plan implementation
is estimated to have reduced wet weather suspended solid
pollutant loads to the river by 1.4 million pounds per year and
BOD by 0.47 million pounds per year and total phosphorous by 3000
pounds per year. Wet weather related total phosphorous loadings
are estimated to be reduced by 3000 to 4000 Ibs. per year
depending on application cf AWT .
(29) Incremental TSS and BOD removals of total wet weather
loadings to river attributable to implementation cf the complete
BMP program (when completed) are estimated to equal about 29% and
30%, respectively. Total phosphorous reduction with secondary
treatment is estimated to equal 16.7% and with AWT would equal
25% above pre BMP conditions. Mass removals due to implementation
of the complete BMP plan (when completed) are estimated as 2.5
million pcunds of SS, 0.68 million pounds of BOD and 70CO tc
10,000 pounds of total phosphorous (latter estimate when AWT
used). Consistent with the data for the reduced EMP plan,
increased reductions cf loadings to the Saginaw River were
greater under low intensity rain conditions.
(30) WWTP 1SS and BOD removal levels noted during the post
construction evaluation period (late 1984) have not diminished,
confirming early Phase 1 and Phase 2 projections.
(31) Figure 2.1 Graphically illustrates the relative annual
wet weather phosphorous loadings to the Saginaw River based on
various treatment scenarios. Two sets of bar craphs were used to
2.6
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TABLE 2.1
Pollution Abatement Effectiveness
of Best MAnageirent Practices Program
Suspended Solids and BOD Emissions
Saginaw, Michigan
A. Annual Percentage
of Total Systemwide
Wet Weather Sewage
Discharge to WWTP
B. Annual Percentage
of Suspended Solids
Loadings to WWTP
C. Annual Percent
Reduction of
Total Systemwide
Wet Weather
Suspended Solids
Loadings to
Saginaw River
D. Annual Percent
Reduction of
Total Systemwide
Wet Weather
Sewage BOD Loadings
to Saginaw River
E. Estimated Capital
Cost (millions)
Pre
Project
Condition
L H T
53.0 28.5 37.7
50.0 26.0 35.6
46.5 24.2 33.1
53.4 27.6 36.6
Results
of Reduced
BMP Program
Implementation
L H T
72.0 39.0 52.3
72.0 38.0 52.3
67.0 35.3 48.7
67.6 41.8 57.0
Projected
Complete
BMP Program
L H T
87.6 50.3 67.7
91.0 48.0 66.0
84.6 44.6 61.4
77.4 50.0 66.7
L = Low Accumulation H = High Accumulation T = All Events (1978 Rainfall )
Rain Event
(0.5" or less)
Rain Event
(greater than 0.5")
2.7
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Key: Total Phosphorous
Soluble
Phosphorous
40 -i
o
S 30
o
20 -
o>
10
o
a.
10 .
Total Vtet
Weather Load
Pre BMP
Load
Reduced
BMP Load
Complete
BMP Load
Secondary Treatment at WWTP
40 -,
U 75
% of
Total Load
- 50
- 25
100
75
% of
Total Load
50
• 25
Figure
^tal W-t Pre BMP Reduced Complete
Weather Load Load BMP Load BMP Load
AWT Tertiary Treatment at WWTP
2.1 Wet Weather Total Phosphorous Loading to Saginaw
2.8
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indicate estimated removals with the WWTF providing secondary
(top of figure) and AWT (bottom of figure). In additior, the
soluble fraction of the tctal phosphorous is illustrated. Figure
2.1 clearly illustrates substantial reductions in total
phosphorous loadings to the river due to treatment at the WWTP
and that implementation of BMP measures greatly enhance total
removals. Soluble phosphorous removal is non-existent with the
WWTP providing only secondary treatment. Based on an annual total
wet weather load of 41,000 Ibs., the total estimated phosphorous
loadings to the river would be 31,000 Ibs. for the reduced BMP
plan and 27,600 Ibs. for the complete BMP plan with secondary
(50%) treatment at the WWTP. The entire decrease is due to
reduction of the non-soluble phosphorous fraction. With AWT
(75%) treatment, residual loads of total phosphorous to the
Saginaw River would be 26,000 Ibs. and 21,000 Ibs. for the
reduced and complete BMP plans, respectively.
(32) Under optimum conditions of interceptor flow (lew wet
well, no upstream East Side flow) the maxinum river crossover
rates would increase from 53 to 73 cfs due to the Weiss Street
Pump Station weir modification. Under the condition of high
WWTP wet well and no upstream East Side flow, the maximum
crossover rates would increase from 25 to 47 cfs due to program
modifications. Upstream East Side Interceptor flow will always
exist and this flow will induce greater heed loss and surcharging
of the interceptor further reducing the potential crossover flow.
It is estimated that the modification of the Weiss Street Station
spillover weir level has increased the crossover rate by about 20
cfs under all conditions and that operation of the WWTP wet well
within the alarm range can handle this range.
(33) The WWTP currently operates in a near optimum manner
during wet weather conditions. Future modification of the WWTP
hydraulic conveyance system between major treatment elements
could increase peak pumpage rates and reduce bypass.
(34) Roughly 500,000 cubic feet of off-line storage is used
at the WWTP. Two aeration basins are used to store combined
sewage delivered to the plant at rates limited by the WWTP
conveyance capacity at the grit chamber where bypass occurs.
Future modifications to increase hydraulic capacity may enable a
greater portion of "first flush" materials to be stored in the
aeration basins prior to bypass at the grit chamber.
(35) WWTF influent is pumped from a wet well tc the grit
chamber using 6 lift pumps. Pump combinations in use at any
time are manually selected to maintain proper wet well
elevations. Wet well alarms exist for high and low conditions
but operation outside the alarm range is possible. Original
2.9
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design drawings indicate a design wet well level 5 feet below the
present low alarm level. Although pump operation at the design
wet well level will increase wet weather river crossover rates,
it tray cause pump cavitaticn fcr certain pump combinations.
(36) With the exception of a few minor reported incidences of
large stick debris cloggage, the flow and solids handling
performance of the new vortex valve flow throttling devices
replacing the mechanical float-operated controllers within the
regulation chambers was satisfactory. No adverse flow backup or
sedimentation problems were reported. On several occasions the
devices were visually observed to pass "first flush" and scoured
solids on draindown. Limited flow calibration measurements
indicated that the devices generally operated as per
manufacturer's specifications.
(37) The performance of the new in-line control chamber at
Salt & Vermont Streets which generated at maxirruir capacity a
transient storage volume cf 175,000 cubic feet was satisfactory.
The new vortex valve flow throttling device which controlled the
wet weather discharge from this facility as well as permitting
passage of normal dry weather sewage worked extremely well. No
blockages, sediment buildup nor adverse backups were reported.
Minor odor problems with organic sediment buildup within "dead
corners" of the in-line control chamber were noted and are
attributable to inccrrectly sloped concrete fillets placed during
construction. This minor problem has since been corrected.
E. Optimization and the Recommended FacdJ-ijty FjLan (Future Actions)
(38) Runoff simulation studies indicate that the most singu-
larly effective measure for handling CSO in Saginaw is the inclu-
sion of Best Management Practices (BMP). The BMP program
consists of extensive in-line storage and system modifications to
increase transient in-line storage and system hydraulic capacity
so that the WWTP can handle more1 wet weather combined sewage.
(39) After implementation of the complete BMP plan, resi-
dual overflows will remain at six locations: Weiss Pump Station,
Weiss Street gravity line, Emerson Pump Station, Fourteenth
Street Pump Station, Webber Street Pump Station and Fraser
Street (at the Queen Street/Fraser Street regulator). CSO treat-
ment is needed to treat these overflows remaining after the BMP
plan implementation. The most cost-effective program cf CSO
abatement was developed using the swirl concentrator technology
at these locations. A non-linear optimization model based on
swirl concentrator suspended solids removal was used as an aid to
identifying optimal abatement configurations.
2.10
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(40) Disinfection using sequential chlorine/chlorine dioxide
dosage rates of 8 ppm/2 ppm for a total contact of 2 minutes is
recommended, as required to maintain bacteria pollution in the
Saginaw River at acceptable levels and would tend to minimize the
production of carcinogenic materials associated with conventional
chlorine application.
(41) The design maximum solids loading capacity at the WWTP
plant is estimated tc be exceeded during high rain events
(greater than 0.5 inch rain) if the entire systemwide swirl
concentrator program is implemented. A swirl degritter would
then be recommended at the Weiss Street treatment complex tc
handle solids generated from the swirl treatment units pending a
more detailed hydraulic investigation of the crossover as well as
the grit removal capacity during high flows at the WWTF. Removal
of solids at Weiss Street using the swirl degritter (followed by
landfill disposal) will maintain acceptable solids loadings at
the WWTP and will eliminate any potential problem of solids
deposition at the river crossing.
F. Cost of the Recommended Facility Plan (Future Actions)
(42) Cost estimates are based on 1985. dollars (ENR = 4500).
Capital costs for the recommended CSO Facility program are
estimated to be 23.7 million dollars. The recommended CSO
Facility plan would use swirl concentrator/swirl degritter
technology, and the BMP in-line storage and system modification
plan. The costs do not include the presently operating Hancock
Street CSO facility (capital cost of $10.4 million, ENR=450Q), nor
the cost of land acquisition for the new swirl facilities.
G. Effects of Facility Plan Implementation On River Quality
(Exerpted from EDP Facility Plan Report (2))
(43) Available storm-related water quality of the Saginaw
River includes limited past storm-related data, an extensive one-
dimensior.al h^drologic and ecological model of the river and bay,
and recent data collected tc characterize the runoff and
impact. These date sources and previous analyses were reviewed
and analyzed.
(44) CSO has been identified as a major contributor of the
dissolved oxygen deficits in the Saginaw River following storm
events. Dissolved oxygen was reduced frcm above 6 mg/1 to as low
as 4 mg/1 as a result of CSO from a storm event with 0.83 inch
total accumulation with typical river flow conditions. Lnder more
critical conditions, the dissolved oxygen deficits will be
greater.
2.11
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(45) Sediirent pollution has been identified as a major problem
in the Sacinaw River. CSC is a contributor to sediment pollution.
(46) Suspended materials have been identified as contributors
to dissolved oxygen deficits by reducing light penetration and
algal productivity. Suspended solids also contribute to aesthe-
tically objectionable turbidity. Suspended solids may be carriers
of other pollutants such as toxic materials and algal nutrients.
(47) CSO has been identified as a source of aesthetic
pollutants including floatable pollutants and suspended solids
that increase turbidity.
(48) A dissolved oxygen model based or. the classical Streeter-
Phelps equation was determined sufficient to model CSO dissol-
ved oxygen impacts on the Saginaw River. DO levels as low as 4
mg/1 have been predicted to be coir mo n as a result of CSO loadings.
(49) Simulation models have been successfully developed and
calibrated fcr predicting the operation of the Saginaw combined
sewer system and the Saginaw River water quality response.
Overflew volumes and quality in terms of suspended solids and
five day BOD can be predicted on an hourly basis. Dissolved
oxygen in the Saginaw River can be predicted in response to CSO
pollutant loadings. The capability of testing CSO abatement
alternatives has been incorporated in the models.
(50) Nonpoint source loadings resulting from combined sewer
overflows in the City of Saginaw are significant contributions to
pollutant loadings to the Saginaw River. CSO loadings were
estimated using a long terrr simulation model to be 8,600,000
pounds TSS and 2,300,000 pounds BOD for the calendar year of
1977 consisting of 78 storns creating overflows.
(51) Implementation of the recommended CSO Facility program
would raise the dissolved oxygen level from 3.2 mg/1 to 4.4 mg/1
for a 1.9 inch storm impacting July 8, 1980 river conditions.
Dissolved oxygen gains for less intense events would be smaller.
Significant protection from excessive dissolved oxygen deficits
would occur primarily for severe rain events at or above-. 0.8
inches of total accumulation with significant rain intensity.
(52) The recommended control plan would substantially eliminate
the sediment pollution component caused by CSO. Settleable
solids wou]d be over 80% reduced.
(53) Over half the wet weather related suspended solids
emmisions would be eliminated. The suspended solids reduction
will aid dissolved oxygen levels by increasing light penetration
and subsequently alc,al productivity, and by lowering algal
2.12
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nutrients associated with suspended solids. Lowered turbidity
levels will also increase the aesthetic appeal of the river
water.
(54) Pollutants that can be associated with the removed solids
in CSO will alsc be; removed. These pollutants include toxic
pollutants such as heavy metals and algal nutrients.
(55) Aesthetic: qualities of the river will be significantly
improved increasing the enjoyment of the river for recreational
purposes. Floatables and suspended materials will be reduced.
2.13
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CHAPTER 3
RECOMMENDATIONS
The conclusions stated in Chapter 2 of this report
clearly indicate the effective use of elements of the BMP plan in
reducing CSO to the Saginaw River. To date, the entire BMP plan
has not been scheduled for completion as the the funding for
implementation of complete facility plan elements is not
available. In addition, the 1984 investigation of the system
hydraulics during the construction and post evaluation phases
indicated areas of system operation where additional review and
"fine-tuning" may be necessary in the future due to hydraulic
changes induced by implemented elements cf the BMP plan. The
following recommendations of this study for the City of Sagiraw's
sewerage system are presented in order cf importance:
1) The reduced BMP plan included modification of only 12
of 35 regulator chambers. All other regulation chambers should
be updated to include new vortex flow regulating devices and
appurtenances designed to maximize storage and minimize bypass to
the river.
2) One of 14 proposed upstream in-line storage chambers
was completed. Facilities for the remaining locations should be
designed and constructed. The recommended order of priority for
implementation of these locations is as follows:
In-line Storage Priority List
1. River & Cambrey Streets
2. Birch & Harris Streets
3. Gratiot & Michigan Avenue
4. Cass & Woodbridge Streets
5. Hamilton & Williams Streets
6. Union Avenue & Delaware Street
7. Jackson & Mason Streets
8. MacKinaw Street & Michigan Avenue
9. Troy & Boxwood Streets
10. 17th & Perkins Streets
11. 14th & Norir.an Streets
12. Hayes Street & Michigan Avenue
13. Weiss & Delaware Streets
The in-line storage facility at Weiss Street and
Delaware Street should be completed as part of the CSO treatment
facility implementation at the Weiss Street Pump Station.
301
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3) Existing gate opening and pump "turn-on" sequencing at
the Hancock Street Pump Station should be reviewed to ascertain
whether the operation is optimal. The existing monitoring
equipment at the Hancock Street Pump Station should be
upgraded, if necessary, for the purpose of monitoring station
operation in compliance with optimization recommendations.
4) The pump initialization equipment at the Weiss Street
Pump Station should be reviewed to optimize turn-on/shut-off
elevations and to ascertain whether supplemental operating
controls are necessary due to the weir modification performed as
part of reduced BMP plan.
5) The operations of the Hancock Street Facility and the
Weiss Street Pump Station should be reviewed to ensure that the
Hancock Street Station operates prior to the Weiss Street Station
during a storm event. Detention storage/treatment currently
available at Hancock Street will thus be utilized prior to
untreated bypass at Weiss Street (for areawide storm events).
6) The CSO control facility for the Weiss Street area
should be implemented as overflows at this location are still the
dominant source of wet weather pollutant load to the Saginaw
River.
7) Under extremely high rate conditions, wet weather flow
pumped to the WWTP grit chamber is split with partial overflow to
the WWTP bypass. Overflow commences at a total rate less than
the existing WWPT flow-through capacity. Possible replacement of
the WWTP overflow bypass weirs with sluice gates may allow
initial storm flow containing "first flush" materials to pass to
the aeration basins for storage. Later cleaner flows would be
bypassed, if necessary due to full basin conditions, by opening
of the sluice gates.
8) Currently potential pump cavitation conditions prevent
maintaining WWTP wet well levels at the initial design elevation.
Although the City WWTP personnel maintain maximum wet weather
throughput whenever possible to the WWTP, the elevations
currently maintained, reduce the hydraulic capacity of the
interceptor system during major events causing overflow at
upstream pump stations. Hydraulic conditions of influent pump
intakes at the WWTP wet well should be investigated to determine
if baffles, spoilers or intake vanes could reduce cavitation and
allow lower operating levels, and result in lesser upstream
overflow magnitudes.
9) Evaluation of the WWTP layout for potential hydrualic
bottlenecks at maximum capacity should be performed. In some
areas, piping systems are believed to be the limiting factor in
3.2
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plant operations as opposed to the performance capability of
treatment processes. This investigation should ascertain whether
any changes to increase flow rate would improve overall WWTP wet
weather capacity/reduce bypass and whether the water quality
benefits that may result would be cost effective.
3.3
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CHAPTER 4
DESCRIPTION OF CITY OP SAGINAW SEWERAGE SYSTEM
4.1 Descriptive Background Material
Saginaw is located in the eastern part of central
Michigan north of Detroit, as shown in Figure 1.1. The Saginaw
River is a short section of a major drainage area leading to
Saginaw Bay, Lake Huron. Saginaw is located at the start of the
river and on both banks for about a five mile stretch. The
Tittabawassee, Shiawassee and Cass Rivers are tributary to the
Saginaw River just upstream of the City. The topography of the
area is flat, and the elevation is approximately 600 ft. The
Saginaw River divides the 10,437 acre area of the City of Saginaw
into an East Side section having an area of 5,634 acres, and a
West Side section of 4,803 acres. The Saginaw River drainage
basin above the City has an area of 6,200 sq. mi. The average
daily stream flow is estimated at 10,000 cfs with miniurnurn daily
flow of 500 cfs. Flood flows of 62,000 cfs have been observed.
The entire river is only about 22 miles in
length and has a gradient of about one inch per mile or
less along its entire length. The river is used extensively
as a commercial waterway, and it is regularly dredged by
the Corps of Engineers to maintain the shipping channel. The
depth of this channel ranges from 16.5 feet at Green Point
to 27 feet at river mouth. There are five dredged turning
basins along the length of the river. The width of the
Saginaw River ranges from 365 feet at Green Point to
1,700 feet near the Middle Grounds. Winds significantly
affect the water level in Saginaw Bay and in turn this
water level strongly affects the direction of flow in the
Saginaw River. Sustained southwesterly winds lower the level
of the bay and temporarily increase the river's velocity
discharge. Sustained northeasterly winds, on the other hand,
raise the water level in the bay and decrease stream veloci-
ty and discharge, often reversing the flow of the river.
The area which is surrounded by the Great Lakes, has a
quasi-marine environment. Temperatures stay warmer later in the
year and cooler during the spring because of the influence of the
large water masses. Saginaw1s normal annual precipitation is
about 28.55 in., over 50% of which falls during the summer
between March and September. Summer storms occur as showers and
thunderstorms. Most of the winter precipitation is snow which
accumulates until the spring thaw. Beginning in March or April,
melting snow combined with rainfall can produce high overflow
volumes and increased discharge of pollutant loadings to the
4.1
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river. Most of the storms that occur are of low average
intensity. Over 90% of the time, the average intensity of
rainfall which produces runoff is less that 0.10 in./h.
The City of Saginaw is serviced by a combined sewer
system. Combined sewer overflows during rain events are a
significant contributor of pollutants to the Saginaw River.
Overflows may occur at 35 regulator chambers during increased
flow events. Overflows may also occur at the five pump stations
designed to relieve the system during flooding conditions.
Overflows occur when the flow in the combined collection system
is greater than three to six times the dry weather flow rate
depending upon the regulator location. It is estimated that over
60 overflows occur per year.
Impacts on the Saginaw River from CSO include dissolved
oxygen depletion in the downstream segments of the river and
increased bacteria levels. Public health impacts can be of equal
importance to the organic loading to the river, because of the
high level of micro-organisms associated with combined sewer
overflows. Suspended solids and floatable material also create
visual problems and further aggrevate the continual need to
dredge the channel for maintaining ccmmercial navigation patterns.
4 .2 Sewerage Sy_sitem Overview
Saginaw is serviced by a combined sewerage system.
The overall service area is depicted in Figure 4.1. Catchment
area boundaries of individual subsystems considered in this study
along with proximate location of regulators are shown in Figure
4.2.
An intercepting sewer shown in Figure 4.3 runs along
both banks of the Saginaw River, eventually joining on the East
Side and running to an advanced secondary WWTP. The West Side
interceptor crosses the river at Weiss Street to join the East
Side Interceptor, which continues to the WWTP at the northeast
limits of the City. A portion of the Saginaw township outside the
city limits is also serviced by the combined sewer system with
dry weather flow joining the Saginaw intercepting sewer system
and eventually treated at the WWTF. There are also a number of
areas within Saginaw whose stormwater runoff is not diverted to
the Saginaw combined sewer system. State Highway 1-75 with
downtown connectors covers an area of about 100 acres and has its
own drainage system. A large newly developed residential area in
the southeast section of the City has a separated storm
sewer/sanitary sewer system. A number of industrial and
commercial areas near the river are drained to the river and are
independent of the combined sewer system.
4.2
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EXISTING PUMPING STATION
A EXISTING,
CHAMBER
EXISTING INTERCEPTOR
EXISTING COMBINED SEWER
AND OVERFLOW(TYPICAL)
CITY LIMITS
LIMITS OF SE^V'CE AREA
OUTSIDE CITY LIMITS
HANCOCK ST PUMPING
STATION
WEBBER ST PUMPING
STATION
WEISS ST PUMPING
EMERSON 51 PUMPING
STATION
EXISTING
WASTE
FOURTEENTH 5T
PUMPING STATION
Figure 4. i Soginow combined sewer service area.
-------
*>.
LEGEND:
A EXISTING REGULATION
CHAMBER
EXISTING INTERCEPTOR
--- CITY LIMITS
LIMITS OF SERVICE AREA
OUTSIDE CITY LIMITS
DRAINAGE AREA
BOUNDARY
Y/v i.
Figure 4 -2 Saginaw regulator catchment areas.
-------
SCALE (theuiondi of r«tt)
O I 2 3
Sewoge pumping station
and treatment plant
Weiss St.
pumping station
EAST SIDE INTERCEPTOR
WEST SIDE INTERCEPTOR
Webhe,
pumping
station
Emerson St.
pumping station
• Hancock St.
pumping station
Figure 4.3General plan of interceptor sewer system.
-------
Because many of the sewers are below flood river stage,
the problem of collecting sewage involves stormwater pumping
during periods of high river level. Typically, flood stages can
exist for periods up to two weeks, during which time rainfall
producing runoff can occur. Flood stages of the Saginaw River
have all occurred during the months of March, April and May.
During flood river levels, storm flows will discharge over the
regulator chamber weirs into the intercepting system. Backwater
gates will prevent discharge of flood river water into the
sewerage system.
Flood pumping stations located at Webber, Emerson, and
Fourteenth Streets on the East Side, and Hancock and Weiss
Streets on the West Side, pump either from the interceptor system
or from tributary lines directly before the interceptor system.
Stormwater and flood pumping stations are of circular caisson
type construction. The station at Hancock Street has eight
electric-driven pumps, and the one at Weiss Street has three
electric-driven pumps. On the East Side the station at Webber
Street has three electric-driven pumps; the Emerson Street
Station has six gasoline engine-driven pumps; and the Fourteenth
Street Station has three electric-driven pumps. All pumps are
similar, each having a fixed capacity of 100 cfs, those at Webber
Street and Fourteenth Street operate at 15-ft head, and the
remainder at 28-ft head.
The interceptor system operates at hydraulic gradients
independent of the invert grade and has sufficient slope to
convey the stormwater laterally to the pumping stations. The
intercepting sewers thus serve the dual purpose of collecting
sewage and carrying storm flows during flood river levels. The
interceptor system consists of tunnel sewers ranging from 42 to
78 inches in diameter. The tunnels are approximately 40 feet
below ground level.
4.3 WWTP Details
The City of Saginaw operates a 32.7 mgd secondary WWTP
located on the east bank of the Saginaw River near the Saginaw-
Buena Vista line. The plant receives wastewatwer from the City of
Saginaw, portions of Saginaw, Spaulding and Bridgeport
Townships, and from a portion of Buena Vista Township including
the Saginaw Steering Gear complex. The City of Saginaw1s sewer
system conveys stormwater as well as municipal and industrial
wastewater. In the early 1970's, secondary treatment facilities
were added to the existing primary plant. By 1975 the secondary
facilities were operational and in 1976 phosphorous removal was
also provided.
406
-------
Wastewater enters the plant in a 72-inch interceptor
sewer. After screening and grit removal, the wastewater is
settled in four primary sedimentation tanks. Primary effluent
passes into the conventional activated sludge system where
ferrous sulfate or waste pickle liquor can be added for
phosphorus removal as necessary to meet effluent discharge
standards. Final effluent is chlorinated before discharge to the
Saginaw River.
The current NPDES permit for the plant requires that
monthly average BOD and suspended solids concentrations not
exceed 25 and 30 mg/Lf respectively. Effluent total phosphorous
concentrations must be less than 1 mg/L. In addition, the permit
calls for fecal coliform concentrations less than 200 per 100
ml, and an effluent pH between 6.5 and 9.0.
A review of plant operating records indicates that the
monthly average BOD and suspended solids concentrations are
consistently below 10-15 mg/L and thus in compliance with the
NPDES permit.
Prior to 1968 sewage discharging from the City of
Saginaw was given primary treatment with chlorination. Average
annual design rate was 32 cfs with a peak hourly capacity of 80
cfs. Wet well pumping capacity at the headworks totaled J.82 cfs.
Overflow weir settings at the regulators in the system were set
to dischage untreated sewage mixed with stormwater at rates
exceeding five times the dry weather flow. Regulator weir levels
have been adjusted several times over the years in an effort to
minimize the amount of untreated sewage.
The primary plant was then upgraded to secondary
treatment including biological activated sludge with phosphorous
removal. Although the modified plant is designed for a nominal
flow of 50 cfs and an estimated maximum flow of 128 cfs, the
secondary treatment unit operations are sized for about 160 cfs
discharge. All storm flows entering the WWTP in excess of 108
cfs are split at the grit chamber with bypass receiving only
chlorination. Currently, bypass beyond 108 cfs occurs at a
spillover weir such that increasing influent flow rates results
in simultaneous increased flow through the plant and increased
bypass. The average dry weather flow is about 32 cfs.
All flow beyond the grit chambers receive primary
treatment. There are four secondary aeration tanks following the
primary clarifiers. Normally two aeration basins are used for
dry weather flow and wet weather discharges up to about 84 cfs.
The two other aeration basins are used as storage for wet weather
discharges above 84 cfs. If these basins are filled, flow
through conditions result. The storage contents after an event
4.7
-------
(or when influent rate significantly decreases) of these two
tanks containing primary treated wastes (plus some additional
detention) then receive full primary/secondary treatment as these
volumes are pumped back to the headworks. Any flows beyond 84
cfs and in excess of the two aeration tank storage volume will
receive primary treatment, limited aeration with phosphorous
removal treatment (if necessary), secondary clarification and
disinfection.
4.4 Regulator Chambers
The regulator chambers of interest are those points
controlling discharge to the interceptor or to the river, from
each of the tributary catchment areas. The simulation model
described in Chapter 6 incorporates the operation of each
regulator in the system. Physical operational details and
dimensions were required such as orifice underflow openings,
weir heights and float operations. Chamber measurements were
compared with details given in the system plans, and missing
values filled-in from the plans. If discrepencies occurred, the
EDP field measured values were used in the analysis of regulator
operation. Regulator details and modification details are
presented in Chapter 7.
4.5 Hancock Street Storage/Treatment Facility
In 1977 the Hancock Street Flood Pumping Station was
modified to include a 3.6 MG storage/treatment facility. The
existing pumping station was upgraded to include electric-driven
pumps. A multi-purpose underground storage/treatment facility
with above ground municipal parking was constructed. In-line
storage potential of the combined sewers in the Hancock Street
area was increased by modifying the existing static regulators in
the system. Modifications to the regulators included replacing
the tide gates at the outfall with motor-operated sluice gates to
increase the maximum storage capacity of the system. Before
modification, only dry-weather flows and some wet-weather flows
were diverted to the interceptor during normal river stages; now,
significant flows are detained and diverted to the interceptor.
Over the last several years severe operational
difficulties during intense rainstorms have arisen due to the
motor-operated sluice gates in the Hancock Street catchment area.
The sluice gates open or close in a finite period of time. If
the gates do not open to permit rapidly developing peak flows to
overflow, then severe surcharge problems will result. Replacement
of these gates with fixed-opening weir structures was included in
4.8
-------
the construction project completed as part of the partial BMP
plan.
During the storm events, combined flows diverted to the
interceptor by the regulators activate the Hancock Street pumping
station as the interceptor flow level increases. Sluice gates
between the interceptor and the pumping station wet well open
automatically and pumping is sequentially controlled by sensing
the wet well water elevations. All flows to the
storage/treatment basins are pumped. During extreme river
flooding, the system will revert back to operation as a flood
control pumping station, with flows to the basin being diverted
to the river once the system has been filled to capacity.
Combined flows pumped to the Hancock Street storage/
treatment facilities sequentially fill a series of paired basins.
The facilities operate under two types of storm flow conditions:
1. For certain flow volume storm events, the flow
will be captured and totally stored, with
subsequent release to the interceptor as
capacity becomes available.
2. For storm events producing flow that exceeds
the basin storage capacity, the system will
store and treat the combined flow by
sedimentation. The facility is designed to
disinfect the overflow before discharge to the
river.
4.6 Dry Weather Flow Characteristics
Formulation of the basis of design for CSO control
facilities required input of data, with regard to the quality and
quantity of dry weather flows, so that network models (See
Chapter 6) could be calibrated. This section summarizes efforts
to determine the quantity of dry weather flows at various points
in the City of Saginaw system. Dry weather flow characteristics
at the Saginaw WWTP are reviewed in section 4.6.1. Results of EDP
measurement program are given in section 4.6.2. Estimates of dry
weather flows per catchment area are given in section 4.6.3.
4.6.1 WWTP Dry Weather Flows
Dry weather flows were investigated at the treatment
plant and throughout the system to establish a basis for
simulating catchment area dry weather flows. The simulation
program described in Chapter 6 required estimates of dry weather
4.9
-------
sewage contributions per catchment area for spring infiltration
(non-rainfall) conditions as well as for non-spring, non-rainfall
periods. These two estimates were necessary since the simulation
model was geared to investigate rainfall/runoff conditions over a
calendar year. The WWTP flow analysis was conducted for the
period of 1978-1979. Flows at the plant were separated between
dry days and wet days, and averaged (Table 4-1). The period was
further divided between spring (April-June) and the other nine
months to account for high groundwater infiltration conditions.
The average dry day, non-spring flow was taken as the long-term
dry weather flow average for the year including industrial
contributions. The difference between the dry day non-spring
average and the dry day spring average, 5.4 cfs, was considered a
rough estimate of spring infiltration.
4.6.2 EDP Field Discharge Measurements
During October of 1979, EDP conducted a field
investigation, including sewer system flow measurements. Flows
were measured both for rain conditions caused by a small storm
that occurred during the investigation period and for dry weather
conditions throughout the system. Dry weather flows were measured
at a number of the more important points throughout the system,
with many of the measurements repeated at different times of the
day for verification. The measured values were used to estimate
flows at points where measurements were lacking to develop a
complete distribution of dry weather flows throughout the system.
Yield factors for known areas were calculated using the measured
flow values and the corresponding catchment areas. For unknown
neighboring areas similar land use yield factors were used to
generate dry weather flow predictions based on catchment areas.
All measured dry weather flows were checked using this same
procedure of comparing similar or neighboring areas' yield
factors.
Accumulations of both measured and predicted values in
the interceptor were compared to measured values in the
interceptor to check for closure of the various flow values.
These results are presented in Table 4.2. From the field
inspection program two areas of possible significant industrial
contribution were identified, the foundry in the Fraser Street
area on the west Side, and the lower industrialized area just
south of the WWTP on the East Side. The differences between
downstream flow measurements and upstream flow predictions and
measurements were used to estimate the industrial contributions
at these two points. A large industrial contribution of
approximately 8.2 cfs was noted for the West Side Fraser area .
A smaller contribution of 4.3 cfs was calculated for the East
Side industrial area. Using the above industrial flow
4010
-------
TABLE 4.1
WWTP FLOWS, 1978-1979
Seasonal Periods
Flow
Daily Average (cfs)
All Events Uet Days Dry Days
Spring
(April-June)
46.9
85.6*
65.5
83.8*
42.8
86.2*
Non-Spring
(Jan-March
& July-Dec)
40.4
86.8*
56.0
86.5*
37.4
88.3*
All Seasons
42.2
86.4*
59.8
85.5*
39.4
87.8*
* BOD Removals
4.11
-------
TABLE 4.2 SYSTEM DISTRIBUTION OF DRY WEATHER FLOW (cfs)
Meas. Pre- Accum-
Flow dieted ulative
Weber (
Birch (
Holland (
Atwater I
McCoskry (
Hoi den (
Emerson (
Hoyt (
Thompson (
Millard (
Janes (
Federal (
Genesee (
Johnson <
Fitzhugh (
Carlisle <
) 1.72
) 1.93
) 0.80
| 3.50 3.65
) 1.01
) 0.28
) 0.46
) 0.06
> 1.33
> 0.12
) 0.38
) 0.44
) 0.58
) 0.08
) 0.31
) 0.72
Washingtonli 9.40 9.56
First <
C) 0.37
Meas. Pre- Accum-
cfs dieted ulative
0.91 <
8.30 t
9.20 9.20 <
0.24 <
C
(
1.41 (
(
12.60 11.4 |j
.05 (
.31 <
.24 (
C
.24 (
.45 C
) Fraser
j Industrial
) Dearborn
llee
) Mackinaw
) Van Buren
)Cass
) Adams
> Court
] Hancock
) Ames
) Hayes
)Throop
)Miller
) Remington
) Genesee
.14 Cronk
12.70 1
15.9CW
3.2
1 Carroll ton
Weiss
L Weiss
Fifth 25.50
16th Street 2.60
14th Street
Industrial
25.50
0.41
4.30
-e-
•e-
WWTP
32.5
Pump Stations
Points on Interceptor
Regulator Points
Before Interceptor
Industrial
4.12
-------
estimates, a reasonable flow balance was achieved throughout the
system. Measured flow values at various points in the interceptor
and at the WWTP closely matched the accumulated dry weather and
industrial contributions developed through the analysis of field
inspection data.
4.6.3 Simulation Model Dry Weather Flows
As the field inspection program occurred in October,
1979 the dry weather flow analysis presented in Table 4.2
represents lower than average flow conditions typical of the
fall. These results (excluding the industrial contribution) were
scaled upwards to match the long-term average dry weather flow as
calculated at the WWTP (See Table 4.1). The ratio of WWTP long-
term average flow (non-spring) to the October, 1979 field
program results (See Table 4.1) were used to scale all the dry
weather flow values throughout the system. The same ratio was
used with the spring WWTP flow average to complete the spring-
time distribution. The results are summarized in Table 4.3. The
non-spring and spring dry weather sewage estimates per catchment
area were then used as inputs in the simulation model.
4.7 Wet Weather Flow Considerations
Wet weather flows in combined sewers consist of dry
weather (sanitary) flow, infiltration, and storm-induced runoff.
The storm-induced runoff includes flows from building
connections, such as roof leaders; cellar, yard and foundation
drains; catch basins; storm sewers; and surface runoff through
manholes. This runoff is collected and transported to trunk
sewers that convey flow to various diversion points. The
diversion points regulate flow entering interceptor conduits,
which carry the flow to treatment facilities. During a storm
event, that portion of the flow which cannot enter the
interceptor, overflows at the regulator connections to the
Saginaw River.
Various data sources and analyses used to assemble the
wet weather predictive features of the simulation model are
described in this section. A discussion of rainfall analysis is
presented in Section 4.7.1. Details of the 31 catchment areas
used in the modeling analysis are presented in Section 4.7.2.
Runoff parameters for the catchment areas are presented in
Section 4.7.3. Details of the stormwater pumping stations are
discussed in Section 4.7.4.
4013
-------
TABLE 4.3 SIMULATION MODEL DRY WEATHER FLOWS (cfs)
Oct.
Field
Analy.
Weber (
Birch (
Holland (
McCoskry <
Hoi den (
Emerson (
Emerson 0
Hoyt (
Thompson (
Mi Hard (
Janes <
Federal (
Genesee (
Johnson <
Fitzhugh (
Carlisle (
First (
) 1.72
) 1.93
) 0.08
) 1.01
) 0.28
) 0.46
]
) 0.06
) 1.33
) 0.12
) 0.38
) 0.44
) 0.58
) 0.08
) 0.31
) 0.72
) 0.37
Model
Non-
Spring Spring
2.12
2.37
0.10
1.24
0.34
0.57.
0.07
1.64
(X.15-
0.47-
0.54
0,7-1,
O.-IO*
0.38
0.86
0.46
2.59
2.91
0.12
1.53
0.42
0.69
0.09
2.01
0.18
0.57
0.66
0.86
0.12
0.47
1.05
0.56
Oct.
Field
Analy.
0.91
8.20
0
0.24
0
0
1.41
0.03
0.05
0.27
0.21
0.03
0.21
0.39
0.12
3.20
Non-
Spring
1.12
8.20
0
0.29
0
0
1.73
0.04
0.06
0.33
0.26
0.03
0.26
0.48
0.15
3.94
Model
Spring
1.20 <
8.20 (
0 (
0.36 (
0 (
0 (
2.13 (
0.05 (
(i
0.07 (
0.41 (
0.32 (
0.04 (
0.32 (
0.59 (
0.18 <
r
I
4.83 (
) Fraser
) Industrial
) Dearborn
) Mackinaw
) Van Buren
) Cass
) Adams
) Court
] Hancock
) Ames
) Hayes
) Throop
) Miller
) Remington
) Genesee
) Cronk
] Weiss
) Weiss
16th Street 2.60
14th Street 0.41
Industrial 4.30
WWTP 32.5
WWTP
(•) Pump Stations
O Regulators
4.14
-------
4.7.1 Rainfall Analysis
Rainfall records were required as data input for the
computer simulation work. A ten year period (1969-1978) of
hourly recorded rainfall records at a number of stations in
proximity to Saginaw were acquired from the National Weather
Service. Daily rainfall records recorded at the Saginaw WWTP and
the Tri-City airport (near Saginaw) were also acquired and
examined in conjunction with the hourly analysis. Hourly
rainfall information are collected in Saginaw.
Pour stations recording hourly rainfall values were
considered including Vassar - 20 miles east of Saginaw; Sebewaing
and Beaverton - over 30 miles northwest and northeast,
respectively; and Stanton - 50 miles west of Saginaw. Rainfall
data collected at Vassar was selected for use in this study due
to its proximity to Saginaw, and due to the lack of any major
geographical features that may render Saginaw rain patterns
substantially dissimilar from Vassar rain patterns. Sebewaing
was not selected due to its location on Saginaw Bay and the
likelihood of local weather anomalies (discussed further below).
Stanton and Beaverton were not considered since their distances
from Saginaw are greater than Vassar.
Standard procedures were followed to analyze the ten
year period storm intensities and frequencies, and for total
annual rainfall. A scatter diagram was developed to compare
Saginaw rainfall as recorded daily at the WWTP to the Vassar
rainfall records (See Figure 4.4). Distinct events were discerned
from the Saginaw records using a decision rule of at least twenty
four hours of low or no precipitation between major rain days.
Rainfall was totalled for the resulting periods and compared to
the totals for the corresponding periods in the Vassar records.
All individual events for a period between 1975 and 1978 were
plotted. Points lying further from the 45 degree equivalence line
were noted to be primarily spring events when local variations in
precipitation are more likely. The scatter diagram shown in
Figure 4.4 suggests a reasonably good comparison between the two
rain gages. Similarity in annual rainfall totals given in Table
4.4 for Vassar, Sebewaing and the Tri-City Airport in Saginaw
further support this conclusion from the scatter diagram.
Since the prior CSO management study (1) in the Saginaw
area had used rainfall records at Sebewaing as the basis for
modeling Saginaw rainfall, Sebewaing rainfall characteristics
were compared to Vassar and Tri-City Airport rainfall
characteristics. The cumulative rainfall of the one-year design
storm used to size the seven detention basins in the prior study
equalled 1.9 inches of rainfall.
4.15
-------
T
1.6
I 1 I
) 1.2
Vassar (rainfall in inches)
T
2.0
Figure 4-4 Comparison of storm events-
Saginaw vs. Vassar -1975 to 1978.
T
Z4
4.16
-------
TABLE 4.4
COMPARISON OF ANNUAL RAINFALL TOTALS
YEAR*
1956 - 1965
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
ANNUAL
Vassar
N.A.
22.12
34.41
22.09*
34.44
28.58
28.00
36.00
35.50
33.00
21.00 +
RAINFALL (INCHES)
Sebewaing
25.35**
23.09
26.61
17.54***
24.06
25.11
25.90
25.92
22.18
26.20
16.28 +
Tri-City Airport
N.A.
20.14
N.A.
N.A.
N.A.
N.A.
N.A
N.A.
30.05
29.33
20.97 +
* Calendar year
** Computed , average per year
*** Missing November
+ Missing December
N.A. - not available
4.17
-------
Annual rainfall totals given in Table 4.4 suggest that
Sebewaing (for a different ten year period) had received less
total rainfall than Saginaw and Vassar during the ten year period
analyzed in this report. A frequency plot comparison shown in
Figure 4.5 of Vassar rainfall (1969-1978) to the plots prepared
for Sebewaing (1956-1965) in the previous study (1) and for
Sebewaing (1969 - 1977) in this study verify the differences in
rainfall exhibited by the annual results given in Table 4.4.
It is interesting to note that the one-year design
storm of 1.9 inches used in the design of the Hancock Street
facility derived from an analysis of Sebewaing data (1956-1965).
The one-year design storm for the next ten year period at
Sebewaing equals 1.45 inches. The rainfall plot at Vassar indi-
cated that the storm with a recurrence interval of one year has a
cumulative volume of approximately two inches. Using a strict
definition of 6 dry hours between events, an average of 67 events
per- year was calculated for the Vassar Station, with an average
of 0 .3 inches per event. The average antecedent dry period
between rain events at Vassar was estimated to be four days.
A full year rainfall period was used in the simulation
modeling efforts. A full year of overflow events would provide a
better assessment of overall CSO control efficiencies since a
variety of different storm intensities including low intensity
but high frequency events would be included. The year of 1977 at
Vassar was selected for the model simulation runs. The annual
total rainfall was slightly above average. It had numerous small
events, yet also contained several events in excess of the one
year storm volume of 1.9 inches used in the prior study, and the
one-year recurrence storm for the Vassar Station. The frequency
plot for 1977 is also shown in Figure 4.5.
4.7.2 Catchment Areas
Catchment areas were outlined for each of 31 regulators
but one minor area was eliminated and was added to a larger
tributary area (there are a total of 34 regulators) while two
other areas have alternative overflow points depending on river
conditions and potential combined sewer overflow points. These
locations and associated catchment areas are summarized in
schematic form in Table 4.5. The areas were outlined on the City
sewer map. Divisions between catchment areas were determined
primarily by review of the sewer system plans. EDP inspected a
number of points along catchment boundaries for further clarity.
These catchment areas are roughly depicted on Figure 4.2.
It was noted in delineating the catchment areas that the
older sewerage system had been upgraded by a number of relief
4.18
-------
12 -
10 -
8 -
I
6 -
4 -
2 -
VOSMT Station
1969-1978
1969-1977
Sebewaing Station
1956-1965
Vossor Station 1977
0.0
I
J.O
I
2.0
1
3.0
Accumulated Rainfall per event (inches)
Figure 4.5 Annual rainfall (accumulated) cumulative frequency plot.
-------
TABLE 4.5
CATCHMENT AREA /RUNOFF COEFFICIENTS
Catchment %
Area (ac) Imp.
Catchment
Area (ac)
Imp.
Webber (
Webber G
Birch (
Holland (
McCoskry (
Hoi den (
Emerson (
Emerson (j
Hoyt (
Thompson (
Mi Hard (
Janes (
Federal (
Genesee (
Johnson (
Fitzhugh (
Carlisle (
First (
)
] 1020
>
) 150
) 550
) 70
) 30
J
) 43
) 290
) 30
) 90
) 80
) 36
) 60
) 130
) 90
) 190
25
10
40
70
85
80
35
90
40
50
90
80
25
30
15
0.34
0.23
0.45
0.68
0.79
0.75
0.41
0.83
0.45
0.53
0.83
0.75
0.34
0.38
0.26
440
10
470
45
1030
45
160
240
20
170
470
380
2100
35
6C
60
95
40
95
50
90
90
70
30
30
20
0.41 (
0.60 (
0.60 <
0.86<
((
0.45 (
(
0.86 0
(
0.53 (
0.83(
0.83 (
0.68 (
0.38 <
0.38<
r
) Fraser
) Dearborn
) Mackinaw
) Van Buren
) Cass
) Adams
) Court
] Hancock
) Ames
) Hayes
) Throop
) Miller
) Remington
) Genesee
) Cronk
Weiss
ki r\
TSu w
0.30 Weiss
14th Street
16th Street
Z = Runoff coefficient
® Pump Stations
O Regulators
4.20
-------
systems on both sides of the river meant to provide additional
capacity during storm events. The result was a complex network of
pipes and overlapping stormwater catchment areas.
A number of bifurcation points where new relief sewers
connect into older systems caused uncertainty in how flow divides
at these points. An EDP field inspection program noted dry
weather flow directions and also checked diversion weirs not
noted on the sewer plans. A hydraulic analysis was performed to
estimate the relative flows in different directions at division
points during high flow events. Dynamics were considered if
obvious, otherwise flow was apportioned to the relevant catchment
areas using a Manning's equation formulation. Fixed flow factors
were computed assuming half-full flow conditions in the upstream
pipe and the plan and profile slopes of the two downstream
receiving conduits. This approach was deemed suitable for the
purposes of dividing average hourly discharge in the simulation
model.
Bifurcation estimates were prepared for the West Side
intersection points at Brockway and Thurman, Adams and Congress,
Houghton and Clinton, State and Carolina, Union and Woodbridge,
State and Woodbridge/ Superior and Vermont, W. Remington and
Harrison, State and McEwen; and on the East Side at Remington and
Alger, Holland and Good, Hoyt and Sheridan, Weadock and Johnson,
and Seventh and Johnson. The results were used to divide the
shared drainage areas between the competing regulators.
There were also a few separated sewer areas not included
in the network, particularly the area south of Webber Street and
the drainage system for the interstate highway. Dry weather flow
from all separated areas were included in the modeling efforts.
Runoff from all separated areas draining directly to the river
was not included in the modeling effort.
4.7.3 Runoff Coefficients
Estimates of imperviousness and calculated runoff
coefficients for each of the catchment areas are summarized in
Table 4.5. Estimates of imperviousness were prepared from aerial
photographs of Saginaw. Representative sections in a few of the
major drainage areas were analyzed by comparing the areas
occupied by housing and streets to open spaces, to arrive at
estimates for percent imperviousness. These estimates were
compared to standard percent imperviousness factors for different
types of land use to check for reasonableness. The 31 different
drainage areas were heuristically scaled to the major areas
analyzed in detail, yielding percent imperviousness estimates for
4.21
-------
each catchment area in the system. The total system average was
34% impervlousness.
Actual runoff coefficients were then calculated on the
basis of the percent imperviousness calculations. Standard
procedures presented in simplified SWMM(2) were computed using
equation 1:
Z = 0.15 + 0.75 x I (1)
where Z is the runoff coefficient representing the fraction of
rain that appears as runoff, and I is the percent imperviousness
of the catchment area (in fractionalized form).
4.7.4 Stormwater Pumping Stations
Of particular interest to the storm overflow analysis
are the five major pumping stations designed to pump flood waters
and/or combined sewer overflows to the river. The Hancock Street
Station on the West Side is presently connected to a 3.6 MG
storage basin, with eight - 100 cfs pumps available. Further
downstream of Hancock Street Station is the Weiss Street Station
with three - 100 cfs pumps. On the East Side the Emerson Street
Station has eight - 100 cfs pumps. The Emerson Street Station
along with Hancock and Weiss are the only stations that can pump
water directly from the interceptor with flows depending on the
heights of weirs separating the interceptor from the pump station
wet wells. The two other pump stations, Webber and Fourteenth
Streets both have gravity outlets to the river, and only operate
when river elevations are high enough to prevent the backwater
gates at the gravity outlets from discharging the high runoffs.
Both Webber and Fourteenth Street Stations have three - 100 cfs
pumps each.
The amount of time each pump in the system operated was
periodically recorded, and this information was used to analyze
the operation of the five pumping stations. It was noted that the
Weiss and Hancock Street Stations are frequently used with
Webber and Fourteenth Street Stations operating much less
frequently, and Emerson Street Station (manual start-up
operation) only rarely . This comparison is not surprising
considering the hydraulic bottleneck at the West Side river
crossing, (see Chapter 6) the relatively high weir height at the
Emerson Street Station above the East Side interceptor and the
potential at the Webber and Fourteenth Street Stations for
gravity discharges short-circuiting these pump stations.
Curves were developed by EDP for the Weiss Street and
Hancock Street Stations relating total volume pumped to the
4.22
-------
amount of rainfall per event. Distinct rain events were
associated with the amount pumped at these two overflow points by
comparing pump usage records to rains recorded at the WWTP. It
was noted, as expected, that both volume pumped and the number of
pumps used increased with increasing amounts of rain. Spring
events resulted in higher volumes pumped due to infiltration and
spring melts. In addition to being a useful indication of system
stress points, the pumping station analyses were used as a rough
check of the simulaton model. Data plots of Weiss and Hancock
Street Stations' pumping operations, as functions of total
rainfall per event, are presented with the simulation model's
predicted values in Chapter 6.
4.23
-------
CHAPTER 5
SCREENING OF COMBINED SEWER CONTROLS
5.1 Foreword
The development of realistic CSO abatement concepts
for Saginaw included determination of the degree of abatement
required, assessment of available technologies and identification
of realistic options based on that technology assessment. In
this chapter available CSO alternatives ranging from inexpensive
system modification to total capture and treatment of overflows
are reviewed. The roost promising and feasible abatement options
are selected in this Chapter and are further described in
Chapter 6.
The three general approaches listed below briefly
describe the state of the art of CSO abatement:
(1) sewage system structural modifications to improve
system operations and to enhance hydraulic conveyance capacity
together with improved sewer system flow controllers at
regulation points to enhance operational ease in flow splitting
and/or to create maintenace free in-line transient detentive
storage; (2) pollutant source control and upstream stormwater
management practices, and; (3) combinations of major off-line
storage and treatment facilities.
Existing system modifications are reviewed in section
5.2. Source control practices are reviewed in section 5.3.
Storage and treatment options are discussed in section 5.4.
Selection of feasible practical and realistic alternatives for
further evaluation is discussed in section 5.5.
5.2 Modifications to Existing System
Reduction of overflow discharges can be achieved by a
wide range of modifications from low cost, minimal structural
procedures involving maintenance improvements to structural
intensive sewer separation. The following methods were
investigated:
Regulator Improvements - Utilization of new vortex
valve technology to enhance the capability of existing regulators
to efficiently pass "first flush" to WWTP in a relatively
maintenance-free fashion and to effectively control underflows to
the interceptor systems at maximum storm conditions. Transient
in-line system storage configurations can be developed where
-------
applicable, at the regulating chambers by modification of
chamber's internal weirs and inclusion of positive discharge
control devices. A discussion of vortex valve flow throttling
equipment is presented in section 5.2.1.
Sewer §ep_arati.on ~ Tne separation of storm and sanitary
sewers significantly reduces combined sewer overflows. Sanitary
flows are treated prior to discharge to receiving waters. Storm
runoff pollutants discharge directly to receiving waters unless
additional treatment is provided. To achieve total separation,
the difficult task of disconnecting roof leaders is necessary.
The principal disadvantage of sewer separation is its tremendous
cost and time requirement.
jLzjatj.on °J[ Existing E££l!lti§s - Unused
and/or increased capacity for conveyance/storage within existing
sewerage system can often be realized at little cost. Increasing
and/or improving hydraulic capacity at critical control points,
i.e., pumping stations, constrictions, etc., are classical
examples .
I^zl-iH6. Storage - System control using in-line storage
represent promising alternatives in areas where conduits are
large, deep, and flat (i.e., backwater impoundments become
feasible) and interceptor capacity is high. Costs for storage
capacity gained in this manner range from 10 to 50 percent of the
cost of off-line facilities. Because system controls are
directed toward maximum utilization of existing facilities, they
rank among the first of alternatives to be considered.
5.2.1 Vortex Va _lve Throttling P.!:Zi£e_s-
In general , the purpose of flow regulating devices
is to control discharge from a combined sewer into an
intercepting pipe leading to the WWTP. In practice, three
classes of devices are used: static, dynamic (semi-automatic),
and dymanic ( fully-automatic) ( 1 ).
The schematic of a dynamic (semi-automatic) device used
in regulator chambers in Saginaw is depicted in Figure 5.1.
During normal dry weather flow conditions, the float is in the
down position permitting maximal aperature opening on the orifice
discharge leading to the interceptor. During a wet weather
event, the flow level within the combined sewer rises and flow
enters through the telltail opening into the float chamber. As
5.2
-------
DIVERSION
wcm
Figure 5.1 Schematic of Typical Dynamic(Semi-Automatic)
Combined Sewer Mechanical Float-operated
Flow Controller
5.3
-------
the level of water in the chamber increases, the float rises, and
through mechanical connections, the moveable shutter lowers, thus
continually decreasing the orifice aperature. As the orifice
aperature decreases with increasing head during a storm event,
the resulting flow to the interceptor will be throttled to pre-
determined limits. Mechanical float-operated systems of this type
were state-of-the-art technology in the 40"s and 50's and
thousands were installed throughout the U.S. and Canada.
Regulation is controlled by movements of the float. In
the larger sizes, the float diameter may be as much as 5 feet.
This requires a large size floatwell which may trap grit that
creates a maintenance problem. Accumulation of floating material
on the float may cause malfunctioning of the system. Since the
entire system is in fine balance, proper operation requires at
least biweekly maintenance (1). Without proper maintenance the
shutter can "stick" and "freeze-up" resulting in an unknown
aperature opening and hence, unknown discharge. Frequently the
shutter head "sticks" in a down position after a storm event due
to its inertial and must be released by physically "kicking" or
jarrying the head. An additional problem arises when the
devices must operate on high head differentials. As the shutter
opening decreases, the risk of cloggage increases. Operational
problems with this type of device needs no documentation.
Justification ^ Vortex Valve Technology
Over the last several decades significant improvements
in sewerage system control have occurred in the USA, Germany and
Scandinavia. It has been recognized that a further improvement
of the efficiency of WWTP will, when viewed in overall terms,
have relatively little effect as long as a large proportion of
the pollutants fails to reach the WWTP during wet weather. This
applies particularly to combined sewerage schemes with numerous
storm overflows.
An improvement of the efficiency of the collecting
system is possible, by installing additional reservoirs with
heavily throttled outflows in the the form of stormwater
detention reservoirs, storm water overflow detention/retention
tanks or through the use of in-system transient storage
configurations. This type of control strategy, however, makes
discharge control from such collecting system storage
configuration, a new and central problem.
Modern CSO control philosophies focus on the "first-
flush" to separate the dirtier water from the less polluted.
This can be done easily and reliably the shorter the combined
passages of foul water and storm water outflows are. This means
504
-------
that collection system storage configurations will have to be
present in greater numbers and will have to be decentrally
situated. It follows then that these units may be infrequently
serviced, but nevertheless, they must operate reliably.
The sophisticated methods of urban hydrology employing
mathematical models to accurately estimate required storage
volumes lose this effectiveness if the flow control element fails
to maintain the desired flow. The accuracy and reliability of
conventional type throttles as described above are not reliable
nor are they accurate (2). Table 5.1 summarizes in a general
sense characteristics encountered and design parameters for an
ideal remote type sewerage system flow controller. The vortex
valve technology satisfies these requirements.
Historical Background of Vortex Valve Technology
The roots of vortex valve technology date back many
years. Around 1930 a non-return valve or vortex diode was
invented in Germany in order to reduce the danger of uncontrolled
blow-off of hot steam in the case of pipe fractures. This
invention was left without any practical application until the
sixties. It was then re-discovered and was modified and used for
control functions in which maximum reliability was required, such
as the control of rocket motors and emergency cooling circuits
for nuclear power stations. In Germany so-called low-pressure
vortex amplifiers have been developed since about 1970 for
purposes of hydraulic engineering (3). The first practical
applications began in 1976 (4). In Germany there are about 1000
vortex devices of different types and size in operation. A
patent was applied for by H. Brombach in USA and was received.
At the same time, independent experiments were conducted
in Scandinavia with vertically arranged "Hydro-Brakes." These
were tested as inlet throttles in catch basins. Later conical
in-line types were developed. Hydro-Brakes have their origin in
this branch of development. There are several thousand such
devices in operation in North America, mostly the catchbasin
throttle type. A patent was applied for in USA by J. M.
Johannessen and was received.
Simplified Justification fif Vortex Flow Controllers
Vortex devices work exclusively with flow effects.
There are no moving parts and there is no external energy supply.
The flow effects are three-dimensional and determined by fluid
friction. To date, there is no satisfactory quantitative
505
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TABLE 5.1
Conditions and Demands for an Ideal
Collecting System Flow Controller (2)
Conditions:
Requirements
decentral and multiple
installation
simple and easy to under-
stand function
rare supervision/ installed
in wet and dark
simple maintanencer no
special tools or meters
required
reliability
no moving parts, no
external energy supply,
self-cleaning
small flows
large cross sectional
openings, no backwater
in dry weather
long-term operation
durability, corrosion
protection
refined hydrology
accuracy, stable
characteristics
changes in catchment
adjustable flow rates
5.6
-------
description of the flow processes by means of a mathematical
model.
The operating principles of this technology can be
demonstrated considering the simplified model shown in Figure
5.2. An infinitely large container is connected via a channel
(C) to a cylindrical vessel (V) . The vessel (V) has a
centralized hole at the bottom of diameter (Do) or of area (Ao).
If the pipe (C) is routed so that the water enters the vessel (V)
perfectly radially, e.g. via a ring pipe with small radial
nozzles, (see Figure 5.2A), the result is a sink flow in the
direction of the outlet orifice. The outflow jet is constricted
so that the flow rate becomes
Qr = S0 mr V2gh
If the outlet is of sharp-edged design (orifice plate), the loss
coefficient is approximatelymr = .6.
Figure 5.2B shows the same setup, but the inlet nozzles
are arranged tangentially. The difference is striking. There is
a free vortex generated under these conditions. The nearer a
water particle comes to the center line of the vessel (V), the
greater its peripheral velocity becomes. The centrifugal force
becomes so great that a vortex core is formed through the outlet
hole and allows the water to flow out in the form of a hollow
jet. This effect can be observed in a bath tub vortex. The flow
obeys the same function
Qt = AQ mt
but the flow coefficient drops to approximately,mt =0.15.
A particularly remarkable feature of this vortex flow is
that each disturbance of the flow, e.g. due to entrained solids
or air pockets, leads to a weakening of the centrifugal force and
thus to an increase of the flow. This unusual hydrualic
behavior, also known as the self-cleaning effect, has obvious
advantages in flow control of waste streams with solids and
debris.
Although the two experiments in Figure 5.2 differ only
slightly in the arrangement of the inlet nozzles, the flow is
very different, namely
VQr =
5.7
-------
PHYSICAL JUSTIFICATION
FOR VORTEX VALVES
A.
,1
-.I- Do
Qr
B.
Do
Qt
A,
O
o
B,
A, RADIAL SINK FLOW
B, FREE VORTEX FLOW
Figure 502 Simple Model of Vortex Valve Representation
-------
The flow rate is reduced to about 1/4 as a result of the
tangential supply of water. Expressed differently, it is
possible under vortex flow conditions to obtain the same flow as
a simple orifice, but the area (Ao) of the outlet nozzle will be
4 times the size of the comparable simple orifice. If it were
possible to switch automatically between the two flow states, the
result would be flow valves whose flow rate is adjustable in the
ratio of 1:4.
Vortex flow controllers can be designed to uniquely
combine both types of orifice and vortex flow principles into a
single stage/discharge characteristic. Operation descriptions of
how this combination of flow effects occurs are provided below
for vortex valve equipment of Scandinavian origin and then for
vortex valve equipment developed in Germany which are relevent
for combined sewer regulator applications.
Conical Type Vortex Valves - Scandinavian Origin
In 1980 J.M. Johannssen of Denmark tested and developed
an in-line vortex control device for in-line applications (inlet
and outlet invert elevations are the same). The conical device
shown in Figure 5.3A can be described as follows. It includes a
truncated cone section, a circular plate at the inlet end, a
cylindrical inlet, an oval plate at the outlet end and a
cylindrical outlet.
The cylindrical inlet section consists of a formed
circular section which lies in a level horizontal position along
its longitudinal axis and is diagonally cut such that the inlet
intersects the cone body at a 45 degree angle. The inlet plate
is circular and is solidly welded to the large end of the
truncated cone and includes an oval orifice located at the bottom
of the plate. The orifice exactly matches the diagonally cut
surface of the inlet segment. The inlet segment is solidly
welded to the inlet plate at the inlet plate orifice. The
truncated cone section acts as the main body of the device and
provides structural rigidity. An oval-shaped end plate is
solidly welded to the small end of the truncated cone segment.
Integral to the end plate is a circular orifice at the base of
the oval end plate sized to exactly match the truncated cone
small end. In the installed position the oval end plate is
parallel to the circular end plate on the inlet end. The
cylindrical outlet is a roll formed pipe solidly welded to the
oval end plate, and is diagonally cut at the same angle as the
truncated cone such that the outlet .tube exactly matches the oval
end plate. The oval end plate and cylindrical outlet are sized
as necessary to match field conditions.
5,9
-------
Cylindrical outlet segments normally incorporate rubber
"0" ring stops for standard push-fit installation. Slip flange
ends, victaulic coupling ends, clamps or other specialized end
connections are constructed as required for special connections.
J. M. Johannessen had earlier developed in 1977 a
proto-type conical device with an inlet slot cut along the
longnitudal axis of a truncated cone with an internal orifice
located at the outlet back plate. Incoming flow would impact the
back plate and then enter the device through the inlet slot. A
family of stage discharge curves is generated by altering the
internal orifice dimension. The large end of the truncated cone
is a fixed multiple of the internal orifice. He was not
satisfied with the performance of this prototype unit for the
following reasons: a) the flow-through pattern was not
satisfactory; b) the vortex braking effect was not satisfactory;
c) the rated flow capacity of the unit was dependent on the
mounting position of the inlet slot (any deviation from absolute
vertical alignment would alter the flow characteristic; and, d)
the structural rigidity of the cone was greatly reduced due to
the inlet slot along the cone length (typical hydraulic surges,
i.e., vibrations may cause large units to collapse) (5). It was
for these reasons that he developed the conical type shown above
in Figure 5.3.A.
A typical stage/discharge characteristic for the
conical device developed by J.M. Jchannessen is shown in Figure
5.3.B and is described as follows: As the unit begins to fill
under increasing head, it will discharge similar to a sharp-edged
orifice (see segment 0-1, Figure 5.3.B) With greater head, air
will become trapped in the upper portion of the chamber and a
special characteristic will be formed as the discharge increases
along segments 1-2-3. Finally, when the head level increases
above the chamber, full braking effect is achieved along segment
3-4, (Figure 5.3.B). As the need for braking decreases (falling
head), discharge follows sements 4-3-5, (Figure 5.3.B and then
drains as a sharp-edged orifice. This sudden increase in
discharge provides a desireable flushing effect on the unit as to
maintain self-cleaning conditions.
Families of stage/discharge curves for this conical
configuration can be generated by simultaneously altering the
dimensions of the truncated cone large end and the internal
orifice located at the truncated cone small end. For example,
increasing the dimensions of the truncated cone large end while
keeping the internal orifice fixed increases the vortex braking
effect. Thus, Johannessen greatly increased design flexibility
with the improved conical version. The opening of the inlet
section is either equal to or greater than the internal orifice.
The outlet discharge pipe is always equal to or larger than the
5olO
-------
A.
AFI MC Series
Inlet and outlet at same
elevation
Figure
discharge
Figure 5.3 Johannessen Type Conical Vortex Valve Flow
Control 1er
50ll
-------
internal orifice. The commercial technology discharge range for
the Johnannessen conical vortex valve is 0.3 cfs to about 20 cfs.
The coefficient of discharge in the vortex braking
for Johannessen 's device ranges from 0.18 up to 0.37, depending
upon the particular geometry configuration. These coefficients
can be favorably compared to the mechanical float-operated
regulator shown in Figure 5.1, which vary from 0.95 (100% shutter
opening) down to 0.725 (5% shutter opening) (6). It is for this
reason that vortex valves can throttle discharge with much larger
aperature openings in comparison to a standard orifice. The
vortex valves can pass more efficiently debris and solids through
the chamber due to the spiraling flow action created by the
vortex action. Furthermore, the vortex valve can operate as an
orifice under low head conditions (and pass large flows) and the
switch to the vortex mode with increasing head. Vortex valves
can automatically switch to an fro, from a orifice characteristic
to a vortex mode. The notion of the name "vertex valve" derives
from the device's ability to vary flew resistence as a function
of inlet pressure.
Valves German Oriin
In the late 70 's Dr. H. Brombach, West Germany
developed the conical vortex valve, shown in Figure 5. 4. A. It
consisted of an inclined housing. The lower generating line of
the conical part of the housing is horizontal . A tangential
inlet pipe joins into the housing. The size of the central exit
port is variable by means of exchangeable orifices. The housing
has a hinged cover as well as vents (an important stabilizing
improvement ) .
The switching to and fro between radial sink flow and
free vortex flow occurs as follows (2): If the pressure at the
tangential inlet to the vortex chamber is low, then the housing
is filled with water only in the lower part. Due to the included
position of the housing the body cf water is not rotaticnally
symmetrical. Despite the tangential inlet it is not possible for
any vortex flow to develop, but instead there is more of a nozzle
flow of low flow resistance, see Figure 5.4.B. The higher the
pressure in the inlet, the more completely the vortex chamber is
filled with water and the excess air escapes. The body of water
loses its non-rotational symmetry more and more. When the
chamber is fill to the peak, Figure 5.4.C, the inclined position
of the chamber no longer has any effect since water is weightless
in water. The vortex now operates unhindered by asymmetry and
greatly throttles the flow. The central air opening draws air
into the vortex core. The vent at the top of the chamber is
subjected to over pressure and must, therefore be extended
beyond the highest water level.
5.12
-------
(y slorm water tank
(?) control shaft
© vortex flow controller
© vent
splash protection
slide valves
bypass
pipe to sewage treatment plant
Typical installation of
a conical single inlet
vortex va1ve
Automatic Vortex Row Controller
A.
tow resistance
B.
Figure 5.4 Brombach Type Conical
Vortex Valve Flow Controller
5013
high resistance
Row pattern in the valve housing
a valve housing
bcpne
c hinged cover
d exit port
e dischauge ba
baffle
f vent.
C.
-------
Figure 5.5.A shows the hydraulic behavior of a model of
valve used in numerous applications in Germany. The left-hand
part of the figure shows the water levels in the vortex chamber
at various inlet pressures and flow rates. If the rate and flow
coefficient based on a pressure of 15 inlet diameters are
plotted, graphs shown in Figures 5.5.B and 5.5.C result (2). The
exit orifice has the same cross sectional area as the tangential
inlet.
It can be seen by inspection of Figure 5.5 that there
are four different flow characteristic regions. The lower-most
section, partial filling, is the region in which the water runs
through the device with a free level. The rapidly increasing
flow coefficient (see Figure 5.5.B) is determined by the
hydrualic behaviour of the tangential inlet. In the second
section, the characteristic of the flow coefficient swings into
the vertical and remains at a value of about 3.25. The maximum
theoretical possible value of 4 is not quite reached. This is
due to the fact that the incident flow on the exit orifice in
this state is not entirely free of circulation. The complete
filling of the housing is reached at a pressure head of about
four inlet diameters. The flow coefficient drops sharply. In
the third section, the transition zone, the device reacts very
sensitively to fluctuations in pressure. This makes it difficult
to obtain precise measurements of the flow coefficient. For this
reason, this region is shown by a broken line. In the upper most
zone of the characteristic, there is stable vortex flow. The
water leaves the vortex chamber at high speed in the form of a
swirling hollow jet. The flow coefficient drops slightly as the
pressure rises. This is because the air-filled vortex core,
which tends to rise upwards due to its buoyancy in the inclined
chamber, is progressively driven towards the axis as the pressure
rises and so is progressively less able to disturb the vortex
action.
Figure 5.5.C shows the discharge-stage relation. The
flow rate rises continuously to a peak flow and then drops back.
This results in a saw-tooth-shaped flow curve. By comparison,
the flow curve of a simple orifice is shown. This achieves the
same desired flow at the end of the curve.
The characteristic of the German vortex valves is
basically the product of the following four geometrical
parameters: a) inlet diameter, b) outlet diameter, c) housing
diameter, and, d) angle of inclination; and the pressure on the
inlet side. If the valve does not freely discharge, but aqainst
a back-pressure, there is a further parameter.
Systematic variation of the geometrical parameters
results in an entire family of vortex valves. Although the
5.14
-------
HYDROVEX
VORTEX VALVE
MODEL K15/30/45
hstot
/ON
"stot
/ON
Planview
vent
15-
10
o
o
-Ullllllllimiiii,,
(A)
1
Water levels at various ( B ) Characteristics of flow coefficient
inlet heads
for com-
parison
ideal
orifice
vortex flow
transition
Illlllllllllllllllll
-O-
iQmax
Q/Q.
(C) Characteristics of volume flow
Figure 5.5 Flow Coefficent and Discharge Variations
For Brombach Type Conical Vortex Valve
5.15
-------
hydraulic properties cannot be adjusted at will, there ia a wide
degree of flexibility. Thus, for example, there are valves with
a highly pronounced saw-tooth, and others where the change from
nozzle flow to vortex flow is such that the flow curve is almost
vertical .
The hydraulic dimensioning of the W. German vortex
valves is based on extensive full scale calibration
measurements. In practical applications of the vortex valves,
slide valves and connecting pipes are often positioned upstream
of the valve itself. Correct dimensioning must, therefore, take
account of the influence of these additional hydraulic
resistances. Only in this way is it possible to guarantee an
accuracy of +/-5% of the desired flow (7).
The discharge loss coefficients for the W. German
vortex valves are below 0.15 and range up to 0.3. The commercial
technology discharge range is 0.1 cfs up to about 100 cfs for a
single device with no upper head limitation. In Europe there is
an installation throttling about 1 cfs of stormwater containing
sand and gravel under a head drop of 1600 feet. All of the W.
German type vortex valves useful for combined sewer regulation
are constructed with hinged hatches allowing for easy maintenance
access and permitting rapid replacement of adjustable plastic
and/or steel orifice inserts to alter the units stage/discharge
characteristic. A wide range of different flow characteristic
curves can be accomplished through replacement of inserts
allowing for capacity expansion/reduction and seasonal effects.
In sum, the W. German devices developed by Dr. H.
Brombach provide more degrees of design freedom than the
Scandinavian devices and are based upon extensive full scale
hydraulic testing. The W. Germany devices include venting
systems which stablize flow characteristics during switching and
minimize any hysterisis effects guaranteeing that rising/falling
stage curves are nearly identical .
Figure 5.6 shows a typical vortex valve
stage/discharge characteristic. As it can be seen from
inspection, the lower portion of the curve increases (rising
head) to a defined peak (orifice characteristic), "kick-back"
occurs in the transition zone (energy re-arrangement from orifice
to vortex made), and then rises when in the vortex mode. On
falling head, the characteristic curve is essentially the same.
5.16
-------
n
Typical
orifice plate
Storm regime
Transition
regime
Fiut*
Dry weather regime
Figure 506 Typical Vortex Valve Stage/Discharge Curve
5.17
-------
This characteristic provides for a number of
interesting design possibilities. First, the "first-flush"
passage can be designed about the initial peak. Second, overflow
spill weirs can be accurately established when the vortex mode is
first established. Third, the upper most portion of the vortex
curve can be used to establish controlled flow rates at the
maximum design storm condition i.e., 25 year design storm such
that discharge at maximum head could be the same or even less
than the peak "first-flush" flow occurring at low head
conditions. The WWTP would therefore receive at most no more
than either of these two hydraulic limits. Fourth, a system-wide
utilization of these positive acting controllers could be
employed to apportion interceptor capacity to carry only "first-
flush" to the WWTP from each of the contributing sewer sheds and
allowing only the clearer flows during increased storm conditions
to overflow. Lastly, the orifice flow characteristic on drain-
down (falling curve) can be explicitely used to ensure self-
scouring when considering in-line and/or off-line storage of
wastes heavily laden with settleable solids. It was exactly for
this last design consideration that motivated Brombach to
explicitly research, hydraulically test and develop vortex valves
having well defined switching (orifice to vortex, vortex to
orifice) characteristics.
The typical characteristic curve shown in Figure 5.6
can be altered by changes in the geometric design of a given
vortex valve to increase/decrease peak initial flow;
increase/decrease height at which the initial peak flow occurs;
increase/decrease the degree of "kick-back"; and flatten/steepen
the slope of the vortex mode portion of the curve.
Commercial Availability Q£ Vortex Valves
Advanced Fluidics, Inc. (AFI) located in Hanover, MA
acquired exclusive U.S.A. and Canadian licensing rights from J.
M. Johannessen to market and sell his technology in 1982. These
devices were sold under the trade name, Hydro-Brake. Conical
type vortex valves were designed, fabricated and supplied to the
City of Saginaw by AFI in mid 1984 and were installed as part of
the reduced BMP implementation program.
John Meunier, Inc. (JMI) located in Montreal, Canada
acquired North American licensing rights in-mid 1984 from Dr. H.
Brombach to market and sell the patented line of West German
vortex valves.
Recently, JMI and AFI have mutually agreed to merge the
two vortex valve product lines and to combine licensing rights
for marketing a a single product line called the "HYDROVEX" .
5.18
-------
5.3 Source Control Practiceg
Management Practices include source control and
collection system management. Whereas storage and treatment
technologies are generally more costly alternatives, management
practices concentrate on the source of pollutants (source
control) and means of conveyance at a minimum cost.
A. Source Control technologies which were reviewed
during screening are listed below:
Street Cleaning - Urban runoff pollution is reduced and
aesthetics are improved by regular street cleaning. Fine solids
fraction of street surface dirt is removed by broom brushes or
the more efficient vacuum-type cleaners. The efficiency of street
cleaning in large metropolitan areas is reduced due to problems
with heavy street traffic and parked vehicles.
Solid Waste Management - Urban runoff pollution is
mitigated by improving trash collection and reducing litter. The
greatest benefit is aesthetic improvement rather than overall
solids reduction.
Erosion ControJ. - Improved construction practices, such
as proper landscaping, protection of drainage channels,
protection of stockpiles, and the installation of sediment
retention basins/dams provide for a reduced fine solids
contribution to existing sewer facilites.
Catch Basin Cleaning - There are several methods
available for catch basin cleaning which will reduce clogging of
storm and combined sewers. Removing a large fraction of the
collected solids can reduce the solids pollution and prevent
shock loadings of grit and silt materials.
Roof Storage - Additional storage of urban runoff for
flow attenuation is available in an urban area of high building
density provided that the roof structure is constructed to
accomodate rainfall storage. A large amount of roof area is
required to make this option attractive.
Parking kot JS tor age - Similar to roof top garage,
temporary storage may be available at parking lots and
playgrounds. Outlet controls are necessary for this method to be
effective. A regular maintenance program for debris removal of
deposited material is necessary.
Natural Flow Attenuation Techniques - Natural drainage
impoundment can be used for runoff attenuation by creating
temporary detention. Specific examples are lagoons, debris dams,
5.19
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and recharge berms. These applications are not feasible for CSO
problems in major urban areas.
Porous Pavements - The use of special pervious subbase
and base course material for streets, sidewalks/ and parking lots
allow rainfall to permeate through the pavement for groundwater
recharge. This technique is generally limited to new construction
in mild climate.
B. Collection System ffajiagement Teghflio^es - which were
screened are listed below:
Polymer injection - The use of polymer can reduce
hydraulic friction and thereby increase system conveyance
capacity, but reasonable results can only be attained in
hydraulic systems with limited capacity. Polymer injection is a
temporary means of overflow control and is relatively expensive
due to high chemical cost.
Sewer Flushing - High flows push settled solids
downstream in sewer reaches which are too flat to be self-
cleansing. Sewer flushing is usually limited to relatively small
diameter sewers.
Sewer Cleaning - Periodic cleaning can restore sewer
pipes to full hydraulic capacity using rodding machines, bucket
machines and drag lines. These methods have proved to be
relatively costly and time consuming.
5.4 Storage and Treatment
The use of storage and treatment technologies to abate
CSO pollution encompasses a broad spectrum of possibilities
ranging from structurally intensive, high cost alternatives to
minimal structurally intensive, low cost alternatives.
Structurally intensive projects are outlined in the following
manner: System conveyance, storage and treatment.
System Conveyance - The collection and transfer of
combined sewer overflow to treatment and storage facilities may
be accomplished either by gravity or by pumping, depending upon
the hydraulic conditions in the system. If storage is not
available or is impractical, conduits and pumps must be sized to
handle peak flows resulting from design storm runoff. With
storage capabilities, conduits and pumps can be sized such that a
combination of storage, conveyance, and treatment will process
peak runoff at minimum cost. The CSO conveyance system may be
continuous, collecting all overflows or selective, intercepting
5.20
-------
and combining only particular overflows. Hydraulic conditions,
design storm, solids composition, and service area determine the
size and shape of the conveyance facilities.
Storage - Off-line storage is used to attenuate storm
flow peaks, reduce storm overflows, and capture the first flush,
or provide treatment in the form of sedimentation when storage
capacity is exceeded. Off-line storage facilities may be located
at overflow points or near WWTP facilities, depending on the type
and function of the storage facility to be used. Off-line storage
may also be used for on-site storage of runoff. Disadvantages of
storage facilities include their large size, high cost, and
dependency on other treatment facilities for processing the
retained water and settled solids. CSO generally results in
solids handling problems so consideration must be given to
conveyance system slopes and flows and also to the number of
storage vessels which can be feasibly maintained. A typical
process diagram is shown in Figure 5.7.
Treatment - Treatment facilities may be localized or
centralized. The number and location of treatment facilities
depends upon system hydraulics, characteristics of the pollutants
and feasibility of operation. If hydraulic conditions are such
that expensive pumping facilities are required for transporting
relatively small amounts of overflow, then localized treatment
may be more cost-effective. If hydraulic conditions allow
consolidation of overflows, larger more centralized CSO treatment
facilities become more feasible. The nature of pollutant loadings
also determines the type and location of facilities. For example,
if a relatively small area contributes a very high grit loading
which would aggravate the conveyance system hydraulics, then it
would be advantageous to locally remove the grit. Treatment
technologies available for intercepted wet weather flows include
physical alternatives which remove settleable, suspended solids
and floatable materials from combined sewer overflow.
5.4.1 Physical Treatment Processes
Physical treatment systems have demonstrated
capabilities to handle high and variable influent concentrations
and flow rates and operate independently of other treatment
processes except for the disposal of residual solids. Primary
level treatment can be achieved by any of several methods
available for high rate application, including gravity
sedimentation, swirl regulator/concentrators, screening,
dissolved air flotation, high rate filtration and high gradient
magnetic separation. Descriptions of each of these methods are
presented below.
5021
-------
NJ
NJ
Inf.
Screenings
to
Disposal
J
COARSE
SCREENING
Clarified
Effluent
DISINFECTION
-*~TO SAGINAW RIVER
STORAGE
TANKS
SETTLED
SOLIDS
•*- TO INTERCEPTOR
Figure 5.7 Soginow study typical storage facility process schematic.
-------
Gravity Sedimentation - Gravity sedimentation of CSO has
been evaluated in facilities utilizing surface overflow rates
higher than conventional primary rates of 800-1,200 gpd/sq.ft.
Early experiments with primary treatment facilities in Los
Angeles demonstrated that suspended solids removal efficiences
did not decrease markedly when overflow rate was increased over.
2,000 gpd/sq.ft. Studies conducted on primary facilities treating
combined sewage in Toronto, Canada; Rochester, New York; and New
York City also show reasonable performance with increased
overflow rates. Studies also show considerable cost/performance
improvements with chemical addition such as polymer and alum.
Despite the apparent improvements, gravity sedimentation requires
tanks, thus introducing significant land requirements and solids
handling problems similar to that of conventional storage
facilities.
Swirl Regulator/Concentrators - Swirl regulator/
concentrators achieve both quantity and quality control of CSO
laden with suspended material. A typical process diagram is shown
in Figure 5.8. The swirl functions on the basis of having a
tangentially induced waste stream which is directed around the
circular unit to form a spiral-type flowpath. Solids/liquid
separation is achieved by two means: centrifugal forces separate
and concentrate solids due to inertial differences; and solids
fall out of the wastestream and are concentrated in the floor of
the swirl due to gravitational effects derived from lowering
particle velocities and elongating the particles flowpath.
Floatables are effectively trapped and stored during storm event
and later discharged to receiving sewer.
Extensive mathematical and hydraulic modeling has been
performed with materials simulating particle size distributions
and specific gravities encountered in combined sewage. These
models were extended to prototype scale using Froude Law scaling
of particle settling velocities and design flow rates.
Verification of model projections has been demonstrated in
facilities at Lancaster, PA; and at Rochester and Syracuse, New
York.
A 12-foot diameter swirl concentrator in Syracuse,
New York with a design flow of 6.8 mgd exhibited total
mass loading removals for suspended solids ranging from
44% to 65% with concentration reductions ranging from
18% to 55%. The foul sewer discharge was approximately
10%. The higher mass loading reduction through the swirl
concentrator is due to both flow and concentration
reduction. Data performance from the Syracuse prototype unit
indicate good removals at the beginning of storms (when
influent concentrations were high) and at the end of the storm
(when flow rates were low) such that a high percentage of the
5023
-------
Grit
To
Disposal
Screenings
To
Disposal
U1
Concentrated
Swirl
Underflow
Coarse
Screening
Pumping
Primary
Treatment
By Swirl
Concentration
Grit
Removal
To Interceptor
System
Clarified
Swirl
Effluent
Disinfection
To Receiving
Water
Figure 5.8 Soginaw study typical CSO primary treatment process scheme.
-------
flow discharged to the foul sewers. The data based on 11 storm
events showed average storm hydraulic loading rates as high
as 6600 gpd/ft. (8).
The 24-ft diameter dual-functioning swirl regulator/
concentrator constructed in Lancaster, Pennsylvania, under a
demonstration grant from the U.S. EPA treats CSO at one of the
City^s overflow points to the Conestoga River. Data from the
evaluation period (1980-1981) conducted by EDP indicated that the
swirl is an efficient treatment device to remove heavier or
"first-flush"-related suspended solids (9). Treatment
efficiencies exceeded 60% for flows exceeding 20 cfs.
A special cross-sectional sampler capable of taking
complete vertical "slices" of flow over an entire pipe cross
section in an automatic discrete mode was developed and installed
by EDP Technologies, Inc., Hanover, MA. in the 36-in influent
conduit to the swirl to obtain representative suspended solids
samples. The new cross-sectional sampler and a Manning model
6000 sequential sampler were used during four storm events. An
anlysis of the data indicated that suspended solids of samples
collected by the new sampler were 6 to 7 times more concentrated
than samples collected (at the same instant) by the Manning
sampler during the first 10 minutes of the storm's peak "first
flush". Concentration factors reduced to 2 to 4 for samples
collected mid-event and then down to 0.5 to 2.0 for end-of-event
samples.
A summary of the swirl suspended solids removals for
five events monitored with the cross-sectional samplers is as
shown in Table 5.2. The removal and efficiency percentages
associated with the indicated estimated flows are also presented.
Removal is defined as the percentage of the influent mass
contained in the foul underflow line. Efficiency is defined as
the removal minus the percentage of inflow contained in the foul
underflow line. These results were derived primarily by
inspection of raw data. Overall flow-weighted removal and
efficiency calculations are not given because of the approximate
nature of flow measurements. Flow meters continuously
malfunctioned during the course of the project.
It appears that the swirl provided significant
suspended solids removal near design flow conditions. As
expected, efficiency deteriorated at lower flow rates because of
the flow splitting phenonomenon. In most cases, efficiency
exceeded 60% for flows of about 20 cfs or greater. As
anticipated, most of the suspended solids were settleable
inorganic grit. The swirl appears to provide the degree of
treatment that it was orignally designed for, i.e., 90% removal
of settleable material (defined as grit having an effective
5c25
-------
TABLE 5.2
Lancaster, Pa. 1980 - 1981
Summary of jSsuLtJ. Regul at or /Concentrator Performance
Dgte of Event
9/10/80
10/2/80
5/10/81
7/2/81
7/20/81 pm
Estimated
Plow rate
CfiisJ
Removal
$
18
7
50
7
2
20
8
6
55
20
5
46
70
50
52
46
80
12
23
35
76
86
41
83
Efficiency
62
39
47
24
5
5
5
10
73
78
11
80
5.26
-------
diameter of 0.35 mm and a specific gravity of 2.61) at design
flow of 40 cfs.
Similar in function to the swirl, the helical bend
concentrator/regulator appears more practical as in-line devices
rather than satellite or off-line devices. Details of the swirl
and helical bend regulator/solids concentrators are shown in
Figure 5.9.
Screening - Screens have been used to attain various
levels of suspended solids and floatable solids removal.
Screening methods can be separated into two groups:
1. Course screening used to remove the coarse floatable
materials and larger suspended solids. In many cases, coarse
screening is used as a pretreatment prior to further treatment to
enhance the control process or to protect downstream equipment.
Suspended solids removals of 5-10% can be expected.
2. Pine screening used as a primary treatment process.
Fine screens include static, drum or rotary screens and also
micro-screens. Microstrainers or microscreens have been applied
to polishing of secondary effluents at conventional rates of
around 110 gpd/sq ft. for 30 micron mesh. Tests of CSO have
indicated suspended solids removals of 17-40 percent when using
420 micron screens, 26.6 percent when using 105 micron screens,
10-43 percent when using 70 micron screens and 20-93 percent when
using 23 micron screens. Microstrainers are available
commercially in a number of configurations. Fine screening
devices tend to perform best with low to moderate hydraulic
loading rates. Fine screening devices are characterized by
relatively high operation and maintenance requirements needed to
maintain adequate removal efficiencies and to dispose of
collected solids.
Dissolved Ail Floatation - Pilot results from treatment
of CSO by dissolved air floatation are being used to design a
full scale plant in San Francisco. These data inciate suspended
solids removal rates of 51 percent at an overflow rate of 4,320
gpd/sq. ft.
High-Rate Filtration - High-rate, multi-media filters
have been studied extensively for polishing of secondary
effluents. CSO have been applied to high-rate filters at
Washington D. C. ; Cleveland, Ohio: Syracuse, Rocheste, r New
York, and New York City. Filter media included fiber flass,
anthracite and garnet in Washington D. C. studies and anthracite
and sand in the Cleveland and Rochester studies. The Syracuse
studies also evaluated use of plastic pellets in conjunction with
sand and anthracite. The Washington D. C. studies employed flux
5o27
-------
INLETV
CHANNEL FOR
OVERFLOW
Ul
•
00
OUTLET TO
STREAM
TRANSITION
SECTION
STRAIGHT
\ SECTION
HELICAL
BEND 60
OUTLET TO
SEWER
ISOMETRIC VIEW OF
HELICAL BEND REGULATOR
SCUM BAFFLE
FENCE
EMERGENCY
WEIR
CONCENTRATE
RETURN TO
SEWER
EFFLUENT
TO STREAM
SECTION
XCONCENTRATE
RETURN TO
SEWER
EMERGENCY
WEIR
: EFFLUENT TO STREAM OR
ADDITIONAL TREATMENT
PLAN
SWIRL CONCENTRATOR
Figure 5.9 Helical bend and smnrl concentrator.
-------
rates of 5-15 gpm/sq/ft while the Cleveland and Rochester work
evaluated loadings as high as 25-40 gptn/sq/ft. Suspended solids
removal rates ranaged from 30-70 percent without chemical
treatment and 85-98 percent with polyelectrolyte treatment.
mBtlc. SeEarjatjj.cn - High gradient
magnetic separation (HGMS) is applicable for CSO treatment
technology. HGMS provides extremely high pollutant removal rates
(in excess of 90%) and permits flux rates in excess of 150
gpm/sq. ft. The disadvantages of this technology are the high
capital and operational costs.
5 . 5 Selection of Alternative Controls
An assessment of alternative CSO control options is
presented in Table 5.3. System modifications, source controls
and collection system management options are broadly encompassed
as preventive BMP controls in Table 5.3. Structural controls
have been assessed as treatment controls.
The overview management concept for CSO emission control
in Saginaw is to provide a fairly moderate to high degree of
physical treatment at low overall capital and operational costs.
Floatables and settleable solids removal are important from the
standpoint of boating and general aesthetics. Settleables
removal will control to a degree, CSO heavy metals emission and
dissolved oxygen sediment demand. Control of fine suspended
solids is more difficult and more expensive but will tend to
reduce oxygen demanding substances and turbidity. Turbidity
reductions in turn provide fcr better light penetration, algal
productivity (to a limit) and eventually enhanced dissolved
oxygen levels.
Acceptable CSO control technologies in Saginaw must be
cost effective from both first cost (capital) and operations cost
standpoints. The City of Saginaw invests heavily in its various
public works departments. The street and sewerage systems are
both well maintained and operated. In addition, the City
efficiently operates the WWTP providing nearly constant high
quality treatment levels and maintains and operates the Hancock
Street CSO storage/treatment facility. Any alternative CSO
treatment technology must have comparable treatment performance
characteristics, but be less expensive to both build, maintain
and operate.
The following CSO control options satisfy the
aforementioned considerations and are further investigated and
detailed throughout the remainder of this report.
5029
-------
PREVENTATIVE CONTROLS TREATMENT CONTROLS
CONTROL TYPE
SYSTEM MODIFICATIONS
Regulator Improvements
Sewer Separation
Improved Utilization
of existing facilities
In-line Storage
Increase WWTP Utilization
OURCE CONTROL
Street Cleaning
Solid Waste Management
Erosion Control
Catchbasin Cleaning
Roof Storage
Parking Lot Storage
Natural Flow Attenuation
Porous Pavement
OLLECTION SYSTEM MANAGEMENT
Polymer Injection
Sewer Flushing
Sewer Cleaning
TRUCTURAL CONTROLS
Storage/treatment facilities
Swirl Regulator/Concentrators
Screening (Coarse)
Screening (Fine)
Dissolved Air Floatation
High-rate Filtration
High gradient Magnetic
Separation
1
H
H
H
H
H
—
.
S
_
S
S
S
S
S
_
-
NG
2
_
.
.
-
M
L
L
-
_
-
S
S
S
IT API
3
H
L
H
H
H
AM
AM
L
AM
P
M
L
P
—
P
AM
PLICAB
4
H
P
H
H
H
.
_
H
L
-
_
_
-
LE
5
Y
Y
Y
Y
.
—
_
-
^
-
_
-
6
M-H
H
M
H
H
H
H
7
8
9
10
11
NOT APPLICABLE
M
L-M
L
M
M
VH
H
H
L
H
H
H
VH
M
L-M
N
M
M
VH
L
N
N
.
M
H
L
S
N
e
J
C
3
1
u
H
12
H
L
L
H
KEY: Preventative Treatment Code (2 Bpmnval) COLUMN HEAI ING KEY-
13
M
L
L
H
14
C
C
C
15
1
-------
A. System Mod if ica_tj._p|i
. regulator improvements
. enhanced hydraulic conveyance
. increased in-system storage
B. Structural Controls
. storage/treatment facilities
. swirl regulators/concentrators
Fine screening (rotary/micro screens), dissolved air
floatation, high-rate filtration and high gradient magnetic
separation are technologies that meet CSO emission reduction
expectations and would attain perceived water quality goals, but
they would not satisfy Saginaw's need for cost-effective capital
and more importantly, operationally inexpensive solutions.
The combination of "system modification" options is
hereinafter referred to as the BMP plan.
5.31
-------
CHAPTER 6
COMBINED SEWER MODELING
6.1 Foreword
The Saginaw CSO Management Model, developed by EDP, is
an inexpensive and flexible tool for preliminary planning and
sizing of CSO facilities. The model provided a means by which the
CSO problem could be analyzed and introduced time and probability
to the quantity, frequency and duration of overflow events by
using actual rainfall data collected over a long period of time.
It was used to screen alternatives based on varying storm
conditions.
The purpose of this chapter is to outline the modeling
tools, and their utilization in the development of the various
proposed and implemented control programs for treating combined
sewer overflows. A comprehensive mathematical computer simulation
program was developed to help determine overflow discharges and
pollutant concentrations as a result of hypothetical occurrence
of various size design storms. Such a model not only provided an
accurate representation of the physical sewerage system, but also
provided an opportunity to determine the benefit of proposed
pollution abatement alternatives.
The value of modeling lies in the ability to quickly
predict the outcome of dependent variables as a result of
hypothetical modification of the system. These quick projections
have allowed for more time-efficient evaluation of abatement
alternatives formulated to meet established goals, concepts, and
criteria. Through this process the best alternatives were
isolated for further cost-benefit analysis.
Model development and calibration was performed over
three time periods. Initially, during 1979-1980, EDP developed
the basic model which was used to prepare the CSO Facility Plan,
(Phase 1 of the project). During 1983 (Phase 2) further modeling
was performed to detail the Reduced BMP program. During that time
minor model modifications were performed to optimize calibration
based on available data. Phase 3 of the modeling work was
performed during 1984 before and after implementation of the
Reduced BMP plan. An extensive (Fall, 1984) field investigation
provided the necessary data base to further calibrate the model
using improved knowledge of rainfall/runoff characteristics,
regulator performance and pump station operations.
The culmination of the preceding efforts provides a
documented assessment of appropriate technologies for
6.1
-------
abating combined sewer overflows. This is a recommended plan of
action resulting from a complex analysis of a complex problem
with a wide range of variables and associated costs and benefits.
Runoff volume and quality are predicted on the basis of
hourly rainfall, dry weather sewerage flow (and infiltration) ,
street washoff. dry weather sewerage and deposits. Regulator
operations are simulated for each of 31 catchment areas
previously defined. Resulting overflows to the river are
retained for statistical analysis and flows to the interceptor
passed into the interceptor model. The interceptor model
simulates the operation of the intercepting system including
overflow and quality into the pump stations on the interceptor,
the river crossing flows, and flows and quality to the waste
water treatment plant. Treatment operation (s) are simulated both
at the existing WWTP and at any overflow point upstream. The
costs and effectiveness of the various options available to
Saginaw for stormwater management are calculated and summarized
for any given combination of alternatives. The entire model
operates on an hourly time increment.
Details of the runoff prediction computations are given
in Section 6.2. Regulator and in-line storage operations are
discussed in Section 6-3 and 6.4, respectively. Interceptor
model details are given in Section 6.5. West Side Interceptor
river crossing details are given in Section 6.6. Water quality
modeling details of the sewerage system are discussed in Section
6.7. WWTP simulation details are given in Section 6.8. Discharge
calibration details are given in Section 6.9. Phosphorous
modeling details are presented in Section 6.10.
6.2 Runoff
An overview of the simulation model runoff volume and
water quality estimation procedure for each of the 31 catchment
areas is shown in Figure 6.1. Runoff volume for each catchment
area is calculated for each hour of rain using the runoff
coefficients, the catchment area and average hourly rainfall
intensity.
For most catchment areas the runoff is considered
delivered to the regulator chamber during the same hour of
recorded rain occurance. For the Weiss and Fourteenth Street
catchment areas, a one hour time delay is used for the section of
the catchment area estimated to be over an hour away during full
pipe flow conditions. Hourly dry weather sewerage flow per
catchment area is added to the runoff flow. For the spring months
of April - June- infiltration estimates per catchment area are
-------
ey>
co
r
Hourly Rain
Storm Runoff Loadings
= f(Rain Per Event)
Deposition
= f(Days Since Last.Rain)
Sewage Loadings Long
Term Average
Runoff
= f(Rain, Catchment Area, K)
Water Quality
= f(Sewage Loadings,
Deposition, Storm
Runoff)
TO REGULATORS
K, Runoff Coefficient
= f(% Imperviousness)
Dry Weather Flow
Spring Infiltration
J
Figure e. i Catchment area modeling.
-------
also added to the runoff. Diurnal dry weather variations are
not considered.
During Phase 3 of the modeling effort, EDP field
investigations and continued model calibration efforts resulted
in increased times of concentration for several catchment areas.
Regulator operation simulations were modified to more suitably
match the expanded data base developed. All other aspects of the
Phase 1 evaluation were unchanged. Regulator operations pre and
post the Reduced BMP Program are discussed in Section 6.3.
6.3 Regulator Operation!
1979-1981 Considerations ^ Phase 1
Three general types of regulators were encountered in
Saginaw. Type "B" regulators have variable underflow openings
altered by a float operation (Brown & Brown mechanical float
operated systems). As water levels rise, underflow orifices
close. Type "A" regulators have fixed underflow orifices,
generally about 1/2 foot by 1/2 foot. The third type of regulator
encountered are the five modified Type "B" regulators located in
the Hancock Street area. These regulators were modified during
the implementation of the Hancock Street storage/treatment
facility to increase the closure rate of the underflow orifices.
At two of the five locations backwater gates were
replaced with automatic sluice gates set to open at regulator
storage depths above the level of the spill weir to the
interceptor. At the other three locations sluice gates were added
downstream of the backwater gates. Increased closure of underflow
orifices will decrease flow to the interceptor. The sluice gates
captured and stored combined sewerage that otherwise would have
passed through the backwater gates to the river (except in
extreme flooding conditions). The intent of these prior
modifications was to increase in-line storage, and to divert flow
in excess of the in-line storage to the interceptor (and
eventually the Hancock facility).
In the unmodified Type "B" regulators high flows not
handled by the underflows would be discharged through backwater
gates to the river. The operation of the backwater gates was
dependent on their seat elevations and relative river elevation,
and could be prevented or hindered from opening in some cases for
high river conditions. Most backwater gates were in the same
chamber as the regulator. At Cronk and Genesee Streets
backwater gates were separated from the regulation chamber and
were proximate to the river.
6.4
-------
Regulator performance data was limited to the operation
of the modified Type "B" regulator chambers in the Hancock Street
area on the West Side. Strip charts recording stage of backed-up
combined sewage as a function of time during storm events were
available for five regulators located at Mackinaw Ave.f Adams
Street, Throop Street, Hayes Street and Remington Street. The
recording devices at the Mackinaw regulator was defective and was
eliminated from the analysis. These data were analyzed to
determine dynamic operation of the regulator float devices during
rain events. Zero reference points on the strip charts were
impossible to determine and the rate of water level increase
during rising portion of the hydrographs were not considered to
be reliable since discharge over the weir levels to the
interceptor may have occurred which would not have been noted on
the strip charts. The fall of water level over time during the
recession of the storm event (drainage/ in-line storage) was
considered accurately recorded. Underflow discharges, as a
function of time were estimated using the strip charts rate of
depth change and estimated storage volume changes associated with
the depth change. Underflow rates as a function of stage for the
four regulators are summarized in Figure 6.2.
System operation data were not available for the other
Type "B" regulators. Underflow dynamics were estimated on the
basis of dimension measurements and visual inspections by EDP
field engineers during storm events. It appeared during the EDP
inspection program that the float mechanisms were slow in
responding to rising water levels, and it was speculated that
many underflow orifices did not appreciably close during high
water conditions. Underflow drain pipes leading to the
interceptor were determined to be large enough to handle maximum
underflow discharge.
The dynamics of existing regulator operation were
modeled as depicted in Figure 6.3 for the hourly averaged runoff
flows. All underflows were calculated as a function of depth. The
available data for the Hancock area regulators were used to
generate functions for simulation . Underflow in these cases
decreased as depth of flow increased. Other regulator underflows
in the system were calculated on the basis of a constant area
orifice discharge to free space given by equation:
underflow = area x square root (2gh)
where h is the depth of flow above the orifice. It was
determined that connecting lines to the interceptor were large
enough to handle high flows, so the limiting aspect of flows to
the interceptor was the operation of the orifice openings.
6,5
-------
2.0-
Ol
o
cT
£ i.
-------
CT>
Catchment Area Runoff Estimates
Hancock Area Discharge
To Interceptor
= Runoff-Storage
Overflow = 0
Other Regulators Dis-
charge to Interceptor
= Underflow
Overflow = Runoff
- Under Flow
- Storage
EDP Regulator
Modifications
r 1
Regulator Discharge to
Interceptor
= f(Runoff, Underflow,
Regulator Operation;
Regulator Overflow to
River
= f(Runoff, Discharge to
Interceptor, Backwater
Gate Operations)
Backwater Gate Operations
= f(River Elevation)
Underflow
= f(Depth of Flow)
s f(Volume)
Storage
= f(Depth of Flow)
= f(Volume, Available
Volume)
4
I
OVERFLOW
WATER QUALITY
OVERFLOWS
FLOWS TO
INTERCEPTOR
EDP In-line Storage
Modifications
Figure 6.3 Schematic of regulator operation.
-------
As a result of later simulation model calibations, the
assumption of free-fall discharge conditions through maximum
regulator orifice openings was used for modeling those regulators
where data was lacking. Type "A" regulator discharges were also
estimated in this manner.
For the five Hancock area regulators, flows in excess
of the underflow and available storage volume were diverted to
the interceptor. During the Phase 1 and 2 evaluations discharge
to the river was considered eliminated in these five cases.
During the Phase 3 investigation it was necessary to allow
extreme flows to outflow to the river to accurately match field
and modeled data.
For the other regulators in the system the dynamics of
the backwater gates were incorporated. The depth of flow that
would cause the gates to open was calculated on the basis of the
gate seat elevation, or the river elevation depending on which
was higher- Backwater gates are typical flap-type swinging gates
(with the exception of the five modified Type "B" regulator
chambers). In most cases only a minimal amount of storm flow
increase is needed to raise water depth enough to open the flap
gates and cause a discharge to the river. The gates are also
sensitive to river elevations as most gate seats are located near
average river elevation.
The Weiss Street gravity line is about five feet below
average river elevations. High river flows can restrict this gate
operation and subsequently require higher depths of flow to cause
discharges to the river. Varying river stage can have a somewhat
random effect in increasing the amount of in-line storage of
storm flow and decreasing overflows. An additional one-half foot
elevation was added to account for the dynamics of the gate
movement itself, and to insure that the simulated regulator
operation would at least divert all dry weather flow to the
interceptor. Any flows in excess of the underflows and available
storage volumes were then diverted to the river.
The modified Type "A" regulator chambers had a weir
placed between the backwater gate and the flow channel, and a
lower weir between the flow channel and the interceptor
connection. Flows in excess of what is discharged through the
underflow orifices or stored in the system behind the weir will
first overflow the lower weir and be directed to the interceptor.
Only extremely high flows will overflow the weir separating the
backwater gate portion of the chamber and be directed to the
river. This weir arrangement was considered by EDP to be both the
least expensive and most available method of limiting overflows
at any of the unmodified regulator chambers in the system.
6.8
-------
Regulator Operation; 1984 Considerations - Phase 3.
Under the complete BMP Plan it is envisioned that all
regulator chambers be converted to act in a similar storage mode
as the Hancock area modified Type "B" regulators, but with the
addition of constant underflow discharge devices. As stated the
Type "B" regulators earlier modifed as part of the Hancock
Street detention improvements had been altered to cause the
underflow orifices to close rapidly, limiting flows to the
interceptor and thus committing the first flush of a rain event
to in-line storage created at the chamber. EDP considered it more
advisable to maintain higher underflow discharges to the
interceptor, limited only to what the interceptor can maximally
handle. Operation in this manner will commit the first flush of a
rain event, generally carrying the highest concentration of
pollutants, to the interceptor, and eventually to the WWTP. This
mode of operation is preferable to capturing the first flush in
system storage which may become overflow at a later time if the
rain continues. Furthermore, this mode can be accomplished with
constant discharge devices that are more reliable and easier to
maintain than the present float mechanisms. These devices will be
discussed further in Chapter 7.
For the five Hancock area regulators, CSO in excess of the
underflow and available storage volume were diverted to the
interceptor- River discharge was considered eliminated in these
five cases except during extreme events. Underflows were set
equal to approximately six times dry weather flow unless higher
underflows were needed to handle the dry hour discharges of in-
line storage pools created further upstream. Weirs were adjusted
to create in-line storage at the regulator chamber, as
appropriate. With the exception of Fraser, Webber, Fourteenth and
Weiss Street regulators, all but extreme excess flows were
diverted to the interceptor. Fraser, Webber, Fourteenth and Weiss
Street regulators were allowed to overflow when runoff flows were
in excess of underflows and available in-line storage volumes.
Under the Reduced BMP plan all West Side regulators
were modified to act in the preferred mode and modeled as such in
the Reduced BMP plan simulations.
6.4 In-line Storage
One concept of this study is to maximize the use of
existing facilities such as in-line storage already available in
the system conduits. The in-line storage concept for the
complete BMP plan consisted of alteration of 31
regulator/backwater chambers for in-line storage purposes and
construction of 14 flow control points upstream of the
appropriate regulator chambers.
6.9
-------
The purpose of the upstream control points was, in some
cases, to avoid the steeply sloping inverts on the West Side near
the river and, in other cases, to simply add a second level of
flow control in addition to control at the regulator. Regulators
on the West Side are typified by conditions where the influent
trunk sewers are on a steep incline to the regulator chambers
which then level-cff not far upstream. Far greater storage
volumes could be generated for these trunk sewers if the flow
control structures were located upstream where the invert slopes
are less steeply inclined. Control structures in the Fourteenth
and Webber areas were moved upstream to avoid possible flooding
due to low ground surfaces. The structure for the Fraser area was
moved upstream to avoid possible negative interaction with
privately owned sewers in that area.
During the Phase 1 modeling, in-line storage potential
was assessed. Pertinent details of the sewer system were
transferred from the sewer plans to a city-wide base map. All
pipes equal to and greater than 36 inches were outlined on the
base map. Pipe sizes, invert elevations and manholes were noted.
Contours of ground surface elevation (2-foot interval) were added
as an overlay to the resulting base map.
An interactive computer program was developed during
Phase 1 to calculate in-line storage that would result by flow
restrictions at any point in the system. Area of flow as a
function of depth was calculated for all typical pipe cross-
sections in the Saginaw system, including: circular, oval, egg
and horseshoe-shaped sections. The in-line storage program used
these area functions to calculate volumes stored behind any
given weir height associated with the level pool in static
conditions. The resulting storage volumes were conservative in
that the dynamics of flow had been ignored in the level pool
approximation. Invert slopes were also included in the
calculations allowing volumes over changing slopes to be
accurately calculated.
One new aspect of the Phase 2 modeling was a detailed
review of in-line storage potential of all piping within the
system. Where potential backup could occur it was included
regardless of pipe size. A more accurate estimate of the actual
potential storage volume resulted by inclusion of pipes under the
previous 36 inch limitation. Storage volume increases due to
this procedure varied throughout the city. In some areas the
trunk lines are shallow and most lateral lines are subject to
backwatering, whereas in others, lateral lines feed deep trunk
lines at drop manholes and backwatering would be nonexistent.
Flow dynamics' implications to storage were also
considered in lieu of the previous static pool level volume
6.10
-------
estimation. Rainfall/runoff data generated in the Phase 1
evaluation were utilized in Phase 2 to predict nominal flow rates
within the piping system. Flow was determined as a function of
overall area drainage and the fractional portion of area upstream
of each pipe segment. Friction-induced head loss calculations
were performed and accumulated with distance upstream to
formulate a hydraulic profile within the system. Use of these
flow dynamics also resulted in a more accurate estimate of the
actual potential storage as the volume of storage increases
beyond the static, level pool model.
Hydraulic profiles and resultant storage volumes at any
time were shown to be a function of flow rate (a direct result of
rainfall intensity). A nominal intensity of 0.1 inches per hour
was selected for final analysis. Estimates of storage volume
also varied throughout the city dependent upon the relative pipe
sizes to areas served. Large areas generate greater runoff
volumes than small areas such that for any given pipe size
frictional head loss and resultant hydraulic profile levels were
greater implying fuller pipe conditions and greater storage
potential.
Table 6.1 shows the relative increases in estimated
storage volume due to the various aforementioned considerations
for the Throop Street catchment area. A substantial volume
increase of 14.8% is attained by considering all pipe sizes, with
an additional 21.7% volume increase based on manhole volumes and
flow dynamics as compared with earlier calculations. These
values are based on a backwatering weir levels at the pipe crown
elevations. Actual volume increase percentages will vary with
weir height at this location and will vary widely at all other
locations.
Although the revised method of storage calculation
tends to increase the predictable storage volume at each
location, the final storage volume may not increase above the
1981 predicted amount. Exact design hydraulic evaluation of each
chamber reduced the final weir elevations in several chambers for
the partial BMP plan implementation thereby reducing anticipated
storage volumes. Similar reductions will probably occur at other
regulators during final complete BMP implementation of East Side
regulators such that overall storage volumes provided may be
similar to those estimated during 1981.
The potential for in-line storage was estimated using
the in-line storage computer program for selected sites
(regulators and further upstream control points). In the
selection of upstream sites no point was considered for which
ground elevation was less than ten feet above the resulting water
elevations after considering weir heights and flow hydraulics at
6.11
-------
TABLE 6.1
TYPICAL IN-LINE STORAGE VOLUME COMPARATIVE ANALYSIS
LOCATION: THROOP STREET - WEIR 5-5 FEET ABOVE INVERT
TOTAL STORAGE PIPES 36" AND ABOVE
NO FLOW DYNAMICS
NO MANHOLE VOLUME
TOTAL STORAGE ALL PIPING
NO FLOW DYNAMICS
NO MANHOLE VOLUME
TOTAL STORAGE ALL PIPING
WITH FLOW DYNAMICS
NO MANHOLE VOLUME
TOTAL STORAGE ALL PIPING
NO FLOW DYNAMICS
WITH MANHOLE VOLUME
TOTAL STORAGE ALL PIPING
WITH FLOW DYNAMICS
WITH MANHOLE VOLUME
18000
20662 FT3
24531 FT3
21233 FT3
25155 FT3
ANALYSIS MODE
ALL PIPING"
FLOW DYNAMICS""
MANHOLE VOLUME*"
FLOW DYNAMICS PLUS
MANHOLE VOLUME
SUMMARY
VOLUME INCREASE
5662
3919
571
4493
PER-CENT INCREASE
14.8
19.0
2.7
21.7
* COMPARISON OF ALL SYSTEM PIPING TO PIPES OVER 36 INCHES
** BASED ON ALL SYSTEM PIPING
6012
-------
peak rates to insure later plan implementation would not flood
basements. Also, no point was considered that would cause backup
beyond a point where trunk sewer lines intersected. The intention
of this limitation was to avoid altering the flood relief
patterns for which the relief system had been originally designed
and built/ and to avoid diverting flows to different regulators
through the bifurcation points.
Empirical functions were developed at each candidate
in-line storage control point relating stage (of back-up) to
storage volume. These functions were prepared by using the
interactive computer program to determine in-line storage
estimates for several plausible elevations and then curve fitting
the results. These empirical functions were then utilized in the
simulation model.
Pre BMP in-line storage conditions were analyzed based
on average river conditions with the gate-river interactions
determining the extent of storage in many cases. The total pre
BMP storage volume was calculated to be 327,000 cubic feet. The
total potential capacity for system storage including the two
aeration tanks at the WWTP is estimated to be 3.93 million cubic
feet, or the equivalent of approximately seven of the Hancock
Street sized storage basins. In-line sewer system storage
including the interceptors account for 58 percent of the total.
Storage estimates for individual catchment areas are presented in
Table 6.2 Storage estimates are provided for pre BMP
conditions and for the final BMP plan as determined by EDP.
Exact storage volumes for locations to be modified
under the complete BMP program will be dependent upon final
selection of weir elevations. This selection will be based on
detailed hydraulic evaluation similar to those performed for the
regulators modifed under the reduced BMP plan and detailed in
Chapter 7.
6.5 Interceptor Mfidj£l
The interceptor model is summarized schematically in
Figures 6.4 and 6.5. Figure 6-4 is an overview of the model while
Figure 6.5 illustrates the computational procedure.
The interceptor model divides the interceptor system
into four sections. Each section is treated as a quasi
independent "tub." A mass balance is performed to account for
influents, effluents and pump station overflows. Dynamics are
incorporated to model the river crossing and to calculate
discharge from one section to the next.
6.13
-------
TABLE 6.2
IN-LINE STORAGE POTENTIAL
Location
of
Flow Control
Device
1 . Downstream
East Side
14th
First
Carlisle
Fitzhugh
Johnson
E.Genesee
Federal
Janes
Millard
Thompson
Hoyt
Emerson
Holden
McCoskry
Holland
Webber
Estimated
"Pre BMP" Storage
(Low River)
(1000 Cubic Feet)
25
2.4
5
36
1.3
0.7
4.5
4.5
1.2
35.2
1.4
2.4
1.4
66
2.7
38
ESTIMATED "BMP"
Storage
Capacity
(1000 Cubic Feet)
25*
4.7
15
70
27
6.9
25
125
6.7
63
5.3
5.8
14
110
22
38
6.14
-------
TABLE 6.2 INLINE STORAGE POTENTIAL (CONTINUED)
Location
of
Flow Control
Device
West Side
Weiss
(ave. river)
Cronk
W. Genesee
Remington
Throop
Hayes
Adams
Mackinaw
Fraser
2 . Upstream
14th area:
at 17th & Perkins
at 14th & Normal
Webber area:
at River St. & Cam
at Birch & Harris
at Troy & Boxwood
Fraser area:
at Vermont & Salt
Estimated
"Pre BMP" Storage
(Low River)
(1000 Cubic Feet)
23
36
1.0
3.8
3.8
3.3
51
1.9
24
-
-
brey
-
-
-
ESTIMATED "BMP"
Storage
Capacity
(1000 Cubic Feet)
66
54
19.0
2.5
4.1
2.6
21
1.6
24
253
106
191
153
42
191**
6.15
-------
TABLE 6.2 IN-LINE STORAGE POTENTIAL
Location
of
Flow Control
Device
Mackinaw area:
Estimated
"Pre BMP" Storage
(Low River)
(1000 Cubic Feet)
at Hamilton & Williams
at Gratoit & Michigan
at Mackinaw & Michigan
Adams area:
at Jackson & Mason
at Cass & Woodbridge
Hayes area:
at Hayes & Michigan
Cronk area:
at Union & Delaware
Totals
Interceptor
Storage
WWTP
Total Storage***
327
770
500
1597
ESTIMATED "BMP"
Storage
Capacity
(1000 Cubic Feet)
92
125
54
60
67
133
2655
770
500
3925
* Storage control was not located at regulator chamber
plan in lieu of upstream control
** Included as part of reduced BMP Plan underflow
control modification
* **
Does not include Hancock street storage basin
6.16
-------
Douglas (OWF only))
Webber >-
Birch J
Holland
McCoskry
Emerson
Hnut .,. .,
Thompson
Ml Hard
Janes
Federal
Genesee
Johnson
Fltzhugh
Carlisle
First
1^ tn e* c». ..«
14th St. (4 Lines)
WEB
•k. ARE
Emerso
BER FW
A AF
fc FMrP^ON PUMP STATION
i i
on 3
n Area
i
Sectl
* Fourtee
Are
HANCOCK
STORAGE BASIN
t
Sectl
Hancoc
ISER < (Fraser
IEA ^ ( Dearborn
Mackinaw
van Buren/cass
Adams
k Area Hayes
Thrnoo
i i
on 4
nth St.
a
RIVER
CROSSING
Sect
Weiss
Miller
Remington
i W. Genesee
Ion 2 « \ Cronk
Area ( Weiss Street
1 1
WWTP WEISS PUMP STATION
1 ._ » ArRATTflN RACTNC AT UUTP
Figure e.,4 Interceptor model overview.
-------
Prediction of Flow
to Interceptor and
Water Quality
Lj
r"
L_.
i —
L_
SECTION 1
Ml
Vol - Flow In
+ Previous Volume
- Flow Out
| ITERATION
Flow Out - f (Head)
'
i *
Pump
Overflow » Vol
- Maximum Vol
1 '
1 •
SECTION 2
1 •
Vol.
,, ITERATION '
Flowout
I
Pump Overflow
SECTION 3
•WM i
j
1
1
1
1
... . ,._
_» Head Down Stream) 1
1
Max Vol. - f (Weir at !
Pump Station) j
Max Head - f (Max. Vol.) |
i
1
1
1
__ i
Head 1
' i
_. .»~.v,.
Max. Head |
1
1
1
Figure 6.5 Interceptor model computations.
6.18
-------
Head, West Side
Effective Head
= f(Applied Head
- Head Loss)
Velocity
= f(Effective Head)
Head Loss
= f(Velocity, Physical
Restrictions)
1
FLOW ACROSS RIVER
Figure 6-6West Side river crossing model.
Head, East Side
ITERATION
6.19
-------
The calculation procedure is to proceed from section 1
to section 4. Volume is calculated from the time stream of
regulator flows to the interceptor added to the existing volume
in the interceptor, minus the flow into the next section.
Overflow is any volume in excess of the available volume after
the volume calculations are completed. Flow between sections is
calculated on the basis of head differentials between sections.
An iteration scheme is used to balance the volume, head and
discharge calculations for each section. The West Side
Interceptor river crossing simulation model depicted in Figure
6.6 operates on basically the same principle of head/discharge
balance through an iteration procedure.
Options for altering the operation of the interceptor
were included in the model. Pump station weirs could be altered
to increase available interceptor storage volume if possible, and
to increase the head differential between sections. This option
was used at the Weiss Street Station to increase the flow across
the river. Alterations at the WWTP as described below were also
built to interact with the interceptor model by altering the
allowable discharge to the plant from interceptor section 4.
6.6 West Side Interceptor £iy_ej: Crossing Consider^tj.pi\s
The junction of the West Side Interceptor river
crossing and the East Side Interceptor has been identified as a
hydraulic bottleneck. The Weiss Street Pumping Station relieves
backwater/surcharge at the crossing and is a major combined sewer
overflow. It is clear from an analysis of the frequency of pump
operation and pumping plant discharge rates at the Weiss Street
Station during rain events, that flow across the river into the
East Side Interceptor is severely limited. Coupling this
understanding with the objective of handling more wet weather
flow through the use of aeration tank storage and/or increased
WWTP flow-through rates suggested consideration be given to
increasing flow across the river. An iterative procedure was used
during modeling to simulate the river crossing as illustrated in
Figure 6.6.
Phase I ModeJ.j.jig Considerations (1979-1981)
Details of the West Side Interceptor river crossing are
shown in Figure 6-7. The crossing is accomplished through a 42
in. pipe under the river, and 48 in. pipes near the end on each
side of the river. Maximum head differential at the river
crossing is based on the spillover weir height at the Weiss
Street Station from the West Side interceptor. This head range
can vary between negative values and 8 feet depending on the
flow conditions in the East Side Interceptor at the junction.
6C20
-------
66'
from east side
from west side and river crossing
72"
to WWTP
r>o
PLAN VIEW
66'
PROFILE VIEW
Figure 6.7 Details of river crossing, Saginaw.
-------
Examination of the river crossing suggests two
important physical restrictions to flow. One. the small pipe
sizes used to carry the flow across the river will limit flow
depending on the energy applied to the flow. The other is the
near right-angled junction of East and West Side Interceptors
which may result in a large energy loss due to the turbulent
mixing of the two flows. The actual head applied to the crossing
was expected to be the primary parameter for determining flow
across the river during storm events.
The relative importance of East/West Side junction
energy losses in Saginaw to the flow across the river during
storm events is summarized in Figure 6.8. Here, the maximum flow
across the river is plotted as a function of flow depths in the
East Side Interceptor. Calculations were made using Darcy's
equation and average friction factors for concrete pipes. A
computer program was developed to handle the changing pipe sizes
in the section crossing the river. Head values on the West Side
were based on the weir evaluations at Weiss Street Station, above
which flow is diverted from the West Side Interceptor to Weiss
Street Station. Therefore, the curves presented represent the
maximum flow across the river just as overflow occurs at Weiss
Street Station.
The lower set of curves in Figure 6.8 represent the
pre BMP conditions. The upper set represents flows under an
additional head of five feet at the Weiss Street Station
(presumed relative easy to accomplish by raising the weir
elevation).In each set of curves, the lower line included K = 1.8
junction energy loss factor, while the upper curve ignores
junction energy loss. Therefore, the two lines in each set of
curves form the upper and lower bounds of what the true flow is
expected to be. Estimates of the ratio Q are also shown for
different levels of stage in the East Side Interceptor.
The most likely range of operation is when high flows
in the West Side Interceptor are matched by high flows in the
East Side Interceptor, probably around full pipe conditions. As
Figure 6.8 demonstrates, flow from the West Side Interceptor is
severely reduced as water level rises in the East Side
Interceptor, and can be entirely shut down if two and one-half
feet of surcharging occurs in the East Side Interceptor. At full
pipe East Side Interceptor conditions, flow across the river has
been reduced from a maximum of around 60 cfs (no flow in the East
Side Interceptor) to less than 36 cfs.
Adding an additional five feet of head on the spillover
weir at the Weiss Street Station, such as by raising the weir
6022
-------
100 -
cr>
ro
CO
Row from West
Flow in East
5 foot head addition
at Weiss
5678
Depth of flow, East Interceptor (feet)
10
Figure 6.8 Analysis of Saginaw River crossing discharge levels.
-------
elevation into the station's wet well, does a great deal to
increase flow across the river. This is particularly true in the
operating ranges of high East Side Interceptor flow. At full
East Side pipe flow, flow across the river can be increased from
below 36 cfs to above 60 cfs, and the gain is even greater for
surcharged conditions in the East Interceptor. However, even for
the more unlikely events of high West Side Interceptor flow and
low East Side Interceptor flow, the gain by increasing the head
differential is still substantial.
Figure 6.8 also demonstrates the relatively unimportant
role played by energy loss at the junction itself. Gains made by
improving head loss conditions at this junction could be no more
than a few cfs, with these gains decreasing as East Side
Interceptor flow rises and becoming very small in the most
likely range of operation ( QR = 3). This result suggests that
the junction itself may not be the best candidate for future
improvements .
The additional five feet of head at the Weiss Street
Pump Station will not significantly impact the pumping pool level
at the Hancock Street Pump Station considering level pool
conditions but due to the increased water elevation (and the net
head reduction between Weiss and Hancock) will serve to reduce
flow rates between Hancock and Weiss. This result will reduce the
pump chattering noticed from the Hancock records. It would be
advantageous to further investigate and optimize the relative
turn-on elevations of the pumps at Weiss Street and Hancock Street
facilities to ensure initial operation at Hancock where
storage/treatment is currently available as opposed to the
untreated pumpage at Weiss Street.
In summary, theoretical analysis of the river crossing
strongly indicates that flow is being severely restricted during
storm events. This is due to the small pipe sizes used to make
the crossing, and the lack of necessary high energy differentials
to overcome friction in the small pipes, particularly when flows
are also high in the East Side Interceptor. Based on empirical
and theoretical work on energy loss at pipe junctions, the nature
of the East/West Interceptor appears to be a relatively trinor
cause of river crossing flow restrictions.
3 Model in Conisiderat ions 934
The above analysis was based on system hydraulic
conditions as established during Phase 1. During the Phase 3
analysis it was determined that the influent pump wet well
includes high and low levels alarms set at 551 and 556 feet,
respectively. Original design and construction hydraulic
6.24
-------
profiles had indicated an operating wet well elevation of 547 ft.
Actual operation at this elevation can cause severe pump
cavitation.
The relative elevations of the WWTP influent pumps wet
well and the 6 foot East Side Interceptor are such that normal
plant operation between these alarm points backwaters the
interceptor to varying degrees. Operation of the WWTP influent
pumps is performed manually and higher or lower wet well levels
are possible. Level pool backwatering at the alarm elevations
translate to depths of 1.5 ft and 6.5 ft in the 6 ft diameter
East Side Interceptor at the junction of the 48 inch West Side
Crossover. Given that the 48 inch crossover line invert is 0.5
ft. above the 6 ft interceptor invert, backwater effects range
from 1 ft depth to 6 ft depth (2 ft surcharge) in the crossover
line.
The crossover analysis prepared in 1979-1981 (Phase 1)
presented in Figure 6.8 was modified in Phase 3 considering
interceptor wet well alarm levels and the results are depicted in
Figure 6.9.
Low alarm (551 ft) and high alarm (556 ft) WWTP wet
well induced backwater levels are indicated on Figure 6.9 at the
interceptor depths of 1.5 and 6.5 ft respectively. In addition,
a line indicating the hydraulic capacity of the interceptor with
varying depth is shown. The significance of this line is that
any wet well level and total interceptor flow condition falling
to the left of the line will induce an interceptor liquid level
governed by the interceptor flow rate and will be unaffected by
backwatering. The actual interceptor depth will be as indicated
by the intereceptor flow rate at the capacity line.
Wet well levels and interceptor flow rates to the right
of the capacity line indicate backwater-controlled conditions.
Flow in the East Side Interceptor and the West Side Crossover
will be a function of the degree of surcharging in each line.
Surcharging of the West Side Interceptor crossover is limited by
spillover into the Weiss Street Station wet well.
Under conditions existing prior to the weir
modifications implemented under the reduced BMP plan, crossover
flow was limited to the rates indicated by the lower "pre BMP"
line shown in Figure 6.9. Assuming a low alarm WWTP wet well
level, the maximum crossover flow was about 53 cfs. Under
potential high wet well conditions, (even during dry weather),
crossover flow was limited to 30 cfs prior to spillover at the
Weiss Street Station (assuming level pool conditions).
Considering head losses between the junction and the WWTP, the
maximum crossover rate would be 25 cfs. As indicated on Figure
6.25
-------
WO -
INJ
X
H-
n
n
o
»
n
5
A
O
Ml
a
,East Side Interceptor
Maximum Capacity at Depth
WWTP Low Met
Well Alarm
Level
WWTP High Wet
Well Alarm
Level
in Crossover
Reduced BMP Levels
East Side Interceptor Surcharged
Pre BMP Levels
Pre BMP Flap
Gate Seat Elev.
.3 I
Post BMP Weiss
Weir Elev. (562.25')
4 9 6 7 8 9 10 1 I
Depth of Flow, East Side Interceptor (Feet)
Figure 6.9 Verification of Weiss Street Pump Station Weir Modification
Effects on Crossover Rates
-------
6.9 the spillover elevation into the Weiss Street Station is 8 ft
above the East Side Interceptor invert and only 1.75 ft above the
WWTP wet well high alarm water level. Head losses within the
East Side Interceptor and the crossover and occurences of wet
well levels above normal may contribute to spillover into Weiss
at minimal crossover rates. Modification of the Weiss Street wet
well inlet by increasing the spillover elevation by 5 ft
eliminated early spillover and maximized crossover flow.
Estimated potential crossover rates after reduced BMP
modification are indicated by the upper line of Figure 6.9. The
maximum crossover rate under optimum conditions (low alarm wet
well level, no East Side Flow) is 73 cfs. The maximum crossover
rate under high alarm wet well level conditions is estimated to
be 50 cfs. Adjusting this value for surcharge due to head loss
in the interceptor between the WWTP and the junction indicates a
maximum crossover of 47 cfs.
In sum, under optimum conditions (low wet well, no
upstream East Side flow) the maximum crossover rates would
increase from 53 to 73 cfs due to the weir modifications. Under
the condition of high wet well and no upstream East Side flow the
maximum crossover rates would increase from 25 to 47 cfs due to
program modifications. Upstream East Side flow will always exist
and this flow will induce greater head loss and surcharging of
the interceptor further reducing the potential crossover flow.
The conclusions of this analysis are that modification of the
Weiss Street Station spillover weir level will increase the
crossover rate by about 20 cfs under all conditions and that
operation of the WWTP wet well within the alarm range can vary
the crossover flow rate by 25 cfs.
Cros_s_:Lng HY-ElH^Jii0-0.
One aspect of the post evaluation (1984) was to
document the improved river crossing flow regime by evaluation of
the WWTP wet weather flow records. It was expected that greater
volumes of flow would reach the plant during storm events after
Weiss Street Pumping Station weir modifications were performed.
Following the Nov. 1, 1984 event high WWTP flow rates
were observed for several days. Total flows were greatly above
additional volumes expected due to Weiss Street weir
modifications. Field investigations discovered a log jarring
open a backwater gate allowing river water into the West Side
Interceptor. Although this situation rendered invalid any
attempt to document relative storm related flow volume increase
at the plant, the several days of additional inflow provided a
near perfect situation for evaluating river crossover flow
conditions. During the period of river inflow, WWTP influent
6.27
-------
rates remained near 71 cfs for several days, and the West Side
Interceptor level was reported to be just at the Weiss Street
weir level. Based on the early morning WWTF flow rates prior
to, during and after this event it was estimated that 37 cfs of
river water entered the interceptor. Remaining flows were
estimated as: other West Side - 16.6 cfs, upstream East Side
9.8 cfs and additional downstream - 8 cfs based on the system
distribution detailed in Chapter 5.
Figure 6.9 was utilized to demonstrate that this data
verifies the predicted potential crossover rates. The only
unknown factor was the WWTP wet well elevation. Estimating head
loss in the interceptor between the junction and the WWTP for the
71 cfs flow rate as 4.2 ft and assuming the low alarm wet well
condition, results in a depth of flow in the East Side
Interceptor of 5.7 ft. Point "A" on Figure 6.9 indicates that
for the estimated crossover rate of 53.6 cfs this data set falls
to the left of the predicted line. Increasing the wet well
liquid elevation above the low alarm level would shift the data
point to the right closer to the prediction line. Alternatively,
using the West Side Interceptor level and estimating the head
loss of 53 cfs through the crossover at 5 ft placed the East Side
Interceptor data point , Point "B", just on the prediction line.
This would indicate a WWTP wet well level of 2.3 ft above the
low end of the 5 ft alarm range, a quite probable condition.
Based on this analysis and the uncertainty of the exact
wet well condition it appears that the prediction line accurately
portrays maximum river crossing flow rates prior to spillover to
the modified Weiss Street Station wet well.
6 . 7 Runof_f_ Wja ter Qua 1 j.ty_
Runcff water quality is calculated from three
components: dry weather sewerage, cumulated dry weather sewerage
deposition and street washoff.
The dry weather BOD and suspended solids (TSS) mass
loadings at the WWTP were used as data inputs in the simulation
model. Total dry weather mass loading at the WWTP was
apportioned to the different catchment areas in the simulation
model on the basis of relative contributory dry weather
discharges. This procedure implies uniform dry weather flow
concentrations throughout the system.
Since most of Saginaw is flat and dry weather sewerage
deposition are expected to be considerable, pollutant deposition
loadings during dry intervals between storm events were included
in the simulation model. Deposition rates were based on the above
calculated long term dry weather flow averages. Empirical
6.28
-------
equations developed by EDP (1) were used to approximate daily
deposition rates for the more important drainage areas. These
equations require as input the following quantities: a) total
collection system pipe length; b) average collection system pipe
slope; and c) the average per capita waste rates. For simulation
work a constant daily deposition rate equalling 15% of the dry
weather pollutant loading for each catchment area was used
throughout the system. Comparison between the empirical results
derived for four catchment areas and an arbitrary assumption of
15% of the total dry weather load is shown in Table 6.3 and
suggest that the 15% simplification is reasonable. Resuspended
deposited loadings are assumed to be distributed evenly
throughout any rain events. It is further assumed that all
deposited loadings would be scoured and completely flushed in an
given event, that is, there would be no carryover of residual
loadings to the next event. This assumption may distort the
"first flush" estimates for both high and slight runoff events,
but would yield on the average, satisfactory estimates.
Street runoff water quality was estimated using
empirical equations based on rainfall and percent imperviousness
of each catchment area (2). The empirical equations given below
for street runoff were adjusted to better match the expected
values in Saginaw. The equations used as a starting point in the
calibration analysis are as follows:
1.05
TSS (Ib/acre) = I/(0.136 + 0.00384 (I)(rain) )
BOD (Ib/acre) = (614/1)(rain)0.82 (2)
where I is percent imperviousness and rain is the total
for the event in inches.
Because street washoff water quality is the most
difficult component of the analysis to predict without adequate
local data, manipulation of the empirical curves developed in
other communities was considered necessary. Dry weather flow
loadings and deposition rates were left unaltered. Initial
simulation runs showed both excessively high TSS and BOD loadings
and runoff concentrations. Street washoff pollutant formulations
were altered (reduced) to better match Saginaw conditions.
Several of these curves for a number of different
municipalities are shown in Figure 6.10. Imperviousness is an
implicit parameter in developing these curves. Saginaw was
considered to be cleaner than the municipalities used to derive
the equations (streets are well swept, for example) and it was
expected that Saginaw washoff solids loadings to be on the lower
end of the group. Saginaw loadings fell to the higher end of the
group of curves shown in Figure 6.10 using a 34% overall average
6.29
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TABLE 6.3
COMPARISON OF COLLECTION SYSTEM DAILY DEPOSITION LOADINGS
Collection
System
Method A
TSS*
BOD*
Method B
TSS*
BOD*
ADAMS
WEISS
WEBBER
McCOSKRY
530
1100
520
280
300
600
300
160
540
1700
960
440
240
720
420
200
Method A: Dally Dry Weather Collection System Deposition Loadings Equal to
15% of Total Daily Load.
Method B: Prepared using empirical equations (1)
* - pounds solids deposition per day
6.30
-------
-------
imperviousness. The solids washoff formulation was reduced by a
factor of four (See Figure 6.10) to lower the solids curve for
Saginaw in comparison to other municpalities, and to better match
the available Saginaw suspended solids data.
The street washoff BOD loading formulation given by
equation was also adjusted. For example, the computed ratio of
TSS to BOD loadings using the equation (2) is 6:1 for a 0.1 inch
storm. More common ratios are 20:1, 24:1 and 7:1 for residential,
industrial, and commercial areas, respectively (3). This
comparison suggested the BOD predicting equations used for
simulation were also high. EDP used data from previous work (4)
to adjust the BOD predicting equations. Literature surveys of
BCD street accumulation rates had found these rates to be equal
to 0.15, 0.21, 0.64, 0.53 and 0.11 pounds per acre per day for
single family, multiple family, commercial, industrial, open land
uses, respectively. An average of 0.3 pounds per acre per day
was estimated for Saginaw land use mix. Using an average of four
days between rain events and a nominal washoff factor, 0.1 inch
rain will produce approximately 0.3 pounds per acre cf BOD. This
value is one sixth the value from the simulation equations. The
equations were therefore lowered by a factor of six.
6.8 WWTP Simulation
The TSS and BOD efficiencies at the WWTP were
established at 93% and 89% using long-term average data. Maximal
plant throughput flow of 128 cfs was allowed. Additional flow
above 108 cfs was assumed to be split at the grit chamber with
half bypassing the main plant facility. Excess flow above 128 cfs
was allowed to backup resulting in overflow at the Weiss Street
Pump Station.
Phase 1 modeling investigations (1979 -1981) indicated
a potential for increased utilization of the WWTP during wet
weather. It was envisioned that increased utilization of the WWTP
capacity during wet weather would be an extremely cost-effective
option in the overall combined sewer control management approach
for Saginaw.
During the Phase 1 modeling, it was believed that
additional wet weather flow could be handled. A rudimentary
analysis was conducted to assess the pollutant removal
effectiveness at the WWTP during wet weather flow conditions. BOD
removal efficiencies were investigated during high flows and
compared to low flow conditions to ascertain the feasibility of
this approach. A year and a half period of WWTP daily operating
records for 1978-1979 was examined. The BCD removal for the WWTP
averaged approximately 89% for both wet days and dry days. It was
6.32
-------
tentatively concluded that the WWTP could handle higher wet
weather flows without compromising the plant's pollutant removal
capabilities.
The WWTP portion of the simulation model used for
assessment of the reduced BMP and complete BMP program
effectiveness is described as follows. Interceptor discharges
beyond a pre-set maximum of 128 cfs was assumed to backwater and
overflow upstream. All flows less than 108 cfs received full
treatment. Discharges beyond 108 cfs but limited to 128 cfs were
flow-split at the grit chamber with half the excess continuing
through the plant and the residual by passed (and disinfected) .
All flows continuing past the grit chamber receive full treatment
(BOD efficiency = 89% and suspended solids removal = 93%) .
These assumptions approximate current plant operations.
For small to moderate intensity storms the model assumptions very
closely replicate practice. For major storms of short intensityr
the assumed procedure is adequate provided the storage volume of
the two aeration basins used for detention are not exceeded. The
model slightly overestimates treatment efficiency for storm
events in which the aeration tank volume is exceeded and through
flow conditions result for the aeration tanks.
6.9 Model Cal ibr a tj op/Ver j. jLJcafrJ-jMl fiffpjts
Phase 1 JHojfleJL Calibration r. 1979 Fj.ow Data
The Saginaw CSO simulation model was designed to
provide a rough approximation of the degree and distribution of
overflow problems. As such, and recognizing the severe limits of
the available recorded calibration data, it was not appropriate
to fine-tune the model to the degree model calibration may imply.
Rather, available data were used primarily as a check for
reasonableness, and actual calibration was kept to a minimum.
The hydraulic simulation as developed on the basis of
the systems physical characteristics was not substantially
altered after initial comparison to recorded values during Phase
1. The major point of concern was the operation of the regulator
chambers as operation data were available only for four
regulators in the Hancock Street area. Different regulator
operational schemes were tested in the simulations analysis in
selecting the scheme that yielded the most reasonable comparison
of the predicted interceptor to measured flow data.
A number of single rain events were simulated to check
the adequacy of the model. The reasonableness of the simulation
model is demonstrated in Figure 6.11 showing the comparison
6033
-------
„
£
!
o
IO
to
O
0
7 M
if.
Ill
o
V)
"c.
o
Q)
0>
•2
o
u
•o
o
T3
"o>
O
c
o
U)
o
QL
E
o
u
I
a>
o>
volume of flow
cubic feet X 10s per hour
a>
!>.
3
O>
6034
-------
between a 0.3 inch modeled event occurring over a two hour
period, and a 0.33 inch actual rain event occurring over two
hours on November 1, 1979. Flow at the WWTP compared favorably
with predicted flows peaking slightly less than recorded values.
Flows at Lee Street on the West Side also compared well. Spot
measurments (not shown) made on the East Side also compared well
to predicted values. As shown in the table in Figure 6.11 the
predicted pumped volumes from the Hancock and Weiss Street
Stations closely approximate volumes computed from pumping
records. For the same rainfall event the predicted temporal
sequencing of flows at the Hancock Station, the Weiss Station and
at the WWTP are shown in Figure 6.12 and agree with observed
operation of the system.
Predicted overflows at the pumping stations compared
well with recorded values. Figures 6.13 and 6.14 show the
comparison of predicted and recorded stormwater pumped per rain
event for the Weiss and Hancock Street Stations respectively. The
circled data points represent recorded values developed in the
pumping station analysis and the square data points represent
predicted values for different rainfall events. The model
somewhat underestimates spring conditions of high snowmelt and
concurrent rainfall. Simulated overflows at the Emerson Street
Pump Station occurred only for extreme rain events in accordance
with the observed operation of the Emerson Street Station.
The results of a full year of simulations (1978) are
compared in Table 6.4 with WWTP records that were available for
the same period. The simulation model summarizes flow and water
quality as rain contributions above a nominal dry weather
loading. This calculation was performed so events of different
durations could be compared with their total loadings. An attempt
was made to discern the same statistic from the recorded WWTP
records. Plant flow records were analyzed to eliminate a period
around a rain occurrence. The estimation of wet weather flow
contribution changes substantially depending on the length of
period selected around a rain event. Table 6.4 demonstrates the
range using two to four days as the period eliminated after a
rain event to average the dry weather loadings. The simulated
rain contribution fell within the range for excess flow at the
WWTP.
Phase 1 - Calibration 19JJH Hatej: Quality
A storm generating combined sewer overflows was sampled
on July 8, 1980. The sampled storm was 0.83 inches of rainfall
occuring over a little less than two hours as recorded at the
Saginaw WWTP. For comparison EDP simulated a 0.8 inch storm
occuring over two hours.
6.35
-------
CT>
CO
CT>
400-
ft
300-
200-
100-
modeled event • 0.3" over 2 hours, beginning hour 1
mwmimi predicted flow Into Weiss pump station
itmiiiiiiiiii predicted flow Into Hancock pump station
mrnrr^ predicted at WWTP
MB^MWV.^
i
|
H
5
} \
1 I
1 I
1 I
IMM
1
78 9 10 II
Hours into event
12 13 14
Figure 6-12 Single event time sequencing.
-------
CTl
CO
6 -
5 -
O
-------
CTi
•
00
3-
O
er
2-
li
n A
I -
O (heavy flows due to spring thow)
°0
O
8
0°
I
.2
I
.4
I
.6
I
.8
I
1.0
I
1.2
LEGEND
O Recorded Values
D Predicted Values
Rain inches per event
Figure 6-14 Overflow into Hancock Street pumping station I978-I9T9.
-------
TABLE 6.4
PREDICTED VERSUS RECORDED VALUES AT WWTP (1978)*.
Predicted Recorded
Total Volume
of Flow
x 106 ft3
Volume of
Rain Contribution
x 106 ft3
TSS
x 106 Ibs.
TSS
Rain Contribution
x 106 Ibs.
BOD
x 106 Ibs.
BOD
Rain Contribution
x 106 Ibs.
1071 1130
57-140
89 (estimated)
11.7 10.3
1.9 0.8-1.2
(estimated)
6.2 5.7
0.7 0.1-0.3
(estimated)
* - (1978: 304 day period, January - October.)
6.39
-------
The EDP simulated storm generated slightly more
overflow volumes and slightly lower flows at the WWTP. Not all
overflow points were measured by the sampling program. The
primary overflow point at the Weiss Street Pump Station was
measured and compared well with the simulated value. Table 6.5
summarizes the hydraulic comparisons.
Measured water quality data was converted to total
pollutant loadings in pounds for comparison to EDP simulated
values (Table 6.5) Concentrations of pollutants were sampled,
however, flows at the time of sampling were not available. Since
the Weiss Street Pump Station uses constant capacity pumps, and
for a storm of .8 inch only one 100 cfs pump would be expected on
at any given time, an identical flow for each sample was
assumed. Total pollutant loads were calculated using the numeric
average of the water quality samples and the times the total
volume pumped. The resulting total loads compare well with EDP
simulated loads.
Phase 2. — Model Calibration
EDP directed detailed wet weather field investigations
peformed by City of Saginaw personnel at several regulators
during the summer of 1983 and an intense program between July and
November, 1984. Completion of the reduced BMP construction
program occurred at the end of September 1984 so that some events
represent pre BMP and others represent post reduced BMP
conditions.
As a check to the accuracy of the model developed in
Phase 1, the hourly rain data for each storm event occurring
during the 1984 pre reduced BMP period was used as a model
simulation input. Modeled results included WWTP flow volumes at
40 to 65 per cent of measured volumes, Weiss Pump Station volumes
at 40 to 125 percent of measured volumes and Hancock Pump Station
volumes at 160 to 280 percent of measured volumes. Based on the
consistently low values at the WWTP and consistently high values
at the Hancock Street Pump Station the model was reviewed and
modified in an attempt to improve field and model data
correlation.
It should be noted that several changes to the Saginaw
sewerage system had occurred since the original Phase 1 model
calibration, the most significant of which was the alteration of
relative initiation points at the Weiss Street and Hancock Street
Pump Stations. This alteration was performed by the City to
better utilize the storage capacity at the Hancock Street
detention facility prior to pumped overflow discharge at Weiss
Street and constituted a major change in system operation.
6.40
-------
TABLE 6.5
MODEL CALIBRATION RESULTS - STORM EVENT, 7/8/80
FLOW/VOLUME RESULTS
A. Sampled Storm: 0.83 Inches July 8, 1980
Simulated Storm: 0.8 Inches
Overf 1 ow jfpl umes LLO.fi. cub Ic -feet)
Measured Mode Ied
Weiss Pump 2.2 2.4
Station
Hancock Basin 0.3 0.6
Fourteenth * 0.9
Street
* pump station was sampled gravity overflow was not so total
overflow volume is not known.
WWTP Flows (mgd)
July 8, I960 Simulated
45 37
B. Weiss Pump
Time
(am)
1:25
1:45
2:05
2.25
2.45
numerical
average
total vol ume
Station Overflow W
of July 8, 1980
Measurements
BODs
mg/l
102
84
158
102
74
104
overf 1 ow = 16 mill
Total Pollutant Loadings at We
ater Quality Calibration
TSS
mg/l
188
192
1032
656
46
423
Ion gal 1 ons
Iss(pounds)
Measurement Simulated by Mode
TSS 56,500 59,300
BOD5 13,900 15,300
6.41
-------
The model was re-calibrated based on improved knowledge
of actual regulator operation, rainfall/runoff characteristics
and intuitive estimation of system hydraulics. For this purpose
the storm event occurring on July 10-11, 1984 was selected as it
included a high rain accumulation (1.14 inches) and occurred
prior to implementation of any elements of the reduced BMP Plan.
Model modification in general included, varying regulator
underflow/backwater gate characteristics, refining estimated
times of concentration in several drainage subareas and
alteration of interceptor stage/discharge dynamics.
The effects of these modifications, particularly of
increased time of concentration, were such that event runoff
durations increased and peak flow rates decreased reducing
modeled pumpage volumes at the Hancock Pump Station and providing
additional flow to the WWTP. For the 7/10-11/84 event final
ratios of field data volumes to modeled data volumes were 1.15 at
the WWTP, 1.05 at Weiss Street Pump Station and 0.90 at the
Hancock Street Pump Station. It should be noted that for each
event, rain data was recorded hourly at the Emerson Street
Station and daily by NOAA at the City Water Works Building.
Variances in rain data values at the two nearby locations, which
represent variable rain conditions within the City, were
typically much greater than the differences in field and model
data recorded for the 7/10-11/84 and most other events.
Considering the close correlation of the 7/10-11/84
field and model data, the model was considered suitably
calibrated for prediction of pre-BMP condition system flow
volumes. Each of the 1984 monitored storm events occurring prior
to completion of the reduced BMP plan construction was rerun
using the upgraded simulation model. Results including field
measured data to modeled data, volumes ratios and rain
characteristics data are included in Table 6.6.
Model results are closely correlated to field
measurements at the WWTP for the first 5 events. For the final
event the field to model ratio of 1.52 is high based on Emerson
Street Station rain data, however rain data also indicates the
NOAA Station recorded 1.95 times the Emerson Street Station rain
accumulation. In this case the average rain at both stations is
1.47 times the Emerson Street value and would probably produce
model data closer to the field value.
Weiss Street Pump Station data tends to differ
substantially from field data after the first event. Later events
with high field to model volume ratios are probably due to the
occurrence of these events during the construction period. A
number of the original regulating devices at the regulator
chambers were removed and a number of weeks passed before new
6.42
-------
regulating devices were installed. This would produce greater
flows to the West Side Interceptor which in turn would require
greater pumpage at the Weiss Street Station (prior to the station
weir modification). High values for the last event correlate with
the previous WWTP flow discussion.
As depicted in Table 6.6, the Hancock Street Pump
Station data indicate reasonable correlation. Typically, the
model predicts higher values than the field data which is
probably due to the model assumption of a 300 cfs station
capacity when potentially only 1 or 2 pumps actually operated
simultaneously. Exact "turn on" water elevations for the three
pumps are unknown and future study is required to optimize these
locations. Data presented is overflow to the river at Hancock
and does not include wet weather flows pumped to the detention
basin and bled back to the interceptor. For this reason events
indicating non-zero model data flow and zero from the field may
be misleading since the event may have actually activated the
Hancock Station but produced no flow to the river. In sum,
variances between Hancock Station field and model data for the
three locations are minor on an actual volume basis.
Phase i - Ppst Construction Model Verification
Monitored Storm events occuring in October and November
of 1984 provided field data representative of field conditions
existing after complete implementation of the reduced BMP Plan.
All West Side regulating devices were replaced with vortex
valve control regulators, one upstream storage chamber was
completed and the Weiss Street Pump Station weir was modified.
Unfortunately, few major events occurred during this period and
for several of these events, field data validity required
intuitive interpretation. Results are included in Table 6.7.
An event on 10/18/84 indicated reasonable agreement
between field and modeled data at the WWTP. The Weiss Street
data indicated a low model value which proved to be a consistent
trend for all events as discussed below. No field data was
recorded at the Hancock Street Facility and the model data was
combined with the 10/21/84 value for evaluation.
During the 10/21/84 event, one regulator flapgate
became lodged-open allowing river water to flow into the
interceptor until manually corrected. Data at the WWTP indicates
good correlation between model data and first day WWTP recorded
flow. Thereafter, plant flows continue to remain above normal,
presumably due to the open gate since similar rain conditions
during other events produced only single day effects at the WWTP.
Weiss Street model data was again typcially low. Model data for
6043
-------
TABLE 6.6
PRE REDUCED BMP CONSTRUCTION
TOTAL FLOW - 1000 CU FT
TREATMENT PLANT
WEISS PUMP STATION
DATE
7/10-11
8/5
8/8
8/18
8/27-30
9/7-11
FIELD
5300
2620
3120
2500
7715
5591
MODEL
4594
2432
2995
2233
6900
3671
R
1.15
1.08
1.04
1.12
1.18
1.52
UJELfi
3360
613
3032
1950
3233
2452
HQfiJSL
3212
791
1837
1160
4320
1533
R
1.05
0.77
1.65
1.68
0.75
1.60
FIELD
1207
0
220
0
-
0
HANCOCK PUMP STATION
E2EEL £
1339 0.90
518 0
309 0.71
112 0
2626
0 1
Ratio of Field/Model
6.44
-------
the 10/21/84 event at the Hancock Street Station when combined
with the 10/18/84 event model data, agreed well with the recorded
value representing both events. Correlation between field and
model data for this event is considered good.
Following a minor rain on 10/25/84, WWTP flow remained
high for several days producing flow equal to the model value
after 2 days and 35 percent greater after the third day. The
NOAA Station recorded twice the rain recorded at the Emerson
Street Station (used in the model) for the three day period which
again indicates the significance of storm intensity variation
throughout the drainage area. The other significant aspect of
the event is that minimal flows were modeled and also recorded at
Weiss Street and Hancock Street facilities somewhat verifying the
"low-end" calibration of the model.
Both events occurring during November in Table 6.7 were
subject to adverse conditions. On November 1 the large Weiss
Street flapgate lodged open, allowing large amounts of river
water to enter the system. On November 8-11 a four day wet
period was mostly snow, making accumulations and runoff
predictions difficult. In general WWTP and Hancock Street
Station flows modeled were in the range of recorded flow and
Weiss Street Station flow volumes predicted in comparison to
measured values were low.
Low predicted flow values at the Weiss Street Pump
Station are probably attributable to reduced river crossover
flows, a direct result of the wet well levels at the WWTP being
manually controlled.
As part of this study's recommendations it is
envisioned that the pump control systems at Hancock Street, at
Weiss Street and the WWTP be evaluated and optimized for maximum
pollution reduction using existing facilities. The general
conclusion resulting from the foregoing discussion is that based
on currently available field data, the model, as modified to
match pre-construction data, reasonably predicts the effects of
the reduced BMP implementation as recorded at the WWTP and at the
Hancok Street Pump Station.
6.10 Phosphorous Modeling Details
Phase 1 .& Phase 2. Considerations (1979-1983)
In addition to the TSS and BOD parameters previously
detailed, an analysis of potential total phosphorous removals
were performed for each simulation. Evaluation of phosphorous
loads in wet weather and dry weather flows and potential removals
6.45
-------
TABLE 6.7
POST REDUCED BMP CONSTRUCTION STORM DATA
TOTAL FLOW - 1000 CU FT
DATE
10/18
10/21
Day 2
10/25
Day 2
Day 3
11/1
Day 2
11/9
Day 2
Day 3
Day 4
TREATMENT PLANT
FIELD MODEL £
3475
4679
68182
935
2139
2807
2807
60162
3060
6444
10900
11400
2889
4862
2121
3379
3333
4367
7700
1.2
0.98
1.4
0.44
1.0
1.32
0.83
1.78
1.48
WEISS PUMP STATION
FIELD MODEL £
1768
**
4000
108
2562
2454
849 2.1
1439 2.8
0
839 3.0
605
387
992 2.47
HANCOCK
FIELD
1136*
0
774
540
HANCOCK PUMP STATION Rain Accumulation
* - Combined Data 10/18 & 10/21
** - Backwater Gate Reported Stuck Open
*** - Rain/Snow Mixture
.g Emerson
0.96 0.75
0.79
1 0.17
2.0 0.61
0.73
NOAA
0.67
1.0
0.35
0.80
***
0.65
£
1.18
1.27
2.06
1.31
-------
at the WWTP, began with a review of existing phosphorous
concentration records at various locations in the system.
A pilot study performed between October and December
1969 for assessing various methods of phosphorous removal
reported WWTP, raw sewerage total phosphorous concentrations to
range from 3 to 10 mg/1 and averaged 6.4 mg/1 (5). Review of
report data indicated wet weather flow concentrations to range
from 3 to 5.3 mg/1. During the July 8, 1980 storm event samples
were collected at selected overflow points. Total phosphorous
concentrations ranged from 0.2 to 7.5 mg/1 at the Weiss Street
overflow and from 0.15 to 1.3 mg/1 at the Fourteenth Street
overflow. Flow rates were not recorded and flow-weighted average
concentrations could not be computed. Total phosphorous
concentrations of several influent samples at the Hancock
Storage/Treatment Facility were averaged to yield a concentration
of 2.8 mg/1.
Table 6.8 presents summary results of total phosphorous
loadings to the WWTP for the period from October, 1978 to
September 1979, as determined from treatment plant records. Total
phosphorous concentrations were highest during fall months
presumably due to the effects of decayed foliage. Average WWTP
influent phosphorous concentrations for all weather conditions
are somewhat less than reported for the 1969 October to December
pilot study. Wet weather concentrations during October and
November, 2.5 and 3.46 mg/1, respectively, are comparable to the
1969 results. It is assumed that the dry weather concentration
reduction was due to a change in consumer use of phosphorous-
based products during the time between the two data periods and
that the more recent data accurately represent existing
conditions.
Average monthly WWTP total phosphorous removals for the
1978-79 period varied from 63.5% to 82.2 % and averaged 75%.
Average monthly wet weather concentrations indicate a yearly
average concentration of 2 mg/1. Further analysis of WWTP
removal efficiencies during wet weather conditions indicated that
the WWTP could adequately pass increased flow without
efficiency reduction. For the simulation model calculations,
total phosphorous entering the WWTP during wet weather flow was
set at a nominal concentration of 2 mg/1 and a WWTP removal was
set at 75 percent during Phase 1 and Phase 2 evaluations. Based
on the range of total phosphorous concentrations observed at
Weiss Street, Fourteenth Street, and at the Hancock Facility, a
total phosphorous concentration of 2.8 mg/1 was set as
representative of all overflows. Considering the floatable
nature of materials within CSO and the post storm draindown of
late event cleaner stormwater to the WWTP it would be expected
that overflow concentrations at regulator chambers would be
6.47
-------
TABLE 6.8
WASTE WATER TREATMENT PLANT
TOTAL PHOSPHOROUS SUMMARY
Month
7/79
8/79
9/79
6/79
5/79
4/79
3/79
2/79
1/79
12/78
11/78
10/78
Average
Influent
Concentration
MG/L
2.3
2.5
3.0
2.86
2.6
2.2
2.2
3.9
3.5
3.5
3.3
3.4
Average
EFFLUENT
Concentration
MG/L
.99
.89
.94
.85
.89
.76
.59
.67
.86
.85
.88
1.06
Average
Removals
a
A*
63.8
63.5
68.9
68.6
65.8
66.2
72.8
82.2
75.4
75.2
71.2
76.3
Wet Weather
Average Influent
Concentration
MG/L
1.74
1.98
-
2.45
2.08
2.1
1.52
-
-
-
2.5
3.46
75.
2.00
6.48
-------
greater than WWTP concentrations. These concepts are reflected in
the above values.
Phase 3_ Additional Considerations (1384^
The above phosphorous analysis was based on data collected
during the late 1970's when standard practice at the WWTP
included the use of waste pickling liquor or ferrous sulfate for
phosphorous removal. In the last several years, lower influent
phosphorous concentrations have enabled the City of Saginaw to
meet effluent standards without the continuous use of this
specialized phosphorous treatment. The effects of discontinued
pickling liquor treatment on overall phosphorous removal rates
were investigated in Phase 3 of this study.
During this period of the study, U.S. EPA requested EDP
to investigate the soluble fraction of the total phosphorous
load as it is the soluble fraction which is most readily
available to aquatic growth in Saginaw Bay.
Up until this time, the standard procedure at the WWTP
included evaluation of total phosphorous concentrations. Plant
records for summer/fall periods in the years 1978 and 1979, the
base data years of the original study, were available and were
used in conjunction with current plant data for analysis of
phosphorous removal efficiencies. Historical data review was
limited to total phosphorous removal efficiency determination.
Soluble phosphorous data was attained as a special task during
this period.
The Phase 3 (1984) field investigation indicated lower WWTP
influent total phosphorous concentrations than reported during
earlier periods. Average WWTP concentrations for all flows for
the 5 month June to October period were 1.55 mg/1. Wet weather
samples at the WWTP grit chamber indicated a weighted average of
1.3 mg/1, although "first flush" values were as high as 6 mg/1.
Wet weather concentration in the Weiss Street Pump Station
averaged 1.74 mg/1.
All loading calculations performed in the evaluations of
Chapter 10 of this report were made using values of 1.3 mg/1 for
wet weather flows to the WWTP and 1.74 mg/1 for system overflows.
Previous model analyses were based on WWTP influent phosphorous
concentrations of 2.0 mg/1 and overflow values of 2.8 mg/1 based
on data generated in the late 1970s.
WWTP data for the summer/fall periods, July to
September, 1978 and July to October, 1979 were separated accor-
ding to dry and wet weather conditions and with and without
6.49
-------
tertiary treatment (pickling liquor or FeS04 addition) and total
phosphorous removal efficiencies were computed. Results were as
follows:
%Removal of Total Phosphorous
Secondary Treatment Tertiary Treatment
Dry Weather 60 69
(No. days) (21) (151)
Wet Weather 56 69
(No. days) ( 9) (34)
Average 59 69
The above results indicate a 9% to 13% removal
increase using tertiary treatment. Although a 4% decrease in
total phosphorous removal occurred during wet weather secondary
treatment, no change was noted from dry to wet conditions with
tertiary treatment.
A review of WWTP data obtained for the summer/fall
period June to September, 1984 indicates an average total
phosphorous removal efficiency of 54% (120 days) for combined
dry and wet weather conditions without secondary treatment.
Beginning on September 17, 1984 both total and soluble forms of
phosphorous were investigated. In addition, on October 7, 1984
teritary treatment (pickling liquor addition) was re-instated
allowing for analysis of the removal efficiency for both total
and soluble phosphorous while under optimum treatment conditions.
Resulting data shown in Table 6.9 indicate a 50% total
phosphorous removal efficiency with secondary treatment which is
9% below 78/79 data and 4% below June to September 1984 average
data. No removal of soluble phosphorous was noted. After the
renewal of tertiary treatment, a 70.4% removal efficiency was
attained.
Inspection of the results in Table 6.9 indicates that
total phosphorous removal with secondary treatment is limited to
the removal of the non-soluble phosphorous fraction. On the
average 95.5% of the non-soluble fraction was removed. Soluble
concentrations actually increased an average of 4%. Considering
this removal efficiency and that the influent phosphorous is 54%
nonsoluble on average, the 50% total phosphorous removal value
reported above is normally attained. Inspection of the results in
Table 6.11B indicates that tertiary treatment provides removal of
both the soluble and non-soluble fractions. Non-soluble removal
was 88%, and the soluble removal increased to 47.4%. Influent
6.50
-------
phosphorous concentrations were 45% soluble (similar to the 45.9%
reported above - see Table 6.11A) such that the total efficiency
of 70.4% was attained.
In conclusion, tertiary treatment increases the soluble
fraction removal by 47%, and reduces the non-soluble removal by
7.5%, resulting in a total phosphorous removal of 70.4% or 20.6%
above that attained without special treatment. The decrease in
non-soluble phosphorous removal (95.5% as compared to 88%) is
apparently due to incomplete secondary clarifier settling of the
floculant material generated by the chemical reaction. Soluble
phosphorous tied up in the unsettled floe would appear as non-
soluble phosphorous in the laboratory analysis. Part of the
soluble phosphorous removal rate reported is attributable to this
apparent increase in the non-soluble fraction and on a total
phosphorous basis the effects tend to cancel each other out.
Results of these analyses were used to evaluate
potential WWTP efficiencies and therefore the net possible
reductions in river loadings under the various treatment schemes.
Values of 50% and 75% removal were selected to represent annual
averages of total phosphorous removal efficiencies for conditions
with secondary and tertiary treatment, respectively.
6051
-------
TABLE 6.9
WWTP Phosphorous Removal Results (1984)
Effects of Treatment With/Without Pickling Liquor (FeS04)
A. Treatment Without FeS04 (17 Days)
Influent
Total P
Soluble P
Non Soluble P
Avg. cone, mg/1
2.70
0.95
1.12
% of Total
100.0
45.9
54.1
Effluent
Total P
Soluble P
Non Soluble P
1.04
0.99
0.05
100.0
95.2
4.8
B.
Influent
Total P
Soluble P
Non Soluble P
% Removal
Total P 49.8
Soluble P -4.0
Non Soluble P 95.5
Treatment HUtti ££SJ24 (8 Days)
1.69
0.76
0.83
100.0
45.0
55.0
Effluent
Total P
Soluble P
Non Soluble P
0.50
0.40
0.10
100.0
80.0
20.0
% Removal
Total P 70.4
Soluble P 47.4
Non Soluble P 88.0
6.52
-------
CHAPTER 7
DESIGN OF REDUCED BMP PLAN MODIFICATIONS
7.1 Foreword
Throughout the preliminary Phase 1 modeling efforts
(1979-1981), simulations were run varying the hydraulic
operations of regulator chambers based on general physical
modification concepts. Design of the exact physical changes
required within each chamber was completed during the design of
the reduced BMP Plan implementation (Phase 2).
Physical details of regulator chambers and typical
modifications are presented in Section 7.2. Special
modifications required at the Adams Street Regulator and at the
Weiss Street Regulator are presented in Sections 7.3 and 7.4
respectively. Section 7.5 details the work performed to increase
the effective head at the Weiss Street Pump Station. Section
7.6 details the single new upstream in-line storage/control
chamber constructed under the reduced BMP Plan at Salt/Vermont
Streets.
7.2 Regulator Chamber Details and Modifications
Three general types of regulators were encountered in
Saginaw and have been classified as Type "A", Type "B" and
modified Type "B". All regulators are underground concrete
structures consisting mainly of the four concrete walls, floor
and ceiling, a central open top conduit, concrete side weirs, a
flap gate to the river, a wall cavity with manual sluice gate in
one side weir and a conduit leading to a drop manhole above the
main intercepting sewer.
Type "A" regulators have fixed underflow orifices,
generally about 1/2 foot by 1/2 foot. Type "B" regulators are
typically much larger than Type "A" regulators and also contain a
Brown & Brown flow regulator consisting of a wall thimble, swing
gate, a float and transmission apparatus. The regulator is
located on the downstream side of the side weir containing the
manual sluice gate. A separate adjacent chamber was constructed
to contain the float device and the transmission apparatus was
located overhead connecting the float to the gate.
Figure 7.1 illustrates the layout of a typical Type "B"
chamber. Type "A" chambers are similar without the float chamber
and Brown and Brown regulator as depicted in Figure 7.2. Figure
7.1
-------
» To River
Manual Sluice Gate
Brown & Brown
Flow
To
River
.
Automatic
Sluice Gate
Flap Gate
Connector
to Interceptor
Plan View
Float
Chamber
Transmission Device
Valve
Float
Brown &Brown Regulator
Section View A-A
Figure 7.1 Type "B" Regulator Chamber Schematics
7.2
-------
To Interceptor
Plan View
Access Manhole
To Chamber
Chamber
Underflow
Section A-A
Figure 7.2 Type "A" Regulator Chamber
7.3
-------
7.3 is a plan view of a Type "B" chamber depicting flow patterns.
Type "B" regulators have variable underflow rates altered by a
float gate operation. As water levels rise, underflow orifices
close. Table 7.1 includes pertinent regulator chamber dimensions
used in the hydraulic calculations and Table 7.2 includes
pertinent original and modified weir data.
In the unmodified Type "B" and Type "A" regulator
chambers high flows not handled by the underflows would be
discharged through backwater gates to the river. The operation
of the backwater gates was dependent on their seat elevations and
relative river elevation, and could be prevented or hindered from
opening in some cases for high river conditions. Most backwater
gates were in the same chamber as the regulator. A few backwater
gates were separated and situated closer to the river (for
example at the Cronk and Genesee Street Regulators).
Backwater gates are typical flap-type swing gates (with
the exception of the five modified Type "B" regulator chambers).
In most cases only a minimal amount of storm flow increase is
needed to raise water depth enough to open the flap gates and
cause a discharge to the river. The gates are also sensitive to
river elevations as most gate seats are located near average
river elevations. The Weiss Street gravity line is notably about
five feet below average river elevations. High river flows can
restrict the gate operation and subsequently require higher
depths of flow to cause river discharges. Varying river stage
can have a somewhat random effect in increasing the amount of
in-line storage of storm flow and decreasing overflows.
The third group of regulators encountered are the five
Type "B" regulators located in the Hancock Street area modified
during construction of the Hancock Street Detention Facility in
1977. The intent of the modifications was to increase in-line
storage, and to divert flow in excess of the in-line storage to
the interceptor (and eventually to the Hancock Street Facility).
The regulators had been altered to cause the underflow
orifices to clcse rapidly, limiting flows to the interceptor and
thus committing the first flush of a rain event to in-line sto-
rage created at the chamber. EDP considered it more advisable to
maintain high underflow discharges to the interceptor, limited
only to what the interceptor can maximally handle. Operation in
this manner will commit the first flush of a rain event, general-
ly carrying the highest concentration of pollutants, to the
inteceptor, and eventually to the WWTP. This mode of operation
is preferable to capturing the "first flush" in storage which may
become overflow at a later time if the rain continues and can be
accomplished with constant discharge devices that are more
reliable and easier to maintain than the present float mechanisms.
7.4
-------
Ul
CS to
Float
Chamber"
DWF to
Chamber
'."<
DWF to
Interceptor
f
| CS to
1 Interceptor
»
f
•"
SO
CSO to River
Figure 7.3 Type "B" Regulator Chamber Flow Patterns
-------
TABLE 7.1
BMP Program Regulator Chamber Weir Alterations
LOCATION
ELEMENT
OF REDUCED
PROGRAM
EXISTING WEIR
LEVEL ABOVE
INVERT FT.
BMP WEIR EXISTING NEW OVERFLOW
LEVEL OVERFLOW WEIR FT.
FT. WEIR FT.
REMINGTON Y
THROOP Y
FITZHUGH
JOHNSON
FEDERAL
W. GENESEE Y
MACKINAW Y
HAYES Y
CARLISLE
E. GENESEE
MILLARD
HOYT
HOLDEN
HOLLAND
EMERSON
WEBBER
McCOSKRY
ADAMS Y
JANES
THOMPSON
CRONK Y
FRASER Y
WEISS Y
FOURTEENTH
FIRST
MILLER
AMES Y
COURT Y
CASS
VANBUREN
DEARBORN Y
5.0
4.4
6.9
3.96
4.36
5.78
3.*
2.94
3.84
3.76
2.58
3.15
3.67
4.35
3-9
0
8.2
5.67
5.2
7.*
6.65
9.0
0
0
3.42
2
1.25
1.1
1.3
.9
.9
2.16
3.17
5.17
.96
1.2
.18
.9*
.14
.37
.5
1.09
1.3
0
1.09
1.34
8
4.16
2.94
.5
6.5
3.28
9-0
10.0
4.8
.5
2
1.25
1.1
1.3
.9
.9
—
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
2
1.25
2.8
2.0
1.9
1.9
6.0
5.4
6.42
2.7
2.9
1.6
4.4
1.2
1.4
1.5
2.65
2.95
1.0
2.7
3-4
3-25
6.5
5.28
2.0
8.5
4.95
5-67
9-0
2.8
2-5
3-6
3-75
2.8
2.0
1.9
1-9
7.6
-------
TABLE 7.2
REDUCED BMP PROGRAM REGULATOR CHAMBER
AND FLOW REGULATION DATA
Name/Location Type
Remington B*
Throop
W Genesee
Mackinaw
Hayes
Adams
Cronk
Fraser
Weiss
Ames
Court
Dearborn
B*
B
B*
B*
B
B
B
B
A
A
A
Salt/Vermont Upstream
* Modified
** Length of
** Length af
Hancock Area
Chamber
Dimensions
Length**Widtn Between
Side Weirs***
Ft.
12'6"
12'6"
18'6"
12'6"
9 '6"
30 '9"
12'6"
-
5'6"
4'
41
4'
Chamber
Ft.
6'0"
6'0"
4'0"
5 '3"
4'0"
7.4..
6'0"
-
2 '2"
3'6"
2 '9"
,,,
Flow Regulator
Design Criteria
Discharge
CFS
1.56
1.56
2.9
1.74
2.0
10.38
8.8
24.0
22.2
.37
.3
.3
Regulator
existing weirs to be altered (see
new weirs to be constructed (see
Table 7.1)
Table 7-1)
7.7
-------
Selection of appropriate vortex valves for each
regulator chamber location modified under the reduced BMP program
was based on apportioned flow rates (six times average dry
weather flow - Table 7.2) considering WWTP capacity and modifed
chamber configurations. Vortex valve head-discharge curves
characteristically include low level orifice peak, switchback and
near constant (low rate of flow increase) vortex flow condition.
Vortex valve selection was accomplished by comparing a particular
chamber's design flow/perceived operating head range with
manufacturer's rating stage/discharge data. The mcst desireable
selection results when the chamber 's operating head range extends
from at least low head orifice peak for the device up to
conditions where full vortex braking occurs. A less desireable
but still acceptable choice (if minor flucuations can be
tolerated) occurs when the upper end of the configuration's head
range does not fall within the devices establihsed vortex
operating range but in the switchback zone. The design
stage/discharge characteristics for each of the vertex valves is
listed in Table 7.3.
The regulators were modified in the reduced BMP program
to ensure that flows in excess of what is discharged through
the underflow regulating devices or stored in the system behind
the weir, will first overflow the side weir and be directed to
the interceptor. Only extremely high flows will overflow the
new cross weir separating the backwater gate portion of the
chamber and be directed to the river. This weir arrangement was
considered by EDF tc be both the least expensive and most
available method of limiting oveflows at any cf the regulator
chambers in the system.
7 . 3 Proposed We_ir Alterations
The reduced BMP program included the alteration of 12
existing regulator chambers. Each of these regulator chambers is
located on the West Side of the Saginaw River. Table 7.1 lists
all the existing regulator chambers and the proposed weir
alterations under the complete BMP program. Regulator chambers
altered under the reduced BMP plan are noted. Typical details of
regulator chamber alterations were shown in Chapter 1, Figure
1.6.
Regulator modifications included construction of a
concrete cross weir wall between the backwater gate and the flow
channel sluiceway of sufficient elevation to insure that
stormwater volume in excess of available in-line storage capacity
flows to the interceptor with only extreme flows discharging to
the river. The new cross weir is located just downstream cf the
7.8
-------
TABLE 7.3
Vortex Valve Stage/Discharge Characteristics*
Discharge (1/s)
Head (ft)
B
H
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
7.
8.0
9.0
10
11
12
470
530
570
600
620
600
570
550
600
658
710
760
804
850
891
240
265
285
300
285
260
255
270
285
300
325
190
230
250
230
190
180
175
180
195
200
220
240
260
68
77
82
72
79
87
95
102
108
113
119
50
57
51
44
46
48
51
54
58
62
64
38
44
39
31
29
31
33
35
36
38
40
43
(1
40
48
42
33
34
35
37
40
44
47
50
55
cfs = 28
10
7
8
9
10
11
12
12+
13
13+
14
15
.3 1/s)
4+
5
5+
6+
7
7+
8+
8+
9+
9+
10+
A - Weiss
B - Adams
C - Salt/Vermont
D - W. Genesee
E - Hayes
F - MacKinaw
G - Remington/Throop/Cronk
H - Ames
I - Court
* As per data provided by Advanced Fluidics, Inc.
709
-------
dry weather sluiceway and extends across the chamber between the
existing side weirs. Lengths of the new cross weirs are
indicated in Table 7.2. Existing side weirs creating the in-line
storage were modified to ensure that the water surface elevation
due to backwatering and flow dynamics satisfied the arbitrary
criteria of a 10 foot buffer zone to the ground elevation in the
area. The side weirs generally extend the length of the
regulator chamber and are modified the entire distance. Side
weir lengths are included in Table 7.2. Extreme stormwater flows
in excess of the interceptor capacity will backwater the
regulator chamber and spill over the side weirs downstream of the
new cross weir and discharge tc the river.
An inter-active computer program was developed to
determine optimum crest elevations of the modified side weirs and
new cross weir. Typical storm flows (2 and 5 year design storm),
extreme flows (50 year storm), weir lengths, and chamber outlet
capacity and other physical dimensions were considered in the
program. Conceptually it was intended to select a modified
configuration wherein maximum storage would be provided prior to
side weir spillover to the interceptor. In addition, maximum flow
to the interceptor would occur prior to bypass to the river. The
cross weir elevation was selected such that flew would top this
weir at the same time bypass to the river occurred due to
interceptor capacity limitations. The need to ensure sufficient
unrestricted passage for extreme storm flows was the limiting
factor in maximizing storage potential. Due to the uncertain
nature of the actual flow hydraulics under probable turbulent
conditions within the chamber, conservative weir elevations were
selected.
Four locations were designated to include adjustable
side weirs and cress weirs accomplished by attaching moveable
stainless steel plates to the concrete weirs. Based on operating
data within the chamber and stcrmwater backup conditions upstream
of the chamber, these plates can be adjusted to increase storage
if excess surcharge does not appear probable.
Curing the 1977 Hancock Street Facility Implementation
the flap gates were removed at the West Remington Street and
at the Throop Street Type "B" regulators, and were replaced with
automatic sluice gates. These flap gates were re-installed under
the reduced BMP plan. Both flap gates and automatic sluice gates
exist at Adams Street, Mackinaw Street and Eayes Street. Under
the "reduced BMP" plan implementation, all automatic sluice gates
were raised and left in the full cpen position at these
locations.
In general the scope of work at Type "A" chambers at
Ames Street and Court Street included: a) removal of existing
7.10
-------
regulator slide gate, gate stem, supports, brackets anchor bolts
and appurtenances; and, b) installation of new vortex valve
regulating device and accessories.
Modifications to the Type "A" Regulator at Dearborn
Street included: a) adjusting the existing slide gate to a 6
inch vertical opening, b) cutting down walls and resurfacing
crest on existing side weirs; and c) constructing new cross weir.
The general scope of work at type "B" chambers included:
a) removing existing float operated mechanical regulators
including float, gate, operating mechanism, cables, supports,
anchor bolts and appurtenances; b) removing existing stainless
steel weir plate and supports, c) installing new vortex valve
flow regulating device and accessories, d) cutting down walls and
resurface crest of existing side weirs, e) constructing new
cross weir, f) installing adjustable stainless steel weirs on
the two modified side weirs and on the new cross weir; and g)
recontouring fleer sections with concrete fillets to prevent
debris buildup and direct flow.
In addition to the above items at Type "B" regulator
chambers at West Remington Street and at Throop Street, ether
modifications included: removing and salvaging the existing
automatic sluice gates and installing new tide gates.
7.4 Sp_ec.ia_l Modification o f_ the Adams_ Street Type "E"
Regulator
The placement of the new flow regulating devices within
most Type "E" chambers was behind the side weir wall next to the
interceptor outlet (See Chapter 8 for additional details). The
installation of the new flow regulator could not be similarly
accomplished at the Adams Street Regulator due to the relative
flow regulator size and the chamber size. Considering the very
large drainage area serviced by the Adams Street Chamber the new
flow regulator was roughly twice the size of other "B" type
chamber devices.
The chamber area downstream cf the side wall containing
the original Brown and Brown regulator is 4 ft. wide and due to
this limited space, it was necessary to locate the new flow
regulator directly in the sluice area of the chamber. As with
all other chambers, the design of the final configuration was to
include the following functions: a) allow dry weather flow to
pass through the flow regulator to the interceptor; b) store
initial wet weather flow; c) pass additional wet weather flow to
the interceptor; and, d) to limit river bypasses to extreme flow
conditions.
7.11
-------
Only one of the typical two side weirs existed at the
Adams Street Chamber which limited the weir length available for
stormwater overflow to the interceptor prior to overflow to the
river. The need for additional side weir length coupled with the
difficulty in placing the new flow regulator and a desire to
minimize debris accumulation in remote chamber areas led to a
complete modification of the chamber interior.
Figure 7.4 illustrates the final configuration selected.
Two new cross weirs were constructed in the chamber. The
upstream cross weir was placed at an angle to the side walls for
the dual purpose of maximizing the available overflow length and
to direct flow to the regulator device inlet. This weir was
constructed at the same elevation as the modified, (cut down)
side weir such that storm flow in excess of storage capacity will
top these weirs simultaneously and pass to the interceptor.
Concrete fillets were used upstream of the cross wall to
assist directing flow to the inlet and prevent debris
accumulation. Downstream of the cross wall, the sluiceway was
concrete filled and the existing regulator device and the manual
side wall sluice gate were removed. No overflow weir existed at
this side wall and to allow passage of new regulator device
outflow and cross wall overflow, a section of the side wall was
removed. A wall cut of 5 ft by 7 ft was selected based on both
flow volume criteria and to accommodate workman passage between
chamber sections.
Concrete filling of the original sluiceway flush with
the chamber inlet floor provided the large area necessary for
installation of the new flow regulator. A cast-in-place wall
thimble was designed for inclusion in the upstream cross weir for
mechanical attachment of the flow regulator. In addition, the
device was secured to a cast-in-place floor bracket. Again,
concrete fillets were designated to minimize areas of debris
deposition and direct flow to the outlet.
Control of flow to the river is accomplished by the
downstream cross weir and the original side weir section
downstream of this cross weir. The intent is that all flow up to
the interceptor capacity be stored or pass either through the 5
ft by 7 ft opening or over the side weir to the interceptor.
Storm flows greater than the interceptor capacity would top both
the downstream cross weir and the downstream section of the side
weir, pass through the backwater flap gates and to the river.
Modification of the downstream side weir section and construction
of the downstream cross weir were designed at the same elevations
as the upstream cross weir and modified upstream side weir. This
7.12
-------
u>
New Downstream
Cross Weir
New Upstream
Cross Weir
Hollow Underflow
Area (Beneath Slab)\
^ ••: fry •.*'.-'. -"• i/•Jsgrr-77
• i; -I'f^-jTT i:
/Side Weir
New Vortex Valve
Flov; Regulator
n • L_IJ EF-Eyd
r."v.v v-: •.::-..-
Concrete Fill
^Concrete Filled
Sluice
To Interceptor
Figure 7.4 Mams Street Regulator Chamber Modification
-------
elevation, 2.4 feet below the original side weir elevation, and 1
foot above the backwater gate seat elevation was calculated to be
optimum to maximize storage and provide sufficient clear passage
to the river under extreme flow condiitions.
7.5 Special Modification Q£ the Weiss Street Regulator Chamber
Flow originating upstream of the Weiss Street area is
regulated within a small structure located between the 120 inch
gravity line serving the area and the Weiss Street Pump Station.
Unlike most other "B" type regulators, this location contains no
side spillover weirs (See Figure 7.5). Flow rates above the
regulated allowance will backwater the chamber, the inlet to the
chamber pipe and the 120 inch gravity line. Flap gates are
located at the end of the 120 inch line with seat elevations 3.6
feet above the invert. Stormwater storage above this level can
pass to the river depending on the river elevation. The average
river elevation is 2.09 feet above the gate seat such that a
normal storage depth of about six feet within the 120 inch line
is attained prior to bypass to the river.
Downstream of the regulator chamber a 36 inch pipe leads
to the diversion chamber section of the Weiss Street Pump
Station. Details of that location are included within the Weiss
Street Pump Station modifications discussed in the next section.
Modifications to the Weiss Street Regulator were limited
to removal of the existing float/gate type regulating device, and
replacement with a vortex type unit and minor structural changes.
These modifications hydraulically altered the flow through
pattern from one of decreasing flow to the interceptor with
increased depth of backwatering to a situation wherein flow
increased with backwatering to a rate of six times the dry
weather rate. This maximum rate is based on the WWTP capacity to
normal flow ratio and was used at all modified regulators.
As with the Adams Street Regulator the area served by
the Weiss Street Regulator is quite large and the size of the
regulating device is about twice the size of those at other
locations. Both the 120 inch gravity line and the pump station
diversion chamber were deemed unsuitable for flow regulation such
that installation options included modification of the regulating
chamber interior and exterior walls or placing the unit in the
existing space.
Although the space within the existing regulation
chamber was extremely limited and required placing the outlet
orifice section in the outlet pipe and removal of one interior
wall section, this option was considered the most cost effective.
7014
-------
SPECIALIZED
INLET TRANSITION
C.I.WALL CASTING
SLIDE GATE x
NEW FLOW REGULATOR
MC TYPE (SEGMENTED)
-o
•
en
FROM 120"
SEWER
6" WIDE WALL CUT
Figure 7.5 Weiss Street Regulator Chamber - Plan View
-------
A specialized adapter was required for the dual purpose of
transforming the flow pattern from the existing rectangular
regulator wall thimble to the required round inlet configuration
and to offset the unit for proper alignment of the outlet orifice
with the chamber outlet pipe. Unit performance would not be
adversely affected by this mode of installation.
An emergency spillway was provided in the chamber by
cutting a 3-1/2 ft. by 5 ft hole in the chamber interior wall
above the wall thimble at a base elevation equal to the crown
elevation of the 120 inch pipe (See Figure 7.6). If extreme high
river elevation conditions surcharged the 120 inch pipe during a
storm event, spillover at the regulator wall would commence,
bypassing the regulating device. Excess flow would then pass to
the Weiss Street Pump Station wet well and be pumped to the
river.
Storage volume at this location remained unchanged.
Alteration of the existing river outlet flap gate assembly was
not a practical method of increasing in-line storage considering
the relative normal river elevation to the 120 inch pipe location
and the need to ensure that extreme storm flow passage to the
river. Benefits of the BMP program implementation at this
location included: a) replacing the float/gate type regulator
with a near maintenance free vortex type regulator, and b)
altering the storm period hydraulic configuration from one which
limits the passage of "first flush" flows to the WWTP to a system
which passes "first flush" flow and maintains a rate as allocated
by the WWTP total capacity.
7.6 Weiss Street Pump Station Wet Well Modification
Simulations of flow conditions in the interceptor
system demonstrated the value of altering conditions at the Weiss
Street Pump Station wet well to produce greater cross river flow
rates and reduce Weiss Street Station pumpage. Optimization
analysis of increasing the water surface elevation required to
spill into the wet well dictated that a 5 foot increase would be
the most effective.
The existing structure at the Weiss Street Pump Station
included a circular cassion wet well diversion chamber. Most of
the cassion was utilized as the wet well serving three 100-cfs
pumps. One section, separated from the wet well acted as a
diversion chamber. All West Side Interceptor flow and regulated
Weiss Street 120 inch gravity line flow enters this chamber. Dry
weather flow exits the chamber through a 36 inch sluice gate to a
48 inch conduit leading to a 42 inch conduit beneath the Saginaw
River connecting to the East Side Interceptor. A 12 inch
7,16
-------
SAW CUT 3'6* BY
-) HIGH NALL HOLE
IN EXISTING MALL
S.S. BACK PLATE
EXISTING SLIDE GATE AND
MALL CASTING .
EXISTING J5
SEWER "IPE
FROM
120" SEWER
S.S. PROTECTIVE DEFLECTOR PLATE
!/<," S.S. FRONT PLATE
NEW FLOW REGULATOR
HC TYPE
I/
EXISTING 3t" PIPE
TO INTERCEPTOR
TO PUMP STATION
DIVERSION CHAMBER
CAST ANCHOR ASSEMBLY IN NEM BASE SLAB
AND SECURE NEM FLON REGULATOR
Figure 7.6 Weiss Street Regulator Chamber Modifications-Section View
-------
concrete wall separates the diversion chamber and wet well areas
and contains two 4-foot by 5-foot flap gates with seat elevations
2.75 feet above the diversion chamber floor (See Figures 7.7 and
7.8).
Several possibilities were considered to increase the
depth of flow in the diversion chamber prior to spillover to the
wet well. These options included, in general terms, construction
of a wall or baffle system in the diversion chamber, removal and
relocation of the two flap gates to a higher elevation or
construction of a wall within the wet well. Although space within
the wet well was limited due to the location of bar screens the
last option was considered to be the most feasible and cost
effective.
Criteria used in the wall design and location were the
following: a) increase the diversion chamber depth five feet at
spillover; b) induce free discharge over the new weir wall; and,
c) maintain water surface levels below the station mid floor
level during maximum pump rates. The selected wall design
maintained an elevation 4.75 feet above the existing flap gate
seat elevation and provided sufficient length such that at the
300 cfs pump capacity flow rate (all pumps on) the water surface
behind the weir wall would be one-half foot below the station's
mid-level floor elevation. Further protection was to be provided
for the station 's mid-level floor by the construction of a 3-foot
splash wall around the open wet well area, with splash plates at
an existing stairway.
Construction of the overflow weir wall created a
separate chamber within the wet well. End-of-storm evert
drainage of this chamber required placing a valve in the wall
base. A manually operated valve was deemed the simplest and
preferable to an automatic valve or a constant-open low rate
orifice.
The final design allowed construction work to be
accomplished during dry weather conditions with no need to divert
dry weather flow or protect the interceptor from loose debris
washout.
7 . 7 New Up_stre^m Regulator Chamber
As part of the demonstration aspect of this project, one
of the fourteen in-line storage control structures upstream of
the regulators under the complete BMP program was selected for
completion under the reduced BMP plan.
An existing junction chamber is located upstream of the
7.18
-------
36" Pipe
From
Regulator
Chamber
Existing Sluice
Gate
West Side
Interceptor
Figure 7.7 Weiss Street Pump Station Wet Well
Modification - Plan View
7019
-------
Pump
Discharg
Bar Screen
Pump Intake I
New 3'
Splash Wall
New Weir Wall
Existing Flap
Gates
Sluice Gate
to River
Crossover
Figure 7.8 Weiss Street Pump Station Wet Well Modification
Section View
7020
-------
regulator at Fraser Street on the West Side at the intersection
of Salt Street and Vermont Street was initially selected. The
chamber consists of a 90 inch reinforced concrete pipe from Salt
Street joining a 72 inch reinforced concrete pipe from Vermont
Street to form a 108 inch pipe. All pipes are circular with the
90 inch and 72 inch pipe inverts elevated above the 108 inch
discharge pipe invert. Concrete fillets within the chamber serve
to provide smooth transitions between pipes. Upon inspection,
the chamber interior was deemed unsuitable for implementation of
the intended stormwater storage and control devices envisioned.
A new regulator chamber was designed just downstream
of this junction chamber which allows for control of wet weather
flow. Locational plan and profile views are shown in Figure 7.9.
Concrete weirs were constructed within the new chamber to
backwater stormwater. A new flow regulating device controls the
outlet rate to 6 times the dry weather flow rate. Combined
sewage flow in excess of the storage capacity overflows the
weir and continues to the Fraser Street Regulator. A special
large diameter vent attached to the center line of the device's
back plate (as can be seen in Figure 7.10) is provided for this
configuration which extends up to the crest of the three-walled
internal weir. When backed up sewage reaches this level within
the chamber, this vent will flood causing the vortex action to
cease, thereby increasing rate of flow discharging from the
device. As the water level recedes below the weir crest, air
will again enter the device through the vent and vortex braking
will again commence. Thus this vent acts to increase the
discharge from the device whenever extreme high water levels are
reached.
Figures 7.10 and 7.11 illustrates the conceptual layout
of the new regulator. The chamber is approximately 20 feet wide,
17 feet long and 14 feet floor to ceiling with a three wall
internal weir providing 23 linear feet of overflow length. A
new vortex valve flow control device is located within the bottom
of the weir wall. This device arrangement allows dry weather
flow to pass through the structure without undue depositon and up
to six times dry weather flow to pass to the Fraser Street
Regulator while backwatering most of the flow for in-line storage
(175,000 cubic feet). Wet weather flow beyond the storage
capacity will overtop the weir. It is estimated that the one
year storm flow would crest 1.4 feet above the weir top and the
25 year storm flow would crest 2.9 feet above the weir top. The
weir top is set at the crown elevation of the 108 inch pipe.
Concrete fillets were designated upstream of the weir
wall to limit debris depositon and to direct flow to the flow
regulator inlet. Downstream, beyond and beside the weir wall,
concrete fillets were again designated to direct flow to the
7021
-------
Existing Chamber
Existing
Chamber
New Chamber
RIPE SEWER
N
72" PIPE SEWER
Location
Figure 7.9 New Regulator Chamber at Salt/Vermont Streets
Location and Profile
7022
-------
~j
*
NJ
CONCRETE FI
CONFORM TO
FOR 1/4 PIPE DIAMETER
THEN SLOPE I
New Vortex Valve Flow
Regulator with Vent
CAST-IN-PLACE ANCHOR ASSEMBLY
SECURE FLOW REGULATOR TO SLAB
CONCRETE FILLETS CONFORM TO 103" PIPE
:>
«o' iewe*.
\
Figure 7.10 Salt and Vermont Streets Chamber - Plan View
-------
New Chamber
9' Weir Wall
v-EXISTING JUNCTION CHAflKR
HP V
I * * « • o « ' ' ». «
X
Flow
<
New Vortex Valve Flow fRegulator
Figure 7.11 Salt and Vermont Streets Chamber - Section View
-------
outlet pipe and limit deposition The ground elevation is nearly
25 feet above the level of the chamber floor. The minimum 10
foot buffer between maximum water elevation and ground surface
requirement was easily attained.
7.25
-------
CHAPTER 8
REDUCED BMP PLAN IMPLEMENTATION
8.1 Foreword
During the period of late 1983 plans and specifications
were prepared for the implementation of the reduced BMP plan.
The contract was awarded in March, 1984 to Gary D. Steadman Inc.,
Bay City Michigan . A startup meeting held on April 30, 1984
marked the beginning of the construction phase which was
completed in September of 1984.
8 .2 Special Construction Requirements
One aspect of the construction project was to modify
existing sanitary/stormwater regulating chambers and to construct
one new in-line control chamber on an existing combined sewer
line. Each of these locations continually passes dry weather
sewage flows and is subject to extreme flow rates during wet
weather conditions.
The Contractor performed all work without bypass of any
dry weather flow to the river. Only stormwater flow conditions
which previously created discharge to the river were allowed to
discharge to the river during the contract work. The Contractor
was required to provide all necessary means of work protection by
backwatering, pumping, and bypassing arcund the work to the
interceptor all dry weather flow and to protect all work from the
effects of wet weather flow and correct any damage caused during
increased flow conditions was required to prevent any material or
debris required for construction or created during demolition
from entering the sewage flow.
The Contractor was made aware that most regulators are
below potential river levels and that he was to prevent the flow
of river water into the regulator chambers, particularly during
sluice gate removal and tide gate installations at Throop Street
and Remington Street. Compliance with these requirements was
ensured by inspection during the work.
The existing flow regulators were to be removed prior to
installation of the new regulators. The Contractor removed the
float-operated regulator at nine "B" type regulators including
the gate, float, operator, cables, suports and appurtenances.
The upstream slide gate, seat, stem, supports and appurtenances
were to remain. The existing cast iron wall casting was left in
place to simplify demolition and new regulator installation. At
8.1
-------
two "A" type chambers existing slide gates, seats, stems supports
and appurtenances were removed and replaced with new regulators.
At one "A" type regulator, Dearborn Street, the existing
regulator was adjusted but not removed. One new flow regulator
was installed in the new control chamber at Salt and Vermont
Streets. A total of 12 new flow regulators were installed.
8.3 Installation
The new flow regulating devices and accessories were
designed to simplify installation procedures. In general each
unit was supplied with accessory plates designed to be attached
to the existing chamber weir wall using through bolts and/or
anchor bolts. Studs or threaded holes on the back plate allowed
for mechanical attachment of the flow regulator. Integral anchor
pads on each regulator allowed for securing the device to the
chamber base slab with anchor bolts set into existing concrete or
onto cast-in-place anchor assemblies where new concrete was
designated. At Adams Street the flow regulator was attached to a
new wall using a cast-in-place wall anchor. At the new chamber
constructed at Salt/Vermont Streets, the flow regulator included
an integral wall mounting plate conforming to the 42 inch wall
thimble cast by the Contractor.
Flow regulators for which the overall size exceeded the
dimensions of available accessways or manholes, were supplied as
segmented units capable of passing through the existing openings.
These devices consisted of two to three segments assembled using
bolted connections. Devices were supplied assembled with the
intent that the Contractor disassemble the units, place each
segment into the chamber, and reassemble the unit. Intact units
were then properly positioned within the chamber and mechanically
secured to the wall plate assembly and the floor slab.
The flow regulator at the new regulator chamber at Salt
and Vermont Streets is equipped with a 6 inch vent pipe. The vent
pipe is removable from the flow regulator and segmented to allow
placement in the chamber. Vent pipes are supported by attachment
to the chamber wall using anchor bolts and an adjustable bracket
assembly.
Three types of flow regulators were suppled including 10
conical "MC"type, one horizontal "MH" type and one orifice plate
regulator. The "MC" types were used to replace existing existing
float-operated regulators at all the "B" type chambers and the
manual gate at the "A" type chamber at Court Street. These
devices are general conical in shape with flow entering through a
circular end plate. One new "MH" type flow regulator, installed
at the type "A" regulator at Ames Street, consists of two flat
8.2
-------
plates connected by a band around the outer edge. The final
device was a simple orifice plate consisting of a square plate
with a circular hole which was installed within the Fraser Street
chamber. Pertinent details of flow regulator characteristics are
presented in Table 8.1 (which was included in the bid document to
provide the Contractor with a means of estimating the handling
involved in the installation of the devices.
8.4 Chamber Modifications
Photographs were taken to document the modification
process. The photograph in Figure 8.1 displays the interior of a
typical "A" type regulator chamber as previously modified under
the Hancock Street Detention Facility construction program in
1977. Sewage enters the chamber via the pipe on the left and
drops into a small sluice. During dry weather conditions flow
then drops through a 6 inch x 6 inch opening in the side wall at
the end of the sluice to a chamber section leading to the DWF
outlet pipe. This pipe, located in the upper left part of the
picture, leads to the interceptor drop manhole. Moderate wet
weather flow, which will not pass through the 6 inch x 6 inch
opening, is backed up in the chamber by the sluice end-walls and
the cross wall seen to the right of the sluice. This cross wall
was constructed during the previous modification program. Prior
to its construction, wet weather flow would continue flowing to
the right and pass through flap gates to the river.
Wet weather flow volume greater than the storage
capacity of the system will pass over the sluice end walls and to
the intercepter. Extreme wet weather flow rates sufficient to
backwater the interceptor will cause flow in the chamber to be
routed around the cross wall, back over the side wall beyond the
cross wall, and through the flap gates to the river.
Although not shown in the photograph, a small manual
gate was located on the back side of the sluice end-wall
regulating flow through the 6 inch x 6 inch opening. As part
"reduced BMP" project the sluice gate was removed and replaced
with vortex flow regulating devices at two locations as detailed
later.
Typical "B" type regulators are much larger than the "A"
type. Figure 8.2 depicts the modified weir area and new flow
regulators within a typical "B" type regulator. Basically the
chambers are enlarged versions of the "A" Type with the addition
of a float chamber next to the chamber outlet pipe. Flow
regulation was controlled automatically by a float-operated
regulator located between the sluiceway and the chamber outlet
pipe. During the current program this assembly was entirely
803
-------
Table 8.1 Flow Regulator Details
00
Regulator
1A Weiss
2 Cronk
5 W.Genesee
6 Remington
8 Throop
9 Hayes
12 Court
11 Ames
13 Adams
16 Mackinaw
1? Dearborn
17A Fraser
Ib Salt/
Vermont
» *
Type
MC
MC
MC
MC
MC
MC
MC
MH
MC
MC
N
0
MC
OVE
Length
(in.)
74
37
38
38
38
38
25
22
60
38
—
18
79
RALL
rtfidth
(in.)
63
28
30
30
30
30
15
22
52
30
...
18
56
Height
(in.)
53
24
25
25
25
25
13
4
44
25
...
0.5
49
•*
Approx.
Wt. (Ib)
700
130
130
130
130
130
40
30
400
130
...
40
500
***
Segmented
Cone No. segments)
—
2
2
2
2
2
—
—
3
?
—
—
...
Diameter
Intake (in)
25
8
12
8
8
10
4"
4"
19
10
—
—
?3
Vented
- Key: Ml - conicjl tym- vortex valve
MH - horuontdl ly|>f vorte* valve
0 - or it ue pldtr
M • no devtcr
* excludes wt. fittings
*** see 6D-3
-------
Figure 8.1 Typical Type "A" Regulator Chamber
8,5
-------
Figure 8.2 Modified Area of Typical Type "B" Chamber
8.6
-------
removed and replaced with vortex flow regulating devices. The
photograph in Figure 8.3 shows parts of a removed float-operated
flow regulator.
The "B" type chambers also included manual gates on the
upstream side of the side wall. Photograph A, Figure 8.4 is a
view looking upstream of the sewer pipe entering the chamber,
spill to the sluice and the manual gate in the sluice side-wall.
Photograph B, Figure 8.4 also includes the sluice and the gate as
viewed from above. Similar to the "A" type chambers most wet
weather flows were originally allowed to pass through backwater
gates to the river. The photograph in Figure 8.5 illustrates a
typical backwater gate.
Modifications to the type "B" regulators generally
included removal of the existing float-operated regulator,
installation of a vortex flow regulating device, cutting down of
the side overflow-walls and the construction of the central
cross-wall. The photograph in Figure 8.6 displays the new cross
weir and the cut-down weir on each side. Adjustable weirs were
installed at four regulator locations and can be seen in this
photograph.
8.5 Construction and Installation of Flow Regulators
Flow regulating devices used in this project were of
variable types and dimensions as required by the degree of flow
regulation and the conditions of the installation. Access to the
existing regulator chambers was typically via manholes or
backwater gate access holes as shown in the photograph in 8.7. In
a number of instances, the sizes of the new flow regulators were
much larger than the available openings such that segmentation of
the device were required. Photographs A and B in Figure 8.8 and
8.9 illustrate a device disassembled, partially assembled and
completely assembled respectively. This device was installed in
the Weiss Street Regulator and included a specialized inlet
transition section. Photographs A and B in Figure 8.10,
illustrate the device for the Salt/Vermont Street regulator
chamber which incorporated an integral wall mounting flange and a
removable high level stack vent. The photograph in Figure 8.11
shows the unit installed in the new chamber weir wall.
As detailed Chapter 7, the Adams Street regulator
chamber vortex flow regulating device installation utilized an
upstream cross wall and wall thimble. The device and detachable
cast-in place wall thimbles are shown in the Photograph in Figure
8.12. The installed device and upstream cross wall, designed to
direct flow to the inlet, are shown in Photograph A, Figure 8.13.
807
-------
00
•
CO
Figure 8.3 Partial Components of Brown and Brown Regulator
Removed From Chamber
-------
-------
Figure 8.5 Type "B" Chamber - Flapgate to River Area
8.10
-------
Figure 8.6 Type "B" Chamber - New Cross Weir
8.11
-------
Figure 8.7 Chamber Access Manholdes and Gate Covers
8.12
-------
(A)
(B)
Figure 8.8 Segmented Vortex Valve Regulator -
Disassembled and Partially Assembled
8013
-------
Figure 8.9 Segmented Vortex Valve Regulator -
Fully Assembled
(Unit Installed at Weiss Street Chamber)
8.14
-------
(A)
(B)
Figure 8.10 Salt/Vermont Street Chamber Vortex Valve
8.15
-------
Figure 8.11 Installed Vortex Valve Regulator at the
New Salt/Vermont Streets Storage Chamber
8016
-------
Figure 8.12 Adams Street Chamber Vortex Valve Regulator
8017
-------
Figure 8.13 Installed Adams Street Chamber Vortex
Valve Regulator
8.18
-------
Most of the vortex flow regulators used in this project
were the conical type as shown in the Photograph in Figure 8.14.
Each unit was provided with a mounting plate, designed to be
permanently mounted to the wall, incorporating studs for
attachment and removal of the device. For most installations,
the unit's inlet sleeve was perpendicular to the wall. In
several instances, the existing wall casting and the chamber
outlet were positioned such that modifications were necessary.
The photograph in Figure 8.15 illustrates a unit with the inlet
sleeve modified by changing the sleeve angle in the wall modified
to orient the device outlet to properly direct flow into the
chamber outlet pipe.
A horizontal type vortex flow regulating device was
deemed most suitable for the Ames Street location since the
chamber outlet was located in a side wall as opposed to the
standard opposite wall, limiting available space for installation
and orientation. Photograph A, Figure 8.16 illustrates a typical
horizontal type unit which has a side inlet and bottom outlet.
On this unit the outlet is located directly below the inspection
port (the cover of which is seen on the top plate). This unit
was mounted flush to the wall with the plate shown and a wall
bracket. Photograph B, Figure 8.16 illustrates the installed
unit with the inspection port cover plate removed. The chamber
outlet is located at the bottom of the wall to the left of the
unit.
8.6 Weiss Street Pumping Station Wet Well Modification
The last program element of the reduced BMP program was
the Weiss Street Pump Station wet well. The intent was to
increase the depth of water five feet in the West Side
Interceptor to maximize flow crossover the the East Side
Interceptor prior to spillover into the pump station wet well.
This was accomplished by construction of a spill over wall inside
the wet well between the flap gates and the bar screens. The
wall is shown in Photograph A, Figure 8.17 and has a crest
elevation 4.75 ft. above the flap gate seat elevation. At the
base of the cross wall a manual gate valve is located to allow
drainage of water trapped between the walls. A three foot high
wall was also constructed at the mid floor level all round the
open chamber area as seen in Photograph B, Figure 8.17 to contain
extreme flow levels and minimum excess splashing conditions.
8.19
-------
Figure 8.14 Typical installed Conical Type
Vortex Valve Regulator
8020
-------
00
o
NJ
-------
(A)
(B)
Figure 8.16 Horizontal Type Vortex Valve Regulator
8.22
-------
oo
NJ
U)
B
Figure 8.17 Weiss Street Pump Station ->New Weir
and Splash Wall
-------
CHAPTER 9
FIELD AND MONITORING PROGRAM
POST BMP IMPLEMENTATION
DATA AND ANALYSIS
9.1 Foreword
Numerous locations were selected throughout the Saginaw
drainage area during all three phases of this study for the
collection of data pertinent to the generation, calibration and
operation of the system simulation model and later for monitoring
of the reduced BMP system modifications.
Field monitoring programs conducted for the purpose of
Phase 1 and Phase 2 simulation model generation and calibration
are presented in Chapter 6. Chapter 9 presents the results of
the Phase 3 field monitoring program conducted after the reduced
BMP program was implemented. Section 9.2 briefly describes the
components of the field program. Section 9.3 summarizes the
results of a program documenting backwatering effects resulting
from partial BMP plan modifications. Sections 9.4 and 9.5
present data collected at the Salt/Vermont Streets chamber (new
in-line storage facility) and at the Adams Street regulation
chamber, respectively. Evaluation program data collected at the
Weiss Street Pump Station and at the WWTP are presented in
Sections 9.6 and 9.7, respectively. Field discharge measurements
for several of the new vortex valves are presented in Section
9.8. Cronk Street regulator chamber data is evaluated in Section
9.9. Field observations of the modified regulators are detailed
in Section 9.10.
9.2 Post Implementation Field Program
Elements of the post reduced BMP implementation field
program were designed to facilitate a final review and
calibration of the simulation model and to determine the
practicality and effectiveness of the regulator chamber
modifications in terms of in-system storage generation and the
suitability of the new flow regulating devices.
Similar to earlier phases of the evaluation program, CSO
rates and water quality data were recorded. In addition, the
post implementation field program included river elevation
determinations, in-line storage evaluation, discharge monitoring
of new vortex valve flow regulating devices and documentation of
maintenance requirements for the new regulating devices.
9.1
-------
Water quality analysis included evaluating combined
sewage passing to the West Side Interceptor at Adams Street and
CSO to the river at this location. Water quality sampling at the
Weiss Street Pump Station wet well and the WWTP grit chamber
which were performed during earlier phases was also again
conducted during this period.
Water surface elevations were continuously monitored at
the new Salt/Vermont regulator chamber, at the Cronk Street
backwater gate chamber, at two locations within the Adams Street
regulator chamber and upstream of the Throop Street regulator
chamber. Peak water surface elevations were monitored at
manholes at five locations in the in-line storage area upstream
of the new Salt/Vermont regulator chamber, at single locations
upstream of two other regulator chambers (Adams Street and West
Remington Street) and within three regulator chambers (Throop
Street, Hayes Street and West Remington Street).
The original intent was to monitor all post construction
rain events within a six week period and select the most
pertinent events for complete review. Storm event measurments
occurring during this period were less than ideal due to adverse
conditions such as faulty backwater gate operation and mixed
rain/snow precipitation, however, sufficient data was attained to
reasonably assess the overall impact of the implementation
program.
9.3 System Backwatering
Monitoring of the post reduced BMP plan implementation
conditions included recording peak water elevations at selected
regulator chambers and at locations upstream of modified
regulator chambers and at the new in-line storage chamber at Salt
and Vermont Streets. Peak water surface elevation determinations
for wet weather periods were accomplished using cup gages
constructed of 1-1/2 inch PVC pipe end caps with aluminum plate
splash covers attached at equal incremental spacings to sections
of electrical tubing. Gages were designed and installed by EDP to
be easily removed after each event for inspection by City of
Saginaw maintenance crews. Most gages were installed in manholes
upstream of regulator chambers and allowed for removal from
street level. Remaining gages were installed in regulator
chambers and accessed from within the regulator chambers.
Table 9.1 includes pertinent data for the 10 cup gage
locations and the downstream regulator chambers. Total rainfall
accumulations for five storm events monitored are also given in
Table 9.1. Locations of these measurement points are shown in
Figures 9.1 and 9.2. The intent of this program was to determine
9.2
-------
TABLE 9.1
CUP GAGES MONITORING OF PEAK WATER ELEVATIONS
co
LOCATION DOWNSTREAM
NO. fi£ MANHOLE REGULATOR
1
2
3
4
5
6
7
8
9
10
GROUT fc STANLEY
SALT t HOLMES
SYLVAN fc HAMILTON
STEWART t SALT
FRASER 6 BRALEY
ADAMS t HARRISON
HARRISON W.
LOCATION AT REGULATOR
HAYES
THROOP
REMINGTON
STORM EVENT PEAK ELEVATION
FRASER
FRASER
FRASER
FRASER
FRASER
ADAMS
REMINGTON
RECORDED
MANHOLE
INVERT
ELEVATION
582
579
582
577
582
580
584
583
579
582
.72
.64
.74
.21
.30
.22
.42
.30
.69
.95
AT REGULATOR
REGULATOR
WEIR
ELEVATION
584.42
584.42
584.42
584.42
584.42
581.50
585.45
584.97
582.60
585.45
FRASER:
ADAMS:
RAIN ACCUMULATION (INCHES)
1984 STORM DATES/PEAK ELEVATIONS
Ifi/JLfi lfl/21 10/26 11/1
584
583
*
584
584
>587
587
585
583
586
584
582
0
.30
.64
.88
.63
.39
.50
.13
.52
.28
.40
.30
.75
<584.30
584.64
>589.00
584.88
584.63
>587.39
587.00
585.63
583.02
585.28
584.65
582.44
0.79
<584.30
583.64
584.00
585.88
584.63
581.89
586.00
<584.13
<580.52
586.28
577.18
581.34
0.17
<584.30
584.64
585.00
584.88
588.63
>587.39
587.50
585.13
583.52
586.28
584.90
582.85
0.61
11/1
584.30
585.64
>589.00
582.88
*
>587.39
587.50
585.63
583.52
585.28
584.40
582.85
0.73
* ALL CUPS PARTIALLY FULL - INDICATES POSSIBLE SPLASHING EFFECT
FROM CATCHBASIN LEADER PIPE DISCHARGE
-------
JLJLJ1
LEGEND:
Modified Chamber
Cup Gage Location
Figure 9.1 Hancock Street Area Cup Gage Locations
-------
ID
•
Ul
Cupgage Location
Figure 9.2 Salt/Vermont Streets Area Cup Gage Location
-------
if any adverse conditions developed due to implemented
modifications. Undesireable levels of stormwater backup would be
recorded as peak upstream water elevations sufficiently above
levels in the regulator chamber to indicate backwater-induced
surcharge conations.
The first five cup gage locations are upstream of the
new Salt/Vermont Street in-line storage chamber (Table 9.1). At
four of these locations peak water elevations indicate that no
surcharge occurred in that portion of the sewer system during
storm conditions. Data at the Sylvan and Hamilton Street
location indicated surcharge conditions for two events. It is
possible that cup gage readings at this location were influenced
by splashing effects from a catchbasin leader pipe entering high
in the manhole, since for one additional event most cups were
noted to be only partially full. No basement floodings had ever
been noted in this drainage area prior to the chamber
construction nor were any noted during the post construction
monitoring. If surcharging had occurred, depths were limited to
less than problem levels which is quite possible since the 54
inch pipe serving the area is 20 ft. below ground level.
No indication of surcharge conditions was evidenced at
the Harrison Street location upstream of the West Remington
Street regulator chamber.
Although four of five events indicated high water
conditions at the Adams Street and Harrison Street manhole
upstream of the Adams Street regulator, available data indicates
that the new weir with a crest elevation of 3.3 ft. above the 7.5
ft. pipe invert does not induce backwatering. Based on
calculation of the pipe capacity at the upstream manhole as 253
cfs, and the estimated hydraulic profile and net flow capacity
over the regulator chamber spillover weir at the recorded depth,
no restriction was evidenced.
Hydraulic limitations of the connector pipe from the
Adams regulator chamber to the West Side Interceptor sewer have
been calculated to cause flow bypass to the river at storm flows
less than the inlet sewer capacity. Overflow to the river would
result and was evidenced during several of the monitored events.
Backwatering due to the connector pipe hydrualic restriction at
the Adams Street regulator is sufficient to cause spillover to
the river but not to surcharge the inlet sewer. Flap gates
allowing flow to the river provide near free-flow conditions and
no excessive depths were noted with the continuous level sensors
within the chamber. High water depths within the sewer line at
the cup gage monitoring station appear to be due to the limited
hydrualic capacity of the sewer in relation to peak flow condi-
tions. No basement flooding has been reported in the drainage
9.6
-------
area either before or after the modification work. As with the
Fraser Street regulator tributary drainage area, the sewer trunk
lines are more than 20 ft. deep and surcharging of the line would
not necessarily create basement flooding conditions.
At the final three locations (Hayes Street, Throop
Street and Remington Avenue regulators) cup gage data from within
the three regulator chambers did not indicate excessive water
levels. Depths were generally less than one foot over the cham-
ber weirs such that no sewer surcharge or spillover to the river
occurred. Under the orignal design it was intended that excess
flows above the allotted rate through the new regulating device
spill to the interceptor. Under extreme conditions, where the
interceptor capacity was exceeded flow would pass both over the
new cross weir and back over the side weirs to the river. Moni-
tored events indicated that no flows have yet passed over the
cross weir which was as expected considering the mild intensity
of the events which occurred. Field data collected to date
indicate that the cross weir elevations selected during the
design phase have been adequate to prevent premature flow to the
river.
In sum, no adverse hydraulic profiles were noted at any
of the locations during the post reduced BMP implementation
evaluation program.
9.4 EvMjflajtijpn M Effectiveness Q£ Hew. In-line Storage
Chamber Constructed at Sal t and Vermont Streets
Prior to the reduced BMP plan implementation, the
Fraser Street regulator chamber controlled flows from a 441 acre
area in the southwest part of the city. Location of a new
upstream storage/regulator chamber was selected to be 450 ft.
upstream of the existing Fraser Street chamber at the
intersection of Salt and Vermont Streets (Figure 9.2). See
Chapters 7 and 8 for design and implementation details.
Monitoring of wet weather flow depths at the Fraser
Street regulator was performed during the Phase 2 field
evaluation period of 1983. Data accummulated are representative
of conditions existing prior to implementation of the BMP Plan
modifications in this area. After Phase 3 construction in 1984,
monitoring of stormwater depths was performed at the new chamber.
The difference in sewer invert elevations between the two
chambers is negligible for comparative hydraulic analysis of
pre/post conditions.
Figure 9.3 illustrates the rain accumulation data for
storms occuring on 8/1/83 and 10/18/84. The 8/1/84 and 10/18/84
907
-------
8'6
DEPTH OF FLOW
O ho .p> o> CO
I I I I I I I I I
N)
00
-P- ^
CO -
N>
O
RAIN ACCUMULATION
o o o o
• • • •
!-• IS> UJ JS
s
O
S
i
oo
co
U)
-------
events were selected for detailed hydraulic evaluation since they
are representative of the hydraulic conditions typical of their
respective pre/post reduced BMP plan implementation period and
are generally similar in terms of rain intensity, duration and
total accumulation.
Sewer flow depths shown in Figure 9.4 roughly indicate
the rainfall to runoff time relationships. The shape of the
8/1/83 event combined sewage depth of flow curve is typical of
all pre-BMP Plan events observed. The rate of depth increases
varied among events dependent upon the rain condition, but all
events displayed the rapid rate of depth decrease at storm end.
Initiallyf the backwater gates allowed rapid discharge of
combined sewage to the river down to a sewer depth of just over
half the 9 ft. pipe diameter. Thereafter, the existing float-
operated regulator controlled the outflow rate.
The shape of the 10/18/84 sewer flow depth curve is
typical of all post-BMP plan implementation events. Depths of
flow during the initial storage volume fill period varied as
before (correlating with storm intensities), but always resulted
in long-term drain down periods.
Since only rainfall and water depths within the chamber
were monitored, calculations were performed using available data
and the manufacturer's rating for the flow control device to
determine the degree of inflow/outflow/storage balance. This
procedure is described below:
Figure 9.5, which indicates the volume of stormwater
storage throughout the 10/18/84 event, was prepared using the
depths recorded in the field (Figure 9.4) and the depth to
storage volume relationship developed during Phase 1 and Phase 2
studies. Using the storage volume curve of Figure 9.5, the rate
of change in storage volume was estimated throughout the event
since it is a direct function of the inflow rate, the outflow
rate through the regulating device and spillover, if any. For
this event total rain accumulation was recorded at the Emerson
Street Station and at the City Water Works Building as 0.57 and
0.67 inches respectively, averaging 0.62 inch. Considering the
land use (and appropriate runoff factor), a total stormwater
volume of 397,000 cu.ft would be expected. Dry weather flow for
the total rain and system draindown period of 18 hours was
estimated to equal 72,600 cu.ft. using dwf rates established
during Phase 1 and 2 measurement programs.
The rate of inflow (Figure 9.6) at any time was
calculated as the rate of volume change plus the rate of outflow.
For periods of no spillover, outflow was limited to rates
controlled by the new vortex valve regulatpr. Using the device's
9.9
-------
FIGURE 9.5 VOLUME OF STORED COMBINED SEWAGE VS TIME
10/18/84 EVENT POST BMP PLAN IMPLEMENTATION
10
o
M
O
200
160
120 -
80 _
40 -
0
0
I
4
8
10
i
12
14
16
18
TIME - HOURS
-------
FIGURE 9. 6 COMBINED SEWAGE INFLOW RATE VS TIME
10/18/84 EVENT POST BMP PLAN IMPLEMENTATION
160 _
120 ^
80 .
40 _
0
0
I
4
i
8
10
12 14
16
i
18
TIME - HOURS
-------
stage/discharge characteristic data (See Chapters 5 & 7) and
sewer flow depth indicated in Figure 9.4, the outflow rates
depicted in Figure 9.7 were calculated. The curve illustrates
the unique ability of the vortex valve throttling device to
maintain a near constant outflow rate with change in depth and
the characteristic final high flow through rate which is intended
to promote scouring. In addition to the curve values shown in
Figure 9.7, inflow would also include the volume of spillover,
if any. Figure 9.4 indicates that the chamber water depth
remained at the weir level for a very short period of time at
the 2 hour duration point of the event implying that little or no
overflow would have occurred.
Integration of the vortex valve regulator device outflow
rate curve (Figure 9.7) over the event duration results in a
total estimated outflow of 454,000 cu. ft. This value is 15,000
cu. ft. less than the estimated combined dry and wet weather
flows noted above and represents either the overflow volume, the
error in values estimated or both. This difference represents 3%
of the total storm flow and since minimal spillover occurred, it
is concluded that the flow analysis is reasonably accurate. This
implies that the vortex valve throttling device operates properly
according to the manufacturer's design curve, the depth to
storage volume relationship developed for the pipe system is
reasonable and the runoff coefficient and land size are
accurately estimated.
A similar evaluation of the pre- BMP conditions is
difficult due to the unknown and variable flow rates through the
existing float-operated regulator and the backwater flap gate to
the river. For comparative purposes of pre and post BMP
conditions, rough estimates of hydraulic conditions were made for
the 8/1/83 event as follows.
Total rain accumulation for this event was recorded at
the Emerson Street Station and at the City Water Works Building
as 0.43 and 0.49 inches, respectively, yielding an estimated
runoff volume of 292,000 cu. ft. Dry weather flow for the 4 hour
event totalled 16,000 cu. ft. Considering the unknown outflow
rates, storage volume fill rates were not used to estimate inflow
rates. Combined sewage depths in the chamber above 5 ft. cause
overflow to the river. Depths above this level occurred for over
2 hours of the 4 hour event. The in-system storage volume of the
87,000 cu. ft. is available and the average outflow rate from the
regulator for the 1 hour drain-down period recorded was estimated
as 24 cfs. Since this outflow rate is much greater than the
allowable rate from this drainage area based on WWTP capacity
constraints, it is assumed that a large portion of the flow would
either overflow directly at this location or be pumped to the
river from either the Hancock Street facility or from the Weiss
9.12
-------
ere
Discharge - cfs
f* T S?
ro-
H
.
H-
d
(D
vo
•
-J
ft
CD
a
o
CO
to-
(D
D
H-
ca
o
cr
(D
50
P»
rt-
(!)
<
CO
H-
I
oo
-------
Street Pumping Station. Using the two extremes of: 1) only flow
through the backwater gates spills to the river or; 2) all flow
above the allotted volumes based on WWTP capacity either flows or
is pumped to the river, CSO discharges are estimated to range
from 124,000 cu. ft. up to 178,000 cu.ft. For the 8/1/83 pre-BMP
event, 40% to 58% of the combined sewage inflow is thus estimated
to discharge to the river.
Comparison of the two pre/post-BMP storm events shows
the effectiveness of the in-line storage concept. As stated, a
typical post implementation event (10/18/84) with 40% more
rainfall than the pre implementation event, resulted in a
discharge of at most 3% of the incoming combined sewage in
comparison to an estimated overflow of 40-58% under pre-project
conditions.
In conclusion, implementation of the BMP plan
recommended upstream storage facility at this location has
substantially reduced pollutant loading to the river by
dissipating peak flow conditions in the system and allowing for
long draindown periods to the WWTP.
9.5 Monitoring and Evaluation at the Adams Street Regulator
Intensive monitoring efforts were performed at the
Adams Street regulator chamber as part of the overall field
evaluation. During the pre BMP period a level sensor was
installed to monitor water elevations within the dry/wet weather
flow channel of the regulator chamber upstream of the float-
operated regulating device. No flow monitoring was performed
during the reduced BMP construction phase in the chamber. After
modifications were completed, sensors were placed to monitor
water levels both in the dry/wet weather flow channel upstream of
the new vortex valve flow regulator and at the downstream end of
the side weir to monitor spillover of extreme event flow to the
river. In addition, automatic sampling devices were installed at
each location, activated by flow elevation, and intended to
produce representative samples of total flow through the
regulator and of spill to the river.
The control concepts used during the design phase
included assuming "first flush" effects within the combined
sewage. This effect is the result of initial flow volumes
during storm events incorporating high concentrations of street
washoff materials and scouring sediment in the sewer lines.
Scouring should occur early in the event followed by relatively
cleaner flow representing sewage diluted with clear stormwater.
At this stage two scenarios may occur. Under low rate stormwater
flow conditions, velocities within the sewer may be conducive to
9014
-------
settling of solids materials. High flow rates may produce
velocities negating any deposition effects. After the end of a
storm event and near the end of the storage pool drain-down
period, an increase in flow rate, designed as part of the
operating characteristic of the vortex valve regulating device,
should occur. It is expected that if settling of solids
materials occurred in the backwatered stormwater, then the final
flow increase would create a second scouring phase and increased
pollutant concentrations.
Samples were collected from within the Adams Street
dry/wet weather flow channel on four occasions and at the weir
spilling over to the river on one occasion. Samples collected at
half hour intervals were composited to represent the "first
flush", "mid-event" and "drain-down" (post storm) periods and
analyzed for SS, BOD and total/soluble phosphorous. In addition,
discrete sample analysis was performed on occasion, to determine
time-variant solids concentrations.
Table 9.2 summarizes the data generated. For each
event, concentrations of the four pollutant parameters are
indicated based on the three storm periods. Discrete samples (if
any) are then listed giving solids concentration and time of
collection. As a rough comparison of peak storm flows, depths in
inches over the side weir to the regulator and over the cross
weir to the river, are included in Table 9.2. It should be noted
that the highest peak flow over the upstream weir is not
necessarily the most likely event to cause overflow to the river.
It is mainly the interceptor capacity that governs if surcharge
and overflow to the river will occur. Rain data for each event
including total accumulation and peak hourly intensity are also
recorded in Table 9.2.
Monthly average influent WWTP concentrations of
suspended solids and BOD were 71 mg/1 solids and 55 mg/1 BOD in
October and 72 mg/1 solids and 51 mg/1 BOD in November, 1984.
Data for the first three events clearly includes initial storm
samples of flow passing to the interceptor with concentrations
much higher than WWTP averages confirming the "first flush"
effects. "Mid-storm" sample concentrations decrease
substantially but are still in the range of dry weather flow
values. Dilution of dry weather flow alone with clean stormwater
would produce lower concentrations such that the "mid storm"
values recorded indicate continued effects of scouring and street
washoff. Considering that the pipe volume upstream of the
regulator is backwatered, it could be expected that not all
scoured material would immediately flow to the regulator.
"Post storm" samples are consistently less concentrated than
"mid-storm" samples and monthly average dry weather flow
indicating a condition of sewage diluted with relatively clean
9ol5
-------
TABLE 9.2
CTl
ADAMS ST. REGULATOR CHAMBER STORM SAMPLES
Concentrations mg/1
PEAK FLOW DEPTH (INCHES)
R
:IVER
SIDE
DATE PARAMETER
START
STORH
MID
STORM
POST
STORM
REG RIVER)
10/21
11/1
DISCRETE
1
2
3
4
5
6
11/9
DISCRETE
1
2
SS
TP
SP
BOD
SS
TP
SF
BOD
SS
SS
SS
SS
SS
SS
SS
TP
SP
BOD
SS
SS
105
1.59
.85
67
424
3.88
.77
258
60
7
40
60
34
30
428
3.81
1.33
138
38
81
73
.83 (.
(.
27
54
.54
.28
51
Midstorm:
Poststorm:
After post
• •
• •
• M
77
1.04
.59
68
Midstorm:
Midstorm:
30
25) .89
21) .73
25
10
.55
.52
21
at max rate of
at predicted
storm: 28 hrs
29 "
30 "
31 "
21
.46
.35
19
OVER WEIR
REGULATOR RV
SIDE S
12.
17.
depth decrease
flush depth
after 12
• •
• •
• •
18.
Just after peak conditions
During end of
stored
RAIN DATA
ACCUMULATION
INCHES
0.79
0.61
PEAK INTENSITY
IN/HR.
0.20
0.32
0.33
0.09
SS
176 Midstorm:
stormwater drain down
Second flow peak level
condition
11/11 SS 21
Suspended Solids
Total Phosphorous
Soluble Phosphorous
Biochemical Oxygen Demand
Code: SS -
TP -
SP -
BOD -
48
0.38
0.09
-------
stormwater possibly in combination with materials settling
effects. The significance from a pollution reduction standpoint
is that the initial highly concentrated flow would pass to the
interceptor and later overflow, if any, would be far less
concentrated.
Visual observations of final drain-down periods were
recorded by EDP personnel during flow calibration of the
installed vortex valve regulating devices. A short period of
noticably concentrated material was visually noted ("black" in
color) discharging from the device during the draindown period
following a rainstorm occurring in early October. Unfortunately,
the flow calibration crew was not setup for sampling at that
instant. The field sampling program thereafter was tailored to
analytically verify "post storm" scouring.
Discrete stormwater samples were visually inspected to
determine if any highly concentrated conditions occurred.
Samples with a darker appearance were tested individually for
solids concentration. If no increase was visually apparent,
samples for discrete analysis were selected based on depth of
flow data to determine predicted peak flow and therefore
potential scouring conditions.
For the 11/1/84 event the first discrete sample (Table
9.2) represented "mid storm" conditions during the period of
maximum depth decrease rate. The resulting solids concentration
value of 60 mg/1 was close to the average storm period value of
54 mg/1 indicating no particular flushing effect at that time.
The second discrete sample was selected from the "post storm"
period and also indicated no flushing effect. The final four
samples were taken over 28 hours after the flow rate stablized at
just above DWF levels. Solids concentrations are high but data
is inconclusive as to whether this is a flushing effect or normal
DWF concentrations.
The 11/9/84 event consisted of two intense rainfall
periods and two distinct water storage periods. Three discrete
sample periods were selected for solids analysis. Discrete
samples from the first two periods indicated solids
concentrations similar to "mid storm" composite conditions.
Analysis of the last discrete sample, collected at peak storage
conditions during the second storage period indicated a definite
increase in the solids concentrations potentially due to the
combined effects of additional street washoff and scouring of
materials settled during the initial drain down period. No
samples collected during the second drain down period were
noticeably polluted and no analyses were run to investigate
flushing effects.
9.17
-------
In sum, "first flush" effects were clearly indicated by
the field data for three complete storm events monitored
justifying the improvement plan concept of modifying regulator
operation to maximize initial flow rates to the interceptor and
maintain underflow during the event. Final flush effects were
visually noted on one occasion but not analytically documented.
"First flush" conditions included rapid depth increase and high
flow rates which would scour most pipe segments nearly
simultaneously. Conditions under which final flush might occur
are limited to less pronounced depth changes and flow rates.
Scouring may occur at various times along the sewer making a peak
concentration undeterminable.
BOD and phosphorous data collected at the regulator
appear to follow similar trends as the suspended solids
results. The correlation coefficient for for paired solids and
BOD data is 0.91. The correlation coefficient for solids and
total phosphorous data is 0.99. It can be concluded that most of
the BOD and phosphorous is tied up in the solids matter. Soluble
phosphorous fractions of total phosphorous loads ranged between
20 and 93 per cent resulting in a poor total to soluble
phosphorous correlation coeficient of 0.75. A trend was noted
toward higher fractions of soluble portions of total phosphorous
increasing from an average of 36% for "start storm" samples to
59% for "mid storm" samples and to 84% for post storm samples.
This trend inversely follows the declining solids concentration
values and indicates that soluble phosphorous is not related to
solids concentrations.
For the single storm event where overflow to the river
occurred, the period of overflow was brief such that only one
sample was obtained and only phosphorous data could be generated.
Total phosphorous concentration for the single "mid-storm"
overflow sample was 30% of the composited "mid storm" underflow
sample phosphorous concentration. Overflow to the river (surface
water of the backwatered flow) was thus much less contaminated
than water sampled at the mid depth sampler intake for the
dry /wet weather flow channel. These percentages reaffirm the
phenomenon of solids settling in the backwatered flow and passing
to the interceptor and confirm the design concept.
9 . 6 Mor^itorvinj; °f ill6, Wei s_s_ Street Pump S ta_t ion
Modifications to the Weiss Street Pump Station were
limited to the construction of a weir wall within the pump wet
well area designed to eliminate or delay pump "turn on" during
storm events. The delay was caused by preventing the West Side
Interceptor flow from spilling (at about springline depth) into
the pump station wet well. Backwatering would result as greater
head would be needed to push flow thorugh the hydraulically
9.18
-------
constrained river crossing. Spillover would finally occur but
only after a higher depth of flow had been reached. The
advantage of this delay is that at both the beginning and the end
of storm periods, greater flows rates will exist in the West to
East Crossover Interceptor due to increased West Side water
elevation. In concept, the crossover modification would
considerably modify and lessen overflows for the smaller
intensity storms and have appreciably lesser impact for large
major storms. Thus an increase in the crossover rate should
reduce the overall pumped overflow at the Weiss Street Pump
Station.
Post-BMP plan system hydraulics are complicated by the
regulator modifications which were intended to increase flows to
the West Side Interceptor leading to the Weiss Street Pump
Station. Net results of the opposing effects of increased flow
to the Weiss Street Pump Station and increased crossover flow
rates could, depending on event intensity, either increase or
decrease actual pumpage volumes at the Weiss Street Station
compared to pre-BMP conditions. The reasons for this flow regime
are as follows. The CSO Facility Plan concept was to reduce the
number and magnitude of individual regulator overflows to a
minimum (by either maximizing in-system storage and/or by
modifying overflow sidewalls within the regulators to enhance
interceptor flows) and allowing any excessive interceptor flows
during major storm events to be handled by CSO control
configurations located at the major pump overflow stations. Such
a wet weather overflow treatment facility was programmed for the
Weiss Street area. Overall, it was envisioned that as part of
the BMP design, pumped overflows volumes at the Weiss Street
Station requiring treatment would be smaller for minor storm
events and be greater for major events as compared with pre-BMP
conditions.
Data collected during the post implementation period
included total operating times of the pumps using the permanent
time clocks and stormwater quality based on samples collected via
a temporary sampler installed by EDP. Total pumpage was
calculated, neglecting minor pump capacity changes due to
variable sump levels, using a value of 100 cfs per pump. Samples
were composited and tested for suspended solids, BOD and total/
soluble phosphorous.
Figure 9.8 illustrates pumped discharge volumes of CSO
to the Saginaw River at the Weiss Street Station. This figure
was earlier used in Chapter 6 to indicate the rainfall to pumpage
relationship and has been updated to include 1984 data for
periods representing pre and post-BMP modifications at the
upstream regulators and at the Weiss Street Pump Station. All
1984 data falls within the range of previous data. On this basis
9019
-------
(/>
M
i
00
Overflow volume
Cubic feet x 10* per event
9020
-------
it would appear that the effects of increased flow to the
interceptor at the regulator chambers has been substantially
offset by the increased East/West crossover flow. There appears,
however, some tendency for post BMP pumped flows to be less than
pre BMP conditions for small storms and higher for rainfall
events exceeding 0.7 inches.
As stated, the present data is limited and as such
exact trends cannot be defined. In general, it can be concluded
that for light to moderate intensity events Weiss Street CSO
pumpage has not increased above pre modification rates. The
important point is, that due to implementation of the partial
BMP plan, overflows at numerous untreated locations were reduced
or eliminated. Stormwater flow is thus directed at an increased
rate to the WWTP where treatment is available with excess
overflow concentrated at the Weiss Street Pump Station. The CSO
Facility Plan concept requires that overflow treatment be
provided in the future.
Water quality data at the Weiss Street Pump Station
consisted of BOD, SS and total and soluble phosphorous analysis.
Evaluation of phosphorous data was included in Chapter 6, where
the primary purpose was to determine WWTP phosphorous levels and
WWTP removal efficiencies. BOD and solids data were both field
collected and predicted for each storm event using the simulation
modeling program.
Figure 9.9 includes suspended solids concentration data
for each event during the 1984 portion of the pre-implementation
evaluation program. Data is seperated by period within an event
including the "pre-peak" condition, during which time the flow
rate in the system is increasing from base dry weather conditions
to the peak flow rate, followed by the "mid-storm" condition when
flow rates remain at elevated levels, and the "post" storm
conditions (flow rates dropped to "pre-storm" conditions).
Figure 9.9 clearly illustrates the effects of "first flush"
conditions at the Weiss Street Station particularly for the first
several events. High "pre-peak" solids concentrations are due to
the combined effects of street washoff and scouring of system
sediments. Lesser "mid storm" concentrations are due to
dilutional effects of increased flow and a reduction in solids
materials. "Post storm" levels are indicative of diluted sewage
and minor amounts of remaining washoff materials.
The simulation model was used to estimate SS and BOD
loadings at the Weiss Street Station for these monitored events.
Average modeled BOD and SS overflow loadings equalled 86 and 75%
of average measured loadings indicating reasonable closure.
9021
-------
1200,
1000-
800-
o
c
o
u
600-
CO
400-
200-
Legend
• Pre Peak
A Mid Storm
D Post Storm
A-" \
8/4 8/8 8/18 8/28 3/30 9/2
Date
Figure 9.9 Weiss Street Pump Station Suspended Solids Data
9.22
-------
9.7 Monitoring a_t the Waste Water Treatment Plant
Data collection at the WWTP consisted of continuous
influent rate monitoring and total bypass flow during storm
events and stormwater quality monitoring based on samples
collected via a temporary sampler installation at the influent
grit/overflow chamber. Samples were composited on a flow-weighed
basis during the storm period.
The intent of much of the reduced BMP plan was to
increase overall wet weather flows to the WWTP. Figure 9.10
illustrates cummulative WWTP wet weather flow volumes above
normal dry weather flow for the day of an event, second and third
calender days (cumulated) if flow rates had not returned to
average dwf values. Discrete pre construction and post
construction data points for the 1984 evaluation are separately
depicted. Figure 9.10 indicates that most of both the pre and
post construction data are similar although there are several
events during the post construction period indicating a
substantially increased flow at the WWTP. On this evidence it is
difficult to definitely verify the effects of the BMP program
elements implementation to date. It appears that there is a
tendency for increased flows at the WWTP.
As with the Weiss Street data, the approach used was to
ensure a reasonable correlation between the field results and
predicted model data. With the model suitably calibrated, the
effectiveness of the program implementation could be reviewed
based on long term data simulations. Results of these
simulations is presented in Chapter 10.
Comparison of WWTP field data to model data included
the flow analysis discussed in Chapter 6, which resulted in
minor modifications to the model and a good correlation of
measured to modeled data. On a water quality basis the relative
measured to model data are presented in Figure 9.11. Discrete
data for pre construction and post construction periods are
included. For both the suspended solids and BOD water quality
parameters, the model reasonably predicted both pre/post
implementation conditions.
9.8 Field Verification p.f FJ.OW Regulating Device Calibration
Simulation of CSO backup and drain-down was performed
at several of the modified chambers by EDP personnel to allow on-
isite calibration of the new vortex flow regulating devices.
Physical chamber conditions precluded direct discharge
measurements at most of the regulation chambers. Backup was
produced either by closing the manual sluice gate or by placing a
flat plate in front of the weir wall thimble. Depth measurements
9023
-------
100-1
M
C
o
rH
rH
flj
C
O
•H
•H
s
O
-P
O
0
.4
.8 1.2 1.6
Rain Accumulation
Figure 9.10 WWTP Wet Weather Flow
2.0
Inches
2.4
2.8
9o24
-------
40 n
30
FIELD
DATA
BOC
MASS 20
1000 LBS
10 •
- Equivalence Line
-t
10 20 30 40
Model Data BOD Mass - 1000 Ibs.
Legend
pre BMP
post BMP
FIELD
DATA
TSS
MASS
1000 LBS
2001
150
100
50-
- Equivalence Line
—i—
100
t
50 100 150 200
Model Data TSS Mass - 1000 Ibs.
Figure 9.11 WWTP Wet Weather Water Quality Mass Data
-------
were recorded at frequent intervals with simultaneous velocity
measurements made with a Marsh-McBirney velocity probe at the
flow regulator inlet pipe. Conversion of velocity data to flow
rates was based on known inlet cross sectional areas. Results
for each location were plotted on the manufacturer's
head/discharge curve for each device. In general, the field data
verified manufacturer's specifications.
Figures 9.12 through 9.16 illustrate the head discharge
characteristics for the five flow regulator devices measured in
the field. Each figure depicts both design characteristics and
field data. In some cases field data is limited to a narrow head
range due to the limited volume of dwf available for backwatering
and in all cases by the range of operation during storm
conditions based on side weir elevations. Each regulator
chamber, except the modified Adams Street chamber, contains a
sluiceway with a top elevation at the influent sewer invert and a
depth of up to 30 inches. At Hayes Street and Throop Street the
volume within this sluice was insufficient to allow low head flow
regulator calibration considering the high rates of discharge and
rapidly falling head conditions.
Figure 9.12 details the data for the Hayes Street
installation. Data is limited to a minimum head of two feet
which corresponds to the top of the sluiceway and the sewer
invert. Field data is somewhat scattered but all within
reasonable limits of the design curve. For this location the
water level at the point of side weir spillover is at an
equivalent head value of 3.5 ft. Thus, the range of field values
shown in Figure 9.12 covers the entire range of unit operation
during storm events and indicates good control of outflow rates.
Figure 9.13 details the data for the Adams Street
installation. The range of field data shown include head values
between the regulating device inlet crown and 9 inches below the
spillover weir crest. Field data indicates that the observed
flow pattern follows the characteristic curve. In sum, flow rate
control at this location is well within reasonable limits for
proper operation of this portion of the BMP plan.
The vortex valve discharge rates field-measured at the
Cronk Street regulator , Figure 9.14, and at the Throop Street
regulator device. Figure 9.15, also demonstrate reasonable
agreement with the design curves. Data scatter may be
attributable to actual unit accuracy limitations and/or to field
measurement techniques. Each of these locations was monitored
twice in the field and two data sets are shown on each curve.
Data repeatability, though not perfect, is quite reasonable.
Field notes indicated that at each location the second run was
less prone to debris fouling the measuring equipment since the
9026
-------
10
Figure 9.12 Hayes Street Vortex Valve Characteristics
9027
-------
00
CO
St
o
200
100
Head - Feet
Figure 9.13 Adams Street Vortex Valve Characteristics
-------
CO
8
Head - Feet
Figure 9.14 Court Street Vortex Valve Characteristics
9029
-------
vo
oo
o
Figure 9.15
34
Head - Feet
Throop Street Vortex Valve Characteristics
-------
10
9
8
7
6
5
0.5
1.5
Figure 9.16 Ames Street Vortex Valve Characteristics
9C31
-------
first run promoted scouring of the sewer line and allowed for
relatively clean water flow during the second run.
The four flow regulator units investigated above were
the conical configuration type devices. The device installed at
Ames Street is of a different design commonly termed the
"horizontal" type as the vortex flow pattern is developed in a
horizontal plane. Field data shown in Figure 9.15 fall slightly
above the vortex flow regulator design head/discharge curve. The
significant aspect of the field data is that it reasonably
matches design data shown and demonstrates a narrow range of flow
rate for the head conditions encountered in this application.
Field calibration at other regulator chambers was
impractical due to field conditions. Based on those units
actually investigated, it is concluded that the vortex valve flow
regulators adequately control outflow rates to ranges within the
design conditions necessary for proper operation of the BMP plan.
9.9 Evaluation of the Cronk Avenue Regulator
Two original regulator chambers on the West Side of the
Saginaw River were unlike all other regulators in that the
backwater gates which allow for excess stormwater overflow to
the river were not located in the regulator chamber, but in
separate remote chambers nearer the river. Each location, Cronk
Avenue and West Genessee Avenue, operated such that flow from two
directions entered the regulator chamber. Under storm
conditions, flow would backwater and reverse direction in one
feed line. A chamber with an overflow gate to the river was
constructed at a remote location.
During the design phase of the reduced BMP program, it
was determined that modifications to the backwater gate chambers
would be costly considering the minimal increase in stormwater
storage attainable, and that all flow not allowed to gravity
spill to the river might be pumped as overflow at the Weiss
Street Pump Station at additional cost. These modifications were
not deemed desireable until satellite wet weather treatment is
provided at the Weiss Street Pump Station. Modification at these
chambers was limited to replacement of the existing float-
operated regulating devices with new vortex valve throttling
devices.
Post reduced BMP plan implementation evaluation
included monitoring of the depth of flow at the Cronk Avenue
backwater gate chamber and the peak depth at a location upstream
in the Cronk Avenue drainage area. Six events were monitored
during the period each demonstrating similar characteristics of
9.32
-------
stormwater draindown rates. Draindown periods consistently
lasted several days such that in some cases drainage was not
complete at the start of a subsequent event. Flow to the river
appears to have occurred for all events which ranged in total
accumulation from 0.17 to 0.77 inches and in duration from 2
hours to 12 hours. The limited storage available is indicated
by the apparent spillover to the river after 4 hours for an event
with 0.17 inches accumulated over 5 hours.
The draindown periods were assumed attributable to the
upstream hydraulic/hydrologic conditions. Based on the estimated
storage volume of 49,000 cu.ft., the estimated dry weather flow
rate and the vortex valve design discharge rate, a draindown
period of 12 hours is predicted. The 65 to 75 hour periods field
recorded appear to be attributable to either continued
inflow/infiltration to this part of the Saginaw sewerage system,
a higher than estimated dry weather flow base rate or both.
Two upstream off-line storage chambers are located
within the drainage area. The Congress Avenue chamber consists
of approximately 1300 ft. of 77 in. by 121 in. pipe and provides
about 86,000 cu. ft. of storage. The second chamber is actually
located in the Township area (above the City of Saginaw limits)
and consists of an underground concrete structure of rectangular
shape providing about 100,000 cu. ft. of storage. During extreme
events creating surcharge conditions, combined sewage overflows
side weirs of the main 60 inch trunk line into the Congress
Avenue chamber. City personnel release the stored water after
events by manually opening a butterfly valve. City records
indicate that for the period of October and November, 1984 no
overflow to the chamber occurred. At the Jameson Street chamber
pumping of stored water is required. Although pump records were
available it was calculated that the volume of storage in the
Jameson Street chamber or even the combined storage volumes of
both chambers were insufficient to account for the volume of flow
noted after each event at the Cronk regulator.
Based on a detailed evaluation of available data, it
appears the long draindown periods are due to a current dry
weather flow rate including infiltration, much greater than
previously estimated during Phase 1 and Phase 2. The only
adverse effects of the existing conditions are the lack of
storage volume available for secondary storm events. No adverse
problems have been reported in terms of excessive surcharge or
basement flooding under modified conditions. In addition, it is
intended that both the Cronk Avenue and West Genessee Avenue
chambers be modified concurrently with the implementation of
treatment at the Weiss Street Station.
9.33
-------
9.10 Post truct ,ion Chamber
Evaluation of new flow regulating devices and chamber
modifications was performed during the post construction period.
Post storm observations were by City of Saginaw maintenance
personnel .
Observations were recorded at each modified regulator
chamber after each storm event. Records indicate the relative
intensity of the storm event, flow conditions in the chamber
upstream and downstream of the new regulating device and
conditions at the device. Observations were made of the sewage
flow to determine if free flow conditions existed without
blockage. All chamber areas and related piping were inspected
for debris accumulation in areas subject to storm conditions and
for debris sedimentation in areas of dry weather flow.
Operating conditions at most chambers were reported as
good with little or no debris accumulation or sedimentation. One
general exception is the occurrence of debris remaining on the
top surface of concrete weir walls. During the design phase this
possibility was noted, however as these surfaces also act as
walkways within the chamber it was deemed preferable to allow
small amounts of debris accumulation than to produce unsafe
footing by sloping or crowning weir tops. Debris accumulations
were predicted and have been found to be insufficient to cause
odor problems.
Locations with adverse conditions reported on one or
more occasions included the Ames Street regulator chamber, the
Court Street regulator chamber and the Salt/Vermont Streets in-
line regulator chamber. At the Ames Street regulator chamber
near complete blockage of the wall orifice leading to the flow
regulator was reported on one occasion and blockage of the device
on two other occasions. Apparently large deposits of scale or
grease were present and the City personnel cleaned the area and
the device. It is believed these conditions resulted from a
combination of factors, including large amounts of grease within
a relatively small discharge waste stream. The particular flow
through pattern of the horizontal type vortex valve may have had
an additional negative impact since no cloggage problems have
been reported for the conical type device at the Court Street
chamber which passes similar low flow rates (0.33 cfs) but not
large quantities of grease noted at Ames Street. Although it is
difficult to conclude from these observations that the horizontal
type device should not be used in the future for very low flow
rates having high grease content, care and discretion should be
used when this type of device is used to regulate small sewerage
flows .
9034
-------
Construction of the new chamber at the Salt/Vermont
Street location included the use of concrete fill material to
contour all chamber areas in an effort to prevent debris and
sediment accumulation. After construction several areas were
noted to be improperly sloped and debris accumulation has
resulted in the production of odors in the chamber. Corrective
action requires only additional concrete material to match design
conditions and should eliminate problem areas. Otherwise the
entire chamber and new regulator have been reported to operate
quite satisfactorily. No upstream deposition problems have been
noted as a result of the in-line storage generated at this
location.
The Cronk Street regulator chamber is one location
where persistent problems related to the new regulating device
have been reported. On several occasions the chamber has been
backwatered due to flow blockage resulting from sticks, rags and
other materials lodged within the flow regulating device and at
the sluice gate. The problem is compounded by the difficult
access at this location. Weir walls extent to within 17 inches
of the chamber ceiling making human access difficult and no
access manhole originally existed for the area between the weir
walls. The City has since provided a new access manhole to the
chamber above the sluiceway simplifying the unclogging process,
when necessary.
Blockages at the Cronk Street regulator appear to be due
to an unusual amount of large floating materials from the
upstream drainage area. The high weir walls within the chamber
prevent any overflow to the interceptor. Accumulations of large
floatable material may ensue and during final draindown combine
to clog the regulating device.
During the design phase of the project it was
determined that altering the remote backwatering gate and the
chamber side weirs at the Cronk Street Chamber would not be cost
effective at this location considering the limited storage
available and the need to pump excess flow at the Weiss Street
Station. The intent was to make these modifications after
treatment was provided at Weiss Street. The problem of large
floatable accumulations due to the lack of an overflow area was
not anticipated. It is recommended that the situation be
observed further and resolved, if found necessary, either by
lowering the weir walls to allow overflow of large floatable
debris or by installing an upstream stick-trapping device.
In general, the new regulating devices have
demonstrated the ability at most of the installations to pass
typical sewage and CSO materials. Any items physically too large
to pass through the device may become trapped.
9.35
-------
CHAPTER 10
ASSESSMENT OF PRE BMP CONDITIONS AND
EVALUATION OF PROPOSED PROGRAMS
10.1 Foreword
The present water quality of the Saginaw River and Bay
is determined by a wide variety of events both induced by man and
of natural origin. CSO are only one aspect of the general
problem. However, CSO have been shown to be significant in their
deleterious impacts yet controllable. Although the proposed
activities will improve river water quality and the degree of
improvement can be assessed for selected parameters, general
water quality improvements will be of a wider nature than can be
presently quantified.
10.2 Overview of Analysis Criteria and Results Presentation
Assessment of "pre BMP" conditions makes use of
EDP's stormwater runoff simulation model to estimate pollutant
emission to Saginaw River. The simulation runs present annual
summaries of combined sewer overflows and loadings at each
overflow point, and for the system in general. Overflows and
loadings are considered to be those resulting from wet weather
rainfall events. Snowmelt and infiltration during non-rainfall
periods are implicitly included in the dry weather flow and are
not tallied in the wet weather loadings.
Dry weather loadings at the WWTP are considered
adequately handled by the plant and not part of the CSO problem.
Total wet weather rainfall impacted loadings to the river include
both loadings caused by overflows in the system upstream of the
WWTP, as well as the WWTP loadings during rainfall events
(excluding normal dry weather effluent contributions). The 1978
WWTP removal efficiencies for TSS and BOD of 93% and 89%,
respectively, were considered maintainable during storm events
and were used to calculate the residual stormwater loadings from
the WWTP. Review of wet weather data for the September to
November, 1984 post construction period indicated TSS removals to
average 93.3% and BOD to average 86.1%. TSS removals were
therefore consistent with earlier 1978 data. Lower BOD values
during wet weather were apparently consistent with slightly lower
overall efficiencies. The three month period averaged 87.4% BOD
removal efficiency. On this basis it was assumed that no change
in removal efficiency for TSS or BOD resulted from the reduced
plan implementation and the original yearly average removal rates
were attainable and as such, used for model simulations. As
10.1
-------
previously discussed, phosphorous loadings to the WWTP were based
on a nominal influent concentration of 1.3 mg/1 and WWTP removal
efficiencies of 50 and 75 percent for treatment without and with
pickling liquor treatment. Phosphorous loadings at overflow
points were based on a 1.74 mg/1 concentration.
Table 10.1 presents the "pre BMP" model run and offers
an example of a typical simulation run summary. Part "A" of the
summary table will typically present overflow and related
discharge information while part "B" will present overflow
pollutant (TSS and BOD) loadings to the Saginaw River. Results
are always presented for the entire period simulation (for 1977,
there are 78 rainfall events), for "low" rainfall events defined
as less than 0.5 inches of accumulated rainfall (for 1977, there
are 60 such events), and for "high" rainfall events defined as
greater than 0.5 inches of accumulated rainfall (for 1977, there
are 18 such events).
For each of the three periods overflow and water quality
loadings are presented for seven major overflow points, for the
rest of the overflow points on the East and West Sides, and for
flows and loadings influent to the WWTP. Gravity and pumped
discharges are lumped together for the Fourteenth Street
overflow. The Weiss Street gravity overflow discharge is
separately reported from pumped overflows at the Weiss Street
Pumping Station. All quantities reported from overflow locations
are effluent discharges to the Saginaw River after treatment, if
applicable. For example, overflow and pollutant loadings from
the Hancock Street Station reflect excess overflow discharge from
the sedimentation units not bledback to the WWTP. Peak WWTP
flows reported such as in Table 10.1 represent the highest hourly
average flow rate into the WWTP. Reported mean and standard
deviations are computed on the basis of non-zero events. Event
durations ranged between one hour and three days for the 78
storms in 1977. Yearly discharge volumes and pollutant loadings
are also reported. Total hours reported in the tables represent
the total number of hours that some overflow occurred (gravity or
pumped). All flow volumes are in thousands of cubic feet. All
pollutant loadings are in thousands of pounds. Average river
elevations were used for all runs unless otherwise noted (580.15
feet - USGS datum).
10.3 Pre BMP CSO nviion Est ima t e s
Simulation analysis results for "pre BMP" conditions,
that is, the original system configuration with Hancock Street
Facility are given in Table 10.1. Although the "pre BMP"
simulation was also run during Phase 1 and Phase 2 of the overall
project (1978-1983), results presented are those based on the
10«-2
-------
TABLE lOolA
PRE BMP CONDITIONS SIMULATION
PLOWS - OVERFLOWS
PERIOD : 1 / 6 TO 12 / 26 78 EVENTS 33 INCHES TOTAL RAIN
WWTP
PEAK FLOW
VOLUME *
MEAN **
STND DEV
NO. EVENTS
FULL PERIOD
128
158968
2038
1707
78
LOW RAIN ***
128
84398
1407
741
60
HIGH RAIN •**
128
74570
4143
2254
18
OVERFLOW POINTS
FULL PERIOD LOW RAIN *** HIGH RAIN ***
VOLUME* VOLUME* VOLUME*
FRASER 76 EVENTS 405 MRS 58 EVENTS 230 MRS 18 EVENTS 175 HRS
YEAR TOT 11199 2507 8692
MEAN ** 147 43 483
STND DEV 391 58 698
HANOOCK 16 EVENTS 50 HRS 5 EVENTS 9 HRS 11 EVENTS 41 HRS
YEAR TOT 15131 1930 13200
MEAN ** 946 386 1200
STND DLV 1390 204 1607
WEISS 76 EVENTS 405 HRS 58 EVENTS 230 HRS 18 EVENTS 175 HRS
YEAR TOT 64306 23010 41296
MEAN ** 846 397 2294
STND DEV 1525 269 2616
WEISS PUMP 63 EVENTS 358 HRS 45 EVENTS 161 HRS 18 EVENTS 197 HRS
YEAR TOT 59013 19375 39368
MEAN ** 937 431 2202
STND DEV 1126 394 1344
WEBBER 20 EVENTS 49 HRS 5 EVENTS 7 HRS IS EVENTS 42 HRS
YEAR TOT 5110 317 4793
MEAN ** 255 63 320
STND DEV 557 43 630
EMERSON 0 EVENTS 0 HRS 0 EVENTS 0 HRS 0 EVENTS 0 HRS
YEAR TOT 000
MEAN ** 000
STND DEV 0 0 0
FOURTEENTH 77 EVENTS 504 HRS 59 EVENTS 280 HRS 18 EVENTS 224 HRS
YEAR TOT 10129 2507 7622
MEAN ** 132 42 423
STND DEV 306 41 532
WEST RESID 76 EVENTS 354 HRS 58 EVENTS 198 HRS 18 EVENTS 156 HRS
YEAR TOT 41249 8319 32930
MEAN ** 543 143 1829
STND DEV 2031 94 3901
EAST RESID 76 EVENTS 405 HRS58 EVENTS 230 HRS18 EVENTS 175 HRS
YEAR TOT 55659 16684 38974
MEAN ** 732 288 2165
STND DEV 1685 225 3023
* - 1000 CUBIC FEET - ABOVE DRY WEATHER FLOW ** - PER NON-ZERO EVENT
*** - LOW RAIN 0.5 INCHES OR LESS - HIGH RAIN GREATER THAN 0.5 INCHES
10.3
-------
TABLE 10.IB
PRE BMP CONDITIONS SIMULATION
WATER QUALITY
PERIOD : 1 /
WWTP
TOT LOAD
MEAN *•
STND DEV
6 TO
FULL
TSS *
3075
39.4
31.7
12 / 26
PERIOD
BOD *
939
12.0
7.3
78 EVENTS
LOW RAIN
TSS *
1673
27.9
15.2
33 INCHES TOTAL RAIN
BOO *
605
10.1
5.0
HIGH
TSS *
1402
77.9
40.8
RAIN *•*
BOD *
334
18.5
9.4
OVERFLOW POINTS
FRASER
TOT LOAD
MEAN **
STND DEV
HANOCCK
TOT LOAD
MEAN **
STO) DEV
WEISS
TOT LOAD
MEAN **
STM) DEV
WEISS PIMP
TOT LOAD
FULL
TSS *
254
3.3
8.8
305
19.1
30.8
1590
20.9
34.2
1001
MEAN *MEAN ** 15.9
STND DEV
WEBBER
TOT LOAD
MEAN **
STND DEV
EMERSON
TOT LOAD
MEAN **
STM) DEV
FOURTEENTH
TOT LOAD
MEAN **
STM) DEV
WEST RESIDUAL
TOT LOAD
MEAN **
STND DEV
EAST RESIDUAL
TOT LOAD
MEAN **
STND DEV
20.4
116
5.8
12.8
0
0.0
0.0
221
2.9
6.7
891
11.7
43.1
1178
15.5
35.6
PERIOD
BOD *
35
0.5
0.8
36
2.2
3.0
496
6.5
6.7
317
5.0
5.0
17
0.9
1.6
0
0.0
0.0
63
0.8
1.3
137
1.8
4.1
245
3.2
4.4
LOW RAIN
TSS *
60
1.0
1.3
31
6.2
5.1
646
11.1
6.5
308
6.8
7.1
7
1.4
0.9
0
0.0
0.0
57
1.0
0.9
198
3.4
1.9
375
6.5
4.5
***
BOD *
13
0.2
0.2
6
1.1
0.7
258
4.5
2.3
126
2.8
2.4
2
0.3
0.2
0
o.b
0.0
22
0.4
0.3
56
1.0
0.4
115
2.0
1.0
HIGH
TSS *
194
10.8
15.8
274
24.9
35.5
944
52.4
59.3
693
38.5
24.8
109
7.2
14.5
0
0.0
0.0
163
9.1
11.8
692
38.5
83.1
803
44.6
64.6
RAIN ***
BOD *
22
1.2
1.3
30
2.8
3.5
238
13.2
10.7
191
10.6
5.4
16
1.0
1.8
0
0.0
0.0
41
2.3
2.2
81
4.5
7.8
130
7.2
7.5
* - 1000 POUNDS •• - PER NON-ZERO EVENT
*** - LOW RAIN 0.5 INCHES OR LESS - HIGH RAIN GREATER THAN 0.5 INCHES
10.4
-------
final model editions as calibrated in Phase 3 (1984). Regulators
were set to operate as they originally existed. In-line storage
was composed of the storage generated by the five modified
regulators in the Hancock Street area, and the available storage
(up to the point backwater gates would open) for all other
regulators. The interceptor system operated as originally
perceived with the Weiss Street Station wet well weir level
unadjusted. The WWTP flow rate was throttled to allow only a
throughput maximum flow of 128 cfs, the maximum rate observed
during the 1984 field investigation.
The total annual wet weather rainfall impacted combined
sewage discharge for 1977 delivered to the WWTP and to all the
overflow/pumping station locations equals 420.8 million cubic
feet. Approximately 37.7% of this total or 159.0 million cubic
feet is delivered to the WWTP with an untreated balance of 261.8
million cubic feet. The fraction of the combined sewage
discharge at the WWTP during 60 low rainfall events is 53.0% of
the overall low rainfall total (140.1 million cubic feet) and is
2.8.5% for the 18 high rainfall events. The high rainfall event
subtotal equals 62.1.% of the annual overall combined sewer
overflows.
The "pre BMP" overflow summary results in Table 10.2
indicate that the Weiss Street area (Weiss Street Pump Station
and the Weiss Street gravity overflow from the Township) is the
primary overflow in the system representing 47.1% of the annual
system CSO (excluding discharge to the WWTP). The Hancock Street
overflow is second, representing 5.8% of the total untreated CSO
suggesting that the bottleneck at the river crossing has a
substantial impact at both the Hancock and Weiss Street Station
discharge points. Overflows at Webber Street, Fourteenth Street
and Fraser Street represent 2.0%, 3.9% and 4.3%, respectively, of
the annual CSO discharge. The Emerson Street Station was not
used during any events. The remainder of the system's CSO
discharge points from both the East and West Side regulators
accounted for 37.1% of the total, 21.3% and 15.8% respectively.
The "pre BMP" total annual (1977) wet weather TSS and
BOD pollutant loadings generated in the system and delivered to
the WWTP and all overflow/pumping station locations equal 8.63
and 2.29 million pounds, respectively (See Tables 10.3 and 10.4).
TSS and BOD loadings to the WWTP represent 35.6% and 41.1% of
the overall wet weather load. (Tables 10.3 & 10.4) After WWTP
treatment, however, the residual wet weather WWTP TSS and BOD
loadings represent less than 10% of the total wet weather
loadings to the river. Pollutant emissions from Hancock and
Weiss Street locations are the dominant source of organic
loadings to the river from the major overflow points. Pollutant
emissions from the 60 low rainfall events represent roughly 54%
1005
-------
TABLE 10.2
FLOW SUMMARY DATA
PRE BMP
TOTAL FLOW
BMP
TOTAL FLOW
REDUCED BMP
TOTAL FLOW
WEISS
HANCOCK
FRASER
14TH
WEBBER
EMERSON
EAST
WEST
SUBTOTAL
WWTP
TOTAL
WWTP % OF
WEISS % OF
1000 FT3
123,319
15,131
11,199
10,129
5,110
0
55,659
41,249
261,796
158,968
420,764
TOTAL FLOW
TOTAL FLOW
*%
47.1
5.8
4.3
3.9
2.0
0
21.3
15.8
100
SUMMARY
37.7
29.3
1000 FT3 %
95,861 66.0
27,228 18.7
5,558 3.8
12,855 8.9
3,752 2.6
0 0
0 0
0 0
145,254 100
303,823
449,077
STATISTICS
67.7
21.3
1000 FT3
81,404
30,017
5,376
13,296
4,144
0
55,709
29,036
218,982
240,508
459,490
%
37.1
13.7
2.4
6.1
1.9
0
25.4
13.4
100
52.3
17.7
* % OF SUBTOTAL FLOW - EXCLUDING WWTP
10.6
-------
TABLE 10.3
TSS SUMMARY DATA
LOCATION
WWTP LOAD
WWTP REMOVAL
WWTP NET TO RIVER
WEISS TO RIVER
ALL OTHER TO RIVER
TOTAL WET WEATHER LOAD
TOTAL LOAD TO RIVER
PRE BMP
TOTAL LOAD
BMP
TOTAL LOAD
REDUCED BMP
TOTAL LOAD
WWTP % OF TOTAL WET
WEATHER LOAD
WWTP % REMOVAL OF
WWTP LOAD
WWTP % REMOVAL OF
TOTAL LOAD
WWTP RESIDUAL % OF
RIVER LOAD
CONTROL PROGRAM NET
% REMOVAL
1000 LBS
3,075
2,860
215
2,591
2,965
.D 8,631
5,771
SUMMARY
35.6
93
33.1
3.7
0
1000 LBS
6,068
5,643
325
2,053
1,031
9,152
3,509
STATISTICS
66.3
93
61.7
9.3
28.6
1000 LBS
5,140
4,780
360
1,778
2,892
9,810
5,030
52.4
93
48.7
7.2
15.6
10.7
-------
TABLE 10.4
BOD SUMMARY DATA
LOCATION
PRE BMP
TOTAL LOAD
BMP
TOTAL LOAD
REDUCED BMI
TOTAL LOAD
WWTP LOAD
WWTP REMOVAL
WWTP NET TO RIVER
WEISS TO RIVER
ALL OTHER TO RIVER
TOTAL WET WEATHER LOAD
TOTAL LOAD TO RIVER
WWTP % OF TOTAL WET
WEATHER LOAD
WWTP % REMOVAL OF
WWTP LOAD
WWTP % REMOVAL OF
TOTAL LOAD
WWTP RESIDUAL % OF
RIVER LOAD
CONTROL PROGRAM NET
% REMOVAL
1000 LBS
939
836
103
813
533
2,285
1,449
SUMMARY
41.1
89
36.6
7.1
0
1000 LBS
1,944
1,730
214
492
163
2,599
869
STATISTICS
74.8
89
66.6
24.6
30.0
1000 LBJ
1,802
1,604
198
466
547
2,815
1,211
64.0
89
57.0
16.4
20.4
10.8
-------
of the total implying that considerable pollutant removal gain
can be achieved by control of overflow during low level storms.
The annual "pre BMP" wet weather related TSS and BOD loadings to
the Saginaw River (for the simulation year of 1977) equal 5.77
and 1.45 million pounds, respectively. See Tables 10.3 and 10.4.
10.4 Analysis of Weiss Weir Alteration
"Pre BMP" conditions were also run during Phase 2
simulations (1983) with the Weiss Street regulator weir raised 5
feet to assess its impact on the system. Summary results of the
earlier simulations are reported here to indicate the
significance of the weir modification.
Model operation simulating the Weiss Street Pump Station
weir alteration as the only change to the Saginaw system
indicated that volumes of overflow at specific locations would
change, particularly at the WWTP where total flow increased
20.2%. The flow increase to the WWTP is mainly offset by the
substantial change in pumpage requirements at Weiss Street.
Increasing the Weiss Street Station weir elevation also acts to
pond more water in the West Side Interceptor system as evidenced
by a minor increase in overflow at the Hancock Street Station.
The flow increase at Hancock Street exactly balanced the WWTP
increase and the Weiss Street decrease. No changes were
recorded in the simulation results for any of the other large
overflow points or for totals of the smaller regulator chambers
on either river side.
Considering the effectiveness of the WWTP in handling
wet weather flow, and using the Phase 3 "pre BMP" model volumes,
overall reductions in wet weather loadings potentially gained
from the single act of raising the Weiss Street weir height are
0.58 and 0.17 million pounds for TSS and BOD, which are 10.0% and
9.2% of the present total loadings.
The results support the hypothesis that the interceptor
river crossing is a major bottleneck to flow. Restricted pumpage
rates at the WWTP wet well quickly back up the East Side
Interceptor which, in turn throttles flow across the river and
backs up the West Side Interceptor. An important step to
relieve the system is to reduce overflow at the Weiss Street Pump
Station by increasing the weir height into the wet well, and
thereby increase the flow across the river and to the WWTP.
Excess system capacity appears available in the Emerson area,
suggesting diversion of all the smaller East Side overflow points
to the East Side interceptor with pumping relief and overflow
treatment provided at the Emerson Street Pumping Station. This
action should also increase the flow to the WWTP.
10.9
-------
10.5 Complete BMP Program Simulation
The complete BMP program incorporates all the low level
structural improvements and management practices that could be
implemented at relatively low cost. The concept of the program
is to maximize the use of existing facilities before further CSO
treatment facilities are implemented. The program maximizes in-
line storage already available in the system conduits and
maximizes the conveyance of storm flows to the WWTP. To
effectuate this plan, the 33 existing regulators are modified, 14
new flow control devices are installed within new control
chambers to increase in-line storage, and weir modifications are
accomplished at the Weiss Street Pump Station to increase flow
across the river.
Complete BMP implementation includes modification of
the Type "B" regulators to yield a constant discharge during
initial storage filling, with excess flows beyond available
storage diverted to the interceptor rather than the river.
Modifying the Type "B" regulator chambers includes adding a
cross weir between the backwater gate and the flow channel, and
altering the existing side weirs between the flow channel and the
drain system leading to the interceptor. In this manner flows in
excess of what is discharged through the new vortex valve flow
regulating device or stored in the system behind the weir, will
first overflow the lower weir and be directed to the
interceptor. Only extremely high flows will overflow the cross
weir separating the backwater gate portion of the chamber, and be
directed to the river. This weir arrangement was considered by
EDP to be both the least expensive and most available method of
limiting overflows at all of the regulator chambers in the
system. The modified Hancock area regulators are also to have
the automatic sluice gates leading to the river replaced with
flap gates. Six additional regulators of smaller size (Type "A")
are to be altered with weirs to divert all flows to the
interceptor. Alterations to produce this effect were proposed
under the previous Hancock area modification plan in 1977 and it
is the intent of the BMP program to complete these modifications.
The regulator chamber at Fraser Street is to be unaltered
except for removal of the float operated swing gate
regulator. An increased weir elevation of five feet is to be
imposed at the Weiss Street Pumping Station to reduce pumped
overflows at that point and increase the flow across the river.
Fourteen upstream structures are to be constructed and vortex
valve regulating devices are to be installed to yield additional
in-line flow control for storage upstream of the existing
regulator chambers. The resulting changes to the regulator
operations achieve the maximum in-line storage potential of the
system without causing system flooding.
10.10
-------
The only points of overflow as a result of these
actions are at Eraser, Hancock, Weiss (pump and gravity), Webber,
Emerson and Fourteenth Streets except in extreme flooding
conditions. Weir elevations at Webber and Fourteenth Street
overflow points would be raised slightly to insure that the
fairly high post rain discharges from upstream in-line storage
devices are totally diverted to the interceptor. An upstream
flow control device is intended only a short distance upstream.
The total annual wet weather rainfall impacted combined
sewage discharge for 1977 delivered to the WWTP and to all the
overflow/pumping station locations equals 449.0 million cubic
feet as simulated by the Phase 3 (1984) model for the complete
BMP program (see Table 10.5). Approximately 67.7% of this total
or 303.8 million cubic feet is delivered to the WWTP with an
untreated balance of 145.2 million cubic feet. The fraction of
the combined sewage discharge to the WWTP during 60 low rainfall
events is 87.5% of the overall low rainfall total and is 50.3%
for the 18 high rainfall events. The high rainfall event
subtotal equals 53% of the annual overall combined sewer
overflows.
The complete BMP plan overflow summary results in Table
10.2 indicate that the Weiss Street area represents 66% of the
annual system CSO (excluding discharge to the WWTP). The Hancock
Street overflow represents 18.7% of the total. Overflows at
Webber Street, Fourteenth Street and Fraser Street represent
2.6%, 8.9% and 3.8%, respectively, of the annual CSO discharge.
The complete BMP plan would eliminate discharge of CSO from all
other points on both the East and West Sides.
The complete BMP plan total annual (1977) wet weather
TSS and BOD pollutant loadings generated in the system and
delivered to the WWTP and all overflow/pumping station locations
equal 9.15 and 2.6 million pounds, respectively. See Tables 10.3
and 10.4. TSS and BOD loadings at the WWTP represent 66.3% and
74.8% of the overall wet weather total before treatment. After
WWTP treatment, the residual wet weather WWTP TSS and BOD
loadings represent only 9.3% and 24.6% of the total wet weather
loadings to the river. Overall, the WWTP reduces the TSS and BOD
loadings by 61.7 and 66-6%, respectively, resulting in wet
weather related discharges of 3.5 and 0.87 million pounds of TSS
and BOD, respectively, to the Saginaw River. Pollutant emissions
from Hancock and Weiss Street locations are the remaining
dominant source of organic loadings to the river from the major
overflow points.
Comparing the above flow and pollutant summary data to
that developed earlier for the "pre BMP" simulation indicates
substantial reductions in overall CSO loadings to the river
10.11
-------
TABLE 10.5A
COMPLETE BMP PLAN SIMULATION
FLOWS - OVERFLOWS
PERIOD : I / 6 TO 12 / 26 78 EVENTS 33 INCHES TOTAL RAIN
WWTP
PEAK FLOW
VDUME *
MEAN **
STND DEV
NO. EVENTS
FULL PERIOD
128
303823
3895
2633
78
LOW RAIN ***
128
183031
3051
1782
60
HIGH RAIN ***
128
120792
6711
3020
18
OVERFLOW POINTS
FULL PERIOD LOW RAIN *** HIGH RAIN ***
VOLUME* VOLUME* VOLUME*
FRASER 18 EVENTS 73 HRS 4 EVENTS 7 HRS 14 EVENTS 66 MRS
YEAR TOT 5558 203 5355
MEAN ** 309 51 383
STND DEV 650 39 719
HANCOCK9 EVENTS 37 HRS0 EVENTS 0 HRS9 EVENTS 37 HRS
YEAR TOT 27228 0 27228
MEAN ** 3025 0 3025
STND DEV 5207 0 5207
WEISS46 EVENTS 237 HRS28 EVENTS 94 HRS18 EVENTS 143 HRS
YEAR TOT 40646 8929 31718
MEAN ** 884 319 1762
STND DEV 1686 210 2435
WEISS PUMP 63 EVENTS 362 HRS45 EVENTS 1 63 EVENTS 362 HRS
45 EVENTS 168 HRS 18 EVENTS 194 HRS
YEAR TOT 55215 12719 42496
MEAN ** 876 283 2361
STND DEV 1529 355 2186
WEBBER11 EVENTS 39 HRS1 EVENTS 1 HRS10 EVENTS 38 HRS
YEAR TOT 3752 34 3718
MEAN ** 341 34 372
STND DEV 661 0 686
EMERSON0 EVENTS 0 HRS0 EVENTS 0 HRS0 EVENTS 0 HRS
YEAR TOT 0 0 0
MEAN ** 000
STND DEV 000
FOURTEENTH 76 EVENTS 837 HRS 58 EVENTS 492 HRS 18 EVENTS 345 HRS
YEAR TOT 12855 4073 8782
MEAN ** 169 70 488
STND DEV 349 56 609
WEST RESID 0 EVENTS 0 HRS
YEAR TOT
MEAN **
STND DEV
0 EVENTS 0 HRS
0
0
0
0 EVENTS 0 HRS
0
0
0
0
0
0
EAST RESID 34 EVENTS 127 HRS 16 EVENTS 36 HRS 18 EVENTS 91 HRS
YEAR TOT 0 0 0
000
MEAN ** 000
STND DEV 000
* - 1000 CUBIC FEET - ABOVE DRY WEATHER FLOW ** - PER NON-ZERO EVENT
*** - LOW RAIN 0.5 INCHES OR LESS - HIGH RAIN GREATER THAN 0.5 INCHES
10.12
-------
TABLE 10.5B
COMPLETE BMP PLAN SIMULATION
MATER QUALITY
PERIOD : 1 /
WWTP
TOT LOAD
MEAN **
STND DEV
6 TO
FULL
TSS *
6068
77.8
47.2
OVERFLOW POINTS
FULL
FRASER
TOT LOAD
MEAN **
STND DEV
HANCOCK
TOT LOAD
MEAN **
STND DEV
WEISS
TOT LOAD
MfcAN **
STND DEV
WEISS PUMP
TOT LOAD
MEAN **
STND DEV
WEBBER
TOT LOAD
MEAN **
STND DEV
EMERSON
TOT LOAD
MEAN **
STND DEV
FOURTEENTH
TOT LOAD
MEAN **
STND DEV
WEST RESIDUAL
TOT LOAD
MEAN **
STND DEV
EAST RESIDUAL
TOT LOAD
MEAN **
STND DEV
TSS *
125
6.9
14.8
559
62.1
108.9
944
20.5
38.1
1109
17.6
31.5
85
7.7
15.2
0
0.0
0.0
268
3.5
7.3
0
0.0
0.0
0
0.0
0.0
12 / 26
PERIOD
BOD *
1944
24.9
13.5
PERIOD
BOD *
12
0.7
1.2
53
5.9
10.3
254
5.5
7.2
238
3.8
4.7
12
1.1
1.9
0
0.0
0.0
86
1.1
1.6
0
0.0
0.0
0
0.0
0.0
78 EVENTS
LOW RAIN
TSS *
3728
62.1
31.0
LOW RAIN
TSS *
4
1.1
0.8
0
0.0
0.0
225
8.0
4.7
252
5.6
7.2
1
0.7
0.0
0
0.0
0.0
91
1.6
1.2
0
0.0
0.0
0
0.0
0.0
33 INCHES TOTAL RAIN
***
BOD *
1364
22.7
12.0
***
BOD *
1
0.2
0.1
0
0.0
0.0
81
2.9
1.5
77
1.7
2.0
0
0.1
0.0
0
0.0
0.0
37
0.6
0.4
0
0.0
0.0
0
0.0
0.0
HIGH
TSS *
2340
130.0
54.0
HIGH
TSS *
120
8.6
16.4
559
62.1
108.9
719
39.9
55.4
857
47.6
45.7
84
8.4
15.8
0
0.0
0.0
177
9.8
12.9
0
0.0
0.0
0
0.0
0.0
RAIN ***
BOO *
580
32.2
15.7
RAIN ***
BOD *
12
0.8
1.3
53
5.9
10.3
173
9.6
10.1
161
8.9
5.4
12
1.2
2.0
0
0.0
0.0
49
2.7
2.6
0
0.0
0.0
0
O.C
0.0
- 1000 FOUNDS "" - PER NON-ZERO EVENT
*** - LOW RAIN 0.5 INCHES OR LESS - HIGH RAIN GREATER THAN 0.5 INCHES
10.13
-------
(Tables 10.3, 10.4). Simulations of the 1977 storm events
indicate that implementing the total EMF would reduce the annual
"Pre BMP" wet weather induced TSS loading to the Saginaw River by
28.6%, the BOD by 30%. As detailed below, implementation of a
reduced BMP plan results in slightly lower overall reductions due
tc increased overflows at the smaller regulators.
10.6 Reduced BMP Program
The reduced BMP program incorporated mcst cf the low
level structural improvements of the complete BMP program for the
West Side. No alterations are recommended on the East Side as
the numerous simulations performed demonstrated that
implementation of East Side improvements in full or in part, will
result in excess flow tc the Emerson Street facility. Under "pre
BMP" flow conditions, use of this manually operated facility was
virtually unnecessary and one preference of the reduced BMP
program was to avoid increased manpower requirements. West Side
regulators were modified as discussed under the complete BMP
program with weirs set to elevations as detailed in Chapter 7.
The five foot weir elevation increase at the Weiss Street
Pump Station was completed.
One of the original fourteen upstream in-line storage
locations was selected as a demonstration site fcr the
construction of a new flow regulation/backwater/storage facility.
This location is upstream of the existing Eraser Street regulator
and provides an estimated 175,000 cubic feet of storage, a major
reason for selection of this site.
Utilizing the reduced BMP program including the Weiss
Street Pump Station weir adjustment, the total annual wet weather
rainfall impacted combined sewage discharge for 1977 delivered to
the WWTP and to all the overflow/pumping station locations equals
459.5 million cubic feet (see Tables 10.6 and 10.2).
Approximately 52.3% of this total or 240.5 million cubic feet is
delivered to the WWTP with an untreated balance of 219 million
cubic feet. The fraction of the combined sewage discharge to the
WWTP during 60 low rainfall events is 72.1% of the overall low
rainfall total and is 39% for the 18 high rainfall events. The
high rainfall event subtotal equals 59.1% of the annual overall
combined sewer overflows.
The flow summary results in Table 10.4 indicate that
the Weiss Street area described earlier as the primary overflow
in the system represents 37.1% of the annual system CSC
(excluding discharge tc the WWTP). The Hancock Street overflow
represents 13.7% of the total. Overflows at Webber Street,
Fourteenth Street and Fraser Street represent 1.9%, 6.4% and
L0014
-------
"TABLE I0.6A
REDUCED BMP PLAN SIMULATION
_________________
PERIOD I 1 / 6 TO 12 / 26 78 EVENTS 33 INCHES TOTAL RAIN
WWTPRJLL~PERl65 LOW~hAlN~»»» HISH~RAIN~««
PEAK FLOW 128 128 128
VOLUME » 24O508 135226 1O52B2
MEAN »* 3083 2254 S849
STND DEV 2336 1387 2690
NO.EVENTS 78 60 18
6viRFLQW~p6lNTS
FULL PERIOD LOW RAIN *** HIGH RAIN ***
VOLUME* VOLUME* VOLUME*
FRASER 18 EVENTS 71 HRS 4 tVENTS 6 HRS 14 EVENTS 65 HRS
YEAR TOT 5376 16O 5216
MEAN ** 299 4O 373
SfND DEV 652 39 722
HANCOCK14~EVENTS~56~HRS3~EVENTS~9~HRS11~EVENTS~4/~HRS
YEAR TOT 3OO17 1186 28831
MEAN »* 2144 395 2621
STND DEV 4351 107 4799
WElii76~EVENTS~&87~HRS5i~IvENTS~34B~HRSIi~EVENTS~239~HRS
YEAR TOT 43037 1OS33 325O4
MEAN »» 566 182 18O6
STND DEV 1402 23O 2473
WElsS~PUMP~48~iviNTS~257~HRS3O~£VENTS~9S~HRiIi~EV£NTS~l62~HRS
YEAR TOT 38367 10238 28129
MEAN ** 799 341 1563
STND DEV 866 306 955
WEBBER13~EVENTi~49~HRS2~EVENTS~3~HRSll~IvENTS~46~HRi
YEAR TOT 4144 99 4O45
MEAN ** 519 50 368
STND DEV 630 11 673
EMERSON0~EVENTi~0~HRSO~IvENTS~O~HRSO~EVENTS~O~HRi
YEAR TOT 0 O O
MEAN *» 0 O O
STND DEV O O O
FOUR?lENTH~76~EVEN7s~79r~HRS58~EVENTS~4i6~HRSlB~EVEN?i~365~HRS
YEAR TOT 13296 41O9 9187
MEAN ** 175 71 510
STND DEV 359 61 621
WEST~RESID~76~EVENTi~692~HRi5i~EVENri~4li~HRiTi~EVENTi~274~HRi
YEAR TOT 29036 9265 19771
MEAN *» 382 16O 1O98
STND DEV 762 125 1316
EASr~RESTD~76~iviNTS~4i5~HRb5i~IvENTS~279~HRSI8~£VENTS~204~HRS
YEAR TOT 55709 16759 38951
MEAN ** 733 289 2164
STND DEV 1688 234 3O29
~»™~IoOO~Cu6lC~FEiT~-~AiovI~5RY~WEATHER~FL5w*»~-~PER~N5N-zlRO~IvENT
*** - LOW RAIN O.5 INCHES OR LESS - HIGH RAIN GREATER THAN 0.5 INCHES
10.15
-------
TABLE 10.6B
REDUCED BMP PLAN SIMULATION
WATER QUALITY
PERIOD t 1/6
WWTP
TOT LOAD
MEAN *«
STND DEV
OVERFLOW POINTS
FRASER
TOT LOAD
MEAN **
STND DEV
HANCOCK
TO! LOAD
MEAN »»
STND DEV
WEISS
TOT LOAD
MEAN »«
STND DEV
WEISS PUMP
TOT LOAD
MEAN **
STND DEV
WEBBER
TOT LOAD
MEAN «*
STND DEV
EMERSON
TOT LOAD
MEAN **
STND DEV
FOURTEENTH
TOT LOAD
MEAN »»
STND DEV
WEST RESIDUAL
TOT LOAD
MEAN »•
STND DEV
EAST RESIDUAL
TOT LOAD
MEAN »»
STND DEV
TO
FULL
TSS *
S14O
65. 9
44.1
FULL
TSS »
121
6.7
14.8
612
43.7
92.0
1OO8
13.3
31. B
770
16. 1
17.4
94
7.2
14.5
O
o.o
o.o
291
3.8
7.9
613
8.1
16.0
1161
IS. 3
35. b
12 / 26
PERIOD
BOD *
1802
23.1
12.7
PERIOD
BOD *
12
0.7
1.2
61
4.4
8.7
277
3.6
6.3
189
3.9
3.2
13
1.0
1.8
O
O.O
0.0
87
1. 1
1.6
133
1.7
1.9
241
3.2
4.4
76 EVENTS
LOW RAIN
TSS «
3041
SO. 7
27.2
LUW RAIN
TSS »
3
0.9
O.8
17
3.7
2.7
271
4.7
5.4
212
7.1
6.3
2
1. 1
O.2
O
0.0
0.0
94
1.6
1.3
206
3.5
2.5
367
6.3
4.6
33 INCHES TOTAL RAIN
«**
BOD *
1233
20.6
10.9
«««
BOD *
O
O.I
0.1
2
O.8
O.3
10O
1.7
1.8
66
2.2
1.9
O
0.2
O.O
O
O.O
O.O
37
O.6
0.4
65
1.1
0.6
112
1.9
l.O
HIGH
TSS *
210O
116.7
51.2
HIGH
TSS •
117
8.4
16.4
595
54.1
101.4
737
41. 0
56.2
558
31. 0
19.5
92
8.3
15.5
0
O.O
0.0
197
10.9
13.8
407
22.6
27.9
795
44.1
64.4
RAIN »»»
BOD «
568
31.6
14.4
RAIN ***
BOD «
11
0.8
1.3
59
5.3
9.6
177
9.9
10.2
123
6.8
2.8
13
1.2
2.O
0
0.0
0.0
SO
2.8
2.5
68
3.8
2.9
129
7.2
7.5
* - 1000 POUNDS »« - PER NON-ZERO EVENT
**» - LOW RAIN 0.5 INCHES OR LESS - HIGH RAIN GREATER THAN O.5 INCHES
10.16
-------
2.4%, respectively, of the annual CSO discharge. The Emerson
Street Station was not used during any events. The remainder of
the system's CSO discharge points on the East Side accounted for
25.4% of the total. CSO discharged from the West Side regulators
accounted for 13.4%. These CSO are due to limited structural
changes at the Crcnk Street and W. Genessee Avenue regulators.
Presently, available storage at these locations is limited and
excess flow if not allowed to pass by gravity to the river would
require pumping at the Weiss Station. Until the control facility
is implemented at Weiss Street to handle pumped overflows, it was
not deemed appropriate to alter the present overflow patterns.
The reduced BMP program annual (1977) wet weather TSS
and BOD pollutant loadings generated in the system and delivered
to the WWTP and all overflow/pumping station locations equal 9.81
and 2.82 million pounds, respectively (see Tables 10.3 and
10.4 ). TSS and BCD loadings at the WWTP represent 52.4% and
64.0% of the overall wet weather total before WWTP. After WWTP
treatment, the residual wet weather WWTP TSS and BOD loadings
represent only 7.2% and 16.4% of the total wet weather loadings
to the river. Overall, the WWTP reduces the loading of TSS and
BOD by 48.7 and 57%, respectively resulting in wet weather
related discharges of 5.03 and 1.21 million pounds of TSS and
BOD, respectively, to the Saginaw River. Pollutant emissions
from Hancock and Weiss Street locations are the remaining
dominant source of organic loadings to the river from the major
overflow points.
Comparing the above flow and pollutant summary data to
that developed earlier for the "pre BMP" simulation indicates
substantial reductions in overall CSO loadings to fthe river.
Simulations of the 1977 storm events indicate that implementing
the reduced BMP plan lowered the annual "Pre BMP" wet weather
induced TSS loadings to the Saginaw River by 15.6% and the BOD
loadings by 20.4%. Comparison of these values to those detailed
at the end of Sections 10.4 and 10.5 indicate removals to be
greater than that attained by altering the Weiss Street regulator
chamber weir and less than that provided by the complete BMP
program.
10.7 Phosphorous_ Ana l%s :L s_
Assessment of total phosphorous loadings and potential
reductions under various simulation schemes is summarized in
Table 10.7. A nominal WWTP concentration of 1 . 3 mg/1 was set for
stormwater flows to the WWTP under "pre BMP " conditions.
Removal efficiencies recorded at the WWTP were typically 50%
for secondary treatment and 75% with AWT phosphorous treatment.
These rates were used in the computations. The total phosphorous
10cl7
-------
TABLE 10.7
TOTAL PHOSPHOROUS SUMMARY DATA
LOCATION
WWTP LOAD*
WWTP AVG CONG MG/L
WWTP BYPASS (2%)
ADD FROM HANCOCK
WWTP REMOVAL 50%
(75%)
WWTP NET TO RIVER 50%
(75%)
HANCOCK LOAD
HANCOCK REMOVAL (13%)
HANCOCK NET TO RIVER
WEISS TO RIVER
ALL QTHER TO RIVER
TOTAL WET WEATHER LOAD
TOTAL LOAD TO RIVER
50% WWTP REMOVAL
(75% WWTP REMOVAL)
**
PRE
BMP
Ibs
12,900
1.3
258
213
6,248
(9,641
6,685
(3,472)
1,642
213
1,429
13,386
13,389
41,317
34,889
(31,676)
REDUCED
BMP
Ibs
21,351
1.42
427
423
10,674
(16,010)
10,676
(5,341)
3,257
423
2,833
8,836
11,675
45,119
34,020
(28,685)
COMPLETE
BMP
Ibs
28,331
1.44
566
384
14,074
(21,112)
14,650
(7,603)
2,955
384
2,571
10,405
2,406
44,097
30,032
(22,985)
SUMMARY STATISTICS
WWTP % OF TOTAL LOAD 31.2
WWTP % REMOVAL RATE 50/75
WWTP % REMOVAL OF
TOTAL LOAD 50% RATE 15.5
(75% RATE) (23.3)
HANCOCK % REMOVAL OF
TOTAL LOAD 0.5
47.3
50/75
23.6
(35.5)
0.9
61.8
50/75
31.8
(47.9)
0.9
NET % REMOVAL OF
TOTAL LOAD 50% RATE 16.0
(75% RATE) (23.8)
CONTROL PROGRAM NET %
REMOVAL 50% RATE 0
(75% RATE) (0)
24.5
(36.4)
8.5
(12.6)
32.7
(48.8)
16.7
(25.0)
* WWTP LOAD BASED ON 1.3 mg/1, ALL OTHER AT 1.74 mg/1
** TOTAL LOAD IS PRE BMP TOTAL LOAD FACTORED BY MODEL VOLUME
RATIOS. WWTP IS TOTAL LOAD MINUS OTHER LOADS AT 1.74 mg/1
10cl8
-------
concentration at all untreated overflow points was set at 1.73
mg/1.
Phosphorous loadings to the WWTP for other than "pre
BMP" conditions were determined as the "pre BMP" total system
load less the estimated loading to the river from the untreated
overflows. Average concentrations at the WWTP were then
calculated based on total WWTP flow and total phosphorous
loading. On this basis the total phosphorous concentration in the
WWTF influent was estimated as 1.44 mg/1 for the complete BMP
and 1.42 mg/1 for the reduced BMP programs, respectively.
Table 10.7 presents summary results of estimated total
phosphorous loadings and removals.
Inspection of Table 10.7 indicates that implementation
of the complete BMP program is estimated to increase the relative
wet weather phosphorous loadings to the WWTP by 30.6% up to
61.8% of the total area load. At this rate, 32.7% removal would
be expected, 16.7% above existing conditions, assuming 50%
removal at the WWTP. Under conditions providing 75% phosphorous
removal (teritary treatment - pickling liquor), the total
phosphorous removal percentage attained would be 48.8% or 25%
above existing conditions.
Performing the construction and alteration measures
outlined in the reduced BMP program will provide 50% of the
phosphorous reduction gain estimated attainable by the complete
BMP program. The WWTP would receive 47.3% of the wet weather
system phosphorous load and remove 24.5% of the total load at the
50% rate and 36.4% of the total load at the 75% rate.
Incremental removal gains above pre BMP conditions would be 8.5%
and 12.6%, respectively.
Based on an annual total wet weather load of 41,000
Ibs. the total estimated phosphorous loadings to the river would
be 34,000 Ibs. for the reduced BMP plan and 30,000 Ibs. for the
complete BMP plan with secondary (50%) treatment of the WWTP.
Using pickling liquor (or FeSO4) for AWT treatment, the residuals
would be about 29,000 Ibs. and 23,000 Ibs., for the reduced BMP
and complete BMP plans, respectively. Figure 10.1 graphically
illustrates the relative annual wet weather phosphorous loadings
to the Saginaw River based on various treatment senarios. Two
sets of bar graphs were used to indicate estimated removals with
the WWTF providing secondary (top of figure) and AWT treatment
(bottom of figure). In addition, the soluble fraction of the
total phosphorous is illustrated. The total wet weather load of
41,000 pounds per year is shown as 100%. River loadings for pre
BMP, reduced BMP, and proposed complete BMP conditions are then
shown in terms of pounds and percentages of soluble and total
phosphorous. The upper figure represents removal rates based on
10.19
-------
standard secondary treatment. Phosphorous removal is due to the
non soluble fraction tied in with solids materials. The lower
figure illustrates the effects of AWT treatment for phosphorous.
Soluble fractions are reduced as shown but no additional
non-soluble reduction occurs. Although some phosphorous remvoal
is provicded with solids settling at Hancock Hancock, most of
the reduction occurs at the WWTP. Figure 2.1 graphically
illustrates substantial reductions in total phosphorous loadings
to the river due to treatment at the WWTP and that implementation
of BMP measures greatly enhance total removals. Soluble
phosphorous removal is non-existent with the WWTP providing only
secondary treatment.
AWT treatment at the WWTP using pickling liquor is
shown in Figure 2.1 as it further reduces total phosphorous
loadings to the river. The entire decrease is due to reduction
of the soluble phosphorous fraction.
10o20
-------
CHAPTER 11
APPLICATION OF INLET CONTROL
TECHNOLOGY TO THE
CITY OF SAGINAW COMBINED SEWERAGE SYSTEM
11,1 Foreword
Surcharging sewer/basement flooding problems, which can
occur during storm conditions within sewerage systems of all
types (seperated, adjacent and combined), have been identified
in many parts of the country. The extent of these problems has
led to investigations in the area of inlet control or stormwater
management to develop inexpensive solutions in comparison to
traditional outlet sewer relief sewer programs.
The focus of the Saginaw sewerage system evaluation so
far has been on the incidence and reduction of CSO to the Saginaw
River. For this reason most of the control technologies have
been focused near the river with only partial emphasis on
upstream control. Upstream control concepts have been limited to
recommendations of in-line structures intended to create in-line
storage.
Basement flooding from surcharging collection systems
has been reported from time to time in the City and this chapter
represents a brief review of this problem and considers
potentially suitable inlet-control technologies and their effects
on mitigating basement flooding and reducing CSO.
Section 11.2 describes the philosophy of inlet control
technology. Section 11.3 details the methods used in the
evaluation and further details the concepts of control
technologies. Stormwater induced problems reported upstream in
the City of Saginaw sewerage system are reviewed in Section 11.4.
The Congress Courts area was selected for detailed analysis as
described in Section 11.5. City-wide implementation of inlet
control technology is considered in Section 11.6.
11.2 Inlet Control Philosophy
In the simplest of terms "inlet control" starts at the
very top of a sewershed and controls/manages sewage/stormwater so
that the pipes do not overload as you move downstream. All
possible forms of above/underground storage are used to hold the
water till the receiving pipe can handle the flow without
surcharge. If sufficient potential cannot be feasibly generated
then additional conveyance capacity, i.e., relief sewers are
11.1
-------
necessary. The analysis begins at the top of the system and
progressively moves downstream to the outlet. If the sewer outlet
is backwatered, then the conveyance capacity has to be adjusted
to properly reflect outlet deficiencies.
The aim of the stormwater runoff control program is to
develop surface and subsurface controls such that the sewerage
system would discharge under full pipe conditions (or acceptable
surcharge levels) during any given design storm without causing
any adverse minor street surface ponding and/or adverse overland
flow across private property. Basement flooding protection for a
given design storm becomes eguatable with ensuring that the
rehabilitated sewer system during a given design storm would flow
at acceptable levels with no adverse street ponding/overland flow.
The following set of control strategies are typically
considered in stormwater management (inlet control)
investigations:
a) Manhole rehabilitation,
b) Placement of overland flow training berms and
depressed gutters,
c) Placement of surface storage berms to maximize
surface storage potential,
d) Reconstruction of low curbs to maximize surface
storage potential,
e) Placement of vortex valves into catchbasins to
either maximize street surface storage or to create
controlled overland flow that can be intercepted by
downstream catchbasins and/or underground storage,
f) Construction of new catchbasins to intercept
overland flow,
g) Construction of shallow drains to dewater low
"trapped" street areas,
h) Construction of underground off-line storage tanks
to detain excess surface runoff and/or spilled
overflow from sewerage system,
i) Disconnection of residential downspouts,
j) Placement of Eave-N-Flow eavestrough regulators to
restrict downspout flows, and
k) Placement of orifice restricting segments or weirs
or vortex valves into sewerage system as to create
controlled surcharge conditions.
Figure 11.1 pictorially shows some of "inlet control"
methods. The various methods and/or the implements, that is,
devices used in the implementation of "inlet control", can be
broadly classified as "small scale technology alternatives for
flooding relief". For example, a widely employed method of "inlet
control" is to reduce direct uncontrolled flow to the sewer by
1102
-------
surface storage
)*jr* underground
flow controller |storage
controller
supplementary
surface water
storage (potent lal source
for groundwater recharge)
directly connected
roof and yard water
(re-route if feasible
or control)
<***«
KEY
main
controlled to
acceptable
maximum flow Ml Rainwater storage
MM System storage
OHH) Underground storage
Figure 11.1 Components of the Inlet Control System
-------
rerouting roof downspouts to splash pads with drainage to dry
wells/created pervious areas/street catchbasins. One device used
to augment this method is a "Eave-N-Flc" eavetrough regulator
placed in the downspout. Soakways, dutch drains, porous pavement
are other examples of potential inlet control methods used to
increase perviousness/infiltration in urban areas.
Temporary street ponding is still another method of
"inlet control". Flow controllers can be placed in catchbasins to
create temporary controlled street ponding. Pipes connecting
catchbasins to the sewer are typically over-sized to prevent
clogging from debris washed into catchbasins. Flow controllers
either regulate flow into a sewage collection system or, after
the water is in the system, they regulate the flow to a
predetermined rate. Controllers placed at stormwater inlets
control the flow of water into the combined sewer system, thus
causing the water to pond in the streets, parking areas, etc. By
preventing or slowing the overload, the sewage system is able to
cope with the water, thus preventing overflows and basement
backups.
Flow controllers can also be placed in catchbasins to
strategically induce overland flow into areas more suitable for
surface/subsurface storage. Speed humps (contoured berms not
speed bumps) can be placed either to direct overland flow away
from sensitive areas and into more suitable storage capture areas
or to maximize street storage potential. Taken together
catchbasin flow controllers and a system of speed humps can
generate at low cost, controlled street storage.
The distinction between speed "bumps" and speed "humps"
is shown in Figure 11.2 Speed bumps are typically not envisioned
as these devices are a vehicular nuisance and interfere with snow
plowing operations.
Placed at specific points within the system in-line
flow controllers can also act as damming devices to utilize
storage space that may be available in the existing sewers and/or
direct flow to off-line storage facilities. Shallow
underground/open off-line storage tanks/basins placed behind
curbline/parkways/back alleys or in open park areas (see Figure
11.3) are other methods of "inlet control" which are meant to
temporarily store excess stormwater beyond street storage for
later controlled bleedback into sewer system. Shallow new storm
drains connected into existing and/or new catchbasins and
draining to storage tanks are often necessary to utilize
underground storage.
The ability to accurately control the rates of flow
entering the piped drainage system enables the effects of the
11.4
-------
Ol
Speed Bump/Speed Hump Comparison
FIGURE 11.2
Asphalt - Contoured Speed Hunp
-------
directly connected (or modified)
roofs and yards
surface storage
or induced overland flow
supplementary
urface water
storage tank
curb
intake
system storage^
mobilized by -^
underground
storage tank
which fills
when system
storage is full
main sewer
controlled to
acceptable
maximum flow
system
control
Figure n.3 Surface / Subsurface Storage
Components of Inlet Control for Congested Areas
11.6
-------
inevitable major storms to be designed for, and consequent
downstream damage and pollution minimized. When rates of inflow
exceed the controlled system inputs any excess will either be
retained adjacent to the intakes in local transient storage
(street ponding and then in off-line storge), or enter the major
overland drainage system to streams and rivers. If all available
forms of storage are fully utilized and overland drainage is
limited, restricted or not possible, then the potential for
excess street flooding becomes a consideration requiring other
forms of control, i.e., positive relief conveyance.
Street surface conditions and street surfacing programs
impact effectiveness of potential street ponding since ponded
waters could infiltrate through cracked pavement potentially
causing subsurface soil problems and could drain back into
infiltrating sewer lines. House foundation drain-back cycling is
a consideration in this regard. Types of manhole lids are
important. Replacement of perforated lids with solid covers is a
traditional method of cutting inflow and is a consideration in
the assessment of street ponding viability. Installation of
vented neoprene inserts, "safeguards", below manhole lids is
another method and has been successfully used in other cities in
the USA to cut inflow.
Street ponding as a form of transient storage is always
carefully engineered to meet specific local conditions. Draindown
times are always a major concern as it impacts emergency vehicle
access and is a public nuisance. Time for draindown is a function
of the surface intake rates, sewer conveyance capacity (and
outlet conditions) and overland flow potential. The singular most
controlling factor is sewer system conveyance capacity and its
outlet condition.
All of the above "inlet control" methods assume that
the sewerage system and its appurtenances can in fact receive and
convey a controlled and predictable amount of combined sewage to
an interceptor system. Local systems are old and have many well-
known problems. Part of "inlet control" must ultimately involve
study of system soundness including, condition of catchbasins,
sewer deposition and sediment accumulations, potential for
siltation, and conveyance capacity limitations. Consideration of
relief sewer segments in upstream areas to mitigate hydraulic
bottlenecks is not beyond the purview of "inlet control". An
integral part of the "inlet control" engineering analysis is to
analyze and portray the physical and economic trade-offs between
creating temporary upstream storage (street ponding/off-line
facilities) and the constructing positive relief segments
(systems) to accomplish the same effect.
11.7
-------
Benefits of using the "inlet control" method in local
areas with combined sewers can generally be summarized as: A)
minimizes the need and degree for sewer separation and local
relief sewers; B) provides immediate relief in areas with most
severe basement flooding problems, leaving implementation in less
critical areas when funds become available; C) lessens combined
sewer overflows and pollution since retained transient stormwater
(and combined sewer stored in-line) drain back to sewers for
treatment; D) lessens local sewer deposition/reduced conveyance
and decreases sewer cleaning frequency and costs; E) provides an
extremely adaptive management approach for overall control that
can be applied inexpensively and quickly in stages and then as
time and funds permit, be integrated with positive relief
measures to provide ultimate protection; and F) greatly enhances
basement flooding protection levels for areas that have already
provided local positive relief.
"Inlet Control" has a strong positive benefit for large
complicated tunnel/lift station/conveyance/treatment systems. The
net effect of applying "inlet control" to a number of catchment
areas tied into a major system is to "base-load" the system
output implying that flow peaks would be smaller and less
frequent and that a higher system-wide base flow would result.
Operational efficiency of any large hydraulic/electrical system
always improves with "base-loading" system throughputs.
The "inlet control" approach can be immediately applied
to provide initial benefits with balance of plan incrementally
applied as funds become available. Community investment levels
for "inlet control" can be relatively continuous in contrast to
other approaches that are more "lumpy" in nature and in
realizeable gains. Communities can expend and realize year by
year incremental low level investments and their additive
attendent benefits in contrast to a single "lumped" investment
taking many years both to accomplish and to realize the benefit.
"Inlet control" can be readily added to areas where new
local positive relief segments have been or are in process of
being installed. The "inlet control" engineering analysis simply
assumes that the existing sewer system supplimented with the new
relief components/system now represents the target conveyance
capacity for restricting inflows. Extremely high levels of
basement flooding protection can be easily achieved.
Furthermore, "inlet control" could be implemented along with the
positive relief program and visibly add no greater inconvenience
to local residents than would the positive relief system
construction. Depending on the area and the potential for
generating off-line storage, street flooding protection may
slightly deteriorate. The exact trade-off has to be assessed on a
case-by-case basis.
11.8
-------
Amount of stormwater that can be reasonably and
feasibly detained by "inlet control" methods is in part a
function of the sewer system's capacity to convey flow. If the
outlet conditions are unfavorable, i.e., backwater conditions
prevail, then the full conveyance capacity of trunks and branch
lines cannot be realized, hence shifting the stress for
additional storage further upstream. If the outlet control for .a
given subsystem is adverse then the benefits of "inlet control"
are obviously limited. "Inlet control" has the intrinsic benefit
of enabling the designer to maximize the detentive storage
potential of any system given its ability to convey flows.
Rigorous application of "inlet control" philosophy does in fact
reveal the true cost effectiveness of positive relief measures.
The commercial availability of a self-acting, liquid
flow-limiting, non-clogging device has made possible the wide
spread and cost-effective implementation of "inlet-control"
drainage and pollution control solutions. Stated simply, the
maintenance-free vortex valve technology detailed in Chapter 5
permits solutions entailing multitudes of "micro" level flow
controls in a given system. Without this technology controlling
hundreds (or perhaps thousands) of inlets in a given sewerage
system would be extremely difficult. Prior to the advent of
vortex valves "inlet control" philosophy for controlling adverse
flow situations was limited.
11.3 Overview of Hydrologic Methodology
Hydrologic analysis within a given study area is
accomplished in the following stages of work. The watershed is
subdivided into logical subcatchments. Subareas are defined on
the basis of topographic divides and on sewer subsystem
configuration. Overall imperviousness per catchment is computed
using aerial maps. Directly connnect areas such as residential
and commercial roof areas are estimated and tabulated per
subcatchment. The number of residential and commercial buildings
is tallied per subcatchment.
Hydraulic analysis of the drainage system within the
study area is performed to determine conveyance capacity of each
manhole to manhole segment throughout the system and per
subcatchment area. Identification of key drainage pipe segments
and their respective full-pipe or allowable conveyance
capacities per catchment forms the basis to compute total
required storage (system, surface and underground) for a given
design storm per subcatchment. Allowable capacity is defined as
some flow rate less than the segment capacity. The additive
capacity of some lateral segments can exceed the capacity of the
main trunk line. Prevention of adverse surcharge of the trunk
11.9
-------
line sometimes requires that the lateral line capacities be
artificially lowered to a selected allowable rate of flow.
Design of rainfall storm intensities for the 5, 10, 15
and 25 year events is extracted from established rainfall
intensity/duration curves. A computer model using the Unit
Hydrograph approach is then used to analyze all subcatchments
for each design storm with and without roof-top directly
connected areas. Design curves are established for each
subcatchment per design storm relating total volume of required
storage to the rate of subcatchment outlet discharge (full-pipe
or allowable pipe flow conditions). These curves are then used to
compute total required storage with/without downspout control per
subcatchment per design storm.
Total required storage per design storm for full pipe
outlet discharge conditions (or allowable discharge) are then
compared with available storage computed for each subcatchment.
Available storage equals the sum of system storage (pipe volumes
plus manholes/catchbasins) and allowable surface storage. Storage
deficits (total required - available) are treated either by
direct underground storage or by allowing overland flow. Controls
are prepared for a given subcatchment and for a given design
storm. If the sum of the uncontrolled peak roof discharge plus
controlled street catchbasin discharge do not exceed full pipe or
allowable subcatchment outlet conditions, then no additional
control is necessary. If outlet flow or allowable conditions
cannot be met, then the downspouts in a given subcatchment are
controlled for a given design storm such that the sum of the
controlled roof peak plus controlled catchbasin flow plus release
rates from underground storage tanks, if necessary, approximately
equals the full pipe or allowable subcatchment conveyance
capacity.
Draindown times from the new underground storage tanks
(a function of release discharge rates) is a critical concern in
the analysis. This problem is further compounded by the need to
control household roof downspouts to a reasonable and feasible
extent.
Control requirements within a subarea are a function of
the hydrologic, topographic and sewer system characteristics of
the subarea and the effect of the subarea sewer system and
overland flows on downstream areas. As described above, allowable
flows are sometimes utilized rather than capacities. Allowable
flow rates are adjusted where possible to ensure that the degree
of control required is reasonably homogeneous throughout the
area. Surface storage usage is maximized in all cases with
overland flow being promoted wherever possible in lieu of
underground storage to minimize the number of underground storage
11.10
-------
locations. Underground storage tanks are utilized to detain
street runoff from catchbasins without flow controllers.
Sewer Hydraulic Analysis
The conveyance capacity of the sewer system within the
study area is analyzed using a computerized network model of
each segment (manhole to manhole). Pipe length, diameter, and
pipe slope for each segment are tabulated and data-processed into
a network system to determine maximum full pipe flow. The purpose
of this investigation is to compute the maximum stormwater flow
allowable in each segment.
Maximum flow capacities per segment are then used in
two further investigations. First, they are compared segment to
segment to ensure that each downstream segment is of sufficient
capacity to handle upstream flow. Next, the segment downstream of
each pipe junction is reviewed to ensure it can pass the combined
capacity of upstream branches.
Control schemes for each subarea are then devised to
ensure adequate protection in each area and adjusted as possible
to utilize consistent control measures among sub areas.
Subarea control plans are formulated as follows. Sub-
areas are reviewed to indicate the "allowable" flow, the degree
of catchbasin and downspout control required to achieve that
flow, required storage at that flow, available storage (system
plus surface) and the net storage deficit. Storage deficit can
then be met using underground storage or overland flow.
Minimizing the number of underground storage sites is always
considered advantageous. Routing of overland flow to common
collection points is always preferred. One limitation to
overland flow routing is the street gutter capacity to pass
accumulated flows without curb topping.
Downspout Regulation
Directly connected roof downspout discharges can exceed
full pipe conveyance capacity. In some cases, no amount of
surface/subsurface storage will eliminate this problem. It is
recognized that control of downspouts is considered undesireable.
All other forms of control are maximized to the extent considered
feasible and practical before downspout control is considered.
The aim of this strategy is to minimize the extent and degree of
downspout regulation. Furthermore, every effort is typically made
in the analysis to develop as reasonably uniform policies as
possible per area per design storm.
11.11
-------
Two different approaches are possible for roofwater
control analysis and include,
a) disconnect both front of the house downspouts
with placement of splash pads,
b) disconnect both of front of house downspouts and
place Eave-N-Flo regulators in rear of the house
downspouts.
Each subcatchment area is analyzed to ascertain what
degree of roofwater control is necessary to ensure that the
resulting roofwater discharge together with catchbasin controlled
flow and allowance for underground storage tank discharges would
not exceed sewerage system full pipe discharge.
Surface Storage Improvements
The concept of surface storage of stormwater requires
that the natural overland routes for surface water be altered to
create storage areas. The degree to which these alternatives can
be accomplished without excessive citizen inconvenience dictates
the overall effectiveness of this flood protection technique. Two
typical criteria established to maximize storage and minimize
inconveniences are that storage berms (speed-humps) constructed
across roadways be spaced a minimum of 300 feet apart and surface
ponding not exceed in the curb height.
Berms are constructed of asphalt with an elevation
equal to the elevation of the curb. The berm at the street edges
would equal the curve elevation. As the street elevation
increases toward the crown the effective berm height would lessen
(elevation constant). This implies that storage berm heights
would vary across the street based on curb heights and street
contours. Construction of storage berms would recognize this
effect by adjusting the length of the berm to minimize the "speed
bump" effect. Based on these criteria the effective storage
capacity of any street section is a function of the street slope,
street cross section and curb heights.
Two types of street storage are available. The first
utilizes existing low areas in the street profile. A maximum
desirable depth of ponding is first determined based on available
curb heights and acceptable center street depths at the lowest
point in the center of street. Street slopes in each direction
are then used to determine the distances to which water will
pond. Ponded water volume is calculated as a function of this
distance and the average cross- sectional area. Volume
calculations for ponding in low areas utilizes the backwatered
distances in each direction. It is necessary that catchbasins
11.12
-------
exist or be constructed in the low area to act as continuous
drains.
The second type of street ponding utilizes the berm
construction (speed-hump) technique to reduce surface runoff on
mildly sloped streets. The effectiveness depends substantially
on the slope of the street. Berm site location is typically just
downhill of existing catchbasins to allow final drainage.
Storage volume is calculated in a similar manner as above using
curb height, street contour and slope data.
Several criteria are used in the final selection of
proposed storage sites. First, storage capacity of low areas,
where the street slopes uphill in each direction, is calculated
on the basis of allowing the stored water to pond to a level up
to the street side of the sidewalks. Storage capacity of slightly
sloped areas is calculated as surface waters being ponded to the
curb line. Second, it is typically assumed that berm
construction is cost effective only if the volume of storage is
provided at a unit cost under $9/cu.ft.
11.4 Saqinaw Sewerage System
Reported occurrences of basement flooding in many areas
within the City of Saginaw have been recorded for many years.
The City has somewhat reduced the problem by simply installing
orifice plates in numerous catchbasins in an effort to reduce
inflow. This effort represents a limited program of inlet
control planning and implementation. Figure 11.4 illustrates
areas within the City where basement flooding problems have
occurred and the catchbasin orifice-plate solution attempted.
Success of this approach has been mixed in Saginaw somewhat due
to the reported practice of residents removing the orifice
plates.
As part of the sewerage system evaluation of this
study, upstream areas of basement flooding were reviewed. A City
supplied base map indicated the historical problematic areas.
(Figure 11.4) Twenty seven areas were identified within the City
to have reported one or more occurrences of basement flooding.
Sizes of areas ranged from individual households to several acres
with a total problem area of roughly 455 acres. Problem areas
are scattered throughout the City.
Each area was visually inspected by EDP personnel to
determine land topography and usage and other characteristics.
In general, it was found that most areas were relatively flat,
densely populated and afforded little open space. The
significance of open space is its potential usage as an
11.13
-------
Figure 11.4 City of Saginaw areas of Reported Basement Flooding
-------
underground storage location. Although streets and sidewalk
areas are useable, construction costs in open areas are less. In
general, areas of Saginaw where little or no open space exists do
include some sidewalk spaces without trees. Underground storage
chamber placement is preferred in sidewalk as opposed to street
areas, but is sometimes not practical due to tree-lined streets.
City records were available indicating basement
flooding complaints by households up until the late 1970's.
Since that time, complaints have lessened and gone unrecorded.
One problem area was isolated for detailed review as reported in
Section 11.5 to illustrate typical evaluation techniques and to
form the basis for system-wide extrapolation of results.
11.5 Analysis of the Congress Courts Area
One isolated area in the northwestern part of the City
has been the source of frequent basement flooding complaints and
was reviewed in detail. This area contains about 16 acres and
includes Congress Avenue between Brenner Street and Bay Street
and the four Congress Courts, (A,B,C,and D). (Figure 11.5)
Each court is approximately 300 ft long extending from Congress
Avenue to a cul-de-sac. The courts are serviced by a combined
sewer system with 12 inch pipes in each street.
As part of the detailed analysis each street was
completely surveyed and a contour map of the area developed.
Figure 11.6 illustrates a portion of the contour map including
one court which is typical of the surface topography in Congress
Courts A, B and C. Each of these streets slopes downhill from
Congress Avenue to the start of the cul-de-sac and rises
thereafter. Catchbasins are located on each side of each street
in the lowest area at the cul-de sac and at Congress Avenue.
Congress Court D slopes downhill from the cul-de-sac toward
Congress Avenue the entire length of the street. Directions of
overland flow are indicated on Figures 11.5 and 11.6. For the
purpose of computer-aided evaluation, each court was designated
as a separate drainage area. Hydrologic and hydraulic analyses
were then performed according to the procedures outlined in
Section 11.3. Standard evaluation procedures would have included
detailed analysis of surface storage potential based on area
topography and street curb elevations. For the purpose of this
illustration a nominal value of 300 cubic feet per acre
(24.4m3/Ha) (typical of this type topography) was utilized in
Table 11.1.
Table 11.1 depicts a standard work sheet utilized by
EDP for subarea evauations and Table 11.2 includes the
computerized hydraulic analysis of the area sewer network. Table
11015
-------
cr
UJ
z
z
UJ
tr
CD
/2W/690J
Figure 11.5 City of Saginaw Inlet Control Study Areas - Congress Court
-------
Contour Interval 0.2 Feet
< - Existing Catchbasin
RMMM-Proposed Berm
«•* Overland Flow
Typical Contours
Congress COurts A, B & C
Court D Slopes Toward
Congress Avenue
Congress Avenue
Figure 11.6 Typical Congress Court Topography
11.17
-------
11.2 was developed based on manhole to manhole pipe segment
lengths and slopes generated from Figure 11.5. Individual
segment capacities, cumulative flows rates and other statistics
are then calculated within Table 11.2 as required for completion
of the worksheet in Table 11.1. In addition, a rainfall/runoff
and storage requirement relationship is developed. Table 11.3
illustrates a typical computer printout indicating the
relationship of allowable subarea outflow rates to required
volumes requirement of storage. For the Congress Court subareas,
the 12 inch pipe capacity of 49 1/s (Table 11.2) necessitates a
total storage volume of 86 cubic meters for the 10 year frequency
storm event as found by interpolation within Table 11.3.
(Downstream restrictions to Congress Courts A and B outflow are
discussed later.)
The concept of the remaining calculations is to select
an appropriate combination of roof stormwater control, catchbasin
inlet rates, surface storage draindown rates, and underground
tank draindown rates, which will minimize post storm surface
ponding, minimize underground tank storage requirements and
draindown times while still maintaining total outflow rates
within allowable levels.
Table 11.1 indicates that available storage would
include surface storage of 24.4 m3 and system storage of 7.9 m3
for a total of 33 m3. For the 2 year design storm, a storage
tank volume of 23.3 m3 (845 ft3) is required and would drain in 1
hour which is generally acceptable. No roof control is requird.
Two of the four catchbasins (those located at Congress Avenue)
would be restricted with vortex valves at an outflow rate of 3
1/s. The two catchbasins at the cul-de-sac would be uncontrolled
and directly connected to the storage tank.
Designs for the 5 and 10 year storms included similar
control except each design required that roof front downspouts be
disconnected and larger storage tanks be provided. Control of
roof discharges allows for increased tank discharge rates and
results in draindown times less than that designed for the 2 year
event. Design for the 25 year storm resulted in a lengthy
storage tank draindown time of 130 minutes for the case of front
roof control. Additional control of rear downspouts would allow
greater tank discharge rates and substantially reduce the
draindown time. In general, the inlet control strategy is often
a case of such alternatives. Here the choice is between the
extent of roof runoff control and tank draindown time. It is at
this point where engineering judgement is required to select the
best combination of options.
Although straightforward, inlet control design is often
a complicated series of analyses. For the Congress Courts area
11.18
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TABLE 11.1
TYPICAL INLET CONTROL WORKSHEET
Congress Courts Saginaw, Michigan
!' !
Description of
i impervious}
Jubarea
Courts A
,B,C • 1.16
Ha 1
i
|
|
Roof Area:
% Roof Area: ?4 I
NO. of Commercial Buildings
Ho. Inlets:
Time of-_ConcentrationXMitu_) L.
Capacity --
49
Half Full Pipe I/S:
_ System Storage Eull-P-ipe-ml-
7.9
„. _ Surf ace-Storage. m3 : _ 24.4
Design Storm
.2 Year ...5. Year .10 Year 2
1 ~^i — '• — r 1 It
! Average RamtaliL.
Intensity
in /I
_mmZ
ir
ir
74
92
105
"124 "
i
-1 '
r ° i »
! i i
; Total
lotal
Street
154 191
~117 145
218 , 258
166
196
Rl Ronf 37 46 52 62
1 Front n-isr.nnnectpd 'R2 Roof .18 23 26 31
..; Rear Restricted. . .]Ra_Ro.o.£
lp Surface Storage
as, .Gutt
i
erJToa,
. ^ •-
^ Design Flow ' Roof '
Storm |
Control
' , 17s ! 1/S
! 2 i 4"9 JRl 37 !
; 5 49 R2 23 i
! ii 10 i 49
! 25 49 j
: 25 alt.
1 i; ; ]
' i F
. H * Notet 2 of 4
1 "IT"
,
R2 26 !
R2 31
R3 13
CB Rat^
jp3
13 |
> * Storage
13 13
13
1
Surface
Req . ± Avail . L Need Storage
Us
2@3=6 '
6
6
6
o X)isch.
m^
m I nP 1/s
56 ! 1 23
75 j
86 !
106
6 T 106
(Total) (j
!B lead tc
i
> tank storage
i
; ii 1
'! 1
I
. — r, ~l " ""
11.19
i
42 !
53
73
73
r
-
-
Tank
!
'
Drain |
Storage* Time j
Disch.
1/s
6
20
17
12
!
66 min
36 min
53 min
103 min
30 41 min
J_ . i
:
*— }
1
i
i i
1
-------
TABLE 11.2 City of Saginaw Congress Courts Sewer System Hydraulic Evaluation
SEEM CRMN CPOA KR CENSES CDLFB
o
1
2
3
4
5
6
7
8
rccKncN
CUKE
CDLFm
:
1 01
I .01
1 .02
12.01
1 .03
1 .04
1 .05
DIA(M)
1.520
0.305
1.520
0.305
1.520
1.520
1.520
SKFE
0.14
0.29
0.12
0.29
0.12
0.12
0.11
IflGffl
76.20
99.10
77.70
99.10
73.20
79.20
88.40
F. FICW(L/S) F. tB/DffiEN VEL.(M/S) TRAVEL (MIN) PEE VCL.(OJ M) lEC KBS(M) TDIEL ICBS(M)
2694.65
54.30
2510.00
54.30
2531.18
2477.89
2467.09
0.00
54.30
2455.70
0.00
21.18
-2563.30
-10.80
1.49
0.75
1.39
0.75
1.40
1.37
1.36
0.9
2.2
0.9
2.2
0.9
1.0
1.1
138.27
7.24
140.99
7.24
132.83
143.72
160.41
0.10
0.29
0.09
0.29
0.09
0.09
0.10
0.10
0.39
0.48
0.29
0.57
0.66
0.76
-------
TABLE 11.3 City of Saginaw Congress Courts Rainfall/Storage
Requirement Summary
SUMMARY OF STORM HYDROGRAPH
FOR
DETERMINATION OF REQUIRED STORAGE AT DESIGN FLOW BASED ON
SYSTEM CAPACITY AND THE STOPM/AREA CHARACTERISTICS
JOB--SAGINAW CONGRESS AVE AREA
CASE—H 10 YEAR
TIME OF CONCENTRATION (MINS)= 7.5
TOTAL IMPERMEABLE AREA (HA) = .4640001
MEAN RAINFALL INTENSITY (MM/HR) = 105
RAINFALL CLASS (%) = 50
MAX. RATE OF STORM FLOW (L/S) = 218.4
-•• ——•••.••.—•.•.-••.•••• .••••••••• ••»••. —•—•••••.••• •••
VOLUMES OF STORM FLOW RELATED TO
DIFFERENT OUTFLOW RATES
RATE OF OUTFLOW VOLUME OF STORMWATER
(L/S) (CU.M.)
0 108
21 98
87 73
109 66
131 59
152 53
174 46
196 37
218 21
11.21
-------
the inlet control plus storage option detailed above must be
compared to a relief sewer system on feasibilityf cost and
consequence basis. The relief sewer option is dependant upon
sufficient capacity at some downstream location to pass all
upstream flows.
Figure 11.5 indicates that a 60 inch sewer serves
Congress Avenue. Field monitoring and/or upstream and downstream
evaluations can be performed to determine if sufficient capacity
is available to carry fully unrestricted stormflow from the
Congress Courts. If so, cost analysis should be performed
comparing storage tank construction to that of a relief sewer
system. As an example, 200 ft. of 18 inch relief sewer at a cost
of $120/ft would require $24,000 to relieve one court area. At a
cost of $9/ft3, 2670 ft3 (75m3) of surface storage could be
constructed for the same sum. On this basis, and reviewing the
storage requirements of Table 11.1, design for the 25 year event
should consider a relief system as an alternative. As detailed
in Section 11.6, inlet control plus storage will afford some
downstream CSO reduction and this aspect must be considered as
part of the overall engineering evaluation.
Hydraulic analysis of the existing Congress Courts
sewer system indicates additional complications within the area.
As seen in Figure 11.5 sewer lines servicing Congress Courts C
and D discharge directly to the 60 inch Congress Avenue trunk
line at drop manholes. Unless extreme surcharge exists in the
60 inch line, then free discharge from Congress Courts C and D is
expected. Sewers servicing Congress Courts A and B do not
discharge to the 60 inch line but join at a 12 inch sewer in
Congress Avenue leading to another 12 inch sewer in Bay Street.
Table 11.2 indicates that this junction represents a flow
restriction based on accumulated flows.
One optional solution would entail designating
"allowable" flow rates in each upstream sewer. Considering the
downstream capacity at the junction of 50 1/s each, the upstream
sewer could be "allowed" a rate of 25 1/s. Calculations similar
to the worksheet of Table 11.1 and data from Table 11.3 for an
outflow rate of 25 1/s indicate that even for the 2-year event,
complete roof runoff control and storage of about 96 m3 would be
required. Clearly an alternative would be desireable.
The most apparent viable alternative would be
connection of the sewer from Court B to the 60 inch Congress
Avenue sewer. This would allow the full capacity of the Court A
sewer to flow to the 12 inch Congress Avenue sewer. This
alternative is again dependent upon conditions within the 60 inch
sewer. However, considering the degree of restriction and
storage required under the "allowable" 25 1/s flow rate it would
11.22
-------
appear preferable to "create" capacity within the 60 inch line by
implementation of inlet control in other upstream and downstream
areas as necessary. This alternative would lead to the storage
requirements detailed in Table 11.1. As stated earlier. Congress
Court D slopes toward Congress Avenue the entire length. If, the
60 inch Congress Avenue sewer can handle the outflow from this
areaf then only suitable catchbasin and connector piping is
required. If the 60 inch pipe capacity allowance is limited,
then underground storage will be necessitated at this location.
In sum, the analysis of the Congress Courts areas
demonstrates the complexity of inlet control/storage technology
planning. The need to evaluate hydraulic conditions of receiving
sewers dictates that even analysis of a small subarea will
require some degree of overall area review. The key to cost
effective inlet control technology is to not overly restrict one
subarea in relation to another or to allow excessive outflow from
one subarea at the expense of the alllowable outflow rate from
another subarea. Outflow rates should be selected both on the
basis of existing hydrualic capacities and the effects of
increased/decreased rates on overall area hydraulics.
11.6 City Wide Implementation of Inlet Control Technology
EDP's city-wide visual review of the storm related
problem areas of Saginaw indicated that these areas are quite
similar to areas of other cities where similar problems existed,
were evaluated and solved using inlet control technology. The
detailed review of the Congress Courts area indicates that
solutions used in other cities including downspout control,
catchbasin control, storage, repiping and construction of relief
sewers are applicable to Saginaw.
Optimum implementation of inlet control technology
requires that the entire drainage system be evaluated to ensure
appropriate allotment of trunk line capacity to subareas. Based
on previous inlet control studies in areas similar to Saginaw, it
is estimated that available surface storage which can be feasibly
generated, amounts to 300 ft3/acre. Analysis of the Congress
Courts area indicated that mixed usage of underground storage and
added relief sewers or short connections is optimal. Although
underground storage requirements are related to sewer capacities
in addition to topographic conditions, most sewerage systems, on
the average, are similarly designed and provide similar
capacities. On this basis, underground storage requirement of
1000 ft3/acre (typical of previous inlet control study results
for 5 year to 10 year design storm protection) is reasonably
applicable and agrees well with the 10 year storm requirement
(900 ft3/acre) for Congress Courts.
11.23
-------
For the 455 acre area of Saginaw reportedly subject to
basement flooding the potential available surface storage is
estimated as 136,500 ft3 while a total of 455,000 ft3 of
underground storage can be feasibly generated. Creation of
storage areas using the methods detailed in section 11.2 may be a
cost effective alternative in comparison to construction of a
relief sewer systems and has the added advantage of reducing peak
flow conditions in downstream areas. In Saginaw peak flow
conditions often translate into CSO and related Saginaw River
pollution.
Creation of upstream off-line storage under the program
of inlet control affects downstream conditions essentially the
same way as implementation of upstream in-line storage. Much of
the BMP plan development of this study evaluated the effects of
upstream in-line storage on downstream CSO conditions. This data
can be used to predict the effects of inlet control strategies.
Since EPA has placed much emphasis on the reduction of
phosphorous in the evaluation of CSO impacts, reductions of total
phosphorous loading to the Saginaw River were therefore used to
evaluate the impact of potentially solving the purported basement
flooding in the 455 acres using stormwater management techniques.
Figure 11.7 illustrates the percentage reduction of total
phosphorous loading to the Saginaw River as related to in-system
storage volumes. Zero reduction would imply complete overflow to
the river with no treatment at the WWTP. Storage values
represented volumes generated at regulator chambers and in
upstream acres. At the present time the reduced BMP plan has
been completely implemented. Storage volumes estimated under
inlet control strategies were added to the reduced BMP plan
storage volumes to represent predicted conditions. Two curves
are shown in Figure 11.7. The solid line represents percent
system wide wet weather phosphorous reduction versus storage
volume based on data for pre BMP conditions, reduced BMP
conditions and complete BMP conditions simulations detailed in
Chapter 10 and included in Table 10.7.
On the basis of this curve (Figure 11.7) total
phosphorous reduction would equal 29% after implementation of the
surface storage provisions (300 ft3/acre) of inlet control
technology and construction of underground storage facilities
(1000 ft.3/acre). This values is 4.5% above the current post
reduced BMP level of 24.5% (Table 10.7).
A substantial portion of the CSO pollution reduction
attributable to the reduced BMP plan was due to increased flow
rates at the Weiss Street crossover junction. The dashed line in
Figure 11.7 represents a revised relationship of total
phosphorous reduction to storage volume without including effects
11.24
-------
NJ
cn
-------
of the increased crossover flow. The inlet control scheme is
estimated to reduce loadings to the Saginaw River by 4.0% above
current post reduced BMP plan levels.
In sum, inlet control technology may be a cost
effective alernative to relief sewer construction in the Saginaw
area. Inlet control combined with provisions for adequate
storage will mitigate basement flooding problems while reducing
CSO pollution to the Saginaw River.
11.26
-------
REFERENCES
CHAPTER 1
1. Pisano, Rhodes and Aronson, "Preliminary Engineering Study
for the Control and Treatment of Combined Sewer Overflows to
the Saginaw River", June, 1980, EDP.
2. Pisino, Rhodes and Aronson, "Facility Plan for the Control
anu Treatment of Combined Sewer Overflows to the Saginaw
River", November, 1980, EDP.
3. Environmental Design & Planning, Inc., Design and
Development Document Webber Street Combined Sewer Overflow
Treatment Facilities, June, 1981.
4. Connick, D. and Pisano, W., "Design Development Document In
System Storage Program, December, 1983, EDP.
5. Personnel Communication, J. M. Johannessen, 1981.
6. Brown & Brown, Inc., "Automatic Sewage Regulators", Bull.
83A, 1960, Lima, Ohio.
7. John Meunier, Inc., HYDROVEX Product Literature, 1984.
8. Drehwing, F. J. et al, "Disinfection/Treatment of Combined
Sewer Overflows, Syracuse, New York", August, 1979, EPA-
600/2-79-134.
9. Pisano, W., Connick, D. and Aronson, G., "Swirl and Helical
Bend Regulator/Concentrator for Storm and cosfcbined Sewer
Overflow Control," October 1984, EDP EPA-600/S2-84-151.
CHAPTER 4
1. Metcalf & Eddy, Inc., "Report to City of Saginaw, Michigan
on Preliminary Design of the Hancock Street Combined Sewage
Overflow Storage and Treatment Facility," March 16, 1973.
2. Lager, Didrikson and Otte, "Development and Application of
Simplified Stormwater Management Model," Aug., 1976, EPA
600/2-76-218.
CHAPTER 5
1. American Public Works Association, "Manual of Regulation
Practice," 1971.
2. Brombach, H. and Meunier, G., "Latest Developments in Sewer
Flow Control Using the Vortex Principle," 57th Conference
WPCF, New Orleans, 1984
Rl
-------
3. Brombach, H., "Vortex Amplifiers for Low Control Pressure
Ratios." Proc. of the 7th Cranfield Fluidics Conference,
BHRA, Cranfield, England, 1975.
4. Quadt, K. S. and Brombach, H., "Practical Experiences from
Vortex Throttles Controlled Storm Water Overflow Tanks"
Korrespondenz Abwasser, volume 1, 1978, p. 5-9, in German.
CHAPTER 6
1. Pisano, Aronson and Queiroz, "Dry-Weather Deposition and
Flushing for Combined Sewer Overflow Pollution Control,"
August, 1979., EPA-60012-79-133.
2. Diniz, E.V., "Water Quality Prediction for Urban Runoff - An
Alternative Approach, "Proceedings of the Stormwater
Management Model (SWMM) Users Group Meeting, May 24-25,
1979., EPA 600/9-79-026, June, 1979.
3. Lager, Didrikson and Otte, "Development and Application of
Simplified Stormwater Management Model," August, 1976, EPA-
600/2-76-218.
4. Environmental Design and Planning, Inc., "Section 208 Area-
Wide Non-Point Source Emissions Analysis," Central
Massachusetts Regional Planning Commission, 1978..
5. Metcalf & Eddy, Inc., "Sludge Management Facilities Plan for
the Saginaw Metropolitan Area," May, 1979.
R2
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
-001 B
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE „...•, .o
In-System storage Controls for
Reduction of Combined Sewer
Overflow-Saginaw, Michigan
B. REPORT DATE
6. PERFORMING ORGANIZATION CODE
5GL
AUJHOR(S)
William C. Pisano, P.E.,
Daniel J. Connick and Gerald L. Aronson
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Department of Public Utilities
City of Saginaw
Saginaw, Michigan
10. PROGRAM ELEMENT NO.
11. C6NTRACT/GRANT NO.
R005359-01
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Great Lakes National Program Office
536 South Clark Street, Room 958
Chicago, Illinois 60605
13. TYPE OF REPORT AND PERIOD COVERED
Technical 9/79 - 12/84
14. SPONSORING AGENCY CODE
Great Lakes National Program
Office-USEPA, Region V
15. SUPPLEMENTARY NOTES
Ralph G. Christensen
Project Officer
16 ABSTRACT
This report details the results of a recently completed five-year Combined Sewer
Overflow (CSO) control program in Saginaw, Michigan (10,000 acres, pop. 85,000)
funded through the U.S. EPA 108 Great Lakes Demonstration Program and conducted
by the engineering contractor, Environmental Design and Planning, Inc. (EDP),
Hanover, Massachusetts. The implemented control program entailed modification of
12 combined sewer regulation chambers together with construction of one new in-
line control chamber to maximize transient system storage of wet weather combined
sewerage for later bleedback to a wel1-operated AWT/WWTP having phosphorus removal
and ample treatment capacity. These improvements, "the partial BMP plan",
represent a partial completion of the first of two phases of the City's CSO
Facility Plan. The objective of Phase I was to maximize WWTP processing of wet
weather combined sewage generated using inexpensive transient system storage
(less than $l/cu.ft.) so as to minimize the extent, scale and cost of satellite
CSO treatment facilities (Phase II). The swirl concentrator technology was
recommended to treat residual overflows remaining after Phase I improvements.
Six major Facilities were recommended and adopted as part of the CSO Facility Plan.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Storm Sewer
Combined Sewer Overflows
Swirl Concentrator
Suspended Solids
Total Phosphorus
13. DISTRIBUTION STATEMENT[)OCUment -j 5
to the public through the National Techni-
cal Information Service, Springfield, VA
19. SECURITY CLASS (This Report)
21. NO. OF PAGES
220
20. SECURITY CLASS (This page)
22. PRICE
EPA Form 2220-1 (9-73)
* U.B. GOVERNMENT PRINTING OFFICE: 1986-841-492/648
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