WATER POLLUTION CONTROL RESEARCH SERIES
11024 EXF 08/70
   Combined Sewer Overflow
   Abatement Alternatives
   Washington, D.C.
ENVIRONMENTAL PROTECTION AGENCY • WATER QUALITY OFFICE

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                   WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Reports describe the results and progress
in the control and abatement of pollution of our Nation's waters.  They provide
a central source of information on the research, development and demonstration
activities of the Water Quality Office of the Environmental Protection Agency,
through in-house research and grants and contracts with the Federal, State
and local agencies, research institutions, and industrial organizations.

Previously issued reports on the Storm and Combined Sewer Pollution Control
Program:
11023 FDB 09/70
11024 FKJ 10/70
11024 EJC 10/70

11023 	 12/70
11023 DZF 06/70
11024 EJC 01/71
11020 FAQ 03/71
11022 EFF 12/70

11022 EFF 01/71
11022 DPP 10/70
11024 EQG 03/71

11020 FAL 03/71
11024 FJE 04/71
11024 DOC 07/71
11024 DOC 08/71

11024 DOC 09/71

11024 DOC 10/71
11040 QCG 06/70
11024 DQU 10/70
11024 EQE 06/71
Chemical Treatment of Combined Sewer Overflows
In-Sewer Fixed Screening of Combined Sewer Overflows
Selected Urban Storm Water Abstracts, First Quarterly
Issue
Urban Storm Runoff and Combined Sewer Overflow Pollution
Ultrasonic Filtration of Combined Sewer Overflows
Selected Urban Runoff Abstracts, Second Quarterly Issue
Dispatching System for Control of Combined Sewer Losses
Prevention and Correction of Excessive Infiltration and
Inflow into Sewer Systems - A Manual of Practice
Control of Infiltration and Inflow into Sewer Systems
Combined Sewer Temporary Underwater Storage Facility
Storm Water Problems and Control in Sanitary Sewers -
Oakland and Berkeley, California
Evaluation of Storm Standby Tanks - Columbus, Ohio
Selected Urban Storm Water Runoff Abstracts, Third
Storm Water Management Model, Volume 1 - Final Report
Storm Water Management Model, Volume II - Verification
and Testing
Storm Water Management Model, Volume III -
User's Manual
Storm Water Management Model, Volume IV - Program Listing
Environmental Impact of Highway Deicing
Urban Runoff Characteristics
Impregnation of Concrete Pipe
                                  To be continued on inside back cover...

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             Combined Sewer  Overflow
              Abatement Alternatives
                   Washington,  D.C.
                            by
                   ROY F.WESTON, INC.
              Environmental Scientists and Engineers
                  West Chester, Pennsylvania
                          for the
                 WATER QUALITY OFFICE
          ENVIRONMENTAL PROTECTION AGENCY
                   Program No. 11024EXF
                   Contract No. 14-12-403
                       August 1970
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $2
                      Stock Number 5501-0102

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                EPA/WQO Review  Notice

This report has been reviewed by the Water Quality Office
of the Environmental Protection Agency and approved for
publication.  Approval does  not signify that the contents
necessarily   reflect  the  views  and  policies  of   the
Environmental Protection Agency, nor does mention of trade
names or commercial products constitute endorsement or
recommendation for use.

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                                     ABSTRACT

Objectives of the project were: 1) define the characteristics of urban runoff; 2) investigate
the feasibility of  high-rate  filtration for treatment of combined sewer overflow; and 3)
develop and evaluate  alternative  methods of solution.

Investigative activities  included: review of pertinent reports and technical literature; field
monitoring  of  combined  sewer overflows and separated storm water discharges  at three
sites;  laboratory  studies   of  ultra-high-rate  filtration  of combined  sewer  overflow;
hydrological analysis; and evaluation of feasible alternatives (based on conceptual designs,
preliminary cost estimates,  and  other  factors).

Reservoir Storage, Treatment at Overflow Points, Conveyance Tunnels and Mined  Storage,
and  Sewer Separation  were the approaches considered sufficiently promising for detailed
evaluation.  Tunnels  and Mined Storage with treatment at the  Blue  Plains plant and at
Kingman Lake after subsidence of the storm is recommended. Estimated capital costs (based
on the 15-year,  24-hour storm) are $318,000,000  (ENR=1800) with annual operation  and
maintenance costs of $3,500,000. This approach  also was preferable to  the others on the
basis of systematic evaluation of  reliability,  flexibility, public convenience and other
non-quantifiable factors.

This report was submitted  in fulfillment of Contract  14-12-403  (11024 EXF) between
the  Environmental Protection  Agency-Water Quality  Office and Roy  F. Weston,  Inc.

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                                CONTENTS


Section                                                                 Page

           ABSTRACT                                                     iii

           CONTENTS                                                      v

           FIGURES                                                      vii

           TABLES                                                       ix

      I     CONCLUSIONS                                                  1

     II     RECOMMENDATIONS                                            3

    Ml     INTRODUCTION                                                 5

             General                                                       5
             Project Objectives and Scope                                      6

    IV     PROBLEM DEFINITION                                           7

             Description of Study Area                                        7
             Description of Present D.C. Sewer System                           12
             D.C. Sewage Treatment Facilities                                  19
             Peak Rate and Volume of Overflow                                21
             Field Monitoring Program                                        29
             Impact of Storm Water Discharges                                 42

     V     INVESTIGATION OF POTENTIAL ABATEMENT MEASURES           47

             Review of Approaches Tried at Other Cities                         47
             Ultra-High-Rate Filtration                                        55

    VI     DEVELOPMENT OF FEASIBLE ALTERNATIVES                     57

             Alternative Approaches                                          57
             Application of Alternative Approaches to D.C.                       64

   VII     EVALUATION  OF FEASIBLE ALTERNATIVES                      79

             General                                                       79
             Cost Ana lysis                                                  80
             Impact on Water Quality                                         99
             Comparison of Non-Quantifiable Factors                           106
             Indicated Appropriate District-wide Solution                       112

   VIII     ACKNOWLEDGMENTS                                          115

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                                 CONTENTS
                                  (Continued)
Section                                                                    Page

    IX     REFERENCES                                                    117

     X     APPENDICES                                                     121

             Appendix A - Geological and Other Natural Conditions                125
             Appendix B - Hydrologic Analysis                                  137
             Appendix C - Monitoring Equipment                                139
             Appendix D   List of Previous Reports on Sewer System               145
             Appendix E   Results of Monitoring Program                         157
             Appendix F - Ultra-High-Rate Filtration                             203
             Appendix G   Kingman Lake Project                                241
                                     VI

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                                     FIGURES


                                                                             Page

 1     District of Columbia                                                       8

 2     Generalized Geologic Map                                                 11

 3     Combined Sewer Study Area                                               13

 4     Combined Sewer Study Area and Combined System Separation Schedule        18

 5     Hyetograph for Various Rainfall Frequencies                                 22

 6     Standard Infiltration  Capacity Curves for Pervious Surfaces                   24

 7     Determination of Infiltration Offset - 5-Year Rainfall Frequency - Pervious       25
       Residential Area

 8     Determination of Point of Intersection of Infiltration Capacity and              26
       Precipitation Rate - 5-Year Rainfall Frequency - Pervious Residential
       Area

 9     Combined Sewer District B-4                                               32

10     Combined Sewer District G-4                                               33

11     Good Hope Run Sewer District                                             34

12     Monitoring Equipment                                                    37

13     Annual Pollution Loads Discharged to Streams from Storm Water               44

14     Storage Reservoir Schematic (Typical)                                       58

15     Treatment at Overflow Points - Treatment Facility Schematic (Typical)          60

16     Tunnels and Mined Storage in Anacostia River Basin                           65

17     General Tunnel Location  - Northeast Boundary Trunk Sewer                   66

18     Anacostia River Tunnel Profile                                             68

19     Maximum Use of Storage Reservoirs in Anacostia  River Basin                   69

20     Treatment at Overflow Points in Anacostia River Basin                        71

21     Tunnels and Mined Storage in Upper Potomac-Rock Creek Basin               73

22     Rock Creek Tunnel Profile                                                 74
                                       VII

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                                    FIGURES
                                   (Continued)
                                                                             Page

23     Upper Potomac Tunnel Profile                                              75

24     Maximum Use of Storage Reservoirs in Upper Potomac  Rock Creek Basin       76

25     Treatment at Overflow Points in Upper Potomac - Rock Creek Basin             78

26     Total Construction Costs of Storage Reservoirs and Appurtenant Equipment     81

27     Unit Construction Costs of Tunnels                                         83

28     Total Construction Costs of Mined Storage                                   85

29     Total Construction Costs of Treatment Plants versus Capacity                   86

30     Investment versus Design Storm Return Frequency for Alternative               93
       District-wide Approaches

31     Percent Reduction in Pollution Load from Various Storms vs Alternative        101
       Design Events

32     Effect of Investment on Discharge of BOD Loading for Various Storm          103
       Return Frequencies

33     Seasonal Probability of Intense 24-Hour Rainfall                             105
                                      VIM

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                                    TABLES


                                                                            Page

 1     Population of the District of Columbia                                       7

 2     Combined Sewer Districts Scheduled for Separation after 1975                 14

 3     Deficiency in Sewer Capacities                                             15

 4     Daily Pollution Loads from Blue Plains Plant                                 19

 5     Combined Sewer Overflow Characteristics                                   27

 6     Physical Descriptions of the Monitoring Sites                                 31

 7     Storms Monitored                                                       35

 8     Major Storms Missed                                                      36

 9     Comparison of Characteristics of Combined Sewer Flow and Separated          40
       Storm Sewer Flow

10     Expected Pollution Loads from Combined and Separated Storm Sewers          45
       in District of Columbia

11     WQO Combined Sewer Overflow Treatment Projects                          53

12     Maximum Use of Storage Reservoirs - Estimated Capital Costs                  38

13     Treatment at Overflow Points - Estimated Capital Costs                       83

14     Conveyance Tunnels and Mined Storage - Estimated Capital Costs               90

15     Sewer Separation Costs - Estimated Capital Costs                             91

16     Comparison of Total Project Costs                                          92

17     Summary of Annual Operating Costs for Maximum Use of Storage              94
       Reservoirs for 15-Year, 24-Hour Storm

18     Summary of Annual Operating Costs for Treatment at Overflow Points          95
       for 15-Year, 24-Hour Storm

19     Summary of Annual Operating Costs for Conveyance Tunnels and Mined         96
       Storage for 15-Year, 24-Hour Storm

20     Comparison of Annual Operating Costs Based on 15-Year, 24-Hour Storm        97
                                       IX

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                                     TABLES
                                   (Continued)
                                                                             Page
21     Comparison of 24-Hour Pollution Discharges from Various Return              102
       Frequency Storms for Various Design Frequencies

22     Evaluation of General Factors                                             110

23     Estimated Capital Costs of Indicated Appropriate Solution                    114

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                                  SECTION  I

                                 CONCLUSIONS

1.  The  indicated appropriate solution to the problem of combined sewer overflows  in
   Washington is one that provides a network of large tunnels and mined areas to convey
   and  store overflow, with treatment of stored overflow at both the Blue Plains plant
   and  at a  facility near Kingman Lake.

2.  The  information developed  in  this study further points to a design capacity  equal
   to the overflow from the 15-year, 24-hour storm. This design would provide effective
   treatment of  more than  99 percent of  the long-term-averaged annual  volume of
   overflow that now contributes  significantly to the pollution of the Potomac and its
   tributaries. Even with this design, the 25-year, 24-hour storm would result in a total
   24-hour  BOD loading of 70,000  pounds, well over  four times the  recommended
   maximum allowable  daily loading  from  all BOD sources in the entire metropolitan
   Washington  area.

3.  A network of tunnels and mined  storage, plus an additional  facility  near Kingman
   Lake, represents the  least-cost  alternative designed for the 15-year, 24-hour storm.
   It would cost $318,000,000 (ENR=1800) to construct and $3,500,000 per year to
   operate and maintain this system; in contrast, a program of complete sewer separation
   would cost  about  $610,000,000 (ENR=1800).

4.  An  evaluation of  non-quantifiable factors such  as  reliability,  flexibility,  land
   requirements, public  convenience, implementation, and solids removal  suggested that
   an approach  incorporating tunnels  and  mined  storage offers  more advantages than
   an approach  based on storage  reservoirs, treatment  at overflow points, or sewer
   separation.

5.  Based on the results  of a field monitoring program  and a detailed  rainfall-runoff
   analysis, the overflow from combined sewers within Washington, D.C. discharges each
   year the following pollutant loads  to the Potomac and its tributaries:

        Biochemical Oxygen  Demand             3,200,000 pounds
        Total  Phosphorus                          500,000 pounds
        Total  Nitrogen                             500,000 pounds
        Suspended Solids                      59,000,000 pounds

6.  Overflows from combined sewers do not occur as continuous steady discharges, but
   rather as  slug loadings. This characteristic,  in combination with  the  long effective
   residence times of estuarine waters, explains the particularly serious impact combined
   sewer overflows have on water quality. For example, the 24-hour BOD load expected
   in the 616 million gallon  overflow from  the 2-year, 24-hour storm (for the existing
   sewer system) is 160,000 pounds, nearly  ten times the recommended maximum
   allowable  daily loading from all BOD  sources in the entire metropolitan Washington
   area.

7.  Any  abatement alternative utilizing storage or in-line treatment will  remove practically
   all of the 59,000,000 pounds of suspended solids  now discharged yearly as overflow
   to the Potomac. The resulting  quantity  of  sludge (30,000 tons per year on a dry

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    basis) is greater than the quantity of sludge generated at the Blue Plains plant. Besides
    this, the generation  of this sludge is  concentrated  in  the 50 to 60 overflows  per
    year,  rather than coming on  a  uniform, daily  basis as at Blue Plains. In  light of
    the general problems of  solid waste disposal in the Washington area, a high level
    of sophistication and a high degree of planning will be required to handle the combined
    sewer sludge as is employed to handle the sewage treatment plant sludge. The handling
    and disposal  of this sludge  will probably cost  $750,000 per year.

 8. A  limited six-month field monitoring program of combined sewer overflow from two
    combined  sewer  drainage basins  and separated storm  sewer discharge from  one
    separated sewer drainage basin during storm conditions suggested  the following mean
    values for certain significant waste  constituents:

                                        Combined           Separated Storm
                                       Sewer Flow            Sewer  Flow

    Biochemical Oxygen Demand            71 mg/L                19 mg/L
    Settleable Solids                      229 mg/L               687 mg/L
    Fecal Coliform                   2,400,000/100 ml       310,000/100 ml
    Total Phosphate                      3.0 mg/L                1.3 mg/L

    Values of BOD as high as 470 mg/L in combined sewer flow and as high as 90 mg/L in
    separated storm sewer flow were detected during the monitoring program.

 9. With  reference  to  the  laboratory  investigations of  ultra-high-rate filtration,  the
    following conclusions are drawn:

    a.   Tri-media filtration  at  rates  less  than  10  gpm/sq.ft.  provides a  satisfactory
         effluent.

    b.   Ultra-high-rate  filtration  (15  gallons or  more  per  minute per  square  foot) of
         combined sewer overflows is not technically feasible for upflow filtration  through
         a garnet  bed,  because  of poor effluent quality.

    c.   The fiberglass filter  operated  successfully at filtration rates of 15-30 gpm/sq.ft.,
         with  removals  of 90 percent suspended solids and 70 percent non-soluble BOD.

    d.   The addition of flocculant  aids did not improve the  removal characteristics of
         the fiberglass filter.

    e.   Soluble  BOD^  was  not significantly reduced  by  the addition  of low dosages
         of activated sludge  to  the filter  influent.

    f.   The economic feasibility of the fiberglass medium will depend upon the extension
         of the useful life of the medium and the improvement of backwash techniques.

10. The selection of the design  storm event is  properly made  only in  the context of
    basin-wide  quality water  management. Many  factors beyond  the  scope of this study
    such  as the impact of wastewater discharges outside the District of Columbia  low-flow
    augmentation,  etc.,  have  too great an  influence to  be  ignored.

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                                    SECTION  II

                               RECOMMENDATIONS

Based on the findings and conclusions developed in the course of this combined sewer
overflow study, the following  actions are recommended.

1.   Discontinue the current sewer separation program and develop pollution abatement
     programs  for  both  the  combined  and separated sewer  areas  if  the  pollutional
     characteristics of storm water determined in  the current study are confirmed in other
     areas of the District.

2.   Proceed with engineering and construction of conveyance tunnels, mined storage, and
     a treatment facility  near  Kingman  Lake, somewhat like the  facilities described in
     reference  (6),  in  conjunction  with  the  following:

     a.   Conduct the sub-surface investigations necessary to confirm the assumed bedrock
         characteristics.

     b.   Initiate a  long-term monitoring program using monitoring equipment developed
         for the current project to obtain long term comparative and detailed information
         to  define long-term impact of  pollution loads on  required treatment facilities
         and receiving waters.

     c.   Confirm the  selection of the design storm frequency  in the context of basin-wide
         water quality management.

3.   Implement additional  EPA-WQO  sponsored laboratory  and full-scale development
     studies on the  use  of fiberglass as  a filter  medium with  the following objectives:

     a.   To develop an improved filter bed design with respect to density gradation, depth,
         and combination  with  granular media.

     b.   To refine the  backwashing techniques, including  underdrain design,  stagewise
         removal of backwash effluent, and regeneration of the fiberglass filter medium.

     c.   To optimize design parameters.

4.   Re-evaluate, under EPA-WQO  sponsorship, the  validity and accuracy  of the present
     conventional approach to the determination of  sewer  flow rates  (combined-sewer
     areas)  during the surge period associated with each storm.

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                                   SECTION  III

                                  INTRODUCTION

                                      General

Recent efforts stimulated by the Federal Water Pollution Control Act of 1956 (amended
in 1961, 1965, 1966, and 1970) have brought to light the significance of combined sewer
overflows as a source of pollution.

Most  United States  cities today  are served both  by  combined sewers  and by  separate
sanitary and storm sewer systems. As determined from  a 1967 survey sponsored by the
Water Quality Office of  the Environmental Protection Agency,  approximately 29 percent
of the total  sewered  population of the United States is served by combined sewer systems.
Approximately three percent of the total annual flow of sewage  and as much as 95 percent
of the sewage produced during periods of rainfall is carried with  combined sewer overflows
to the surface waters.

The District of Columbia follows this pattern,  with an  area of  approximately  20 square
miles  (one third of the total area of the District)  being served  by combined sewers. The
hydraulic capacity of  the system  is often exceeded during periods  of precipitation, and
raw sewage  mixed with surface runoff is discharged to  the watercourses of the  District.

The Potomac Estuary is polluted and continues  to experience  problems with low dissolved
oxygen,  excessive  algal  growths,  sediments,  high  concentrations of fecal bacteria and
repulsive floating matter. All  of  these  problems, except sediments, are complicated  by
combined sewers.  Although  combined  sewer overflow  adds to the sediment load,  the
primary source of  sediment is the heavy silt  load  included  in the runoff from areas with
significant agricultural and construction activity. In addition  to the effects of combined
overflow on the Potomac River, overflows  into Rock  Creek detract  from the natural and
recreational  features of this small, scenic stream flowing through  the  District.

In 1957, the District prepared  a separation schedule for conversion of all combined sewers
into  separate storm  and  sanitary systems.  This conversion,  however, would not  be
completed until after the year  2000. The cost of this program is extremely high, estimated
at $610  million  (ENR=1800), and  budgeting and other problems have delayed progress.
In the meantime, the overflows from unseparated sewers will continue  to  contribute to
pollution  problems  in the Potomac Estuary.

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                            Project Objectives and  Scope

The primary objectives stipulated for this study were  to: define the problem of combined
sewer overflows within the District  of  Columbia; investigate the feasibility of high-rate
filtration  (greater than 15 gallons/square foot/minute)  for treatment of combined sewer
overflows; and study alternative methods of solution  to  the problem

The general scope of the project is  outlined below as taken  from the Statement of Work
of Contract No. 14-12-403 (between the Federal  Government and Roy F.  Weston,  Inc.)
and as stated in the latter's proposal  "Study of Pollution Abatement from Combined Sewer
Systems"  dated 21  November 1967:

     1.    Develop  a  quantitative definition  of  the combined  sewer pollution problem by
          review  of  reports,  studies, and  data  concerning  water quality and  rainfall
          intensities, surface runoff, frequency of occurrence, and hydrologic data pertinent
          to assessing  methods  for  controlling combined sewer system pollution.

     2.   Collect data and subsequent water quality analyses of continuous rainfall and
          sewer flow measurements  made at three selected  sites.

     3.   Evaluate by laboratory  research the  possibility  of  removing flocculated solids
          and  associated  BOD  by high-rate  filtration of combined sewer  overflows.

     4.   Define  the technical  and  economic feasibility  of flocculation  and high-rate
          filtration as a  means  of treating combined sewer  overflows.

     5.   Investigate other selected practical solutions to provide a meaningful evaluation
          of the relative merits of high-rate filtration and to provide a comprehensive study
          of the combined sewer problem  of  Washington, D.C.

     6.   Present generalized capital cost and annual  cost estimates for alternatives which
          appear to  be technically feasible for the Washington, D.C. system.

     7.   Develop   technical,   economic,  and  operational   comparisons   of practical
          alternatives.

     8.   Further  develop the  general formulation and application of a methodology of
          analysis  for determining  feasible  solutions  for  eliminating  combined sewer
          pollution from  municipal  systems.

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                                    SECTION IV

                              PROBLEM DEFINITION

                             Description  of Study Area

General Conditions

The District of Columbia lies largely along the "Y" formed by the junction of the Anacostia
and Potomac  Rivers,  extending eleven miles  along the northeasterly side of the Potomac
and straddling the Anacostia for six miles. Figure 1 illustrates the general area. The average
flow of the  Potomac River is 13,300 cfs, whereas  the  Anacostia averages 150 cfs. The
total land area of the District is approximately 61 square miles, and the water area within
the District is some seven  square miles.  The District is the center of a metropolitan area
which  includes parts of Maryland  and extends across the Potomac River into Virginia.

The  central and  older  portion,  comprising approximately one-third the total land area
of the District, is  the  principal area of interest for the present investigation. This area
rises gradually from the confluence  of the Potomac and Anacostia Rivers  to the encircling
hills, and  was originally drained by several sizable streams discharging to  these two rivers.

The  metropolitan Washington area has experienced  a  phenomenal  growth in  population
since  1930. Although the  population of the area surrounding  the  District continues to
increase significantly  each  year,  the District  itself may have  reached its peak population,
for some  time, in  1950.  Out-migration  since  then  has  outweighed population increases
from  in-migration  and the birth-less-death  increases.  It is  uncertain  whether or  not
population will continue to decrease  or  increase; nevertheless, existing and  planned land
use will probably impede any drastic increases in population. The population of the District
from  1900 to 1970  is given  in Table 1.  The  possible  future populations are indicated
in a February, 1957 Board of Engineers report to the  District on  improvements to the
sewerage system  (1); the  report projected a population of 1,125,000 in the year 2000.
However,  the same  report  projected 1,010,000 population  in  1970.


                                            Table  1

                           Population of the District of Columbia


       Year            Population                Year            Population

       1900            278,718                  1940           663,091
       1910            331,069                  1950           802,178
       1920            437,571                  1960            763,956
       1930            486,869                  1970            746,1691


       1 Preliminary value from 1970 Census.

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00
                              DISTRICT  OF  COLUMBIA
1500  0  1500 3000 4500 4000
     SCALE IN FEET
                                                                                                                                           FIGURE 1

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District activities largely concern government offices, public buildings, and related activites;
there are no large  industries within its borders. The many large government  buildings in
the  District cover  extensive  areas  and  generate  heavy  concentrations  of  employees.
Considerable areas  of the  District are occupied  by  parks, recreational areas, institutional
grounds, and cemeteries;  for example,  in  1966, approximately 7,830 acres  (20  percent
of the  total land area of the  District) were  occupied by  parks and  playgrounds.

The District had a very low ratio of  runoff to rainfall when the original combined sewer
system  was installed, primarily  because  of  the numerous parks  and other  unpaved areas.
However, as the population  density increased, as more and more buildings were erected,
as street pavings grew wider and wider, and as  parking areas were paved, the rainfall-runoff
coefficient  has  increased tremendously. This  has contributed to the present  inadequacy
of all  storm water  facilities in  the central portion of the District.

The land surface in the District varies  in elevation from the low  areas (elevations of about
4 feet,  USGS Datum) adjacent to the  Potomac River and in East and West  Potomac Park,
along the  Washington  Channel, and along the  Anacostia  River, to elevations as  high  as
410 feet near the intersection of Wisconsin  and  Nebraska Avenues NW.  The  area west
of 16th Street  NW, in Rock Creek Park,  is quite rugged, with a number of places where
the  land rises  to elevations of  300 feet and  more.

Southeast  of the Anacostia River and  east of  the Potomac  River  in the  southern park
of the  District, the land surface is low  and flat along  the rivers, as  in the  area of Boiling
Air  Force Base and  the Anacostia  Naval  Air Station. The  remainder of  this  southeast
part of  the District  is hilly, reaching elevations of 200-300 feet  in  several  areas.

Except for the low-lying lands  along the rivers, the terrain of the District favors the design
of gravity  sewers. The  District  generally drains well because of  the good  slopes that can
be obtained. There are a few bowl-like depressions surrounded by higher territory; however,
except  for  the  area in the vicinity  of 5th  and  Ingraham Streets NW, none is subject to
severe flooding in  times of heavy  rains. Some basement flooding has been experienced
from backup of storm water in  surcharged sewers. This problem  is a  function of the sewer
system  itself and will be discussed in greater detail  in a subsequent  section. Surface water
draining from  the  land areas  of the  District  is carried  off  by  the Potomac River, the
Anacostia  River, Rock Creek,  Foundry Branch, Oxon  Run, and their minor tributaries.

Geological  Features

Information on  the  geologic  and other  natural conditions  is  essential  to  a  complete
evaluation  of the various  possible approaches to the  abatement of pollution caused by
the  inadequacies of combined  sewers, including the feasibility  of tunneling beneath the
City of Washington to provide for storage of  combined sewer overflows.

Data were  obtained  from published geologic  reports,  from engineering reports prepared
under  the  auspices of  the Metropolitan Area Rapid Transit Authority, and from verbal
communication  with personnel of the Authority. The published geologic  data  are fairly
broad  in coverage,  yet sufficiently detailed to provide information helpful  in forming
conclusions in regard to the feasibility of tunneling.  The engineering  reports are extremely
detailed and  provide  an  abundance  of  data  concerning  the soils, bedrock,  and rock
mechanics  in certain  restricted  areas developed for  the purpose  of underground tunneling
for  rapid transit. Although somewhat  restricted  as to area-wide  application, the data
included in  these reports  provide enough  coverage to be representative  of  the  general
Washington area.

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The  District  of Columbia  lies within  portions of  two  physiographic  provinces;  the
southeastern  portion  is  located within  the Coastal  Plain province, which consists  of
relatively  flat-lying sediments  overlying deep bedrock, and  the northwestern portion is
in the Piedmont province, which in general is characterized by a thin layer of overburden
covering crystalline bedrock. The Fall  Line  separating the two provinces extends roughly
southwest from Blair Park in the northeast  through Farragut Square and  on toward the
Pentagon. Figure 2  presents the generalized geology  of  the District of  Columbia.

Previous sub-surface investigations  in the District have resulted in  grouping  the  materials
into five  major categories: bedrock, Cretaceous sediments,  Pleistocene terrace  deposits,
recent river alluvium, and drainage channels and man-made fills. These major categories
of materials in various parts of the  District are found in the following five vertical profiles:

     1.   Recent alluvium over bedrock or  Pleistocene  terrace  deposits.

     2.   Overburden  of  Pleistocene terrace and Cretaceous coastal plain soils above deep
          bedrock.

     3.   Comparatively  thick cover of Pleistocene  terrace and Cretaceous  coastal plain
          soils above deep bedrock.

     4.   Thin  to  moderately  thick cover  of Cretaceous coastal  plain materials  above
          decomposed  rock  and bedrock.

     5.   Relatively thin  cover of  man-made fill and  decomposed rock over bedrock at
          shallow to moderate depths.

Geological and related natural conditions in the Washington, D.C. area and the implications
for tunneling are described  in  more detail  in  Appendix A.
                                          10

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DISTRICT   OF   COLUMBIA

GENERALIZED GEOLOGIC  MAP
                                                                                                                                            LEGEND
                                                                                                                                  PRIMARILY ALLUVIUM AND ARTIFICIAL FILL
                                                                                                                                  UNDIFFERENTIAIED CRETACEOUS, TERTIARY AND
                                                                                                                                  QUATERNARY FORMATIONS CONSISTING OF
                                                                                                                                  CLAY, SILT, SAND AND GRAVEL

                                                                                                                                  RIVER TERRACE DEPOSITS CONSISTING OF
                                                                                                                                  GRAVEL, SAND AND LOAM
                                                                                                                           iS-I-S-a  PRIMARILY CRETACEOUS CLAY, SAND AND GRAVEL
                                                                                                                                  MASSIVE LIGHT GRAY, COARSE -TEXTURED GRANITE
                                                                                                                                  GRANITE GNEISS WITH LAYERS OF SCHISTOSE
                                                                                                                                  GRANITES, GNEISS AND SILICEOUS MICA SCHISTS
                                                                                                                                  1500   0  1500 3000 4500 6000

                                                                                                                                        SCALE IN FEET
                                                                                                                                             FIGURE  2

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                      Description of Present  D.C. Sewer  System

 Historical  Development

 Several studies have been  made of the District of Columbia  sewerage system and sewage
 treatment  facilities. A list of pertinent reports and related technical articles, which were
 reviewed  to obtain detailed information relevant to the  present pollution problem,  is
 presented  as Appendix  B.

 The  installation  of culverts and  drains in the  District began as early as 1810.  In 1840,
 the first piped  water supply to  a few homes began;, it was followed  by  a few sewers
 discharging to the  nearby  culverts. This was the beginning  of the combined sewer system
 in  Washington, D.C. With  the introduction of the Potomac River water supply  in 1859,
 the extent  of the combined sewer system discharging into nearby watercourses  increased
 very rapidly, and by 1874 there were approximately 80 miles of sewers. The sewers drained
 into the principal watercourses and thence to the Potomac River. The  discharges to the
 watercourse from  the combined sewers resulted in pollution of the streams and created
 unsanitary  conditions along the waterfront.

 Upon the  recommendations of the  Hering-Grey-Sterns  Report, a comprehensive  system
 of  sewer  construction began in  1890. Interceptor sewers  were then installed to collect
 all  of the dry-weather flows and some surface-water runoff from  the  combined sewers
 for conveyance to an outfall  sewer  for  ultimate  discharge into the deep  water of the
•Potomac  River.

 Through 1890, the sewers  constructed in the District were combined sewers. Subsequently,
 however, the approach generally adopted was  that combined sewers were tolerable in the
 areas already sewered but that any additions (new areas of the District) must be separated
 storm and sanitary sewers. By 1929, the construction of separated sewer systems  in the
 new, outlying areas was common practice.

 Existing Sewer System

 The present District sewer  system  is designed to serve an area of approximately 725 square
 miles, comprising the entire  District of Columbia and  adjoining areas in  Maryland and
 Virginia. The U.  S. Congress authorized the District to serve the upstream  adjacent areas
 of  the  two states  so  that  the streams flowing through  the District could be protected
 from pollution.

 Approximately 12,000 acres of the sewage-producing areas of the District are served by
 the existing combined sewer system  Substantially all of this acreage is in the central  part
 of  the District. The remainder of the District  and substantially all  of the adjoining areas
 of  Maryland and Virginia  are served by separated sewers. The existing sewer system  is
 shown in Figure 3. Table  2 lists the acreage  of  the combined  sewer districts scheduled
 for separation after 1975.

 The District of Columbia has been divided into some 93 sewer drainage  districts, arranged
 in  11 groups under the names of  the principal sewers to which the districts are tributary.
 A tabulation of  the statistics  pertinent to these districts  is presented  in  Chapter 6 of
 the  investigative  report of  June  1955  (2). The existing and required  capacities  of the
 intercepting sewers are described  in  Chapter  16  of the same  report.
                                         12

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      ^M»U*ND\ PtiNCi_r,'\ Gtoasts  	COUNT'
      \«._ .    .  ••  ',     DIStRlCT OF COLUMUA
                                                                                                              \ - yjs
                                                                                                               » .;V*
                                                                                                               ';i*l

                                                                                                            jg^i5-. JjJ| CUPPER ANACOSTIA HIVES,.''
                                                                                                             
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                              Table 2
 No.
A-10
A-11
A-12
B-3
B-4
B-5
B-6
B-7
C-23
C-24
C-25
C-26
C-28
C-29
D-4
D-5
D-6
D-7
D-8
D-9
D-10
D-11
D-12
D-13
D-14
D-15
D-16
D-17
E-2
E-3
F-1
G-2
G-3
G-4
G-5
G-7
Name
                      Combined Sewer Districts
                 Scheduled for Separation after 1975


                                     Net Area
 37th. St.-Georgetown
 Georgetown
 KSt. -Wisconsin Ave.
 Q Street
 Q Street -31st. St.
 Olive Street  29th St.
 MSt.   27th. St.
 28th. St. - Wisconsin Ave.
 Kalorama Circle, East
 Kalorama Circle, West
 Slash Run
 N St.  25th.  St.
 KSt. -Penna. Ave.
 I St. - 22nd. St.
 Piney Branch
 Oak St. - Mt. Pleasant
 Ingleside Ter.
 Park Road
 Lament Street
 Ken yon Street
 Irving Street
 Quarry Road
 Ontario  Road
 BiltmoreSt.
 Belmont Road
 Mass. Ave.  24th Street
 Northwest Boundary
 26th. St. - M  St.
 Easby Point
 Trunk Sewer
Tiber Creek
 Northeast Boundary
 Barney Circle
 14th. St. -Penna. Ave.
 12th. St.-9th. St.
 6th. St.  7th. St.
(acres)

   19
  183
   32
    8
  105
   14
   35
   13
    8
   14
  417
   12
   20
   95
 2,175
   26
   18
   17
   17
   17
   76
   36
   22
   21
   44
   70
  534
    6
  518
  375
 1,000
 3,728
   41
  252
  151
  121
                                             Drainage
                                              Basin
Upper Potomac
Upper Potomac
Upper Potomac
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Rock Creek
Upper Potomac
Anacostia
Anacostia
Anacostia
Anacostia
Anacostia
Anacostia
Anacostia
Source:  Board of  Engineers (Greeley, S.A. et al), "Report to District of
         Columbia Department of Sanitary Engineering on Improvements
         to Sewerage Systems, " February 1957.
                                14

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There  are  three  principal interceptors which serve  the major  portion  of the combined
sewer  area:  Upper  Potomac Interceptor,  Rock  Creek Main Interceptor, and East Side
Interceptor.  All  three  serve large areas of separated systems along the  upstream reaches
and  essentially are separate trunk sewers  in these areas. They become interceptors  in the
true sense  in the downstream reaches in the combined sewer areas, and convey this flow
through  an  outfall  sewer to the sewage  treatment  plant at Blue Plains.

The District sewer system is  generally in  good physical condition; however, many of the
combined  and separated  sewers and certain intercepting sewers do  not have  adequate
capacity. As development in  the combined-sewer area of the District (39 percent of the
land area in 1957)  increased, it was  noted that the hydraulic capacity of the  system was
exceeded during  periods of precipitation. In order to prevent local flooding and the spilling
of sanitary sewage  onto the surface of the  ground, overflow structures and  interceptor
chambers were built to  relieve the excessive sewer flow by discharging it directly into
the  natural  watercourses.

In the past, the  District  has conducted detailed studies to evaluate the contribution to
the   problem   of   pollution  at   these   overflow  structures.   Nine   automatic,
continuous-recording,  depth-of-flow gauges were installed at various critical storm  water
points to obtain  data  on the  frequency  and duration  of  overflows. It was  found that
some of these overflow  structures  discharge  as  many as 40 to 50 times a  year,  while
others discharge  only  2 to 3 times a year, depending on the drainage area characteristics
and  the  available interceptor capacities.

One of the most significant and comprehensive studies was  the 1957  investigation of the
Board  of Engineers. The Board of  Engineers study  indicated that many of the combined
and  separate sewers were  inadequate by generally accepted design standards. Considerable
surcharging occurred in the combined sewers, and there were excessive overflows of mixed
sewage and storm water to the  streams, even  including some overflows during dry weather.
It was evident that certain interceptors needed  relief.

The situation relative  to  the  inadequate capacities of various trunk sewers is summarized
in Table 3. This gives a picture of the magnitude of the problem. The required capacities
were based  on conditions of development estimated for the year 2000.
                                        Table 3

                               Deficiency in Sewer Capacities


                                         Percent of
                                        Total Length      Present Capacity
                                         Deficient in          as Percent of
             Description of Sewer             Capacity        Required Capacity

        Upper Potomac Interceptor                98                40
        Rock Creek Main Interceptor              77                54
        East Side Interceptor                     69                71
        Piney Branch Trunk Sewer               100                56
       Northwest Boundary Trunk  Sewer          92                57
       Slash Run Trunk Sewer                   85                53
       B St.-New Jersey Avenue
         Trunk Sewer                         98                49
        Easby Point Trunk Sewer                  93                47
       Tiber Creek Trunk Sewer                  70                50
       Northeast Boundary Sewer                86                54

                                          15

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To evaluate the problem of pollution of streams attributable to the overflows, the Board
of Engineers collected  data on the  frequency and duration of overflows at critical points
for a  period of one year. It was found that the average number of overflows per month
at the various  locations ranged from 5 to 16.8 during the summer months, and from
3.8 to 4.7 during the winter months. The average duration of overflows per month ranged
from  24 to 110 hours during the summer months and from 26 to 38 hours during the
winter months.

Sewer Separation  Programs

Studies by  Eddy, Gregory and Greeley in 1933  and by Sherman and Horner  in 1935
recommended separation of the  combined sewer system in several smaller  areas of the
city.  However,  it was not until the 1957 Board of Engineers study that a unified program
for the elimination of  combined sewers was presented.

The  Board  of  Engineers outlined several alternative plans for abating or eliminating the
pollution  that results from combined sewer overflows and from  inadequate  capacities of
combined  sewers  and  interceptors. Two of the alternatives deemed to have the greatest
merit were those designated as Project A and Project C. Both of these alternatives require
the conversion of some combined  sewers  into separate sewers.

Project A  was  defined to convert all combined sewer areas to  the separated system  and
to provide  interceptors to carry  all  sewage to the water pollution control plant. At the
completion of  Project  A, there  would  no longer be any overflows of untreated sewage
into  the  river. However, no appreciable reduction of pollution  in the river would result
until  substantially all  of  the work outlined  in Project  A  was completed.  Minimum
construction time required to complete Project A was optimistically estimated at twenty
years, and  the estimated cost for  this project was 238 million dollars at  1957 prices.

 Under Project  C, only 10 percent  (approximately) of the combined sewer area was to
be separated initially, but new interceptors would be provided to carry additional quantities
of  mixed  sewage and  storm  water  flows to the pollution control  plant.  Wet-weather
discharges to the river  would occur even with these enlarged interceptors, but only during
heavier rainfall and on a scale substantially below present volumes. It was estimated that
 Project C  could  be completed  in ten  years or less  at an  estimated cost of 72  million
dollars at  1957 prices.  Between July 1957 and July  1970 the  Engineering News  Record
Construction Cost Index has increased from 725 to 1414, an increase of 94 percent; thus,
 in terms  of 1970 dollars,  Project  C costs would be approximately  140 million dollars.

The  Board had recommended Project C over  other alternatives  because it was the least
expensive and  could be completed  in about ten years, and because the benefits (in terms
of reduction of  pollution) could be realized as the work  progressed.

The District of Columbia approved the Board's recommendations and later modified Project
 C,  the principal  change being to  design  a two-level  conduit for  the Upper Potomac
 Interceptor Relief Sewer and  two force mains from the Potomac River  Sewage Pumping
 Station to  carry  the flow  to the sewage treatment plant.  One  reason for conveying the
flow  in  two conduits was to prevent  a complete breakdown of the system  in  case of
 any problems. Another factor was the advantage, from the long-range  standpoint, of being
able  to separate the flow of sewage from  the combined flow of sewage and  storm water.
 By this modification, all sewage originating  upstream of Georgetown (in Maryland, Virginia,
                                         16

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and the District) would be handled by an interceptor serving only separated system areas.
No overflow structures would  be provided  in this interceptor, and  all the facilities could
be so designed that most of the objectionable overflows would be  eliminated at an early
date.

As  the  sewers in  the older  section of  the city are gradually  converted to a separated
system under the  Storm Sewer Separation  Program the  two-line interceptor would have
the built-in capacity  to carry the entire flow of sanitary sewage to the  treatment plant.
Eventually, Project C would  achieve the same result  as Project A but  at reduced cost.
When the work outlined under modified Project C is completed, there will be no overflows
to the streams until  the average sewage  flow is diluted  at least five times by storm water.

Work outlined  under the separation program has  been  initiated,  and  conversion, until
recently, has kept pace with the schedule.  Budgeting problems have delayed the progress
of this program. Figure 4 shows the District's present combined sewer separation schedule.
A large segment of the central section is not scheduled for separation  until after the year
2000, but it  is possible that  areas listed to be  separated after  2000 could  be acted on
sooner,  depending  upon other improvement programs and  the availability of funds.

Nevertheless, the problem of combined  sewer  overflows  still exists. In 1961, there were
approximately  86 permanent  built-in  storm water  overflow structures  (some combined
sewer districts have more than  one overflow structure) that discharge to the watercourses.
A few of these overflow structures have been plugged  since then, but about 60  are still
operative, and a mixture of combined sewer overflows and storm water discharges through
them with  each  rainfall.
                                         17

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00
                                                                                                                                     \   I
                                                                                                                                     i  i  t.-'/~ """"• •""
                                                                                                                                     i »•  >t- /  '">•" -«'" ""
                                        DISTRICT   OF   COLUMBIA
                                   COMBINED  SEWER  STUDY AREA AND
                             COMBINED   SYSTEM  SEPARATION   SCHEDULE
                                                                                                                                                                                          LEGEND
                                                                                                                                                                                POtlTICAl  BOUNDARY
                                                                                                                                                                                COMBINED  SEWERS
                                                                                                                                                                               1 SANITARY SEWERS
                                                                                                                                                                               , OTHER  EXISTING  SEWERS
                                                                                                                                                                                (COMBINED AND  SEPARATE |
                                                                                                                                                                                SEWER  DISTRICT NUMBER
                                                                                                                                                                               • LIMITS OP COMBINED-SEWER SYSTEM IN 1970
                                                                                                                                                                               . SEWER  DISTRICT  BOUNDARIES
                                                                                                                                                                                PUMPING STATIONS
   COMPLETION
AREA  DATE
I   I  BEFORE 1973
IS  1985
E3  2000
E2  AFTER 2000
                                                                                                                                                                          COMBINED SEWER OVERFLOW DISTRICTS |1975)
                                                                                                                                                                                 UPPER POTOMAC ROCK CREEH
          SAUL
      37TH ST.-O1OIOITOWN
      OEOROETOWN
      K  ST.—WISCONSIN AVI
      M ST -17TH  ST
      JITH ST-WISCONSIN AV
      SLASH IUN(PANn
      PINET ItANCH
                                                                                                                                                                             D   INOLESIDE TEI.
                                                                                                                                                                             D   PAU ID.
                                                                                                                                                                             D   LAMONT ST.
                                                                                                                                                                             D   KENYON ST
                                                                                                                                                                             D 0 IRVING ST
                                                                                                                                                                             D 1 QUAIIT ID
                                                                                                                                                                             D 1 ONTARIO tO
                                                                                                                                                                             E   EAUY POINT
                                                                                                                                                                                    ANACOSTIA  RIVER
                                                                                                                                                                             NO      NAMt
                                                                                                                                                                             1-3  I ST.-NEW  JEIIEY AVI. TIUNK MWI« 0/1 FOITKM
                                                                                                                                                                             F.I  TIIER CREEK
                                                                                                                                                                             O-3  NORTHtAST IOUNDAIT
                                                                                                                                                                             O-l  IARNEY CIRCLE
                                                                                                                                                                             Q.i  UTH ST.-PENNA.  AVE
                                                                                                                                                                             O-J  13TH IT.-VTH }T.
                                                                                                                                                                             Q-7  6TH ST.—7TM IT
         0  1500  30C9  4500 6000
          SCALE  IN  FEET
                FIGURE 4

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                          D.C. Sewage Treatment  Facilities

The first primary treatment plant to serve the District of Columbia was put into operation
in 1938, and secondary treatment facilities were added by  1959. The present treatment
facilities consist of:  a  pumping  station;  screening  and  grit  removal  units; primary
sedimentation, aeration, and secondary sedimentation tanks; chlorination facilities; effluent
outfall  into the river; and sludge heating, thickening, digesting,  elutriating, and vacuum
filtration facilities.  The secondary  (biological) treatment process is modified  aeration.

The  most recent improvements and additions to the plant  include:  secondary treatment
by modified  aeration and sedimentation;  new thickeners and heat exchangers; a doubling
of the elutriation tanks; mixing of the contents of the sludge digestion tanks; and a series
of improvements to the sludge-gas  piping.

The  treatment plant has  the capacity  to handle peak flows up  to  300 mgd  and in  the
present setup, flows in excess of 300 mgd would bypass the treatment plant. In reviewing
the performance of the plant (3), operating data of the past three years (fiscal 1966-1968)
were  utilized. It was observed that the plant was providing 70 to 80 percent reduction
of BOD and suspended  solids, with removals lowest  for the year 1968. For fiscal year
1969, the average flow to the treatment plant was  248 mgd. Table 4  lists the 1969 average
daily  pollutant loadings discharged  in the effluent from the Blue  Plains  Plant. Also listed,
for purposes of comparison,  are the maximum allowable loadings recommended by  the
conferees of the May 8, 1969 conference  on pollution  of the  Potomac River (4).

                                            Table 4

                          Daily Pollution Loads from Blue Plains Plant
                                       BOD        SS         TP      TN
                                      Ibs/day      Ibs/day     Ibs/day   Ibs/day

       Average 1969 Effluent          124,000    139,000     87,000   75,000

       Recommended  Maximum
       Allowable Discharge             12,700         --        560    6,130


The District has made concerted efforts to maintain plant efficiency  under increased flow
conditions  and  has had  to  develop  specialized  operating  procedures  and techniques.
However, major  modifications and  additions to  the  plant  are  required  to  meet the
recommended waste  loadings. The  District  has  prepared  a  plan  to  complete  these
improvements by the  year 1974. The requirements for advanced waste treatment and the
limited land area available restrict the ultimate capacity of the plant to 309 million gallons
per day.  The plant will be  constructed to handle this 309 mgd capacity by 1974. However,
in addition to the  309 mgd  flow, the plant will  be constructed  to provide complete
treatment for an  incremental  increase of 289 mgd for a period not to exceed 400 hours
per year. For short durations, the  plant will  also  be able to  provide partial  treatment
of flows  2  to 5  times the 309  mgd flow.
                                         19

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Although  the sewage  flow from the  District is not expected to increase significantly in
the future,  the  sewage flow  from the suburbs served by the plant is  increasing  at such
a rate that  the  309  mgd capacity will be exceeded  in 1977. Therefore, the responsible
agencies  outside  of  the District have  scheduled  the  construction  of additional regional
plants.
                                         20

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                         Peak  Rate and Volume  of Overflow

General Basis of Data

The  significance  of  the combined sewer problem  is measured  by the pollutant loadings
discharged in the overflow to the District's watercourses. The selection of the capacities
of facilities required  in alternative solutions to the problem must rest, in part, on parameters
such as volume of overflow and peak flow rate. Particular values of each of these parameters
vary  with each  storm, and  it is  necessary to perform  an  analysis  of  rainfall-runoff
relationships to define the frequency and range of values. This type of information would
provide a  basis for  evaluating  alternatives.

To perform  this analysis, extensive  data are required concerning rainfall intensities and
frequencies, characteristics of each drainage  basin and the existing sewer system, average
dry-weather flow, etc. Most of the required data have been developed in previous, unrelated
investigations.  To avoid the duplication of  previous efforts and to assure that the best
available data were used, the analysis was coordinated with District officials. In this analysis,
only  the  areas scheduled for  separation after  the year  1975 were  considered  in  the
determination  of the magnitude and intensity  of the combined sewer  overflow problem.

For the purpose of this investigation, an attempt had been made to use the existing design
storm basis for the Washington, D.C. sewer system to  evaluate the peak flow rates and
volume of runoff.  This design  storm, one which occurs once every fifteen years  with  a
duration of one hour, provides a basis for calculating peak flow rates, but does not provide
a sound basis for calculating the volume of  runoff.  For example, the  amount of rainfall
associated with the  15-year, one-hour storm is 2.66 inches, whereas the maximum daily
rainfall occurring once  in fifteen years for a 24-hour duration is 5.5 inches. It is obvious
then  that all further considerations  of volume of overflow should be based on a 24-hour
duration.  The  peak  flow rates,  however, should  be based on storms of shorter duration,
since the mean intensity is higher.

Rainfall-Runoff Analysis

The hydrologic analysis of the current study  involved two procedures. The first procedure,
the  Rational Method, is  limited to  estimation of peak  flow rates; it cannot provide  the
second necessary component   of the  analyses,  i.e.,  volume of  runoff.  In  the  second
procedure, for  determination of the  volume of  overflow, several  different approaches were
examined. Some methods  seemed  to provide reliable results,  but were too elaborate,
requiring  lengthy and involved  data collection and analysis, to be completed within  the
time  and  budget limitations  of this  study. Some  simpler  approaches  such  as  the unit
hydrography method seemed  to provide unreliable results. After a thorough examination,
an approach was selected similar to the approach  used  in another combined sewer study
(5) in Washington,  D.C.  This  approach  incorporates two methods. In  the first method,
the volume of  surface runoff of rainfall into combined sewers was calculated by subtracting
the losses due  to infiltration into pervious soils and retention in surface depressions from
the total  amount of precipitation.  An explanation of the methodology  used  for  the
calculations  of  runoff  is  given   in   detail   in  Appendix C   as   "The  Hyetograph
Method   Volume of Overflow". In general, the  methodology  includes:

     1.   Construction  of hyetographs  for storms  of various frequencies  (Figure  5).
                                         21

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ro
NJ
  10.0




   8.0





   8.0



oc

<=  7.0


UJ

""  6.0
«/>
UJ

«->

=  5.0

»-


£  4.0

UJ
>—


I  3.0
      i.o
      0.0
                                      FIGURE  5

              HYETOGRAPH FOR VARIOUS  RAINFALL FREQUENCIES
          0    10    20   30   40    50   60    70    80   90   100   110  120

                           TIME FROM BEGINNING OF SIGNIFICANT RAINFALL, MINUTES
130   140  150
                                                                                160

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     2.   Determination  of the relative  percentages of pervious  and impervious areas of
         each  sewer district.

     3.   Determination  of the relationship of infiltration capacity to time (Figure 6).

     4.   Construction of  "accumulated mass rainfall curves" and  "actual  accumulated
         mass  infiltration  curves" and subsequent determination of rainfall  in  excess of
         infiltration  (Figures 7 and  8).

     5.   Determination  of the volume  of rainfall  retained in surface  depressions.

     6.   Use of an area-depth  correction factor to account for application of point rainfall
         data  to  the drainage basin.

The calculated  volume of  runoff accounted for all runoff from pervious areas during the
period of a storm when rainfall was in excess of infiltration capacity, and from impervious
areas during  the  24-hour  period of  extreme  rainfall. The rainfall  intensity values were
read from  the updated  Washington, D.C.  intensity-duration-frequency  curves  (recorded
values  1896-1897,  1899-1950, 1951-1969).

This method provides reliable  values for the volume of  runoff  from any sewer district;
however, this value may differ from  the resulting volume of overflow. To determine the
volume of overflow, a method  of hydrograph routing was employed. Appendix C likewise
presents a discussion  of  this method. In general, this method  used  the  Rational Method
to  predict the  peak flow rate, which was  plotted at the  time of concentration for each
drainage basin. Based on  the peak  runoff and the  total volume  of runoff  previously
calculated,  a simple triangular hydrograph  was assumed  and  plotted.

The results of the hydrograph routing were smoothed  and extended  to reflect the pattern
of actual hydrographs, yet the volume of  runoff determined by the hyetograph method
was maintained. Following this, a cursory examination was made of each point of overflow.
Proposed interceptor  capacity,  dry-weather flow, the particular operation of the diversion
structure (when it closes, when it opens),  etc. were accounted for to  determine the peak
rate of overflow  and  the  volume of overflow. Table 5  lists  the results for four storm
frequencies.

Not all of the existing  combined sewer districts are included in Table 5. Two districts,
A-9 and part of B-2, were  scheduled for separation prior to 1975. It should also be noted
that overflow will  not occur at  13  combined sewer districts along  the lower reaches of
Rock Creek,  even during storms as intense as the 25-year  storm. There will be no overflow
at these districts due to the relief provided by the capture of combined sewer flow upstream
(any District-wide solution must deal with the  overflow along  the upstream reaches of
Rock Creek)  and the  large  capacity of the relief interceptors in the lower reaches of Rock
Creek. While the  relief interceptors have the capacity to  contain the peak rates  of  runoff
along Rock Creek, the  pumping station  near the mouth of Rock  Creek does not have
the capacity  to force the peak rates to the Blue  Plains plant. For  example,  the Rock
Creek interceptors have a capacity of  over 1,200 mgd, while the Potomac Sewage Pumping
Station  has  a capacity of less than  500 mgd available  to  pump the Rock Creek flow
plus sanitary  sewage from Maryland and Virginia and combined sewer flow from the Upper
Potomac. It is  obvious that although some districts will  not experience overflows  within
the districts  themselves,  their  runoffs will  overflow at a subsequent point  in the sewer
system.


                                         23

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                                         FIGURE 6

   STANDARD  INFILTRATION-CAPACITY  CURVES FOR  PERVIOUS  SURFACE
NJ
-Pi.
                                                      INDUSTRIAL AND COMMERCIAL AREAS
 O
      0   10   20  30   40   50   60   70   80   90   100  110   120   130   140  150  160  170   180

                                       TIME, MINUTES

SOURCE:  DESIGN AND CONSTRUCTION OF SANITARY AND STORM SEWERS. ASCE, MOP.NO.37, NEW YORK, I960.

-------
01
           3.5
           3.0
           2-0
        CJ
        C-3
           i. o
                                                   FIGURE  7
                              DETERMINATION OF  INFILTRATION  OFFSET
                                     5-YEAR  RAINFALL  FREQUENCY
                                      PERVIOUS  RESIDENTIAL AREA
                             ACCUMULATED  MASS  OF RAINFALL
RAINFALL LESS  INFILTRATION
                 ACCUMULATED MASS OF  INFILTRATION
                        (BEFORE OFFSET)
                                                                 ACCUMULATED MASS OF INFILTRATION
                                                                      (OFFSET 36 MINUTES)
                                  40    50    60    70    80    90    100   110   120
                                 TIME FROM BEGINNING OF  SIGNIFICANT RAINFALL,  MINUTES
                 OFFSET 36 MINUTES
                 POINT OF TANGENCY
                   48.5 MINUTES

-------
                                            FIGURE 8
                        DETERMINATION  OF  POINT OF  INTERSECTION
                   OF INFILTRATION CAPACITY  AND  PRECIPITATION  RATE
                               5-YEAR  RAINFALL  FREQUENCY
                                 PERVIOUS RESIDENTIAL AREA
NJ
O
                                             HYETOGRAPH
            INFILTRATION CAPACITY
                   FOR
              RESIDENTIAL AREA
             (OFFSET 36 MINUTES)
                                                             JF LTRATION
                                      CAPACITY -- PRECIPITATION RATE
              10   20    30   40
00
50   60   70    80   90    100   110   120  130

  TIME FROM BEGINNING OF SIGNIFICANT RAINFALL
40   150  160
70

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                                                                                       Table 5

                                                                        Combined Sewer Overflow Characteristics
                                                                                     (After 1975)
NJ
             Location of Overflow
District
 No.                  District Name

 A-10      37th St. - Georgetown
 A-11      Georgetown
 A-12      K Street - Wisconsin Ave.
 B-6       M Street - 27th Street
 B-7       28th Street - Wisconsin Ave.
 C-25      Slash Run (Part) at 22nd and M Sts.
 D-4       Piney Branch
 D-5       Oak Street - Mt. Pleasant
 D-6       I ngleside Terrace
 D-7       Park Road
 D-8       Lamont Street
 D-9       Kenyon Street
 D-10      Irving Street
 D-11      Quarry Road
 D-12      Ontario Road
 E-2^      Pre-Potomac Sewage  Pumping Station

             Sub Total
       E-3       0 Street Pumping Station
       F-1*      Main Pumping Station
       G-2       Northeast Boundary
       G-3       Barney Circle
       G-4       14th Street - Penna. Ave.
       G-5       12th Street - 9th Street
       G-7       6th Street - 7th Street

                   Sub Total

               Districtwide Total

               Inches of  Rain
                                                                                                          Storm
2-Year,
Volume
mil. gallons
0.2
11
2
0.0
0.0
1
64
1
0.9
0.8
0.5
0.4
2
1
0.5
97
182
58
70
280
0.2
15
6
5
434
616
24-Hour
Peak Rate
mgd
25
330
81
0
0
120
1,500
45
29
24
15
13
51
14
8
450

1,500
1,600
3,600
31
420
200
190


5-Year,
Volume
mil. gallons
0.4
15
3
0.3
0.3
4
100
2
1
1
0.7
0.6
4
2
1
158
293
79
96
370
0.4
20
9
7
581
874
24-Hour
Peak Rate
mgd
32
400
100
50
30
240
2,100
65
40
34
26
19
96
34
20
620

1,800
2,000
4,400
38
550
250
230


15-Year,
Volume
mil. gallons
0.5
20
4
2
1
8
160
3
2
2
1
1
6
2
1
214
428
100
130
490
0.8
28
13
10
772
1,200
24-Hour
Peak Rate
mgd
42
480
110
90
40
380
2,700
71
47
39
29
19
120
45
25
810

2,200
2,400
5,500
54
660
320
290


25-Year,
Volume
mil. gallons
0.8
24
4
2
2
11
190
4
2
2
1
2
6
3
2
260
516
120
150
560
1
32
15
12
890
1,406
24-Hour
Peak Rate
mgd
45
500
120
110
50
440
2,900
81
50
41
32
26
126
50
27
890

2,300
2,500
6,000
62
630
340
310


                                                               3.3
4.3
                                                                                                                5.5
                                                                                                                                         6.0
      ^Overflow results from runoff in all sewer districts in Rock Creek Basin. Overflow occurs through overflow structures located between
       Rock Creek Pumping Station and Potomac Sewage Pumping Station. Sewer District E-2 is the nearest district and the major contributor
       to overflow.
      ^Overflow results from runoff in sewer districts along the Anacostia River. Overflow occurs at Main Pumping Station, and Sewer
       District F-1 is the major contributor to overflow.

-------
In all, there would still remain many points of overflow beyond 1975. The largest volume
of overflow was observed  from the Northeast Boundary Trunk Sewer, which would have
490  million gallons of overflow with a peak rate of  5,500 mgd  for a storm of  15-year
frequency.  For this storm the volume of  overflows,  in general,  ranged from 0.1 to 35
million gallons for small  drainage districts, up  to 490 million  gallons for the Northeast
Boundary area, and the peak rates ranged from 19 mgd to  5,500 mgd. As can be noticed,
the peak rates of overflow were generally high, even for the drainage districts where the
volume of  overflow was small.
                                       28

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                              Field  Monitoring Program

General

A  significant  secondary objective  of this  study was to obtain data concerning  actual
overflows from some of the combined sewers in the District. Data concerning actual rates
of overflow,  pollutant concentrations  versus  time, etc. provide a basis to  predict the
characteristics of combined sewer  overflows  at  other locations  in  the  District.

The comprehensive field survey conducted as part of the definition  of the pollution problem
involved three automated  monitoring systems installed  in  different sewer  districts; two
for combined sewer overflows and one for separated storm water discharges. The monitoring
systems were  operated during the period  April  1, 1969 to  September 23,  1969.

Selection  of Sites

Three  sampling sites were selected at  different  geographical  areas  in Washington,  D.C.,
based  on the following considerations:

     1.   Size  of Drainage Area-The drainage area of  the sewer  district must be large
          enough to have a good combination of different  surface development but also
          small enough to  be monitored economically. The  optimum size was determined
          to be in  the range of 100 to 300  acres.

     2.   Population Density--The population density within the monitored district should
          be reasonably close to the overall  population density of the entire combined
          sewered  area,  which was estimated to be about  33-35 people per  acre.

     3.   Integrity and Simplicity of  the Sewer System-Multiple  diversion or intercepting
          points in the system to  be monitored  interfere with valid correlation between
          runoff and rainfall. All the sewage  flow and the surface runoff of the sewer
          district must converge into one  trunk line equipped with one overflow  point.

     4.   Feasibility  of  Construction   and  Equipment  Installation-The   geographical
          configuration at the  monitoring  site  must  be flat, a power source must  be
          available  at  or near the site, and there must  be  reasonable expectation  of
          obtaining permission to  use the site.

     5.   Traffic and  Public  Impact-The  monitoring site  must not  involve any  public
          annoyance or traffic congestion attributable to the installation of the monitoring
          equipment. Exposure  to  malicious  vandalism  must also  be avoided.

     6.   Parity Between the  Sites for  the Combined  and Separated Sewer Systems-The
          site  for the separated sewer system and one of the sites for the combined sewer
          system  should be as similar  as possible. Their drainage areas and population
          densities  should  also  be  similar. This  makes  comparison of the hydrological,
          geological, geographical,  and  meteorological  data  for both kinds  of monitored
          areas more meaningful.

     7.   Size of the  Trunk Sewer-In view of  the necessity of installing  various  items
          of equipment in  the sewer, the trunk  sewer must be spacious enough to work
          inside. Minimum usable  size  was set at  three feet in diameter.


                                         29

-------
     8.   Underground  Installation-The  existence of any sizable underground structures
         or installations in  the  vicinity  of the monitoring stations is undesirable because
         of  possible  interference with the  underground conduits  required  for the
         monitoring operation.  The  information  concerning different utility lines such
         as gas, water, and electricity, must be reviewed and their  exact locations  noted.

Based on the detailed study of various pertinent information and field observations, three
sewer districts were selected as meeting these criteria:

     1.   Sewer  District B-4
     2.   Sewer  District G-4
     3.   Sewer  District of  Good Hope Run

Sewer Districts B-4 and G-4 (as designated by the D.C. Department of Sanitary Engineering)
are in the combined sewer system  whereas the Good Hope Run Sewer District is in the
separated sewer  system. Sewer District B-4 is in the Georgetown area, and G-4 and Good
Hope Run  are along the Anacostia River.  The basic data for the physical descriptions
of the sewer districts selected for monitoring are  summarized  in Table 6. Figures  9, 10,
and  11  show the major sewers in each of  these districts and the locations of monitoring
equipment.

Operation of  Monitoring  Systems

The  monitoring systems were operated by ROY F. WESTON personnel, with the assistance
of personnel of the Sewer Operation Division of the Washington, D.C. Sanitary Engineering
Department. Storms of varying intensities were  monitored at each of the three sites; seven
in Sewer District B-4,  seventeen in Sewer District  G-4, and ten in Good Hope Run  Sewer
District. Starting time,  duration, total  rainfall, maximum  intensity, numbers of samples
collected, and monitoring sites involved for each storm are  listed in  Table  7. Storms were
missed at each of the monitoring sites from time to time, mostly because of storm caused
damage to equipment located in the sewers; these storms are listed, along with the problems
involved, in Table  8.

The stations were designed to operate automatically, because of the difficulties of predicting
the  beginning of  significant precipitation,  assembling personnel  on  short notice,  and
assembling  personnel during the  night  hours. A schematic diagram  of  the monitoring
equipment  is shown in Figure  12.

Selection of a satisfactory technique for flow measurement presented a problem. A weir
setup could not  be  used, because backwater elevations  would have caused  surcharging and
flooding at the anticipated high flow rates. Depth-of-flow measurements  with the  use  of
one  of  the  steady  state empirical equations (Manning, Kutter, etc.) for calculating flow
would  not  be applicable, since  flow conditions were not steady-state during periods  of
precipitation. The approach finally selected for measuring flow rates was to use a tracer
solution and a form of the continuity equation; this procedure is described mathematically
in subsequent paragraphs of this  section.  Physically,  it involves the  release of a tracer
solution (lithium chloride in this case) of  known concentration and feed rate at an upstream
manhole, sampling of combined sewer overflows at a  downstream  manhole, and analysis
for tracer concentration.  From  the upstream feed rate and concentration  and from the
downstream concentrations, the flow  can  be calculated  accurately. Previous experience
with this method  on steady-state flows has indicated that accuracy within ±4 percent
                                         30

-------
CO
            Sewer
           District
       B-4
       G-4
                                                              Table 6

                                              Physical Descriptions of the Monitoring Sites
      Location


Rose Park Playground


Rock Creek Parkway

26th - 0 St.

14th-LSt. S. E.
                          14th-MSt. S. E.

                          14th-LSt.S. E.

       Good Hope Run    17th - Minn. St. S. E.


                          1630 16th S. E.

                          16th - Minn. St. S. E.
Monitoring
Operation
Lithium Chloride
Release
Sample Collection
Rainfall Measurement
Lithium Chloride
Release
Sample Collection
Rainfall Measurement
Lithium Chloride
Release
Sewer
System
Combined
Combined
Separated
Storm
Population
Drainage Density
Area 1970
acres persons/acre
105 43.6
252 52.6
265 37.6
Trunk
Sewer
Size
4' Diam.
5'-6"Di£
6'x6'
                        Sample Collection

                        Rainfall Measurement

-------
25TH ST.
                             FIGURE 9
                    COMBINED SEWER DISTRICT B 4
                                                RAINFALL MEASUREMENT
                                                LITHIUM CHLORIDE RELEASE
                                                SAMPLE COLLECTION
                                               500  250
500
                                                    SCALE IN FEET
               RF
                                32

-------
                                                       FIGURE 10
                                        COMBINED SEWER  DISTRICT
                                     XS
CO
CO
           500   250   0        500      1000
                   SCALE IN FEET

            RF     RAINFALL  MEASUREMENT
            LiCI   LITHIUM CHLORIDE RELEASE
            SC    SAMPLE COLLECTION

-------
                                                                  FIGURE  11
                                                       GOOD HOPE  RUN  SEWER DISTRICT
O
400  200   0	400	
         SCALE IN FEET

 RF    RAINFALL MEASUREMENT
 LiCI   LITHIUM CHLORIDE RELEASE
 SC    SAMPLE COLLECTION

-------
  Date
Starting
 Time
Site
                                            Table 7


                                        Storms Monitored
 Total
Rainfall
(inches)
                                                            Duration
                                                             (min.)
May 9
May 19
May 20
June 1
June 2
June 3
June 8
June 8
June 15
July 6
July 27
July 27
July 28
July 28
July 28
July 28
July 28
Aug. 1
Aug. 1
Aug. 2
Aug. 2
Aug. 2
Aug. 3
Aug. 9
Aug. 9
Aug. 9
Aug. 9
Aug. 9
Aug. 10
Aug. 19
Sept. 4
Sept. 17
Sept. 17
Sept. 20
9:25 a.m.
1:42 a.m.
11:42 p.m.
7:25 p.m.
7:45 p.m.
12:25 a.m.
5:44 p.m.
5:50 p.m.
2:00 p.m.
7:40 p.m.
11:35 p.m.
11:35 p.m.
2:30 a.m.
11:30 a.m.
1:20 p.m.
1:28 p.m.
5:00 p.m.
7:30 p.m.
8:45 p.m.
8:05 p.m.
8:10 p.m.
8:17 p.m.
10:30 p.m.
9:20 p.m.
9:20 p.m.
11:00 p.m.
11:20 p.m.
11:22 p.m.
12: 25 a.m.
6:40 p.m.
3:45 p.m.
8:15 p.m.
8:20 p.m.
3:00 p.m.
G-4+
G-4
G-4
B-4°
B-4
B-4
G.H.R.*
G-4
G-4
G-4
G-4
B-4
G-4
G-4
G.H.R.
G-4
G.H.R.
G-4
G.H.R.
G-4
B-4
G.H.R.
B-4
G-4
G.H.R.
G.H.R.
G-4
B-4
G.H.R.
G-4
G-4
G-4
G.H.R.
G.H.R.
0.8
0.4
0.6
1.4
0.9
0.95
0.7
0.7
0.7
0.4
2.1
1.3
0.6
0.6
1.6
1.3
0.2
0.6
0.5
2.8
3.9
2.9
0.4
1.1
1.5
0.4
1.6
1.6
0.65
1.35
3.4
0.7
0.6
0.1
20
3
7
22
20
15
6
13
40
20
39
20
22
15
40
35
30
210
135
65
50
73
30
17
25
30
10
15
20
13
75
5
100
90
Maximum
Intensity
 (in./hr.)

   2.4
   3.0
   6.0
   7.2
   6.0
   6.0
   6.0
   2.8
   6.0
   0.8
   8.0
   7.0
   4.6
   4.0
   6.0
   5.6
   0.4
   1.0
   1.6
   6.0
   7.5
   5.6
   4.0
   8.0
   7.2
   2.0
   7.2
   8.4
   0.6
 •  8.0
   6.0
   4.2
   0.6
   0.1
Number of
 Samples
Collected
                                                                                                 1
                                                                                                 4
                                                                                                 3
                                                                                                 6
                                                                                                 3
                                                                                                 3
                                                                                                 1
                                                                                                 3
                                                                                                 4
                                                                                                 2
                                                                                                12
                                                                                                 2
                                                                                                 6
                                                                                                 6
                                                                                                22
                                                                                                 5
                                                                                                 8
                                                                                                 1
                                                                                                 1
                                                                                                 8
                                                                                                 6
                                                                                                12
                                                                                                 3
                                                                                                 5
                                                                                                 7
                                                                                                 5
                                                                                                 2
                                                                                                 3
                                                                                                 2
                                                                                                 4
                                                                                                 1
                                                                                                 1
                                                                                                 4
                                                                                                 1
G-4+ Combined Sewage in Sewer District G-4
B-4° Combined Sewage in Sewer District B-4
G.H.R.* Storm Runoff in Sewer District Good Hope Run
                                                 35

-------
Date
June 1
June 2
June 1
June 1
June 2
June 15
June 15
June 18
July 20
July 22
Aug. 19
Sept. 4
Sept. 4
Sept. 8
Sept. 8
Starting
Time
10:40 p.m.
12:40 a.m.
10:18 p.m.
7:20 p.m.
7:45 p.m.
1:53 p.m.
12:45 p.m.
9:30 p.m.
5:38 p.m.
7:00 p.m.
6:50 p.m.
3:52 p.m.
3:45 p.m.
1:10p.m.
12:55 a.m.
Site
G-42
G-4
G.H.R.3
B-44
B-4
G.H.R.
B-4
All Sites
All Sites
All Sites
G.H.R.
G.H.R.
G-4
G-4
B-4
                                         Table 8

                                   Major Storms Missed^


                                            Loss Involved

                                         LiCI and Sample

                                         LiCI and Sample

                                         Sample

                                         Instruments Flooded

                                         Instruments Flooded

                                         Sample

                                         Sample and LiCI

                                         Sample and LiCI


                                         Sample and LiCI

                                         Sample and LiCI


                                         Sample and LiCI

                                         Sample and LiCI
                                         Sample and LiCI
                                         Submersible Pump

                                         None
                                        Sample and LiCI
          Problems

Submersible Pump Clogged

Submersible Pump Clogged

Bubbler Line Broken

Poor Drainage at Site

Poor Drainage at Site

Bubbler Line Broken

Electrical System Flooded

In Process of Repairing
Equipment in Sewers

Submersible Pump Clogged

In Process of Repairing
Equipment

Sampling Head not in Barrel

Sampler Switch System
Broken Down

Submersible pump Washed Away
Submersible Pump and Cage
Being Repaired

Submersible Pump Clogged
11ntensity-duration information for many of the missed storms can be found in Tables E-1, E-2  and E-3 of
 Appendix E.
^Combined Sewer District G-4.
^Separated Sewer District - Good Hope Run
4Combined Sewer District B-4.
                                               36

-------
                                                                                           FIGURE  12

                                                                                 MONITORING  EQUIPMENT
                                       Lid RELEASE  STATION
                                                                              ELECTRIC CLOCK
                         LiCI METERING  PUUP-
L
                                                         /DIFFERENTIAL
                                                          PRESSURE
                                                          REGULATOR

                                                       , JESSURE
                                                       REGULATOR
                                                                            ELECTRIC POHER
                                                                            SUPPLY AND
                                                                            T8IGGERINC
                                                                            SrSTEN
                                                                          -KERCURt PRESSURE SWITCH

                                                                         -PURGEMETER
PROCESS PRESSURE TO
CURRENT TRANSMITTER
        ELECTRONIC
        STRIP-CHART
        RECORDER
                                                                                                            3-COH1UCTOR
                                                                                                            JACKETED  CABLE
                                                                                                                                                   SAMPLE COLLECTION STATION
                LiCI  RELEASE
                LIKE  	
                             ELECTRIC CONDUIT
                                     UPSTREAM

                                    •SEKEfl  MANHOLE
                                               ,RAMSET STUDS
                                                                  = ELECTRIC  tONDUIT
— -— , TSIB'IS, |

i*




	 1>
n DOINSTDEAM
-SEIER MANHOLE
LEGEND
'/ 	 HASTEHATE8 OR LiCI RELEISE L
' 	 AIR LINE
, 	 ELECTRICIir LINE
                                                                                                                                                                                      fl
               BUBBLER LINE
                                                                                                             RI»L PLUGS
                                                                                                                                                                                                    12

-------
can be obtained. It should  be pointed  out that the method has never been verified for
runoff flow  measurements; however, because the tracer  dilution  method  is based  on
continuity  of mass rather  than energy,  unsteady-state conditions  should  not introduce
errors.

Flow  rate estimates based on depth-of-flow measurements and the Manning formula were
compared to the results of the tracer method. The depth-of-flow estimates showed only
a general  correlation, having a significant  spread, in comparison with the tracer  results.
Three possible sources of error explain  these differences:

     1.    Incomplete  mixing of tracer solution
     2.    Inaccurate measurement of depth-of-flow
     3.   Assumption of steady-state conditions  in using  Manning's formula.

Sufficient steps  were  taken  to  assure practically complete  mixing of the tracer solution,
and therefore, the  other two sources of error explain the differences  in flow estimates
and the  relative  inaccuracy of the depth-of-flow  procedure.

During dry-weather periods, the operating effort was minimal, because the stations operated
only  during  periods of precipitation. Thus, dry-weather periods  provided adequate time
for maintenance work,  routine  operating checks,  and preparation of  equipment for
forecasted  storms. The triggering  depth  at each site was set according to the minimum
depth requirement for operation of the submersible pump, the maximum dry-weather flow
depth, and the expected magnitude of the impending storm; the metering rate for  lithium
chloride  was also pre-set  on the  basis  of  expected  storm magnitude.

For  the  short intense storms, the concentration of each waste constituent was observed
to increase with the discharge  rate in the sewer;  the peak  concentrations of many waste
constituents  were concurrent  with the  peak flow. The concentrations were  significantly
high and  remained so throughout most of the monitoring period.

The time variation of the quality and quantity of wastewater generated by a long-duration,
high-intensity storm shows that the  flow rate of  the wastewater  generated by this long,
intense storm is much higher than that of short storms. However,  the concentrations of
various constituents were observed to be  lower,  which is an anticipated  result of high
dilution  by storm water.

Chemical oxygen demand and suspended solids concentrations of wastewater from  a long,
intense storm are reduced to approximately one-third of the comparable values for a short,
intense storm.  The biochemical oxygen  demand  for the long, intense storm  wastewater
were about one-seventh of that in short-storm wastewater.  This also implies that a higher
fraction  of  surface material was eroded by the long,  intense storm. However, the ratio
of COD  to BODs  was essentially the same as that for short-storm wastewater.

The  characteristics  and quantities of wastewater  generated by  four consecutive  storms
during July 27-28, demonstrated  the initial flushing effect in all  cases, even when the
storms were only  a  few hours apart.  However,  the  average concentrations of specific
contaminants  were  observed to follow  a decreasing trend with consecutive storms. For
example, the  average concentration  of  chemical  oxygen demand  (COD) decreased from
307  mg/L  for the first storm to 154 mg/L for the fourth storm.  This decrease may be
attributed to  the reduction of waste material accumulation on  the surface  and  in the
                                         38

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collection system. The ratio of COD to 6005 was essentially the same as the comparable
ratios for short storms and  for long-duration, high-intensity  storms. The  characteristics
of long-duration, low-intensity storm wastewater probably will  be similar to that observed
for consecutive storms.

The  average organic and nutrient concentrations in separated storm water discharges were
observed to  be approximately  one-third  of those  in combined  sewers, but  the solids
concentrations (especially non-volatile solids and settleable solids) were much higher than
those in combined sewer overflow. However, this phenomenon may be attributed to  the
differences in  surface development in  the monitored areas.  Silt was  found to be  the
dominant factor in  separated storm  water discharges.

In general, the time variation in  characteristics of wastewater from separated storm sewers
is  very  similar  to that from combined sewers. One significant difference  observed  for
separated storm sewer discharge is the broader range of COD to BOD$ ratio (1.8 to 32).

The  bacteriological examinations were made on selected  individual samples of  combined
sewer flow and on storm-composite samples. The range of variation  and the mean values
of different bacteria species  are summarized in Table 9. The bacteriological counts varied
with the flow rate of combined  sewer overflow during each storm  and the initial flushing
had  a  significant effect on various bacteria counts. The  variation  of  bacteriological data
for the  separated storm sewer discharge was similar to the variation in the combined sewer
discharge.  Bacteria counts were  high at  the  beginning of the storm  and then  decreased
as the storm progressed. Also, bacteria were  present in  storm  runoff in  fairly significant
amounts although less  than  in  combined sewage, as cited in Table 9.

To assess the relative contribution  to pollution throughout the duration of a storm,  the
total  waste materials  discharged were  expressed in units of  pounds per unit  time.  As
expected, these waste  loading expressions indicate that most waste materials were carried
by the  initial  flushing and scouring of the sewer. Waste loadings carried  by  the  secondary
flushing in a  prolonged storm  were  limited.

The  rain gauges were operated by a local Washington, D.C. subcontractor. The waste-level
recorder charts required changing only once every 30 days, but the readings were observed
and  the equipment  was checked  on a routine weekly basis. Equipment installed in  the
sewer was inspected at  least once a week.

Detailed discussions  of monitoring practices and techniques are presented in Appendix D.

Monitored  Wastewater Flows and Characteristics

As shown in Table 7,  storms of varying  intensities and  durations were monitored during
the six-month program. Wastewater flows and characteristics under storm conditions were
studied  both  in the combined sewer districts and in the separated storm sewer district.
The  effects of short-duration storms, long-duration, high-intensity  storms, and consecutive
storms  were  observed  and evaluated. The  range  and mean value of each  of  the waste
constituents in  storm  wastewater (for  both combined sewer and separated storm sewer
flow) are presented  in  Table 9.

Appendix E presents a  detailed  comparison of the  characteristics of the combined sewer
and  separated  storm  sewer flows generated by storms  representative of the wide range
                                         39

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                                               Table 9
                         Comparison of Characteristics of Combined Sewer Overflow
                                  and Separated Storm Water Discharge
   Waste Constituents ^
Chemical Oxygen Demand
Biochemical Oxygen Demand
Total Solids
Total Volatile Solids
Suspended Solids
Volatile Suspended Solids
Settleable Solids
Total Phosphate
Total Nitrogen
Orthophosphate
Ammonia Nitrogen
Total Coliform 6

Fecal Coliform^

Fecal Streptococcus^
                          o
   Combined Sewer Overflow
Range
80 - 1 ,760
10- 470
120-2,900
40- 1,500
35 - 2,000
10- 1,280
0 - 1 ,308
0.8 - 9.4
1.0- 16.5
0.1 -5.0
0-4.7
5.6-6.7
Mean
382
71
883
344
622
245
229
3.0
3.5
2.0
1.5
6.3
420,000 - 5,800,000     2,800,000

240,000 - 5,040,000     2,400,000

  1,000-   49,000        17,200
 Separated Storm Water Discharge"
      Range            Mean
                                            29-  1,514
                                             3-     904
                                           338- 14,600
                                            12-  1,004
                                           130- 11,280
                                             0-    880
                                             0-  7,640
                                           0.2 - 4.5
                                           0.5-6.5
                                           Not Sampled
                                           Not Sampled
                                           7.2-6.0
                         335
                           194
                        2,166
                         302
                        1,697
                         145
                         687
                            1.3
                            2.1
                      Not Sampled
                      Not Sampled
                            6.5
120,000 - 3,200,000     600,000

 40,000 - 1,300,000     310,000

  3,000-   60,000      21,000
1mg/L unless otherwise noted.
       on analysis of 94 samples
%ased on analysis of 64 samples
^Excluding sample from June 8 storm, which had a BOD concentration of 600 mg/L.
5pH units.
6Countsper 100ml.

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of  durations  and  intensities.  Appendix  E  includes   figures  that  relate  measured
concentrations and loadings of various contaminants with time, cumulative rainfall, and
sewer flow  rate. Although  Appendix E  presents a  detailed and  complete discussion of
the results of the monitoring program, it is convenient to highlight the more  significant
results.
                                         41

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                         Impact  of  Storm Water Discharges

Annual  Discharges

Results of the 1956-1958 studies of the Washington Sewer System indicated that an average
of 3.31  million gallons  per day  (mgd)  of  sanitary sewage  had  overflowed from the
combined-system  areas during rain storms and  0.34 mgd  during  dry weather. In terms
of percentages, about 3 percent of the annual sanitary sewage produced was discharged
directly to the streams during rain storms and about 0.31 percent during dry weather.
Estimates were also made for the  future, when  the program of improvements (Project  C
as previously discussed) would be completed. At that time,  the overflow from  rain storms
would amount to an average of 0.38  mgd, equivalent to 0.42 percent of the sewage flow
from the areas which  would  still  have combined sewers.

The approach  to assessment  of the  effects of overflows used in the present study is slightly
different. The effect on  receiving streams was determined in  terms of pollution load
discharged  into the  streams.  The parameters  used  were  BOD, suspended solids,  total
phosphates, and total nitrogen. The amounts of these elements discharged into the streams
from storm water and combined  sewer  overflow  were calculated  separately.

From a  probability plot of the average rainfall  for the period 1900-1968 based on Weather
Bureau records, the annual rainfall  with a 50 percent probability of occurrence was derived.
This value, 40.2 inches, was used  to calculate the volume  of total  storm water reaching
the streams from the entire area of the District. After obtaining the median annual rainfall,
certain basic assumptions were made to determine the quantity of storm water and sanitary
sewage that would  overflow into  the streams. The  parameters  used in the calculations
were obtained from prior reports, from literature review, from current study data, or from
conservative estimates  based on general  technical  knowledge.

The  first assumption  was that 90 percent of the runoff  will  reach the streams.  Other
assumptions,  based  on the  field monitoring  program  were made  for concentrations of
pollution parameters. The following are the values  of these parameters used for runoff
in this assessment of pollution  effects, as taken from Table 9.

          BOD                                  19mg/L
         Suspended Solids                       622 mg/L
         Total PO4                              1.3 mg/L
         Total Nitrogen                          2.1 mg/L

The  suspended solids concentration of 1,697 mg/L suggested for storm water  runoff by
Table 9 was not used. In  comparison with the suspended solids concentrations measured
in the two combined sewer districts and with the concentrations reported in other studies,
the value of 1,697 mg/L seems extremely  high and  unreasonable.  A value of 622  mg/L,
an average measured for  the  two  combined sewer districts, should be more  valid.

The  overall runoff coefficient for the entire  District had  to be determined in order to
estimate  the total volume of storm water runoff reaching the streams. The overall runoff
coefficient value was derived by calculating a  weighted average of  the  runoff coefficients
obtained for individual drainage districts.  The annual volume of storm  water  runoff was
then calculated by multiplying 0.9 (only  90  percent was assumed  to reach the streams)
by the overall runoff coefficient,  the total area in  acres  of the entire district, and the
                                        42

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median annual rainfall. The average  values of pounds of  BOD,  Suspended Solids, Total
Phosphate, and  Total  Nitrogen were  then calculated on the basis of this  annual volume
and the  listed concentrations of pollution parameters.

Pollution  load data for sanitary sewage discharged through the overflow structures were
calculated separately.  One of the assumptions made was that approximately 95 percent
of the sanitary  sewage in the combined  sewers would overflow into the  streams during
periods of overflow. The  data for average flow per capita and for sewage characteristics
were obtained from the February 1969 (3)  report  on the District of Columbia's sewage
treatment plant. Duration  of  overflow for an average year for various interceptor sewers
was derived from  the Board  of  Engineers'  1957 report (1).

The volume of sanitary sewage discharged directly into the stream through the overflow
structures was then calculated to be  an average of 545 million gallons in  1970 and 346
million gallons in  1975 (when less overflow  would result because of improvements in the
sewer  system). In veiw of the delays encountered in the sewer improvement program,
it  appears to  be more realistic to use the 1970 estimate to assess the pollution load to
the river. In comparison with the value obtained  in the prior studies, the current values
are approximately  1.0 percent of the  total  annual sewage flow to the treatment plant
or about 3.4  percent  of  the  total  annual sewage flow from  the combined-system areas.

The  average annual  quantities of BOD and  other pollution  elements discharged to the
streams through dry-weather overflow were calculated from the  volume of overflow and
concentrations of  these elements  present in sewage. Upon obtaining the data on pollution
loads from storm  water and sanitary sewage overflows,  the total quantities of BOD, SS,
P04 and  Total Nitrogen discharged into the  streams annually were calculated. The values
obtained  initially were for the 50 percent  probability of occurrence. However, once these
values  were obtained,  similar data  for other  probabilities were calculated  by applying
appropriate factors from the  probability plot of average annual rainfall.  Probability plots
for BOD, SS,  Total P04 and Total Nitrogen  discharged annually to the streams in  million
pounds were  plotted.  These plots are shown on  Figure  13, and  the data for 50 percent
probability are summarized in the first part of Table  10 (Annual Loads).

Individual Storm  Loadings

A  definition   of the combined sewer problem based solely on annual pollution loadings
is  incomplete. Overflows  from  combined sewers do not occur  as  continuous  steady
discharges, but rather  as slug  loadings.  This  characteristc,  in combination  with the long,
effective  residence times  of  estuarine  waters,  explains the  particularly  serious  impact
combined sewer overflows  have  on   water quality.

The  sources of  pollutants in  combined sewer overflow are the storm  runoff from the
urban  area,  the sanitary sewage  mixed with the  runoff,  and the  initial flushing  action
in  the sewers. The average concentrations of pollutants in storm  runoff from an urban
area  have been established  in this  study.  It  is  reasonable  to assume  that  pollutant
concentrations of  sanitary sewage included  in combined  sewer  overflows are typical of
normal domestic sewage. An  independent  study (6) of the flow in combined  sewers B-4
and G-4 during storm conditions estimated  that flushing  action results  in a total  added
BOD  loading  of 3 pounds per acre  of drainage  area. An extension  of this calculation
to phosphate  and nitrogen  pollution  indicates  that flushing  action  results in  total
phosphorus and total  nitrogen loadings of 0.2 Ibs. and 0.3  Ibs. per acre,  respectively.
                                         43

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               FIGURE  13
               ANNUAL  POLLUTION   LOAD  DISCHARGED
               TO  STREAMS   FROM  STORM  WATER
  12.0
   1.0
  10 0
I
   9.0
   6.0
   7.0
   6.0
   5.0
   4.0
          250
          225
          200
          175
          150
          125
          100
           75
           50
           25
   2.0
   1.0 L
                 0.2
O.I
                       59.2     53.0
                     ANNUAL RAINFALL ,  INCHES
                        46.4        40.2
                                                              35.0        30.7
                                                                                   0.2
                        12     5    I"    20   30   40 50  60   70   BO    90    95    98  99
                                         PROBABILITY OF OCCURRENCE
                                           44
                                                                               FIG.
                                                                                     13

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                                                  Table 10
                                          Expected Ppllution Loads
                                 from Combined and Separated Storm Sewers
                                           in District of Columbia
                                    Based on Annual Rainfall of 40.2 Inches
    Overflows from
    Combined Sewer Areas1
      Storm Water
      Sanitary Sewage
      Sub-Total

    Direct Discharge from
    Separated Storrn Sewers

    TOTAL
Discharge from D.C. Combined Sewer District
  for 2-Year, 24-Hour Storm

Discharge from D.C. Combined Sewer Districts
  for 5-Year, 24-Hour Storm

Discharge from D.C. Combined Sewer Districts
  for 15-Year, 24-Hour Storm

Discharge from D.C. Combined Sewer Districts
  for 25-Year, 24-Hour Storm
  Districts4
Recommended Maximum Allowable
Volume
mil.gal./yr.
1 1 ,000
1,000
12,000
16,000
28,000
BOD
mjl.lb./yr.
1.8
1.4
3.2
2.5
5.7
SS
mil.lb./yr.
57
2
59
83
142
24-Hour Pollution
TP2
mil,lb./yr.
0.1
0.4
0.5
0.2
0.7
Loads from
Various Return Frequency Storms
Volume BOD TP2

ter District

»er Districts

ler Districts

/er Districts

bined Sewer
e
Washington Area
million gallons

616

874

1,190

1,396
33

Ib.

160,000

200,000

250,000

280,000
8,000
16,500
T67~

12,000

13,000

14,000

15,000
1,400
740
Tl\|3
mil.lb./yr.
0.2
0.3
0.5
0.2
0.7

Tl\|3
Ib,

19,000

24,000

29,000

33,000
1,400
8,000
1Combined Sewer Overflows occur approximately 50-60 times per year.
^Total Phosphorus.
^Total Nitrogen,
4Determined by dividing annual loads by 365 days/year.
                                                    45

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The  previous  analysis of rainfall-runoff relationships  to determine volume of overflow
provides a sufficient basis  to determine  pollutant loadings.  The  total  pollution  load
overflowing from the combined sewer district during a storm is estimated by adding the
following  values:

     1.   Volume  of storm water  runoff times  the  average  pollutant  concentrations
         previously  established.

     2.   Acreage  of the drainage district times the flushing unit  loadings.

     3.   Typical sanitary sewage pollutant concentrations times the average dry-weather
         flow generated  in the district.

The 24-hour pollution loads calculated for the combined sewer system for storms of various
return frequencies are presented in the second half of Table 10. Also included for purposes
of comparison are the maximum allowable contaminant loadings  if water quality objectives
in the  Potomac  are  to  be  met. Examination of these figures shows  that the BOD and
phosphorus discharges, even  from a 2-year, 24-hour storm are from ten-fold to twenty-fold
greater  than the recommended loadings in the entire  metropolitan Washington  area. In
fact, even  the  average  daily loadings (determined by  dividing  annual loadings  by  365
days/year)  in combined  sewer  overflows account for  a good portion  of  or exceed the
recommended  loadings.   It  is  pointed out that there  is no uniform  daily discharge of
combined  sewer  overflow; the annual loadings are concentrated  unevenly  in the  fifty to
sixty overflows  that occur  each  year.  It is this characteristic  combined  with the long
residence times of estuarine waters that explains the particularly serious impact of combined
sewer overflows  on  the  water  quality of the Potomac.
                                        46

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                                    SECTION V

            INVESTIGATION  OF  POTENTIAL  ABATEMENT MEASURES

                     Review of Approaches Tried at Other Cities

Many municipalities and some private companies have been and are continuing to investigate
methods for dealing with the problem of combined sewers. The methods being considered,
separately or in combination, can be classified under four headings:  1) sewer separation;
2) off-system  storage; 3) treatment processes; and 4)  miscellaneous.

Sewer Separation

Complete separation of sanitary and storm  sewers is an enormous project. It requires the
following:

     1.  Separate storm and sanitary  sewers
     2.  Separate roof  drains and downspouts
     3.  Separate yard  and areaway drains
     4.  Separate air conditioning and cooling system  drains
     5.  Separate foundation  drains
     6.  Separate catch  basin inlets

The  costs of  complete separation  of any extensive existing combined sewer system are
prohibitively high. In  a recent study (7), the American Public Works Association estimated
that  it would  cost 30  billion  dollars to separate all the combined  public sewers in the
country, and another  18 billion to make  the related plumbing changes on private properties.
Costs  for partial separation, involving  separation  of only the most  troublesome sewers
and  the related storm water drains would obviously be less, but still would be substantial.
According to District  of  Columbia Department of Sanitary Engineering figures, the typical
cost  encountered within  the  District of  Columbia  in 1957 was $18,000 per acre.

There are other complications. Complete separation projects would  take many years to
complete,  even if concentrated  construction effort were applied.  Communities  and
businesses would suffer inconveniences and losses during construction, when streets would
be closed to  traffic.  Extensive  policing would be required  to  ensure the separation of
all storm water connections (e.g. roofs,  yards, etc.). Furthermore,  recent studies  (8, 9,
10)  reveal that storm water runoff itself is polluting the streams, and,  in many situations,
should receive treatment. This has also been confirmed  in this study.

Even with these complications, sewer separation is by far the most commonly used remedial
method in the  900 communities surveyed by the APWA; however, separation has generally
been confined to  portions of sewer systems and  has not very often been applied  to an
entire system.  Only rarely have all roof  drains, air-conditioning drains, etc., been separated.
The  method of separation which appears to  be the most practical is to construct a sanitary
sewer within the larger existing combined sewer. This was accomplished in Ottawa, Canada
using 15-inch cast iron pipe at a cost of  $20-25 per foot in place (11). Minneapolis  installed
a flattened 42-inch corrugated steel sanitary sewer along the invert of a 102-inch tunnel,
at a  low but undisclosed cost (12). A different approach is used in  the ASCE Combined
Sewer Separation Project, which involves pumping comminuted sewage  from individual
buildings through pressure tubing to pressure conduit installed within existing combined
sewers (13).

                                         47

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Off-System Storage

The  use of storage  (surface  or sub-surface) in connection with the problem of combined
sewers is  being applied in two  general ways:

     1.   Temporary storage, with  return of the retained flow to the sewer system for
         conventional  treatment when the  storm subsides;  and

     2.   Temporary storage, followed by discharge  of the retained flow directly to the
         watercourses.

The  latter approach may be  acceptable in certain situations, because some degree of solids
removal will  occur while the  wastewater is stored; however, application  is limited to
situations  where  water  quality  requirements are not severe and/or when  other pollutant
concentrations  (dissolved  materials) are low.

     Chicago  Underflow and Deep  Tunnel Plans (14) (15)

Several  cities have  or  plan  to  have facilities for temporarily storing  overflow for later
release to  a conventional waste treatment plant. The Chicago Underflow and Deep Tunnel
Projects are the biggest and best known of these plans. For years, Chicago has experienced
basement  and underpass flooding,  as  well as storm and beach pollution resulting from
combined sewer overflows. The Underflow-Storage Plan and the Deep Tunnel Plan represent
viable alternatives for solving the problems of  flooding and water pollution  by handling
the  runoff from  a  100-year storm.

"The Underflow-Storage Plan proposes the construction  of a  pattern of  large tunnels in
the dense  Niagaran limestone rock formation, 200 to 300 feet  below the surface waterway
system.  These tunnels would be sized  to provide a linear distribution  of storage volume
and  conveyance capacity  in a  pattern which would  intercept all of  the approximately
400  outfalls of the existing combined  sewers. The tunnels would be sloped down to low
points and pumping facilities opposite the  existing sewage treatment plants. Overflow from
the combined sewers, during storm periods, would drop through shafts to the large storage
tunnels. In the post storm period, the tunnels  would be dewatered  by pumping directly
to the existing treatment works."

"The Underflow-Storage Plan takes advantage of  the  lower water  level to be established
in the Illinois Waterway at Lockport, Illinois,  for improvement of navigation  and flood
control  of the  waterway  system. The  new water level, 70 feet or more  below the level
of Lake Michigan, will  allow the construction of tunnels with large underflow conveyance
capacity to  Lockport and provide  flood  protection for the  largest storm  of record."

"Storage of 18,000 acre-feet or 1.12  inches of runoff in the tunnel system  will provide
98.5 percent reduction of pollutants entering the waterway from combined sewer spillages."
(This represents sufficient capacity to handle  the  100-year  frequency storm.)

"During the study of the Underflow-Storage Plan, it was decided to modify  a large relief
sewer proposed by the  City  of Chicago, as an Underflow Sewer similar to the Metropolitan
area-wide  plan but on  a much  smaller scale.  The Underflow  Sewer would be constructed
in solid rock, 250 feet  below the ground surface. This sewer is now under  construction
with  a portion  being funded by a demonstration grant from  EPA-WQO. Two  additional
Underflow Sewers are  also  under construction by the Metropolitan Sanitary District at


                                        48

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widely separated locations  in  the  Chicago area in the same  dolomitic  limestone rock
formation. Each of the three Underflow Sewers are being mined by a machine of different
manufacture. The construction of these Underflow Sewers has confirmed the  structural
integrity  and the dense  impermeability of this underlying rock  blanket throughout the
entire Chicago  area."

"Prices per cubic yard of rock excavation vary from $60.00 for a 10-foot diameter single
tunnel with two headings to $5.65 per cubic yard for cavern (room and pillar) excavation
with multiple headings. The principal governing factor appears to be the  size or face area
of the headings. For the combined Underflow-Storage tunnels, with  26-foot wide by 50-foot
high tunnel faces, the estimates  are  $8.81  per cubic yard for single tunnels and $8.03
per cubic yard for twin tunnels."

"The Deep Tunnel Plan is a multi-purpose plan, including hydroelectric power development,
with a "pumped-storage" scheme, now widely  used throughout the world  as adjuncts to
hydro-power developments on surface streams or to  thermal power plants. In  the  Deep
Tunnel Plan, storage for hydro-power would be provided  in rock caverns,  600 feet or
more below the  surface and  in  surface reservoirs  above ground in the vicinity of the
underground caverns. Reversible  pump-generator units  would be used intermittently to
move water upward  and to  develop  power during downflow. Power would be  generated
and sold  daily during the hours of peak demand for electricity. Power would be purchased
for pumping daily,  during the periods of  low demand for  other uses in the Metropolitan
area.  Based on an estimated net  revenue, in excess of  cost of  operation, revenue bonds
would be sold  by the Metropolitan Sanitary District  to provide capital for a portion of
the multi-purpose project."

"The underground caverns and the surface reservoir  would be over-sized beyond  the needs
for power development  to  provide for entrapment and storage  of  excess spillage  from
the combined sewer  outlets.  Primary  sedimentation  would be provided  underground at
the entrance to the  caverns,  and  the  sediment pumped to  the  existing treatment works.
Controlled outflow from the surface  storage  would also be directed to the  existing major
treatment works."

"The total volumes of the proposed multi-purpose storage is 35,000 acre-feet below ground
and 45,000 acre-feet above ground, or a total in the system of 80,000 acre-feet, of which
20,000 acre-feet  was considered  to be normally needed for power development, leaving
60,000 acre-feet  normally available for pollution and  flood control."

"The tunnel system  to  deliver the  combined  sewer spillage to  the  storage and power
development site or  sites would  be  generally of the  same pattern as for the Underflow
Plant."

The  underflow tunnels under construction  are compatible with  future extensions along
the conceptual lines  of  the  Deep Tunnel  Plan.

     Other Storage Applications

Most of the applications  of storage have been for treatment followed by release to receiving
waters rather than  by return to  the sewer systems. The  treatment may  be removal of
solids, or possibly some degree of stabilization, with or without disinfection by chlorination.
                                         49

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This type of storage was originally used at points along a sewer system where overflows
would  normally enter streams  that have  relatively low flows.  Columbus, Ohio has been
employing  uncovered standby surface storm water  tanks  for  35 years. The tanks hold
only part of the combined overflow, with the excess released  to  nearby  streams (16).
Because no means for frequent removal  of settled  solids was originally provided, odor
problems were experienced when anaerobic decomposition occurred. Also, periodic cleaning
of the settled sludge  resulted in a serious overload on the activated sludge treatment plant,
unless the cleaning operation could be stretched out over a  week or so. However, facilities
for regular  removal of solids have been installed, and the odor and treatment plant overload
problems have  been  minimized.

Halifax, Nova Scotia  began  the construction of two 1,000,000-gallon surface storage tanks
in 1965 at a cost of $400,000 each (17).  In contrast, complete separation was estimated
at 4.3  million dollars, and  partial separation (which  would not prevent overflows in large
storms) was estimated to cost 1 million dollars. These storage  tanks, designed to provide
15  minutes retention at peak flow, will reduce the average frequency of overflow during
the 4-month swimming season from  fifteen overflows to  two, and the volume of total
overflow will be reduced by about  85 percent. Chlorination facilities will  provide a dosage
of 30  ppm for flows up  to 40 cfs and a  constant chlorine flow for the more diluted,
higher  flows. The  city is  now considering partial  separation as a supplement to surface
storage. This could be accomplished for  one million dollars, and the retention tanks would
then have  capacity for  the 5-year  storm.

Other  applications of storage for treatment are Grosse Point Woods, Michigan  (18) (7.5
minutes detention of 1-year storm in surface tank, sludge  removed by flushing with water);
and Johnson County, Kansas (7) (30 minutes detention at maximum design rate). Planned
applications are Milwaukee  (19, 20)  (underground,  concrete tank with  3,900,000-gallon
capacity  providing 15 minutes of  detention, screening of influent, and chlorination of
effluent    before    discharge   to   river;   Boston   (19)    (10-minute   minimum
sedimentation-chlorination,  with chlorinated effluent discharged to river); and New York
City (19)  (system of basins designed  to contain 25  of 40  summer storms, with overflow
chlorinated to protect beaches). The reports of these  planned applications did not identify
the design  storm.

For  many  years, British  cities  have been  employing surface storm  water tanks  to store
and treat combined sewer overflows. Their general practice is as follows (21), using British
terminology:

     1.   Flows up to three times the normal dry-weather flow are treated at the municipal
         treatment plant.

     2.   Flows between three and  six times the normal  dry-weather flow are  diverted
         to storm  water tanks for sedimentation prior to  discharge to the receiving stream.
         Any flow in excess of six  times the normal dry-weather flow is discharged to
         the stream without any  treatment.

     3.   Influent to the  storm water  tanks is screened  (6-inch and  1-inch openings).
         Effluent  is not chlorinated.

     4.   Minimum number of  storm  water tanks  is  two, and capacity must be sufficient
         to provide  at least a  two-hour  detention period at the  maximum  flow (not
         disclosed)  or must equal  one half of  a day's  average dry-weather flow.


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     5.   Settled solids and remaining wastewater are returned to  the sewer  systems  for
         treatment  when  the storm  subsides. Sludge  can be  removed  by mechanical
         equipment or  by flushing with  municipal  water.

Current studies supported  by EPA/WQO research  grants are investigating  the use of
polyelectrolytes and tube-type clarifiers to improve sedimentation  in storage tanks (19).
A  study in Cleveland  involves the feasibility of using storage basins for stabilization of
combined sewer overflows (19); secondary  effluent and flow from polluted streams would
also  be  diverted to these basins.  Little information  is available now  but there is enough
to  indicate  that  a  higher  degree  of  pollution  abatement  can  be  obtained  with
stabilization-retention basins than with sewer separation, and at approximately  one-third
of the  cost  of separation  (22).  The  amount of  land required, however,  prohibits this
application in  many cities.

     Effectiveness of Storage  in  Abating  Pollution

Studies  (10)  at the EPA/WQO Robert  A. Taft Sanitary  Engineering Center (Cincinnati
Water Research Laboratory) on sedimentation and concurrent sedimentation-disinfection
of urban  storm water runoff  from a separately sewered residential and light-commercial
area indicate that removal of 55 percent of suspended solids (normally expected of sanitary
sewage  in primary treatment)  is  not obtained within 20 minutes, but takes one hour of
settling. The variations in removal appeared to be independent of the seasonal occurrence
of the  storms.

Studies  in  England and  Canada (21, 23, 24)  indicate similar results with combined sewer
overflow.  One consulting firm in Toronto,  Canada maintains that a one-hour detention
of the one-year storm overflow can effect a  BOD  removal of 30 percent and a suspended
solids removal of 60  percent  (23). For storms of  less intensity,  BOD reduction could
be as high as  45 percent,  and suspended solids removal  could be 65 percent.  None of
these studies  used  polymeric  flocculants or any  other chemical additives.

Eliassen (25)  investigated  the  aftergrowth of coliforms resulting from average  discharge
of  combined  sewer  overflows into  a  brackish  water  tidal   basin.  He  reported  that,
"Chlorination  of the  overflows to the  15-minute  chlorine demand...will  limit  the peak
aftergrowth to approximately 500,000 per 100 ml in 40 hours...Chlorination to the chlorine
demand will result  in average MPN aftergrowth values in the basin  of from 10 percent
to 30  percent of those which would  develop if unchlorinated overflow were discharged
to the  river  in the  normal ranges of summer  dilutions."

All studies stressed  that their results, in  general, cannot be  applied to other  sewerage
systems. The composition of combined sewer overflow is extremely variable, varying from
drainage area to drainage area  as well as with intensity, duration, and  frequency of storms
and  probably  with  the  time  of  day.  No  data could be obtained which would correlate
variations in composition  with intensity and duration  of  rainfall. Suspended solids and
BOD removal  by sedimentation  depend on  concentration as well as  on the period of
detention.  This further complicates establishing  a pattern for Chlorination efficiency,
because it depends  in  part on the nature and concentration of the suspended solids.

Combined  Sewer Overflow Treatment Processes

There are approximately 15 current EPA/WQO-funded R and  D projects for investigation
and/or  demonstration  of varied,  non-conventional processes for treating combined  sewer


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overflows; however, these projects have not been completed, and the available information
is not conclusive (19). Very  few of these treatment methods involve biological processes;
most are concerned with screening or filtration.  Some of the more interesting  projects
are  listed  in  Table 11.

Microstraining, a form of simple filtration using specially-woven wire fabric mounted on
the periphery of a revolving drum, is one of the more promising approaches. In this process,
wastewater passes through a partially submerged drum  from inside to outside. Downstream
water is used to flush  any solids  that build up  on the  inside.

Preliminary results of microstraining at a demonstration site in Philadelphia indicated that
a 30 to 60 percent removal  of both BOD and  suspended solids could be obtained  with
a 35-micron fabric; filtering rates were approximately 10gpm per square foot (submerged).
The contractor feels that better results are obtainable, because  the  overflows tested  were
pumped to the Microstrainer,  and pumping should be avoided since it tends  to break
up  any fragile solids,  thereby  reducing the  efficiency of their removal.

The advantages of  microstraining are: compactness; continuous and automatic operation
(backwash  is continuous and employs a non-clogging jet); the low  head-loss of  12 to 18
inches;  and economical operation.  For best performance, a holding tank providing 10 to
20  minutes detention should precede  the Microstrainer; this tank would tend  to equalize
the flow rates and would catch any  heavy  material, but  it should  not  be designed as
a sedimentation tank.

Miscellaneous  Solutions

Besides sewer separation, off-system storage and  in-line treatment, there are other  possible
solutions,  which can be categorized  as  in-system  storage, land-use  improvements,  and
monitoring and regulations.

In-system  storage is  concerned with  using the storage capacity of the sewer  conduits
themselves to hold the storm water and deliver it to the treatment plant over an extended
period.  This  can be accomplished  by reducing infiltration or  friction to increase sewer
capacity. It can also be  accomplished by adding inter-connecting branch sewers or relief
sewers.  In-system storage will serve  to prevent overflows from  smaller storms, but is not
practical for  larger storms.

Some problems associated with combined  sewers result from changes in zoning and  land
use, which in  turn change surface characteristics to conditions for which existing sewer
systems were  not designed. Advanced urban planning on  an area-wide basis and stricter
control  of land-use practices would assure continued efficient use of  a sewer system and
should lower the incidence of  pollution in urban storm water runoff.  A study to develop
such a  relationship has  been conducted  in Tulsa, Oklahoma (19).

In-system  monitoring,  with regulation and diversion,  is one method being explored  by
Seattle, Detroit, and the  Minneapolis-St. Paul  Sanitary District (19).  It assures maximum
utilization of  available capacity and minimizes  the pollutional  effects of  any overflows.
With proper instrumentation, the large flows could  be diverted to those sewers with low
flows; this is essentially a  refinement of in-system  storage. Instrumentation required  includes
flow  measurement,  rain-gauge  telemetering,  conduit  liquid-level  sensing,  and  remote
operation of  diversion gates.  Computer-controlled  operation would  be required for rapid
transmittal, recording, and feedback of data.


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                                    Table 11

                WQO Combined Sewer Overflow Treatment Projects
      Contractor
City of San Francisco
Rand Corp.
American Process
Equipment Corporation

Cornell, Howland,
Hayes &  Merryfield

Autotrol
Rex-Chainbelt


Crane Co.


Fram Corp.


Hercules, Inc.



Hydrotechnic


Battelle-Memorial
 Project Site        Description of Treatment

                Short-term sedimentation followed
                by dissolved air flotation and chlorina-
                tion

Cleveland,       Percolation through a shallow bed
Ohio            of coal to filter coarser materials.
                Coal-solids mixture is later incinerated.

Los Angeles,     Ultrasonic filtration.
California

Portland,        High-rate, fine-mesh, vibrating
Oregon          screens for removal of solids.

Milwaukee,      Biological treatment  by a rotating
Wisconsin       biological contactor.

Milwaukee,      Fine screening and dissolved air f lota-
Wisconsin       tion for solids removal.

Philadelphia,     Microstraining, ozonation, and
Pennsylvania     chlorination

Providence,      Strainer followed by self-cleaning
Rhode Island    diatomaceous earth filter.

Cumberland,     Self-cleaning filter of a flexible, filament-
Maryland        wound structure that will flex during
                storm flow to become permeable.

New York,      Multi-media filtration
New York

Richland,       Activated carbon adsorption, chemical
Washington      coagulation, sedimentation
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Water quality monitoring of such characteristics as turbidity could assure that less-polluted
flows are selected for discharge. This concept can be further refined by including techniques
to provide  selective discharge of overflows at different points in a manner which minimizes
their  pollutional  effects on a  waterway. Such  a system is being studied in Seattle.

Another alternative  method   is  to  flush  the  sewerage system  intermittently  during
dry-weather conditions with municipal water. This would flush out any solid matter which
may have settled along the bottom of the sewer during the slow, dry-weather flows. The
flushing flow must be controlled so as to not overload the hydraulic capacity of the sewage
treatment plant.  This  method  is  being studied by  FMC (19).

Summary of Previous Approaches

It is highly  improbable that a community would have the economic capability to completely
separate  its combined sewers.  Furthermore, complete  separation  could be accomplished
only over a long period of time at great inconvenience to urban existence. Partial separation
is less costly, but it probably would not provide the abatement required in many situations.

Extensive land areas are required to provide surface storage  sufficiently large either to
hold the larger  overflows  for later return to  the sewerage  system  or to detain the flow
long enough  for  proper  sedimentation. Sub-surface  storage appears to  be  far more
promising,  and it can also  provide additional  benefits beyond  those of pollution control.
It,  too, would be an  enormous  project and  feasible  only  if  the  bedrock  is suitable.

Some treatment processes  appear promising,  but there is a dearth of  basic information.
EPA/WQO  is supporting continuing studies  in an effort to  develop basic data which can
be used to help work  out  economical solutions; however, few of these projects have  yet
produced definitive results. Even so, the extremely variable character of combined sewer
overflows will inhibit  general  application of  these data.

No  particular method  of  solution has been  proven to be the  least costly for  general
application. Each  city  must evaluate its local  situation and  determine the method  or
combination  of  methods (and  their priority) which will reduce  the polluting impact  of
this problem to  the  desired level at the  lowest cost and with  the  least inconvenience to
the  citizenry.
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                             Ultra-High-Rate  Filtration

General  Discussion

High-rate filtration has been  extensively applied  for  the  removal of suspended impurities
from  raw water or wastewater, especially when  the  impurities are primarily  non-volatile
discrete  particulates, such as  the wastewater from steel mills. In combined sewer overflow
and  storm  water  discharge,  large  fractions  of the suspended waste  constituents  are
recognized to be non-volatile discrete  solids; thus, high-rate filtration may be  an effective
treatment method.  Despite  the many studies that have been  undertaken, the status of
filtration development  is still in transition from  an art to  a science. The practical design
parameters for application of the  filtration process to treatment of a specific wastewater
must  still be determined from results of specific laboratory or pilot-scale investigations.
Moreover, ultra-high-rate filtration (greater than  15 gpm per square foot) must be  applied
in order to cope economically  with the unique hydraulic characteristics of the combined
sewer overflow  or  storm water discharge-high discharges within a short time period. This
adds another dimension  of uncertainty to the development  of a feasible  filtration  process
to treat the  excess  urban wastewater derived from intense  storms. Therefore, a filtration
study was conducted with  the following objectives:

     1.    To evaluate  the applicability  of ultra-high-rate filtration to  the  treatment of
          combined sewer overflows.

     2.    To determine the flocculation  effects  of chemical additives on the removal of
          solids and organic material.

     3.    To provide a conceptual design basis for pilot-scale or full-scale treatment units.

The principal process  variables evaluated in  the laboratory program were:

     1.    Filter media, including  type,  depth, size,  and arrangement.

     2.    Filtration rates.

     3.    Effects  of addition of flocculants  and flocculant.

     4.    Variation of solids concentration  in the wastewater.

     5.    Backwash rate and quantity.

     6.    Air-souring rate, duration, and sequence in the  backwash procedure.

     7.    Effluent  quality characteristics, including suspended solids, COD, total five-day
          BOD, and soluble  five-day  BOD.

     8.    Length  of filter run.

     9.    Head  loss requirements.
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Detailed discussion  and  results  of ultra-high-rate  filtration  studies  are  presented  in
Appendix F  and are summarized as follows.

Summary of Findings

The laboratory test program indicated that ultra-high-rate filtration, at rates  of 15 or more
gallons  per  minute per square foot, is  a technically  feasible process for the removal  of
solids and non-soluble BOD from combined sewer overflow. While actual combined sewer
overflow was not used in these tests,  a synthetic waste was made using an appropriate
mixture of sanitary sewage, silt from the District area, and lake water. Of the three filter
systems tested, the fiberglass filters  performed best, achieving at least 90 percent removal
of suspended solids and  70 percent removal of non-soluble BOD^ at  filtration rates  of
15-30 gpm/sq.ft. and with  reasonably  long  filter runs  (1-3 hours). Comparable effluent
quality was  not achieved in tri-media filter runs at filter  rates above 10 gpm/sq.ft. Upflow
filtration through a garnet bed was unsatisfactory,  largely  on the basis of  poor effluent
quality.

Soluble BOD removal  was negligible in all  three  filter systems.  Even the addition  of
activated sludge to the influent  wastewater did not  significantly  improve  soluble  BOD
removal. The organic content (6005, COD) of the influent wastewater appeared to have
a greater impact on head-loss building than did the suspended solids content. The addition
of flocculants and flocculant aids was not effective in improving the performance of the
fiberglass filters.

The economic  feasibility  of the fiberglass filter  process for ultra-high-rate  filtration will
probably require extending the useful  life of the fiberglass medium  beyond  the limits
indicated by the  laboratory tests.  Improvement of  the  backwash operations  through
modification of underdrain design,  stagewise removal of  backwash effluent, the use  of
air-scouring  driven backwash, etc., and  development  of improved  fiberglass bed designs
and fiberglass filter regeneration techniques appear to be promising approaches to extension
of filter life.
                                         56

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                                 SECTION  VI

               DEVELOPMENT OF FEASIBLE  ALTERNATIVES

                             Alternative Approaches

After thorough review and interpretation of the pertinent information, four methods of
abating pollution from combined sewer overflows appeared to offer sufficient promise
to justify consideration  as alternative approaches for the District:

     1.   Sewer Separation.

     2.   Storage Reservoirs  (with treatment at the Blue Plains Plant  or other centralized
          facilities after  the  storm  subsides).

     3.   Treatment at Overflow Points.

     4.   Tunnels and Mined Storage (with treatment at the Blue Plains Plant or other
          centralized  facilities after  the  storm subsides).

Sewer Separation
                                                                                o
As the name implies, this approach consists of complete separation of storm and sanitary
sewers. The initial steps  of this program involve continuing the sewer separation program
of Project C as modified  by the City of Washington. The details of Project C are contained
in the 1957  report (1) of the Board of  Engineers. Storm  water would be discharged to
the  surface  streams  through what  is now the combined sewer system,  and sanitary
wastewater would be  conveyed through a  new sewer system to the Blue Plains sewage
treatment plant for treatment.

Storage Reservoirs

The  concept in this approach is to provide sufficient underground storage volume to hold
the combined sewer  overflows  caused by  each storm until the  storm subsides and then
to pump  the stored wastewater back  into the  sewerage  system for  conveyance to a
centralized treatment plant. This would  be accomplished  by the construction of shallow,
multi-cell, concrete tanks located five to  ten  feet underground  at reservoir top.  Depth
of each reservoir would depend on  land availability and  volume to be stored; however,
there are various technical, economic, and aesthetic factors that prevent the use of storage
reservoirs  in  certain locations.

Each  reservoir  would  be compartmented.  The  initial compartment would function  as a
settling chamber to  remove  grit and heavy solids,  with the  overflow going  to other
compartments for storage. The number  of compartments used  during any  storm  would
depend on the rainfall intensity, the  duration  of the storm  and the amount of  stored
water remaining from any  previous storm  A schematic of a typical  installation is shown
in Figure  14.

Each  reservoir would  be  equipped with trash  racks, a system for flushing sediment from
the reservoir bottom,  a  ventilation  system, pumps for returning stored wastewater  into
the regular sewer system  and special  pumps for transferring accumulated  sludge back into
the system or to tank trucks for disposal.


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                                                            FIGURE U
                                                      STORAGE  RESERVOIRS

                                          STORAGE  RESERVOIR  SCHEMATIC  (TYPICAL)
en
00
                         SCREENINGS
                         TO LANDFILL
          EXISTING OVERFLOW
          TO STREAM
          GO

          X
                                         CONTROL
                                         EQUIPMENT
                  VENTILATION
                  EQUIPMENT
                                                                                                         FRESH AIR
                                                                                                         INTAKE
S   SETTLED  OVERFLOW
S   PUMPS	
                  CO

                  s
                  CO

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Due to the extensive urban development within the District, little vacant land is available
near overflow points for storage reservoirs.  In  certain areas of the  District scheduled for
redevelopment (e.g., Georgetown Waterfront), storage reservoirs could be constructed under
planned open spaces and coordinated with the razing phase. In most other overflow areas,
the only  available  vacant land is  park land under the jurisdiction  of the National Park
Service; full  cooperation of the Park  Service  would  be  necessary  to use these sites for
reservoir purposes.  Since the reservoirs themselves would be underground, only relatively
small pump  houses would  extend above  grade,  and the surface area could  be used for
parks and playgrounds.  Sufficient  care to preserve  the natural park landscape by  proper
architectural  design of  both  the  pump houses and maintenance-access structures would
tend to offset objections of the  National  Park  Service.

Treatment at Overflow  Points

In this method, there would be a treatment  facility  at each existing overflow point, except
where  conditions either  prevent this or dictate that certain overflow points be combined.

The treatment sequence would be sedimentation in the storage reservoirs, followed by
ultra-high-rate filtration  and chlorination. A  schematic flow diagram for a typical treatment
facility is presented in  Figure 15.  The individual filters would be ultra-high-rate pressure
filters  similar to those used in the  treatment of industrial  water supplies. Each  installation
would  include a battery of filters, the number of which would vary depending  on the
design   flow  rate   at   each   location.  In  addition   to  the  filters, various  pumping,
chemical-mixing, and flocculant-aid equipment would  be needed.

The filtered wastewater would be disinfected  (by chlorination) and discharged to the surface
streams.  However,  a portion of the filtrate would be stored for use as backwash, initiated
when a predetermined  head  is reached at  any individual filter.  The backwash from the
filters  would  be pumped back into the regular system for conveyance to the  Blue Plains
treatment plant. Backwash  requirements were estimated to be approximately eight percent
of  the forward flow.

In  addition  to actual  treatment  facilities,  each installation  would require equalization
storage because of  the extremely high flow rates that would be encountered. (The smallest
sewer district would require a treatment facility with a capacity  of  several million  gallons
per day if no equalization storage were provided.) Even with  the  high rates (15 gpm/sq.ft.)
involved  in  ultra-high-rate  filtration, the capacity  required  for equalization  would be
essentially the same as that required to capture the entire storm overflow. Therefore, the
actual  treatment facilities in this  alternative would have to be supplemented by the same
storage capacity required  in  the  storage  reservoir  method.

The capacity  of any treatment facility, since  it determines the drawdown rate, is  related
to the  probability of overflow from a subsequent storm exceeding the capacity of a  storage
facility. Regardless of any selected  capacity  of a  storage facility  or treatment facility,
it is possible that the combined effect of two or more storms, occurring within a relatively
short period  of time, will result in runoff in  excess of the reserve  storage capacity, even
though the separate runoff from each storm is less than the design capacity. The capacity
of  the  treatment  facility  should  be  sufficiently  large so that the  probability of two
consecutive storms  overflowing a storage facility is reasonably low. A preliminary statistical
analysis suggests that  the  maximum  capacity  that can be considered  reasonable  is one
that draws down a filled storage  facility within five days. A drawdown rate of five days,
as compared to 10 days, certainly reduces the possibility of  malodors resulting from long
residence  times.

                                          59

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                                                              FIGURE  15
                                                TREATMENT  AT  OVERFLOW  POINTS
                                            TREATMENT  FACILITY   SCHEMATIC  (TYPICAL)
                         CHLORINE
                         CONTACT
O)
o
          UJ     CO
                                                    ;LUDGE
                                                   PUMP
                                                              UNDERGROUND STORAGE
                                                                                                       -BACKWASH
                                                                                                         SUPPLY
                                                                                                          ^VENTILATION
                                           BACKWASH DISCHARGE TO INTERCEPTOR
SCREENINGS
TO LANDFILL
                                                             FIBERGLAS  FILTERS
                                                          BACKWASH
                                                          PUMP
            TO RECEIVING STREAM
          EXISTING OVERFLOW
                                                         VENTILATION
                                                         EQUIPMENT
                                                   FLUSHING
                                                   WATER SUPPLY
                                                                            STORAGE ZONE
                  SLUDGE DISCHARGE


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Tunnels  and Mined Storage

In this concept, combined  sewer  overflow  would drop through a vertical shaft down to
an  underground  system of tunnels and  mined  storage.  The  tunnels would convey  the
overflow at high velocity to mined storage.  After the storm subsides, the retained overflow
would be pumped  back into the  regular  sewers  for conveyance either to the Blue Plains
sewage treatment  plant or  to  a separate,  centralized facility constructed specifically to
treat  combined  sewer overflow.

     Vertical Shaft Considerations

In a tunnel-mined storage system, each of the overflow points would have a vertical shaft
for dropping the overflow to the underground system. Certain  vertical shafts may be used
for purposes other than the  primary function to convey overflow to the tunnels. The
shafts used for  access  of men  and equipment and  for  removal of drilling muck would
be  larger than those to be used  for conveyance of  overflow.

The larger-diametered (20 and 30-feet) access shafts would be constructed by conventional
techniques  (i.e., by drilling and blasting, and by  lining  with either jacking  or slip-form
construction). The smaller (5-foot diameter)  shafts would be constructed by simply augering
down from  grade to  the  storage tunnels or by  raise-boring  of a  pilot hole  from  the
tunnel,  followed by  pulling a  larger-diameter auger up  from the tunnel.

Each  shaft  would be concrete-lined (for  structural purposes and to prevent ground water
from  entering the  system)  and would have  a baffle to  permit  the escape of entrained
air  to the atmosphere.  The tunnel bottom  at the junction with each vertical shaft would
be  designed to  dissipate the  energy of the falling water  and  to provide  transition from
the vertical shaft  to the conveyance tunnels.

Land  requirements for  shaft construction (and, therefore, tunnel construction) would be
limited  to the land needed for storing construction  equipment and a small amount of
excavated material. Preliminary  site investigation  has shown that sufficient land is available
at nearly all reasonable  vertical shaft sites and that only slight modifications to the existing
sewer system would be  required to connect the overflow points to the appropriate vertical
shafts.

     Tunnel Considerations

The tunnels would be  concrete-lined and constructed in  bedrock at sufficient depths to
assure the  structural integrity  of the foundations  of all  existing bridges,  buildings, or
monuments. They  would also  be  located  so as to avoid  interference with any planned
underground facilities of the Washington Metropolitan  Area  Transit Authority.

In  general,  the  bedrock geology of  the area  involved  in the proposed storage tunnel
construction meets the  significant  criteria for  successful rock tunneling. As depth increases,
the rock types tend to become less weathered, and the secondary openings become tighter
and less  frequent. The  Washington area is  relatively  stable tectonically, and  no problems
traceable to rock deformation  or faulting  are anticipated. The geology of the area  and
its  impact on tunneling are discussed in more  detail in Appendix A.
                                         61

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Material excavated during tunneling would be transported to the surface through the vertical
shafts. Depending on  its  quality, this material  could be used for landfill or as concrete
aggregate. If so used, it could substantially reduce the construction cost of this alternative,
but in the cost comparisons to be presented in a later section of this report, the excavated
material  will be  considered  as  being hauled  away  as  waste.

Recent developments  in  the tunnel construction  and the  tunneling  equipment  fields
contribute to the feasibility of this approach and to the realistic consideration  of available
maximum tunnel diameters.  Tunneling equipment, or "moles", capable  of boring 28-foot
diameter tunnels are already in use, and those providing 32-foot diameter bores are in
the  design stage and  should be ready  within  a few  years. Therefore, the size of the
conveyance  tunnels  would  present no added problem  in the drilling operations.

The Conveyance  Tunnel/Mined  Storage approach has many of the conceptual features of
the  Chicago  Deep Tunnel Plan. The Chicago Plan also incorporates a  pumped storage
hydroelectric  generating system to provide additional electric  power  during the  peak
consumption  periods.  However,  preliminary   investigation   has  indicated  that   such
supplementary power generation is not economically feasible for the Washington D.C.  area.
Therefore,  power generation has not been included  in the  Conveyance Tunnel/Mined
Storage alternative.

     Mined Storage  Considerations

The mined storage would consist of a network  of criss-crossed chambers at atmospheric
pressure. Conventional deep-mining methods (i.e., drilling and  blasting to remove the rock)
and mine-railroad or rubber-tired earth-moving equipment to convey the excavated material
to the access shaft would be used in construction of this mined-storage area. Storage area
would be compartmented, with some compartments used as settling basins to facilitate
solids removal. The chambers would be concrete-lined only in areas where faults or fractures
would otherwise  permit excessive inflow  of ground water. Final design, as with the  final
design  of  tunnels,  would  depend  on  data  collected during   sub-surface geological
investigation.

     Pumping  Station  Considerations

A pumping  station  would be included with  each storage system  either at  the bottom
of one of the vertical shafts, or in a specially-excavated chamber nearby. The shaft involved
would have elevators, discharge  piping, ventilation, and electrical  conduits. The design of
the pumping system would  be  based on the capability of the existing sewer system to
handle the stored overflow after the storm subsides.  This capability in turn would be
influenced by  variations in the dry-weather flow, and the pumping of the stored overflow
would have to be programmed to coordinate with the off-peak hours of normal dry-weather
flow.
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     Solids  Removal  Considerations

If  the tunnels are constructed on a  reasonable slope,  sufficient flow velocity  will result
to convey most of  the  solids to the  mined-storage  area. The  initial chambers in the
mined-storage area will provide sedimentation and will concentrate the deposition of solids
there rather than uniformly over the  entire bottom of the mined-storage area. This should
permit effective removal of at least the lighter solids by pumping.  If the removal of heavier
solids in this manner presents a  problem, their  removal may be effected at the point
of overflow  by using vortex separators  (compact, cyclone-type  equipment that  remove
grit with centrifugal force). The separated  grit would be discharged as a slurry to a classifier
which washes and dewaters the grit for  pickup  by truck.
                                          63

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                   Application of  Alternative Approaches to D.C.

General

It is especially fitting to evaluate each of the four approaches by individual sewer drainage
basins  because the method selected  to deal with the combined sewers in  one part of the
District does  not have to  be the  same  method  used  in  another part. Actually,  the
appropriate  solution to the total  combined sewer problem  in the District may include
features from each of these four methods.

Although  it is possible to apply  each  of these four approaches at any  sewer drainage
district, physical and economic factors dictate that only one or two  methods be employed
for  each district. The very large volume of overflow from certain districts  in combination
with existing  land use requires the  use of mined storage rather than reservoir storage if
a storage  method is used. The proximity of some overflow points or existing land  use
suggests  that  certain districts be interconnected.    Because the available  or proposed
interceptor capacity is quite large in  places, it is appropriate to use this capacity to convey
combined sewer flow from certain districts during storm conditions  to a more centralized
storage facility at a subsequent point  in  the  sewer  system.

For the purpose of this evaluation, the District was divided into two large  drainage basins,
Anacostia and  Rock Creek-Upper Potomac. The basic layout of the alternative systems
was based on retaining and treating the  overflow  from the 15-year, 24-hour storm (see
Table 5);  however, the same design  should apply to  other  major return frequencies with
the exception that certain dimensions  (e.g., tunnel  diameter)  will  change.

Anacostia River Area

    Conveyance Tunnels and  Mined Storage

The basin layout for this approach  is shown  in  Figure 16. Essentially  the plan proposes
the dropping of all overflows  through vertical  shafts into conveyance tunnels that empty
into a  single mined-storage area near the  Robert F. Kennedy Stadium.  As mentioned in
the description  of the present D.C. sewer system (in Section  IV of this report)  and as
shown  in  Table 2, the Northeast Boundary Trunk Sewer does not have sufficient capacity
to  convey the  runoff from  a 15-year  storm. The  District of Columbia currently  has
preliminary  plans  to construct a  relief sewer  in the Northeast Boundary area at a cost
of $33,600,000  (1968 dollars, ENR = 1117); however,  the  relief sewer would behave as
a combined sewer for a considerable period of time until sewer separation  was completed.
Even  after  complete separation,  the  relief  sewer would discharge with each storm a
considerable  pollution  load represented  in the runoff  from  a  drainage area one  half as
large as the  G-2 district.

The construction of storage facilities in the upper and central  reaches of the  G-2 sewer
system would not only provide additional storage  capacity,  but more importantly, could
also provide sufficient relief to ease surcharging during the 15-year storm.  In contrast
with the relief sewer, the relief/storage system has the added feature of preventing discharge
of  untreated runoff and  sanitary  sewage  to  surface streams.

A  recent  study  (6)  proposed  a combination relief/storage tunnel  in the  central part of
the sewer district as presented  in  Figure 17.  This tunnel  would  reduce  most  of  the
                                         64

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o
CJ1
                                                  EAST SIDE INTERCEPTOR
                                                  RELIEF  SEWAGE PUMPING
                                                  STATION
             LEGEND
   "	— 'POLITICAL BOUNDARY
   —— COMBINED SEWERS
                                                                             llhllUIIHIMIH SANITARY SEWERS
                                                                             ,_._,_.» OTHER EXISTING SEWIRS
                                                                                      (COMBINED AND SEPARATED)
                                                                               A-10    SEWER DISTRICT NUJMCt
                                                                             —_-^--^ LIMITS OF COMBINED SEWER SYSTEM IN 1970
                                                                             -—	 SEWER DISTRICT BOUNDARIES
                                                                                D     PUMPING STATIONS
                                                                             »^~^~^« TUNNEL
                                                                                £    VERTICAL SHAFT
                                                                                •    PUMPING STATION

                                                                                      MINED STORAGE
                                                                             NO.
                                                                                          NAME
E-3  B ST.-NEW JERSEY AVE. TRUNK SEWER D/S PORTION
F-l  TIBER CREEK
G-2  NORTHEAST BOUNDARY
G-3  BARNEY CIRCLE
G-4  UTH ST.-PENNA. AVE.
G-5  12TH ST.-9TH ST.
G-7  6TH ST.-7TH ST.
                                                                           1500
                                                                                      1500  3000   4500
                                                                                      SCALE IN FEET
                                                                                                      6000
             DISTRICT   OF  COLUMBIA
                    TUNNELS  AND MINED STORAGE  IN
                         ANACOSTIA  RIVER  BASIN
                                                                                                               FIGURE 16

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                                   FIGURE 17

          LOCATION OF NORTHEAST BOUNDARY RELIEF/STORAGE TUNNEL
                                                       MICHIGAN
                                                       AVE.
                                            MC MILLIAN
                                            RESERVOIR
                                UNION
                                STATION
LEGEND

 ^??' - TUNNEL AREA


      - VERTICAL SHAFT


      - PUMPING STATION
NO SCALE
PUMPING
STATION
                                    66
                                                                          17

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surcharging in this sewer district; however, it would not provide total relief. It is conceivable
that construction of only part of the proposed relief sewer or some strategically located
storage reservoirs, in combination with the relief/storage tunnel, could prevent surcharging
at a lower cost than  the  entire relief sewer. It  is also possible that a different tunnel
layout, with  tunnels running perpendicular to the trunk sewer but beneath  critical branch
sewers,  may  also prevent surcharging at a lower cost.

The other basic components of the tunnel and  mined-storage  approach  include:

     1.    A 20- to 22-foot I.D. tunnel extending from the Main Sewerage Pumping Station
          on  the west bank of  the Anacostia River  northeastward  (parallel to the river)
          to  the  vicinity of the Robert  F.  Kennedy Stadium.  The total  length of the
          Anacostia  conveyance  tunnel  would be approximately 10,600 feet. The first
          3,900 feet  (starting from the Main Sewerage Pumping  Station) would be 20
          feet I.D., and  the  remainder would be 22 feet I.D. Figure 18 provides a profile
          of  this tunnel.

     2.    A  3,700,000-cubic yard  mined-storage area  in  bedrock near the Robert  F.
          Kennedy Stadium. This underground storage facility,  to be located beneath the
          parking  lot of the Robert F. Kennedy  Stadium, would eliminate the need for
          a separate tunnel  or other facility to convey the extremely  large  flow from the
          Northeast  Boundary Trunk Sewer. This location for the mined  storage would
          also relieve  portions of  the Northeast  Boundary Trunk Sewer during periods
          of  high  flow.

     3.    An  underground  pumping station and  a series of vertical overflow and access
          shafts.

     Storage  Reservoirs

Figure 19 shows the basic  layout of a storage system incorporating shallow underground
reservoirs wherever they are reasonable. Storage  reservoirs are not applicable throughout
the Anacostia River area; they would be attractive only for the Sewer Districts with smaller
flows,  namely G-3,  G-4, G-5, and G-7.  The required capacities  for these concrete  tanks
range from  800,000  gallons to 28,000,000 gallons.

The very large volume  (490 million  gallons)  and overflow rate (5.5  billion gallons per
day) from sewer district G-2 dictate the  use of an  underground mined-storage chamber
beneath  the  overflow point near Robert F. Kennedy  Stadium as  the most effective means
of capturing  the overflow from the Northeast Boundary Trunk Sewer. This mined-storage
area is similar to the mined-storage area proposed before, except that the capacity  is not
as large.

For Sewer Districts F-1 and E-3, existing land use and  the high volume (230 million gallons)
of overflow for the outfall at the Main Sewerage Pumping Station dictate that the overflow
at these  two structures  be  conveyed to the east side of the Anacostia River for retention
in a mined-storage facility. These mined-storage areas are suggested only if storage reservoirs
are utilized  in the Anacostia River; otherwise, a single  larger mined-storage area near the
stadium  is suggested.
                                          67

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                                            FIGURE  18
                          CONVEYANCE TUNNELS AND MINED STORAGE
                 ANACOSTIA RIVER TUNNEL  PROFILE   (SEE  FIGURE  16 FOR PLAN)
                             VERTICAL
                             SHAFTS
EAST  SIDE
INTERCEPTER
ROBERT  F.  KENNEDY   E»ST SIDE
STADIUM         /"RELIEF
                   INTERCEPTER
                                                                                           -100
                                                                                           -300
MAIN  SEKERAGE
PUHPING  STATION
              RAVEL,SAND.
             SILT.AND CLAY
                                                                                           0   SEA LEVEL
                                                                                           -350
                                                                                           -400
                        G-5        G-4      C-3

                       20 1.0.  TUNNEL
     PUMP STATION
     WITH ACCESS
     SHAFT
   7
   G-2
MINED
STORAGE
                                                                                        == -450
                                                                                           -500
                                                                                           -550
                                                                                           -600
                            li'  i 0  TUNNEL
                                                                                       FIG
                                                 68
                                                                                              18

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            •£ -
                                     EAST SIDE  INTERCEPTOR
                                     RELIEF  SEWAGE PUMPING
                                     STATION
         LEGEND
     POLITICAL BOUNDARY
     COMBINED SEWERS
                                                                IIIIIMllll	 SANITARY SEWERS
                                                                ,_._._,. OTHER EXISTING SEWERS
                                                                        (COMBINED AND SEPARATED)
                                                                  A-10    SEWER DISTRICT NUMBER
                                                                ,~-»_-^ LIMITS OF COMBINED SEWER SYSTEM IN 1970
                                                                	_ SEWER DISTRICT BOUNDARIES
                                                                   D    PUMPING STATIONS
                                                                        STORAGE RESERVOIRS
                                                                        STORAGE TUNNELS
                                                                        MINED STORAGE
                                                                NO.

                                                                E-3
                                                                F-l
                                                               G-2
                                                               G-3
                                                               G-4
                                                               G-5
                                                               G-7
B ST.-NEW JERSEY AVE. TRUNK SEWER D/S PORTION
TIBER CREEK
NORTHEAST BOUNDARY
BARNEY CIRCLE
14TH ST.-PENNA. AVE.
12TH ST.-9TH ST.
6TH ST.-7TH ST.
                                                              1500
                                                                        1500  3000   4500
                                                                        SCALE IN FEET
                     6000
DISTRICT    OF   COLUMBIA
  MAXIMUM  USE OF STORAGE RESERVOIRS IN
            ANACOSTIA RIVER BASIN
                                                                                                 FIGURE 19

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The relief/storage tunnel in  the central  reach  of the Northeast Boundary Trunk Sewer
is  required in view of the surcharging frequency of this sewer; however, in this approach,
total  use of  storage  reservoirs rather than a tunnel  may  be desirable.

An independent  study (6) of the G-2 Sewer District has  identified  a feasible location
for a large storage reservoir  near the  Robert F. Kennedy  Stadium. This location could
be  developed into a  storage  capacity of  235 million  gallons. While this is  not  sufficient
for the overflow  from the 15-year, 24-hour storm, this storage capacity plus the capacity
of  the  relief tunnel would  be more attractive than  mined storage for design storms of
less overflow volume.

     Treatment at Overflow  Points

The conceptual  design  of this approach  essentially  follows the  layout for  the storage
reservoir approach, except that treatment plants are required  near points of storage. The
locations of the treatment facilities are shown in Figure 20. As stated before, the treatment
plant capacities are sufficiently large to draw down each filled storage facility within five
days.

The most attractive feature  of this  method  is that  is provides facilities to treat stored
overflow. As  mentioned in the discussion of the D.C. sewage treatment facilities, the average
dry-weather flow to  the only sewage treatment  facility within the District  will exceed
the ultimate  capacity at this plant  in  1977.  While the Blue Plains plant can handle for
short  durations flow  in excess of this ultimate capacity,  the plant will not be able  to
fully treat all increased flows when stored overflow is  returned to the sewer system  unless
some  of the  dry-weather flow to this plant is diverted  and treated elsewhere. Hence,
treatment facilities at overflow points will probably  be needed.

A  recent study (6) has suggested  an  approach for the Northeast Boundary Trunk Sewer
District (G-2) similar to the method of treating at overflow points,  except that the project
would serve  many  purposes  other than pollution abatement. The project  is referred  to
as  the Kingman  Lake  Project.  It envisions the retention of  overflow from the G-2 sewer
district  in a  surface  reservoir, followed by treatment of the stored overflow and reuse
for recreational purposes, e.g., swimming and fishing. The  degree  of treatment  required
at  the Kingman Lake  treatment facility is obviously higher; but other than this, the features
of the  Kingman  Lake project follow exactly  the basic concepts suggested  in this study,
i.e., relief  tunnel and  surface storage,  possibly  augmented with mined  storage.  The
EPA/WQO, the National Park  Service, and the District of Columbia have shown considerable
interest in this project since  it would bring a much needed  recreational  park to the urban
dweller  and would rid the  urban area of  a  serious  source of pollution.

Another attractive  feature of local  treatment,  is  that  treatment  plants can be  located
underground  near some of the artificial pools in Washington that  sometimes are polluted
by  storm water runoff. Treatment of the pool water will restore their beauty rather than
let  debris and biotic  growths  accumulate.
                                         70

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•f)   -^
EAST SIDE INTERCEPTOR
RELIEF  SEWAGE  PUMPING
STATION
                 "**-\
                         *v
                                                                        LEGEND
                                                              '	•— POLITICAL iOUNDARY
                                                              ——— COMIINED SEWERS
                                                            NIIIIIIIIIIHIIII SANITARY SEWERS
                                                            ,_,„,_,. OTHER EXISTING SEWERS
                                                                    ICOMIINED AND SEPARATED)
                                                              A- 10    SEWER DISTRICT NUMBER
                                                            *-.—«-—•. LIMITS OF COMBINED SEWER SYSTEM IN 1970
                                                            - • -- SEWER DISTRICT BOUNDARIES
                                                               D    PUMPING STATIONS
                                                                    TREATMENT FACILITIES
                                                                    STORAGE TUNNELS
                                                                    MINED STORAGE
                                                            NO.
                                                                          NAME
                                                            E-3  B ST.-NEW JERSEY AVE. TRUNK SEWER D/S PORTION
                                                            F-l  TIBER CREEK
                                                           G-2  NORTHEAST BOUNDARY
                                                           G-3  BARNEY CIRCLE
                                                           G-4  UTH ST.-PENNA. AVE.
                                                           G-5  12TH ST.-9TH ST.
                                                           G-7  6TH ST.-7TH  ST.
                                                          1500
                                                             1500   3000  4500
                                                             SCALE IN FEET
                                                                                   6000
DISTRICT  OF  COLUMBIA
     TREATMENT  AT OVERFLOW  POINTS IN
           ANACOSTIA  RIVER BASIN
                                                                                           FIGURE 20

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Rock Creek   Upper  Potomac Area

     Conveyance Tunnels and Mined Storage

The  basic layout for this approach is shown in  Figure 21. Essentially the plan proposes
the dropping of all overflows  through  vertical shafts into conveyance tunnels that empty
into  a single mined-storage area near Water Gate. The basic components of  this system
include:

     1.   A 15- to 18-foot I.D. tunnel extending from  the outfall  of the  Piney Branch
         Trunk Sewer  in  a southerly direction  (approximately parallel to Rock Creek)
         to the vicinity  of the Water Gate. The total length of the Rock Creek conveyance
         tunnel would be approximately 19,800 feet, of which the first 4,600 feet (starting
         from D-4) would be 15  feet I.D. The profile of this tunnel is shown in Figure
         22.

     2.   A 2- to 7.5-foot I.D. sewer/tunnel extending from the intersection of 36th Street
         NW  and  the Potomac  River eastward to intersect with the Rock  Creek Tunnel
         near  New Hampshire Avenue NW (see  Figure 23). The Upper Potomac tunnel
         would be 5,300 feet long, of which the first  1,600 feet would be  24-inch sewer
         pipe  and the remainder 7.5-foot I.D. tunnel.

     3.   A 1,100,000-cubic yard  mined-storage area in bedrock beneath Water Gate plus
         a  pumping  station.

     4.   A vertical shaft at each  point of overflow. Three 30-foot diameter access shafts
         are contemplated, one each in sewer districts A-10, D-4, and E-2.  The E-2 shaft
         would have the  additional  function  of providing  space  for  the  pumping
         equipment.  There will be  no overflow  from  a  number of  sewer districts along
         the  eastern  lower part of Rock Creek (e.g., Districts D-13 through D-16 and
         part  of  C-25)  due  to  the large interceptor capacity available and the relief
         resulting  from  capture  of flow upstream. Any plan in the Rock  Creek Area
         should propose routing  this  flow directly to the Blue Plains plant  rather than
         retain it  in any  storage facility.

     Storage Reservoirs

Figure 24 shows the  basic layout  of a  storage system incorporating as many underground
storage  reservoirs  as reasonable.  Storage  reservoirs offer promise in  the  vicinity  of
Georgetown; however, in other parts of the Rock Creek-Upper Potomac area, tunnel tunnel
storage  and mined storage are indicated.

Storage reservoirs would  be attractive only for the sewer districts with smaller flows: A-10,
A-11, A-12, B-6,  B-7, and C-25.  Because of the present land  use in the vicinity of the
A-11  overflow  point,  it would be  necessary to convey  the overflow to the A-10 overflow
point for reservoir  storage or treatment. Likewise, districts B-6 and B-7 should be combined.
The  required  capacities  for these concrete tanks range  from  3,000,000 to  21,000,000
gallons.

The  large volume  (160  million gallons) and high flow rate (2.7 billion  gallons per day)
from the overflow  point at Piney  Branch  (D-4)  indicate  that mined  storage or a network
of underground tunnels would  be  the  most effective  method of  handling the storm


                                         72

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-J
CO
                                                                           Illlllllllllllllfl
                                                                              A-10
            DISTRICT  OF  COLUMBIA
                  TUNNELS AND MINED STORAGE IN
                 UPPER  POTOMAC-ROCK CREEK BASIN
        LEGEND
    POLITICAL BOUNDARY
    COMBINED SEWERS
    SANITARY SEWERS
    OTHER EXISTING SEWERS
    (COMBINED AND SEPARATED)
    SEWER DISTRICT NUMBER
    LIMITS OF COMBINED SEWER SYSTEM IN 1970
    SEWER DISTRICT BOUNDARIES
    PUMPING STATIONS
    TUNNEL
    VERTICAL SHAFT
    PUMPING STATION

    MINED STORAGE
NO.
A-10
A-ll
A-12
B-6
B-7
C-25
D-4
D-5
D-6
D-7
D-8
D-9
D-10
D-ll
D-12
E-2
    NAME

37TH ST.-GEORGETOWN
GEORGETOWN
K ST.-WISCONSIN AVE.
M ST. -27TH ST.
28TH ST.-WISCONSIN AVE.
SLASH RUN (PART]
PINEY BRANCH
OAK ST.-MT.PLEASANT ST.
INGLESIDE TER.
PARK RD.
LAMONT ST.
KENYON ST.
IRVING ST.
QUARRY RD.
ONTARIO RD.
EASBY POINT
                                                                               1500
                                                                                         1500   3000
                                                                                         SCALE IN FEET
                    4500   6000
                                                                                                             FIGURE  21

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  200
                                                                            FIGURE  22
                                                         CONVEYANCE TUNNELS  AND MINED STORAGE
                                                   ROCK CREEK TUNNEL PROFILE  (SEE  FIGURE  21  FOR PLAN!
                                  XISTING POTOMAC  RIVER
                                  FORCE MAINS
                                             UNCONSOLIDATEO
                                                                        (30'  DIAMETER
                                                                         FOR  ACCESS)
           ZONE OF
           DISINTEGRATED  ROCK
                                                                           r~^-^-^rI.~=--^=r=-- SHIFTS
                                                          7.5'  I.D.
                                                          UPPER  POTOMAC
                                                     __-: /  TUNNEL
                                                         :SEE FIGURE 4B:
(30' DIAMETER
 FOR ACCESS)
-250-
                                   E-
                                                                     C-  5
     22
                                                                                                                  D 11 D 9

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                                  FIGURE 23
                CONVEYANCE TUNNELS AND MINED STORAGE
        UPPER  POTOMAC  TUNNEL PROFILE  (SEE  FIGURE  21  FOR PLAN)
         UNCONSOLIDATED
         MATERIAL
       24"I.D.SEWER
           BEDROCK
(CAM EXPECT SOME OUTCROP
 OF BEDROCK,AND ZONES
 OF UNCONSOLIDATED
 MATERIAL APPROX.30-40'
 THICK)
                               ZONE OF DISINTEGRATED
                               ROCK
                                                        S= 0  SEA LEVEL
                                                                8'  I.D. ROCK CREEK
                                                               TUNNEL
                                                               (SEE  FIGURE  22)
                                                              150
                           ^f^_:: .IT .~^C_! ~^ n.--^i:=L ^ 7.5 •  I.D.  TUNNEL
                         A-10
A-ll   A-12 B6.B7
                                                   r~—"^  -200
                                        75
                                                                            23

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-J
O)
                                                                                         LEGEND
                                                                               	-— POLITICAL IOUNDARY
                                                                                     COMIINED SEWERS
                                                                            IIINNHMNMI SANITARY SEWERS
                                                                            1 —,_1 —.. OTHER EXISTING SEWERS
                                                                                     ICOMUNED AND SEPARATED)
                                                                               A-10    SEWER DISTRICT NUMtER
                                                                            *—~*~,-~* LIMITS OF COMIINED SEWER SYSTEM IN 1970
                                                                            —	SEWER DISTRICT lOUNDARIES
                                                                               Q     PUMPING STATIONS
                                                                               H    STORAGE RESERVOIRS
                                                                                     STORAGE TUNNELS
                                                                                     MINED STORAGE
NO.
A.10
A-ll
A-12
B-6
B-7
C-25
D-4
D-5
D.6
D-7
D-8
D-9
D-10
D-ll
D-12
E-2
    NAME
37TH ST.-GEORGETOWN
GEORGETOWN
K ST.-WISCONSIN AVE.
M ST. -27TH ST.
28TH ST.-WISCONSIN AVE.
SLASH RUN (PART)
PINEY (RANCH
OAK ST.-MT.PLEASANT ST.
INGLESIDE TER.
PARK RD.
LAMONT ST.
KENYON ST.
IRVING ST.
QUARRY RD.
ONTARIO RD.
EASBY POINT
                                                                                1500
                                                                                           1500   3000
                                                                                          SCALE IN FEET
                    4500   6000
             DISTRICT   OF   COLUMBIA
               MAXIMUM USE OF STORAGE RESERVOIRS IN
                  UPPER  POTOMAC-ROCK  CREEK  BASIN
                                                                                                              FIGURE 24

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overflow. Since the D-5 outfall is only about 300 feet downstream of D-4 and since the
D-5  overflow volume would  be small, it is logical to combine  the overflows from these
two  districts and collect them in the  underground  storage required  for D-4. Likewise,
mined storage  is indicated for sewer  district E-2 by itself if storage reservoirs  are  used
in the Georgetown  area. The close proximity of the points of overflow from sewer districts
D-8  through D-12  and  the relatively low  hydraulic characteristics make it advantageous
to connect these overflow points by means of tunnels (or conventional cut-and-fill sewer
construction).  Likewise, districts  D-6 and  D-7 should be connected in a similar manner.
Having  connected  these districts,  simply  expanding  the  connecting system  into shallow
tunnel  storage  is  probably   less expensive  than  construction of  storage reservoirs.
Nevertheless, the small  volume of overflow (less than three million gallons) from these
seven districts  indicates that  the  costs to  control their overflow is minor in comparison
to other sewer districts.

     Treatment at  Overflow  Points

Again, the conceptual design  of this approach follows the layout for the storage  reservoir
method, except that treatment facilities are required near points of storage. The locations
of the  required  treatment facilities  are shown  in Figure 25. Again, the most attractive
feature  of this approach  is that  it  provides facilities for treating stored overflow.
                                          77

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00
                                                                                        LEGEND
                                                                              ' --- — POLITICAL lOUNOAiY
                                                                                    COMIINED SfWfIS
                                                                            IIIIMMIMIimil SANITAIY SfWEIS
                                                                            ._._,_.. OTMfl EXISTING SEWERS
                                                                                    (COMBINED AND SEPARATED)
                                                                              A. 10   SEWER DISTRICT NUMIER
                                                                            «— «^_—». LIMITS OF COMUNED SEWER SYSTEM IN 1970
                                                                            - ---- SEWEi DISTRICT IOUNDARIES
                                                                               O    PUMPING STATIONS
                                                                                    TREATMENT FACILITIES
                                                                                    STORAGE TUNNELS
                                                                                    MINED STORAGE
NO.
A-10
A-11
A-12
B.6
B-7
C-25
D-4
D-5
D-6
D-7
D-8
D-9
D-10
D-ll
D-12
E-2
    NAME
37TH ST.-GEORGETOWN
GEORGETOWN
K ST.-WISCONSIN AVE.
M ST. -27TH ST.
28TH ST.-WISCONSIN AVE.
SLASH RUN (PART]
PINEY BRANCH
OAK ST.-MT.PLEASANT ST.
INGLESIDE TER.
PARK RD.
LAMONT ST.
KENYON ST.
IRVING ST.
QUARRY RD.
ONTARIO RD.
EASBY POINT
                                                                               1500
                                                                                          1500  3000
                                                                                         •SCALE IN FEET
                    4500  6000
             DISTRICT    OF   COLUMBIA
                  TREATMENT AT OVERFLOW  POINTS IN
                   UPPER POTOMAC-ROCK  CREEK  BASIN
                                                                                                            FIGURE  25

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                                    SECTION VII

                   EVALUATION  OF FEASIBLE ALTERNATIVES

                                       General

The  preceding sections of this report have defined the variability and impact of combined
sewer overflows in the  District and have presented four approaches for dealing with the
problem. From these approaches, it is possible to develop numerous alternative strategies
within the  District for collecting, storing, and treating overflow. For example, one strategy
may involve conveyance  tunnels and mined storage for the overflow from the 2-year,
24-hour storm in the Anacostia River area while calling for storage reservoirs and treatment
for the overflow from the 25-year 24-hour storm in the Rock Creek-Upper  Potomac area.

To provide a sound basis for decision-making, it is necessary to define the consequences
of promising alternatives in  detailed and comparative terms.  Costs  and  impact on water
quality  demand  the  most  attention,  but  non-quantifiable  aspects,  such  as public
convenience, also influence the selection  of the  appropriate solution. The four District-wide
approaches previously presented  in  Figures  16 thru 25 are considered sufficiently varied
to offer a  wide  choice  of strategies  throughout  the  District. The  approaches presented
were:

     1.   Maximum use of storage reservoirs
     2.   Treatment at points of overflow
     3.   Conveyance tunnels and  mined storage
     4.   Sewer separation

Again, it  is pointed  out that  the  approach selected for one sewer basin does not have
to be  used in  the other basins; the  appropriate District-wide  solution  may incorporate
features from each  of  these four  approaches.

The  following  sections  present the costs and  facilities  associated with individual sewer
districts for each approach. The  indicated reduction  in pollutant loadings for alternative
design-storm frequencies is  also indicated. Finally,  to  permit a  balanced assessment,
non-quantifiable  factors (those other than  cost and pollutant  reductions)  are discussed
and  compared.
                                         79

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                                    Cost Analysis

Construction Costs

Cost is an essential factor  in  selecting the appropriate alternative for abating combined
sewer overflows. Estimates have been made for the costs involved in the alternatives which
have been specifically discussed. A construction cost and  escalation contingency of 15
percent has been  included  in  all estimates, as  well as 6 percent  for engineering and 15
percent for resident inspection, bonding, etc.; but it should be noted that the cost estimates
do  not include Surveying,  Soils Investigations,  Land Acquisition, or Rights-of-Way.

If it will  take the  responsible agencies two years from the  time of release of this report
to act on appropriation of  funds  for any alternative (which is a reasonable assumption
in view of the magnitude and complexity of the  project),  construction would probably
start about the middle of  1973. To  assure that the cost  estimates are consistent with
that date, the total cost estimates  reflect  an Engineering News-Record Construction Cost
Index  of  1800, the projected index for June,  1973. The construction costs specific to
any  date  can be determined by multiplying the costs presented herein  by the ratio of
the then  current ENR index to 1800.

     General  Procedure

The same general procedure was used to estimate the construction costs of the alternative
methods of storage reservoirs, treatment at overflow points, and tunnel and mined storage.
First, a detailed cost estimate  was  made  of  the facilities required to handle the 15-year,
24-hour storm at each sewer  district.  This  was done for each of the three approaches
illustrated in  Figures  16  through   25.  This cost  analysis  included  preliminary on-site
inspection to  consider land  availability, terrain, etc.  in  selecting sites for facilities. All
the unit cost  estimates are  based on December  1969 costs  for similar construction, with
the total costs increased by  the ratio of the 1800 ENR index to 1300, the national average
during December  1969.

Following the analysis of the 15-year,  24-hour storm  graphs were  made  of total  costs
versus  capacity  relationships for the following components:

     1.   Storage reservoirs and  appurtenant equipment
     2.   Tunnels
     3.   Mined storage
     4.   Vertical  shafts
     5.   Treatment plants
     6.   Pumping  stations

The many different capacities required for the  various sewer districts provided a suitable
span of plotting points. These costs  curves were then used to estimate the costs for handling
the overflow from each sewer district for the 2-year, 5-year, and 25-year frequency, 24-hour
duration  storms.

     Storage  Reservoir Construction Costs

The storage reservoirs would be shallow-underground, multi-cell, concrete tanks. Figure
26 shows  the  relationship for construction costs of reservoirs and  appurtenant equipment
versus  capacity. Typical  costs range  from  $900,000 for  a 600,000-gallon  reservoir to


                                         80

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                       FIGURE 26

            TOTAL CONSTRUCTION COSTS OF

  STORAGE RESERVOIRS AND APPURTENANT EQUIPMENT

                       ENR= 1800
20
10
 1
 .2    .3  .4  .5 .6  .8  1        2    3  4  5  6   8  10     20   30

                 STORAGE  CAPACITY, MILLION GALLONS
                             81
26

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for a  32,000,000-gallon  reservoir.  The  construction  costs include  the costs of  site
preparation,  excavation,   concrete,  backfill,  buildings,  landscaping,   roadways,  and
mechanical and  electrical construction.

Costs are based on  simultaneous  construction of all reservoirs.  Some advantage may be
gained by building only a  portion of the reservoirs at the beginning of the program.  The
knowledge and experience gained during the design and construction of the initial reservoirs
could be  used  to reduce the construction  costs  of subsequent reservoirs.

     Tunnel Construction  Costs

These costs were based  on up-dated bid prices of current tunnel  construction  projects
in Chicago and  California  in which  the boring  method  is utilized.  Information  obtained
from  one of  the largest manufacturers of  drilling equipment  indicated that the rapid
development of boring equipment will tend to moderate  increases in these  prices even
in the face  of rising costs. Figure 27 defines the unit  cost versus diameter relationships
for tunnel construction. The following important assumptions have been made  with regard
to construction  costs for  tunnels:

     1.    One machine would be used to construct  the Upper Potomac-Rock Creek tunnels,
          and  a separate machine for the Anacostia River  tunnel.

     2.    All tunnels would be concrete lined. (12" lining  at an unit cost of $100 per
          cubic  yard of  concrete).

     3.    Material excavated from the  the  tunnel would be hauled  away as waste at a
          cost of $5.00  per cubic yard.

     4.    Boring would be at  an  average  rate  of 36 feet  per day.

     5.    There  would be no salvage value for the  boring  machine or mucking  equipment.

If the quality of material excavated from tunnel  and mined-storage construction is such
that it  could  be used as a building material, the construction  costs would  be  reduced
substantially. The structural characteristics  of the material would be determined during
the sub-surface  investigation, and the physical properties (size and shape)  of the aggregate
would be determined at the time of construction.

Although  boring rates of  approximately 200 to 300 feet per day  have  been considered
possible in rock similar  to that underlying  Washington, an  average  of  36  feet  per  day
over the construction period  seems more reasonable for purposes of cost estimating.

Boring machines are  generally custom built for a particular project and may not be usable
on  a different  project.  For  this reason,   no  salvage  value has  been  allowed.  Other
equipment-muck cars, locomotives, dust, cable, etc.,-will have some small salvage value,
but this will be negligible  compared to total construction  costs.

The construction costs also include power and  labor. Labor  costs and concrete costs are
the most  significant, accounting for  over  60 percent  of all costs.
                                         82

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                          FIGURE  27

          UNIT CONSTRUCTION COSTS OF TUNNELS

                          ENR = 1800
     1500
c/o
I—
CO
1000

 900


 800


 700



 600
      500
        7.5
             10
     15        20

DIAMETER,   FEET
25
30  32
                            83
                                                            27

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     Mined  Storage  Construction Costs

Mined storage construction costs are based on  similar costs for underground mining and
include labor, equipment, and handling of excess material. The unit cost for mined-storage
construction is  about $20 per  cubic  yard but varies depending  on the volume to be
excavated.  Figure   28  illustrates  the  relationship   between  construction  costs   and
mined-storage capacity. This  curve  accounts only for the cost of mining and does not
include pumping stations  and vertical  shafts.

     Vertical Shaft  Construction  Costs

Three basic types of  vertical shafts are expected:

     1.   Relatively  small  shafts (for the smaller sewer districts) drilled from the ground
          surface to the tunnel.

     2.   Slightly larger  shafts,  five to  six feet in diameter, (for the larger sewer districts)
          to be constructed by  the raise-boring  method. The unit cost of these shafts
          is about $200-$250 per vertical  foot.

     3.   Large-diameter (30  feet)  shafts, to be used  for access by men and equipment
          as well as for  diverting flow to the tunnel.  Construction techniques  would be
          conventional slurry  trench or jacking methods.  Large-diameter shafts would also
          be used for  pumping  and appurtenant equipment. The unit cost of these shafts
          is about $5,000-$6,000 per  vertical foot.

     Pump  Station  Construction Costs

Pump station construction  cost estimates include the cost of pumping equipment, controls,
sludge facilities, superstructures,  heating, ventilating and electrical  work, instrumentation,
metering, inside piping and valves, and sitework. The cost of the access shaft for pumping
equipment  is  included in  the vertical  shaft construction costs.

     Treatment  Plant  Construction  Costs

The treatment process recommended is filtration preceded by sedimentation and followed
by  disinfection.  Three  cost  estimates were  developed  from  the costs of the major
components of 1-mgd, 10-mgd, and 100-mgd plants. Figure  29 illustrates the relationship
of total construction costs  to  capacity as suggested by these three estimates. For a 10-mgd
plant,  the costs (ENR =  1300)  of various  plant  components were as  follows:

                                                                Construction
                       Component                                   Costs
                                                                $  500,000
                Cnlormator and Contact Tank                              gg
                                                                     '
                Pumps                                               40'OQO
                Chemical Feed and Mixing                                gg QQQ
                Instruments, Electrical, Piping                             2?o'oOO
                Building                                             250:000

                „   .                                            $1,240,000
                Contingency                                          190.000

                TOTAL                                          $1,430,000
                                         84

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                     FIGURE 28

TOTAL CONSTRUCTION COSTS OF MINED STORAGE

                     ENR= 1800
200
CO
<=>
100
 90
 80

 70

 60

 50


 40



 30




 20
  0
   50  60 70 80 90 100        200    300   400 500


                  CAPACITY,  MILLION GALLONS
                                                    800 1000
                           85
                                                               28

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 00
 o>
ro
>o
                                                   FIGURE 29
                     TOTAL CONSTRUCTION COSTS OF TREATMENT PLANTS  VERSUS CAPACITY
                                                   ENR= 1800
                  10
                   9
                   8
                   7
                   6

                   5
3    4    5   6  7 8  910           20      30

   TREATMENT PLANT CAPACITY, MILLION GALLONS PER  DAY
40   50  60  70 80   100
              90

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Two important assumptions have been  made in determing the flow rate of the treatment
facility to be  located at each  overflow point:

     1.   The  maximum residence  period  in  a  storage  structure will  be five  days.

     2.   The  minimum  capacity of  a  treatment facility will be  0.2  mgd.

The relationship illustrated  in Figure 29 was used to determine the costs of the centralized
facilities required  to  treat stored overflow, in addition to being  used to  define the costs
of treatment  facilities at points  of overflow.

     Total Construction  Costs

The .four alternative District-wide approaches are  as  follows:

     1.   Maximum  use  of storage reservoirs
     2.   Treatment  at  points  of overflow
     3.   Conveyance tunnels and  mined storage
     4.   Sewer separation

Tables  12,  13, 14, and  15 present the construction  costs by individual sewer drainage
basins  for  the four approaches.  It must  be  emphasized again that  the  appropriate
District-wide solution may  include  features from each of these approaches. To facilitate
the selection  of this solution,  the  costs and facilities associated  with each approach  are
identified by  sewer  district.

As stated before,  these costs correspond to an ENR index  of  1800. Also, these costs
exclude the costs of dealing  with those sewer districts scheduled for separation prior to
1975.  However, budgeting  problems have stopped the program of  separating those sewer
districts: therefore, in the  final  analysis, the total costs in Tables  12 to  15 will have to
be increased.  The  incremental costs attributable to those sewer districts is probably slight
because their total  area is about 400 acreas, representing less than 4 percent of the collective
area of all  combined  sewer districts.  The added costs would  be from $6,000,000 to
$12,000,000,  depending on the design  storm, for  projects not involving separation, and
$27,000,000 for the separation project.

In the approach proposing treatment at overflow points, equalization storage in the amount
equal  to  the  total volume of  overflow would be required because the rate  of overflow
(even from the smallest drainage area) is extremely high. The cost of constructing treatment
facilities is,  therefore, in addition to the reservoir storage  construction  costs. The difference
in costs between this approach and the reservoir approach is explained by the economies
of scale resulting  from  constructing  a  single centralized treatment facility.  Inclusion of
the Kingman   Lake project  in  the  approach proposing  treatment  at points  of overflow
would increase the costs of the G-2 sewer district from $45,000,000 to $56,700,000 for
a  2-year,  24-hour design event. The relatively small increase in cost  for incorporating an
approach  that proposes  complete treatment is explained by the  fact that,  for the 2-year
design storm,  it is feasible  to construct  a sufficiently  large storage reservoir. In contrast,
the cost estimate  listed  in Table 13 for District G-2 was based on more costly mined
storage.
                                          87

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                                                                                          Table 12



                                                                              Maximum Use of Storage Reservoirs'
Sewer
District


A 10
All
A 12
B-6
B7
C25
D-4
0-5
D-6
D7
0-8
D-9
D-10
D-11
D 12
E-2

E-3
F 1
G-2
G-3
G-4
G-5
G-7
Storage Total
Northeast Boundary
Relief/Storage Tunnel
Centraliz-d Treatment
Plant
Total Construction Cost
Engineering Design at * 6%
Other Costs (resident
inspection, legal, bonding.
and administrative)
at J 15%
Total Project Costs^
Type of
Storage



Reservoir
Reservoir

Reservoir
Reservoir

Mined

Tunnel/Reservoir



Tunnel/Reservoir
Mined


Mined
Mined
Reservoir
Reservoir
Reservoir
Reservoir













2 Years • 24-Hour
Volume Cost
million
gallons


11. S 7,600,000
2 2,200.000

-
1 1,300,000

65 15,200.000

1.7 2,000.000



4.4 3.900.000
97 o 18,300,000


128 23,300,000
280 45,000,000
0.2 400,000
15 9,600,000
6 4,800,000
5 4,300,000
$138,000.000

27,000,000

10.000.000
175,000,000
1 1 ,000,000



26,000,000
$212.000,000
Estimated Capital Costs
IENH Index = 1800)
Storm Frequency and Duration
5 Years • 24-Hour 15Yei
Volume Cost Volume
million million
gallons gallons
Rock Creek - Upper Potomac E

15. $ 9,600,000 21
3 2,900,000 4

0.6 900.000 3
4 3,600.000 8

104 21.500,000 168

2 2,200,000 4



8.3 5,600,000 1 1
158 27,700,000 214
Anacostia River Basin

175 30,500.000 230
370 57,000,000 490
0.4 700.000 0.8
20 1 2,000,000 28
9 6,600,000 13
7 5.400,000 10
$186,000,000

27.000,000

10,000.000
$226,000,000
14,000,000



34,000,000
$274,000,000

ITS • 24-Hour
__Cast 	

lasln

$ 12.200.000
3,600,000

2,900,000
6.000,000

30,900.000

3.600.000



7,600,000
35,500,000


38,300.000
73.000.000
1,100.000
15,000,000
8,600,000
7,200,000
$246,000,000

27,000,000

16.000.000
$289,000.000
17,000,000



43,000.000
$349,000.000

25 Years - 24-Hour
Volume Cost
million
gallons


24 $ 13,800.000
4 3,600,000

4 3.600.000
11 7,600,000

190 33.300.000

4 3,600.000



14 9.100,000
260 41.700,000


270 43,900.000
560 82,000.000
1 1,300,000
32 17,000,000
IS 9,500,000
12 8,000,000
$278.000,000

27.000.000

18.000,000
$323,000,000
19,000,000



48,000,000
$380,000.000
'Basic layout illustrated in Figures 19 and 24.




       ''              ValU" ""' '"" '° "
                                              re"e" "V «.«W»W««O.WO. to reflec. the costs o, dealing with those sewer district, scheduled for
                                                                                              88

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         Table 13



Treatment at Overflow Points1
Sewer District

A-10, A-11
a. Storage
b. Treatment

A-12
a. Storage
b. Treatment

B-6, B-7
a. Storage
b. Treatment

C-25
a. Storage
b. Treatment

0-4, 0-5
a. Storage
b. Treatment

0-6, 0-7
a. Storage
b. Treatment

0-8, 0-9, 0-10,0-11,0-12
a. Storage
b. Treatment

E-2
a. Storage
b. Treatment


2 Years.


$ 7,600,000
600,000


3,200,000
170,000


...
...


1 ,300,000
100,000


15,200,000
2.100,000


2,000,000
150,000


3,900,000
300,000


18.300,000
2,900,000


24-Hour




$ 8,200,000


2,370,000







1 ,400,000



17,300,000



2,150,000



4,200,000



21,200,000
Estimated Capital Costs
(ENR Index = 18001
Storm Frequency and Duration
SYeai
Rock Creek •

$ 9,600,000
780,000


2,900,000
220,000


900,000
100,000


3,600,000
280,000


21,500,000
3.000,000


2,200,000
170.000


5,600,000
460,000


27,700,000
4,000,000

-s, 24-Hour
Upper Potomac Basin



$ 10,380,000


3,120,000



1,000.000



3,880,000



24,500,000



2,370,000



6,060,000



31,700,000
15Yei


$12,200.000
960,000


3,600,000
280,000


2,900,000
220,000


6,000,000
400,000


30,900,000
4,100,000


3,600,000
280,000


7,600,000
570,000


35,500,000
4,900,000

srs, 24-Hour




$ 13,160.000


3,880,000



3,120,000



6,400,000



35,000,000



3,880,000



8,170,000



40,400.000
25 Years,


$13,800,000
1,100,000


3,600,000
280,000


3,600,000
280,000


7,600,000
560,000


33,300,000
4,400,000


3,600,000
280,000


9,100,000
690,000


41,700,000
5,600,000

24-Hour




$ 14,900,000


3,880,000



3,880,000



8,160,000



37.700,000



3,880,000



9,790,000



47,300,000
Anacostia River Basin
E-3, F-1
a. Storage
b. Treatment

G-2
a. Storage
b. Treatment

G3
a. Storage
b. Treatment

G-4
a. Storage
b. Treatment

G-5
a. Storage
b. Treatment

G-7
a. Storage
b. Treatment
Storage and Treatment
Construction Cost
Northeast Boundary
Relief/Storage Tunnel
Total Construction Cost
Engineering Design at ± 6%

Other costs (resident
inspection, legal, bonding
and administrative) at ± 15%

Total Project Costs2

23,300,000
3,400,000

a
45,000,000
5,800,000


400,000
100,000


9,600,000
730,000


4.800,000
370,000


4,300,000
360,000















26,700,000



50,800,000



500,000



10,330,000



5,170,000

4,660,000

$155,000,000

27.000.000

$182,000,000
11,000,000



27.000,000

$220,000,000

30,500,000
4,200,000


57,000,000
7,300,000


700,000
100,000


12,000,000
900,000


6,600,000
540,000


5,400,000
440,000















34,700,000



64,300,000



800,000



12,900,000



7,140,000

5840QOO

$209,000,000

27.000.000
$236,000,000
14,000,000



35,000,000

$285,000.000

38,300,000
5,200,000


73,000,000
8,400,000


1,100,000
100,000


15,000.000
1,300,000


8,600,000
680,000


7,200,000
580,000















43,500,000



81,400,000



1,200.000



16,300,000



9.280,000

7,780,000

$273,000,000

27.000.000
$300,000,000

18,000,000



*t5,ooc.ooo
4363,000,000

43,900.000
5,800,000


82,000,000
9,500,000


1,300,000
100,000


17,000,000
1,500,000


9,500,000
750,000


8,000,000
650,000















49,700,000



91,500,000



1,400,000



18,500,000



10,250,000

8,650,000

$309,000,000

27,000,000
$336,000,000

19,000,000



50.000,000
$405,000,000
^ Basic layout illustrated in Figures 20 and 25.
2ln the final analysis, those values will have to be increased by $6,000,000-$! 2,000,000, to reflect the costs of
dealing with those districts scheduled for separation before 1975.
             89

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                                                            Table 14

                                              Conveyance Tunnels and Mined Storage'
 Overflow Volume, million
                   gallons
    Rock Creek
    Upper Potomac
    Anacostia River
 Costs
    1. Tunnel Construction
      a. Rock Creek
      b. Upper Potomac

    2. Vertical Shafts
      a. Rock Creek
      b. Upper Potomac

    3. Mined Storage

    4. Pumping Station
 Costs
    1. Tunnel Construction

    2. Vertical Shafts

    3. Mined Storage

    4. Pumping Station

    5. Northeast Boundary
      Relief/Storage Tunnel

      Sub-Total

 Centralized Treatment Plant

 Total Construction Costs

 Engineering Design at 6%

 Other Costs (resident
 inspection, legal, bonding
 and administrative) at ± 15%

 Total Project Costs
                                                     Estimated Capital Costs
                                                      (ENR Index = 1800)
                                                                          Storm Frequency and Duration
2-Year, 24-Hour
169
13
434
Rock Creek
$ 14,900,000
1,800,000
4,400,000
2,100,000
26,500,000
2,600,000
5-Year, 24-Hour
275
18
581
• Upper Potomac Area
$ 16,800,000
1 ,900,000
4,400,000
2,100,000
40,000,000
4,300,000
15-Year, 24-Hour
404
24
772

$ 18,200,000
2,000,000
4,400,000
2,100,000
57,000,000
6,200,000
25-Year, 24-Hour
487
29
890

19,000,000
2,100,000
4,400,000
2,100,000
67,000,000
7,600,000
Anacostia River Area
9,400,000
5,800,000
58,000,000
6,100,000
27,000,000
$159,000,000
10,000,000
$169,000,000
10,000,000
25,000,000
$204,000,000
10,400,000
5,800,000
74,000,000
8,300,000
27,000,000
$195,000,000
13,000,000
$208,000,000
12,000,000
31,000,000
$251,000,000
11,100,000
5,800,000
94,000,000
10,900,000
27,000,000
$239,000,000
16,000,000
$255,000,000
1 5,000,000
38,000,000
$308,000,000
11.500,000
5,800,000
108,000,000
12,600,000
27 000 000
$267,000,000
18000000
$285,000,000
17,000,000
43,000,000
$345,000,000
 Basic layout illustrated in Figures 16 and 21,
*ln the final analysis, these values will have to be increased by $6,000,000-$ 12,000,000, to reflect the cost of dealing with those sewer districts
 scheduled for separation before 1975.
                                                            90

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                               Table 15

                        Sewer Separation  Costs
                      (Based on the 15-Year Storm)

                        Estimated Capital Costs
                          (ENR Index = 1800)
  Sewer District                                         Separation Cost
A-10                                                    $    900,000
A'11                                                        9,400,000
A-12                                                         700,000
B-3                                                          500,000
B-4                                                         4,300,000
B-5                                                          600,000
B-6                                                         1,500,000
B-7                                                          300,000
C-23                                                         200,000
C-24                                                         500,000
C-25 (Small Part)                                            4,100,000
C-25 (Large Part)                                          20,500,000
C-26                                                         600,000
C-28                                                        1,500,000
C-29                                                        6,900,000
D-4                                                      97,000,000
D-5                                                        1,400,000
D-6                                                        1,200,000
D-7                                                        1,000,000
D-8                                                         800,000
D-9                                                        1,000,000
D-10                                                        5,600,000
D-11                                                        2,500,000
D-12                                                        1,900,000
D-13                                                        1,500,000
D-14                                                        2,300,000
D-15                                                        2,200,000
D-16                                                      35,000,000
D-17                                                         300,000
E-2                                                       28,000,000
E-3                                                       18,000,000
F-1                                                       49,000,000
G-2                                                     177,000,000
G-3                                                        1,300,000
G-4                                                      13,000,000
G-5                                                        7,700,000
G-7                                                        6,600,000

Total Construction Costs                                  $507,000,000^

Other Costs (resident inspection, legal, bonding,
 and administrative) at + 15%                               76,000,000

Total Projects Cost                                       $583,000,0002
1 Includes Engineering Costs
2ln the final analysis, this value will have to be increased by $27,000,000, to
 reflect the costs of separating those sewer districts scheduled for separation
 before 1975.

                                  91

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The construction costs for sewer separation have  been estimated from cost information
in the  1957  Board of Engineers Report (1).  The estimated costs, updated to an ENR
index of  1800, for separating those sewer districts scheduled after  1975 is $583 million.

Table  16  and  Figure 30  summarize the total construction costs  of  each District-wide
approach.  The costs of sewer separation is considerably higher than  the costs of the three
other approaches,  which are about  the same. The  alternative of total  use  of tunnels and
mined storage represents about a 10 percent cost  savings over the next lowest  approach.


                                           Table 16

                                      Preliminary Estimate
                                 Comparison of Total Project Costs


                         	Design Storm Frequency	
  Districtwide Alternative        2-Year           5-Year          15-Year          25-Year	

 Maximum Utilization of1    $212,000,000     $274,000,000     $349,000,000     $380,000,000
   Storage Reservoirs

 Treatment at Points of1       220,000,000       285,000,000      363,000,000      405,000,000
   Overflow

 Total Use of Conveyance1     204,000,000       251,000,000      308,000,000      345,000,000
   Tunnels and Mined Storage

 Sewer Separation2                                            583,000,000
 11n the final analysis, these values will have to be increased by $6,000,000-$ 12,000,000, to reflect the
  cost of dealing with those sewer districts scheduled for separation before 1975.
 ^In the final analysis, this value will have to be increased by $27,000,000, to reflect the cost of separat-
  ing those sewer districts scheduled for separation before 1975.

 Operating Costs

 Preliminary estimates of annual operating costs have been  prepared for each of the various
 alternatives and are presented in Tables 17 through 20.  These estimates are  prepared for
 the 15-year,  24-hour storm only.  The annual  operating costs for various alternatives are
 similar except  for  a significant difference  in  maintenance costs. The maintenance costs
 for the reservoir approach and the local treatment approach are higher because there are
 fourteen storage or storage-treatment facilities to be maintained, as compared to only two
 central storage facilities for the tunnel approach. The treatment plant cost for the  local
 treatment approach is higher  because this approach  requires many local plants rather than
 a  single centralized facility.

 The handling and  disposal of sludge  represents a significant cost for  all the  approaches
 except sewer separation. As  listed in  Table  10,  combined  sewer overflows will contain
 approximately 30,000 tons of dry  suspended solids per year. In any system utilizing storage
 or  in-line treatment, most of  these solids will be removed, and consequently will require
 handling  and disposal.
                                           92

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                                                              FIGURE  30

                                   INVESTMENT VERSUS DESIGN  STORM  RETURN  FREQUENCY

                                          FOR ALTERNATIVE DISTRICTWIDE APPROACHES
  CD
  CO
CJ
o
                            450,000
                            400,QOO
                       e/o
                       I—
                       00
                       a
                       CJ
                            350,000
                       _,   300,000
                            250,000
                           200,000
                                  2-YR.
        5-YR.               10-YR.      15-YR.


DESIGN STORM  FREQUENCY  (24-HR DURATION)
                                                       TREATMENT AT POINTS
                                                       OF OVERFLOW

                                                       MAXIMUM USE OF

                                                       STORAGE RESERVOIRS
                                                       TUNNELS AND MINED
                                                       STORAGE
25-YR.

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                              Table 17

                         Preliminary Estimate

                  Summary of Annual Operating Costs
                                 for
                  Maximum Use of Storage Reservoirs
                      for 15-Year, 24-Hour Storm


Administration                                            $  290,000

Labor
   Permanent Staff               $  200,0001
   Auxiliary Staff                   160,0001                 360,000

Maintenance
   Structures                    $  370,000
   Mechanical                     2,000,000
   Electrical &
     Instrumentation                730,000                3,100,000

Utilities
   Electrical  20,520 x 0.746 x 952 x $0.010/KWH               150,000

Treatment Plant (Additional Facilities to treat
   storm water flows at Blue Plains Plant or
   other location)
     Sludge Handling and Disposal                              750,000
     Operation and Maintenance - 4% of Capital Cost             640,000

       Sub-Total                                          $5,290,000

Operating Contingency at 5 Percent                             270,000

         TOTAL                                         $5,560,000
1
 Includes overhead and benefits
                                94

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                              Table 18

                         Preliminary Estimate

                  Summary of Annual Operating Costs
                                 for
                     Treatment at Overflow Points
                      for 15-Year, 24-Hour Storm


Administration                                           $  300,000

Labor
  Permanent Staff               $  170,0001
  Auxiliary Staff                   200,0001                370,000

Maintenance
  Structures                     $  370,000
  Mechanical                     2,100,000
  Electrical &
     Instrumentation                750,000               3,220,000

Utilities
  Electrical - 20,520 x 0.746 x 952 x $0.010/KWH              150,000

Filter System (per 1,000 gals.)
  Filter Replacement and
     Installation Cost             $0.08
  Operation arid Maintenance      0.10
  Power and Backwash            0.02
                975,000 x $0.20 = 195,000                    200,000

Treatment Plants
  Sludge Handling and Disposal                               750,000
  Operation and Maintenance - 4% of Capital Cost            1,500,000

       Sub-Total                                        $6,490,000

Operating Contingency at 5 Percent                           330,000

         TOTAL                                        $6,820,000
11ncludes overhead and benefits.
                                 95

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                              Table 19

                         Preliminary Estimate

                  Summary of Annual Operating Costs
                                 for
                 Conveyance Tunnels and Mined Storage
                      for 15-Year, 24-Hour Storm

Administration                                              $  250,000

Labor
  Permanent Staff                 $ 140,000]
  Auxiliary                          BO^OO1                   200,000

Maintenance
  Structures                       $400,000
  Access Shafts                      60,000
  Mechanical                       450,000
  Electrical &
    Instrumentation                 370,000                  1,280,000

Utilities
   Electrical - 23,850 x 0.746 x 952 x $0.010/KWH                170,000

Treatment Plant (Additional Facilities to treat
  storm water flows at  Blue Plains Plant or
  other location)
  Sludge Handling and Disposal                                  750,000
  Operation and Maintenance - 4% of Capital Cost                  680,000

         Sub-Total                                         $3,330,000

  Operating Contingency at 5 percent                             170,000

         Total                                              $3,500,000
'Includes overhead and benefits.
                                 96

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                                                         Table 20
CO
                                                   Preliminary Estimate
                                            Comparison of Annual Operating Costs
                                             Based on 15-Years, 24-Hour Storm
Administration

Labor

Maintenance

Utilities

Sludge Handling and Disposal

Treatment 0 & M Costs

  Sub-Total

Operating Contingency at 5 Percent

    TOTAL
Maximum Use of
Storage Reservoirs
$ 290,000
360,000
3,100,000
150,000
750,000
640,000
$5,290,000
270,000
Treatment at
Overflow
Points
$ 300,000
370,000
3,220,000
150,000
750,000
1,500,000
$6,490,000
330,000
Conveyance Tunnels
and
Mined Storage
$ 250,000
200,000
1,280,000
1 70,000
750,000
680,000
$3,330,000
170,000
                                                           $5,560,000
$6,820,000
$3,500,000

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This quantity is greater  than the quantity of solids generated  at the entire  Blue Plains
plant (26); therefore, the  quantity of  sludge from  combined sewer overflows probably
could not be handled entirely at the  Blue Plains plant. However, in view  of  the  general
problems  of  solid waste  disposal in the  Washington area, perhaps the same order of
sophistication will be required to handle the combined sewer sludge as is employed to
handle the sewage treatment plant sludge. To handle and dispose  of  one  ton  of  dry
suspended solids at the Blue Plains plant costs about $25.00 (26). This suggests that annual
costs of sludge disposal  for a combined sewer pollution abatement approach  (other than
separation) will  be $750,000.
                                        98

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                              Impact on Water Quality

Indicated Requirements

As  previously presented in this  report, the Water  Quality  Office of the Environmental
Protection  Agency has determined the maximum allowable contaminant loadings to  the
Potomac if water  quality objectives are to be met. These recommended loadings are quite
stringent, requiring, at  all  treatment  plants,  the  removal of at least 96  percent of 5-day
BOD, 96 percent  of phosphorus, and 85 percent of nitrogen. These  removals are based
on existing flows to these plants; as population increases, even greater degrees of treatment
will  be  required.

These reductions assume no other source of pollutants to the Potomac and no allowance
for combined  sewer overflow loadings.  Even  if these reductions are achieved  at  the
treatment plants,  the combined  sewer overflows (occuring fifty to sixty  times  a year)
will  in themselves result in loadings greater  than recommended. At times, these overflow
loadings  will be from  ten  to  thirty times greater than the recommended  loadings. It is
apparent that some measures must be taken to reduce the discharge of untreated combined
sewer overflow, or the water quality objectives will almost certainly fail to be achieved.

These  pollutant  reduction percentages  should  not apply  directly to  combined  sewer
overflows. A statistical analysis (6) indicates that a system of storage and treatment facilities
sized for the overflow  from the  one-year, 24-hour storm  will retain  over 99 percent of
the  long-term-averaged  annual volume of overflow.  Nevertheless, infrequent storms will
at times have an  overflow volume far in excess of  this storage capacity. This will result
in the discharge of a significantly high shock loading to the Potomac,  enough to  interfere
with many uses of the  river, possibly enough to result in the mass destruction of a desirable
fish  population  which may have reappeared with the cleansing of the Potomac. The  primary
decision  focuses not on selecting a reduction percentage but on selecting the storm event
and  degree  of control  for which storage and treatment  facilities will  be designed.

Reduction in Pollutant Loadings

The selection of the design frequency is  properly made  only in the context of basin-wide
water quality management. The  Potomac pollution problems to  which  combined sewers
contribute are interstate in scope, and require evaluation on a regional  basis. Many factors
beyond  the  scope of this  study, e.g. flow  augmentation, financing,  population  growth,
have too great an influence to be ignored. To provide part of the information basis upon
which this decision  is made, this  section of the report indicates the reduction in pollutant
loadings expected from storage  and treatment  facilities based on various design  storm
frequencies.

Although sewer separation will stop the discharge of untreated  sanitary sewage into  the
Potomac, a  significant loading will  still  occur with each  rainfall in  the form of storm
water  runoff. Table 10 shows that,  on an annual basis,  storm  water  runoff from  the
combined sewer districts accounts for more organic loading than the sanitary sewage in
the  overflow.  This effect, in combination  with the  extremely  higher costs, the long
implementation period, and the  public inconveniences  associated with  sewer separation,
tends to disqualify  the sewer-separation approach  as  a  feasible District-wide solution.
Therefore, the  remaining discussion of impact on water quality focuses on the other three
approaches.
                                          99

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A  two-year frequency is  suggested as the minimum design  frequency. While  a  two-year
design  frequency may seem small, it will retain and treat over 99 percent of the  expected
annual volume  of overflow on a long-term basis. Two reasons explain this seemingly high
value:

     1.  Practically all of the fifty to sixty overflows occurring yearly have volumes less
         than  the  volume  of  the  overflow from the  2-year, 24-hour storm.

     2.  The volume  of  overflow does not differ greatly among significant storms, e.g.
         a facility  designed to retain the overflow from the 2-year, 24-hour storm could
         retain 70 percent of  the overflow from the 5-year, 24-hour  storm.

Regardless  of the selected  design-storm  frequency,  there  exists the possibility, however
remote, of occurrence of  a storm which  would  result in  an overflow  in excess of the
design  storage and  treatment capacities.  Nevertheless, implementation  of  a program based
on  a design  storm  whose  recurrence  interval  is less  than 25  years may represent an
injudicious use  of public funds. On the other hand, the very high storm recurrence intervals
(50 years and more) are generally associated  only with projects involving immediate risk
of human  life  and/or  catastrophic property damage.

The abatement  of  pollution from  combined  sewers requires storage facilities. Since any
stored  flow  is to  be  treated, the quantity of retained overflow represents  a  practical
measurement of the reduction  in the  pollution load.  Figure 31  illustrates the reduction
in BOD, SS, PO/j,  or N  corresponding  to various retention capacities.  It was assumed
the percentage reduction  in any pollution load is equal to the percentage of the total
overflow collected, multiplied by the percentage removal  efficiency of  the subsequent
treatment  method  (assumed to be 85  percent).  Examination of Figure 31 shows that
facilities designed to handle a  2-year, 24-hour storm (and  provide 85 percent treatment)
will  provide  60 percent  treatment for a 5-year, 24-hour storm but only 38 percent for
a 25-year,  24-hour storm. Table 21 summarizes  some of the information illustrated in
Figure 31.

Figure 31  and  Table 21 illustrate the necessity of evaluating combined  sewer overflows
in terms of their true  impact as shock loadings. For example, effective  storage capacity
equal to the overflow from the two-year, 24-hour storm probably will reduce the expected
annual  loadings by just under 85 percent  (the maximum  possible). Nevertheless,  with  a
storage capacity equivalent to the two-year, 24-hour storm  it is expected that once in
five years a loading equal  to or exceeding 40 percent of the total loading  in the five-year,
24-hour storm  will  be  bypassed to the  river.  In terms of BOD, this represents a loading
of 80,000 pounds,  almost  five times the maximum  allowable daily  loading in the entire
metropolitan  Washington  area. Again,  it is pointed  out that this shock  form of loading
in combination  with the  long effective  residence times of estuarine  waters explains the
serious  impact  of combined sewer overflows in the Washington areal

In making the final analysis  of alternative  strategies.  Figure  31 can be used  with  the
information in  Tables  5 and  10 (in  the Problem Definition  section) to  determine the
pollutant loadings from any sewer district.  While this procedure requires some  simplifying
assumptions,  it  will provide  a sufficiently  accurate estimate of pollutant loadings for
comparison with other factors such as costs. Figure 32 represents the relationship between
investment and the discharge of BOD  for  three intense-storm  return frequencies. The
                                         100

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                         FIGURE  31
PERCENT REDUCTION IN POLLUTION LOAD FROM VARIOUS STORMS
                            VS
                ALTERNATIVE DESIGN EVENTS
        100
        80
         60
        40
         20
MAXIMUM REDUCTION












= 85%
V
\











X^
\ /
» » s
V*S? ^
» cT>
^i^p
*^'
»





V
v^
\'*
""•f '^!
m* ^
X
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^ »
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25 15 5











2
YEARS YEARS YEARS YEARS
                         DESIGN STORM EVENT
                             101
31

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                                                         Table 21


                        Comparison of 24-Hour Pollution Discharges from Various Return Frequency Storms

                                               for Various Design Frequencies
                                                                               Design Storm
o
N)
Storm
2-Year, 24-Hour Storm
BOD, Ibs.
TP, Ibs.
5-Year, 24-Hour Storm
BOD, Ibs.
TP, Ibs.
15-Year, 24-Hour Storm
BOD, Ibs.
TP, Ibs.
25-Year, 24-Hour Storm
BOD, Ibs.
TP, Ibs.
No
Treatment
1 60,000
1 2,000
200,000
13,000
250,000
14,000
280,000
15,000
2-Year,
24-Hour
24,000
1,800
80,000
5,000
140,000
8,000
1 70,000
9,000
5-Year,
24-Hour
24,000
1,800
30,000
2,700
93,000
5,000
130,000
7,200
15-Year,
24-Hour
24,000
1,800
30,000
2,700
38,000
2,100
76,000
4,000
25-Year,
24-Hour
24,000
1,800
30,000
2,700
38,000
2,100
42,000
2,300

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                                                            FIGURE  32

                                           EFFECT OF INVESTMENT ON  DISCHARGE OF

                                  BOD LOADING FOR VARIOUS STORM  RETURN FREQUENCIES
               350
               300
 o
 CO
               250
            CO

            t—
            GO
               200
                150
                  20,000
40,000
60,000
80,000
100,000
120,000
140,000
160,000
180,01
                                                        24-HR. BOD LOADING, POUNDS
CJ

-------
construction  costs correspond to  the  approach which employs conveyance tunnels and
mined  storage District-wide. Note  that each even-increment increase in investment results
in a  far greater proportionate decrease in BOD  loading from intense storms. For example,
an increase  of  investment from $250,000,000 to $300,000,000 results in a decrease  of
BOD loading, due to the  25-year, 24-hour storm  from  about 130,000 pounds to about
84,000 pounds.

Besides examining the costs and possible pollutant loadings when determining the design
frequency, consideration must be  given to  the  probability of an intense storm occurring
during  critical stream conditions. The recommended maximum  pollutant loadings for the
metropolitan Washington area were determined for summer conditions, when fresh water
flow is low (less dispersion of waste), temperature is  high  (higher temperatures increase
biological activity and  reduce the dissolved oxygen saturation concentration), and  plant
respiration overnight has somewhat depleted the available dissolved oxygen. Water quality
conditions usually are not as critical during other seasons of the year.  A graph in a U.  S.
Weather  Bureau Technical Paper  (27) is reproduced as  Figure 33 to provide insight  as
to the  seasonal probability of intense storms. Note that  in  the months of July, August,
and September  there is a 15 percent probability of obtaining a rainfall equal to or exceeding
that  corresponding to a 5-year return period, while the probability of a similar occurrence
during  the remaining nine months is only 5 percent.

The  preceding discussion has focused on the removal of those contaminants that deplete
dissolved  oxygen levels. However, the overflow from combined sewers also contributes
to high bacteria  levels  and repulsive floating matter in  the Potomac  and its tributaries.
While only 85 percent BOD removal can probably be effected from any retained overflow,
total removal of floating matter and almost total  disinfection is possible. Therefore, facilities
based on  a  15-year design frequency would rid the Potomac  of high  bacteria levels and
repulsive floating matter from  combined  sewers for  14  years  out of a 15-year period,
and  for practically all  of  the recreational  season  in the fifteenth year.
                                        104

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                                    FIGURE   33

         SEASONAL  PROBABILITY OF INTENSE 24-HOUR  RAINFALL
                    MIDDLE ATLANTIC REGION
                                                      PROBABILITY IN  PERCENT OF OBTAINING
                                                      A RAINFALL IN ANY MONTH OF A PAR-
                                                      TICULAR YEAR EQUAL TO OR EXCEEDING
                                                      THE  RETURN PERIOD VALUES.
            J   F   M   A  M   )   J  A   S   0  N   D

                         MONTH OF YEAR


SOURCE: U.S.  WEATHER BUREAU TECHNICAL PAPER  NO.40
                                         105
33

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                       Comparison of Non-Quantifiable  Factors

To determine which of the feasible alternative approaches would offer the best opportunity
for abatement of the combined sewer overflow problem requires careful consideration of
many factors. Cost comparison obviously is essential, but there are other factors which
also  have a  significant bearing  on the selection  of the most favorable  plan. The most
important of these other factors are Reliability, Flexibility,  Land  Requirements, Public
Convenience, Implementation, and Solids  Deposition  and Gas Production. In general, the
effects of these factors on the various alternatives are either non-quantifiable or are difficult
to quantify. The relative impact on each alternative is discussed in the following paragraphs.

Reliability

An important consideration  is the reliability of any system to perform its designed function
whenever a  storm  occurs; there is no time to get things ready after  the onset of a storm
In regard to collection of the storm waters, all four approaches are equally (and strongly)
reliable,  because all rely primarily on  gravity  for  capture and collection.

However, efficient  capture  and collection presupposes sufficient storage  capacity, which
means that  the  wastewaters collected from previous storms must have  been moved  out
of the  storage spaces to  the treatment  facilities  or to  the  streams. This obviously is
dependent on the  readiness  and  capacity  of the  pumping facilities (except for sewer
separation).   In this regard, there is a  difference, however small,  between the  various
alternatives. Sewer  separation would be the most reliable overall, because it would involve
no dependence on  pumping equipment.  Conveyance tunnels and mined storage would be
the next most reliable. Its requirement for two large pumping stations in  comparison with
many smaller pumping stations for the reservoir and local treatment approaches constitutes
a  reliability  advantage, because of the inherent higher reliability of a larger installation
and  the  relative ease of routine  preventive  maintenance.

In addition  to the  same number of pumps required for the reservoir approach, treatment
at overflow  points would involve equipment at treatment facilities, and this equipment
would also  have to  be constantly maintained and  operated  to  assure  reliability. This
dependence  on additional equipment makes  this  approach not quite as  realizable as  the
others.  Nevertheless,  no severe  problems  are  anticipated with regard to  reliability.

Flexibility

In addition  to  random  occurrence of storms and  the variations  in storm  duration and
intensity for the Washington, D.  C.  area  as a whole, there will be  variations within  the
area.  These  local variations could be significant.

Each storage reservoir (in the storage reservoir approach) would serve a discrete sub-drainage
area, and the probability of occurrence of a storm of such duration and  intensity as to
cause overflow is greater for any of  the  smaller discrete areas than for  the overall area.
Treatment at overflow points  has reservoirs based on the  same  discrete drainage areas
and is subject to the same  degree of inflexibility as the reservoir approach, and the same
is  true for  sewer separation.

A  network of tunnels and mined storage would provide the greatest  flexibility. Variations
in  storm occurrence, intensity, and duration  within the Washington  D. C.  area would  not
                                         106

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per se consititute a problem, because flow from all sub-drainage districts would be dropped
to the mined-storage chambers and  equalized  over  the whole  study  area.

Land Requirements

Site  investigations have  been made to determine whether land is available at outfall points
for construction of facilities required  under the various approaches. In general, there is
vacant land available at each  of the overflow  points. However, it should be noted that
most of  the potential  sites are under  the jurisdiction of the National  Park  Service, and
their full cooperation would be necessary to obtain  the  sites.

Since construction at storage  reservoirs  would  be underground, the only land required
would  be for access and  maintenance. The  ground above the reservoirs could be used
for parks and playgrounds, with only relatively small pump houses extending  above grade.
Architecturally,  the pump houses could be built to  preserve the national park landscape.

The land required would  be greater for  the approach  proposing treatment at overflow
points. The additional  housing for the pressure filters and appurtenances would require
construction of  buildings at each overflow point.  Again, the structures could be built to
preserve  the aesthetics of the land under the jurisdiction of the National Park Service.

Land required  for tunnel and mined-storage construction would be minimal.  Only the
land necessary for temporary occupancy during shaft construction would be required. Upon
completion  of  construction, the work area  would be  landscaped to restore the original
condition.

Sewer  construction  under  a  separation  program would be   in the  City  streets  and
rights-of-way. Therefore, for purposes of this  report,  no land is  required for this approach.

Public Inconvenience

The disruption  of  public travel in  Washington during the construction  period  is a  major
factor in the selection of an alternative approach. In  fact, this may be the most important
factor, possibly  carrying more weight than costs  or water quality. The present  construction
of the Washington Metropolitan Transit  Authority  subway  illustrates the severe impact
of a construction program  that requires  the  closure of streets  to traffic and the erection
of  barricades to pedesterians. Many businesses  have had to close for indefinite periods,
since customers refuse to frequent establishments on the disrupted streets. Traffic problems
worsen as fewer  avenues  of travel and  fewer  parking spaces  remain  available.

Reservoir construction would be  off the public streets. Traffic disruptions would be caused
only by the construction vehicles required  to  move  equipment and materials from the
reservoir site.

For the local treatment approach, traffic disruption again would be only for  movement
of construction  equipment and materials. However, due to additional equipment and more
complex construction,  the  construction period  and attendant traffic disruption would be
for  a  longer period  of  time.
                                         107

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The tunnel  and  mined-storage approach  would  require  virtually  no  disruption  or
inconvenience to residents and visitors. All  construction would be underground and off
the City streets. The only movement of vehicles would be to remove drilling muck. This
operation could be done  during the off-peak traffic hours; however, if moling progresses
at a fast rate, continuous muck removal  may be  required.

Sewer  separation would be the most disruptive to public travel. Virtually every street
in the study area would be excavated at some point  in time. The ramifications of such
disruption  would be difficult to assess  completely, but  it is certain  that  the disruption
would  be much more serious  than  with any of the other approaches.  Besides this, sewer
separation  would require considerable work on private property to separate roof  drains
and  other  plumbing.

Implementation

Each of  the four approaches can be implemented, but some will be easier and/or quicker
than others.  Considerations affecting the  relative ease of  implementation  are:

     1.   Public attitudes and  reaction.
     2.   Cooperation of other District and  Federal  Agencies.
     3.   Political  implications and restraints.
     4.   Staging of  construction  and possible benefits with phased construction.
     5.   Financial  schedules  and  monetary assistance programs.

Construction schedule,  i.e. time required to  complete each of the alternatives, is one of
the  critical elements involved in  evaluating the  adaptability of  each approach  to the
establishment  of stricter  requirements,  particularly in view of the strong  pressures  to
improve  the  environment at the earliest possible date.

Before final design  of  storage  reservoirs could be started, additional studies would have
to be made to determine their exact location and the  design parameters of each. The
necessity to design  reservoirs unique to each drainage  district complicates the design; and
the  number  of  facilities required  extends  the  construction  period. It  would  take
approximately  eight years to  complete the facilities required if this approach is applied
District-wide where  feasible.

Additional  studies and individual design would also be  necessary for treatment at overflow
points. Due to the  necessity  to design  special equipment,  and taking into account the
need to  fabricate and  install  the  special equipment,  the time for completion would  be
longer than for the storage reservoir approach. It is estimated that a District-wide approach
of treatment at overflow points could be completed  in ten years.

The District-wide  tunnel  and mined-storage  approach would take  about  eight  years.
However,  the  boring techniques  are  sufficiently  advanced  to allow  relatively  rapid
construction.

Sewer separation would take the longest time, by far, to  complete. On the basis of data
presented in the 1957 Board of Engineers Report, it is estimated that the sewer separation
program  would  be  completed  sometime after 2000.
                                         108

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Solids Deposition and  Gas Production

Another major  consideration in the selection of  an approach  is the problem of solids
deposition and  concomitant gas production. Solids deposition  would  have a three-fold
effect:

     1.    Deposition of solid  material could reduce storage capacity.
                                                       i
     2.    Organic solids may decompose to form  malodorous compounds thus causing a
          nuisance condition.

     3.    Organic solids may  decompose to form  explosive organic gases.

Settleable solids deposited in  the settling zone of each  reservoir could be  pumped back
to the existing system for  ultimate disposal at Blue Plains. Solids carried over to the storage
zone  would  be pumped to Blue Plains  through the raw sewage pumps. If  the  reservoirs
are emptied  relatively soon after the  storm subsides and regular maintenance by flushing
is provided,  neither septicity nor  gas  production  is expected to be a problem. To insure
that gas production  is not  a  problem  each of the reservoirs  would be equipped with
adequate  ventilating  and air-pollution control devices.

The solids  deposition  and  gas production would  have about  the same impact  on the
approach  using treatment at overflow points as for the reservoir approach.  In addition
to solids removed in the settling zone of the storage structures, backwash from the fiberglass
filters would be discharged to the existing system and conveyed to Blue Plains.

The field studies presented in the first  part of this report have determined  that a high
concentration of solids occurs during the first  few minutes of the storm  Therefore, the
major portion of the solids will be carried into the tunnels (under this approach) during
the first  few minutes. This flushing  action will  carry  the solids to the low point and
facilitate  solids removal. The mined storage would be compartmentized and the first few
compartments used as settling basins to facilitate  removal of solids. However, the great
depths  and  vast extent of  these tunnels may present problems in regard  to effective solids
removal.

With  a  separation program, solids  carried ..into the storm  sewer would be  discharged to
the receiving stream. As determined during the field studies, the amount of solids delivered
to the  stream would be  significant.

Evaluation  of Factors Other Than Cost

The results  of the evaluation of comparative reliability,  flexibility, land  requirements, and
other non-cost factors are summarized in Table 22. In  view of the difficulty in properly
assessing  the  relative worth  of   each  factor  in  quantitative terms, no  quantifiable
measurement is employed  in this presentation. Instead, a  measurement scale of X's indicates
the degree of the problems possible with each approach. An  overall  evaluation indicates
a clear advantage for conveyance tunnels and mined storage over the other three approaches,
provided  the solids question can  be  answered.
                                          109

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                                           Table 22

                                   Evaluation of General Factors
                           Maximum Use of
       Factor

Reliability

Flexibility

Land Requirement

Public Inconvenience

Implementation

Solids Deposition and
Gas Production
Storage
Reservoirs
X
X
XX
X
XX
Treatment at
Overflow Points
X
X
XX
X
XX
Conveyance Tunnels
and Mined Storage
X
—
—
—
X
Sewer
Separation
—
X
—
XXX
XXX
X
X
XXX
Key:      —   No Problem
          X   Possible Minor Problem
        XX   Possible Moderate Problem
       XXX   Possible Major Problem

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As  previously pointed out  in  the  comparison of the cost estimates presented in Tables
15 though  20, the conveyance tunnel-mined storage approach would also involve the lowest
construction  cost  of any of the four  approaches and lower operating costs than either
storage reservoir or treatment at overflow points (Operating costs, which would be primarily
maintenance, were not calculated for sewer separation). Thus, the evaluation of general
factors reinforces the selection (on a cost basis) of conveyance tunnels and mined storage
as the approach to  be adopted.
                                        111

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                     Indicated  Appropriate District-wide Solution

The  preceding  sections of this  report illustrate how it  is possible to develop within the
District numerous strategies for  collecting, storing, and treating combined sewer overflow.
Each  strategy offers a different level of costs, pollutant loadings, and benefits. While the
selection of the appropriate  strategy must rest, in part,  on  factors beyond the scope of
this  study,  the  information presented  in  this  report indicates  that the appropriate
District-wide solution may be one which centers  on a single approach, the use of mined
storage and conveyance tunnels.

The  recreational  and other values of the Potomac River and  its tributaries demand that
these waters be protected from pollution. Further study is  needed to predict the effect
of shock contaminant loadings to the Potomac and its tributaries. Therefore, the selection
of the appropriate  design frequency requires a somewhat arbitrary  decision at this time.
It is common practice to use a  10-year minimum  flow recurrence frequency as the design
basis for treatment  facilities on fresh water streams. While the situation for estuarine waters
is different, this basis can be interpreted to mean  that all combined  sewer overflows from
storms-of-lower magnitude than  the design storm must be entirely intercepted, stored, and
treated.  Quite  possibly,  extending  this  to  the   15-year design frequency represents  a
reasonable  and conservative  decision in view of  the small  increase in  costs (see Figure
30) and the  significant decrease in pollution loadings from the intense storms (see Figure
32).  Selection of the 15-year, 24-hour  design event is further supported by consideration
of the  water-contact activities  proposed for  the  Potomac River and its tributaries. The
indications are that  facilities based  on this  design  event would permit all the desired
recreational  activities with practically no interruption.

Table 10 in  this report shows that the expected annual volume of combined sewer overflow
from  the District is  12 billion  gallons. The Blue Plains plant can  completely  treat 289
mgd  above  the  average  dry-weather  flow for  400  hours per  year.  This is equivalent  to
an annual reserve capacity of 5 billion gallons. While the Blue Plains plant can partially
treat  some of the remaining  7 billion gallons,  it  is obvious that treatment  at some other
location is required. The conceptual engineering study (6) of  the Kingman Lake project
has identified the  feasibility of constructing a multiple-purpose treatment plant in that
area. Actually, as brought out in that study (see Appendix G), this location for a treatment
facility offers a  wide number of benefits, probably more than any  other location in the
District. The original concept of a 50-mgd plant in this  area could probably be expanded
to a  150-mgd  plant (the 100-mgd  increase could  be directed simply  to  filtration and
chlorination rather  than to complete treatment). This would handle in   about five  days
the 772 million gallons of overflow from the Anacostia River area for the 15-year, 24-hour
storm. This single facility, in combination with the reserve hydraulic capacity of the Blue
Plains plant, would provide  sufficient capacity to treat the annual volume of combined
sewer  overflow from the  entire District.

Concentrating treatment capacity at  these  two  locations,  rather  than at  many  more
locations, affords another  advantage. Even with complete retention of overflow  from the
15-year, 24-hour storm, the assumed 85 percent treatment efficiency  would still allow
a 24-hour discharge of about 38,000 pounds of BOD to  the  Potomac. This  loading equals
twice the recommended maximum daily loading in the Metropolitan Washington area, and
perhaps  this would  deplete dissolved  oxygen  below  the  minimum  acceptable levels.
However, the treatment provided at the  Blue Plains advanced plant and at the  Kingman
Lake reclamation plant  would  result  in  an overall  treatment efficiency higher than  85
percent, and less than  38,000-pound loading  would result.


                                         112

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A network of conveyance tunnels and mined storage is suggested because no other approach
offers  capacity for the overflow from the 15-year, 24-hour storm at a lower cost or at
a higher level of  benefits.  The total  project costs of the indicated  appropriate solution
is about $318,000,000, as shown in Table 23. Note that this cost includes the costs of
dealing with those sewer districts scheduled to be separated before 1975 whose separation
has been  delayed indefinitely. A solution  incorporating mined storage in the Anacostia
River area and with both storage reservoirs and mined storage  in the  Rock Creek-Upper
Potomac  area  (see  Figure  24) comes somewhat  close  to  this figure, with a  cost of
$325,000,000.  By  inspection of Tables  12  and 15, it  is possible  to  reduce this figure
by  $4,800,000 if the method of separation  rather than storage reservoirs is applied to
Sewer  Districts A-10, A-11, and  A-12.

Actually, a cost less than  $318,000,000 is possible with a solution designed for the 2-year,
24-hour storm in one area  and  the 20-year, 24-hour  storm in another.  This represents
both overdesigning  and  underdesigning, and produces the same  reduction in pollutant
loadings  from  the  25-year storm  as a  uniformly applied 15-year  design  frequency.
Economies of scale explain this cost difference. However, this scheme would allow a higher
loading from the 5-year storm than would a  uniformly applied  15-year design frequency.

Although  the selection of  the appropriate solution  must consider some  factors beyond
the scope of this study, the information developed herein does point  to a particular
solution. In summary, this  solution is  one that provides a network of  tunnels and mined
storage, with  treatment at  the Blue Plains  plant and  at a facility  near  Kingman  Lake.
A 15-year, 24-hour storm event (or one based on a longer recurrence interval) is suggested
at the design basis, in the  public's  best  interest.
                                        113

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                              Table 23

        Estimated Capital Costs of Indicated Appropriate Solution
                         (ENR lndex = 1800)
              Feature                                           Costs

Rock Creek  Upper Potomac

  1. Tunnel Construction
     a. Rock Creek                                          $ 18,200,000
     b. Upper Potomac                                           2,000,000

  2. Vertical Shafts
     a. Rock Creek                                              4,400,000
     b. Upper Potomac                                           2,100,000

  3. Mined Storage                                            57,000,000

  4. Pumping Station                                            6,200,000

Anacostia River Area

  1. Tunnel Construction                                      11,100,000

  2. Vertical Shafts                                              5,800,000

  3. Mined Storage                                            94,000,000

  4. Pumping Station                                          10,900,000

  5. Northeast Boundary Re lief/Storage Tunnel                   27,000,000

  6. 150-MGD Treatment Plant at Kingman Lake"1                 12,000,000

Sewer Districts Scheduled for Separation  prior to 1975             10,000,000

Total Construction Costs                                      261,000,000

Engineering Design at 6%                                       16,000,000

Other Costs (resident inspection,  legal, bonding, and
  administrative at 15%)                                       41,000,000

Total Project Costs                                          $318,000,000


'Costs based on 150-MGD plant incorporating processes depicted in Figure  15
 (filtration and chlorination) rather than  complete water reclamation processes.
                                 114

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                                   SECTION  VIM

                               ACKNOWLEDGMENTS

Roy F. Weston, Inc. gratefully acknowledges Mr. Paul Freese and Mr. George A. Moorehead,
of the  Department  of  Sanitary  Engineering  of  the District of Columbia, for general
assistance and particularly for their  efforts in connection with  the construction of field
monitoring stations and  installation  of equipment.

Acknowledgment is made  to Mr.  John F. Miller, Special Studies  Branch, United States
Weather  Bureau,  for furnishing  local climatological  data and for providing assistance in
interpretation  of those  data.

Acknowledgment is made to Mr. Al  Cywin, Director of the Division of Applied Science
and Technology, Mr. William Rosenkranz, Chief of the Storm and Combined Sewer Branch,
Dr. Henry R. Thacker, Project  Officer, and  Mr.  Darwin R.  Wright, Project Manager, all
of the WATER  QUALITY OFFICE, for  their interest and guidance during  the course
of this  project.

Acknowledgment is also  made to the members of the  staff of  Roy F. Weston, Inc. who
have participated in this  project.

Roy F. Weston,  P.E.,  President

J. E. Germain, P.E., Vice President            Concept Technology Division
V. T. Stack, P.E.,  Principal Consultant         Consulting Division

J. A. DeFilippi,  P.E.,  Project Manager

M.  S. Neijna, P.E.                             Concept Technology Division
P. L. Buckingham,  P.E.
E. F. Gilardi, Ph.D., P.E.
C. S. Shih, Ph.D.,  P.E.
U. C. Mankad, P.E.
J. A. Lee
C. J. Cahill

R. E. Coleman, P.E.                           Engineering Design Division
T. E. Taylor
J. G. Ryan

J. K. Kane                                   Geology Section
                                        115

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Special acknowledgment is made to the Technical Editing, Report Preparation, Duplicating,
and  Report  Graphics groups.
J.  L.  Simons
J.  P.  Jarosh
A. M. Tocci
N. L. McVey
J.  L.  Smith
D. L. Rimel
S.  M. Jones
W. McDermott
J.  W. Hitzelberger
J.  C. Allison
D. 0. Thompson
D. W. Syphard
W. J. Costello
E. J. Burke
D. Angevine
R. E. Towson
                                      116

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                                  SECTION IX

                                  REFERENCES

 1. Board of Engineers (Greeley, S. A. et al), "Report to District of Columbia Department
    of Sanitary Engineering on  Improvements to Sewerage Systems," February  1957.

 2. Metcalf &  Eddy,  Inc., Engineers,  "Report Upon Investigation of Sewerage System,"
    June  1955.

 3. Metcalf & Eddy, Inc., Engineers, "A General Plan for Development of Water Pollution
    Control 1969-1972,"  1969.

 4. U. S. Department of the  Interior, Federal Water Pollution Control Administration,
    "Potomac  River Water Quality, Washington, D.C.  1969,"  1969.

 5. Tholin, A.  B. and Keifer,  C. J., "The Hydrology of Urban Runoff," Journal of the
    Sanitary Engineering Division, ASCE, March  1959.

 6. U. S. Department of the Interior,  Federal Water Quality Administration, "Conceptual
    Engineering Report,  Kingman Lake Project," by ROY F. WESTON, Water Pollution
    Control Research Series,  11023  FIX 08/70, U.  S.  Government Printing  Office,
    Washington, D.C., 1970.

 7. "Problems  of Combined  Sewer Facilities and Overflows,  1957," American Public
    Works Association for the U. S.  Department of the  Interior,  FWPCA Publication
    WP-20-11,  December  1967.

 8. Burm, R. J. et al,  "Chemical and Physical Comparison of Combined and Separate
    Sewer Discharges,"  JWPCF,  January 1968, p.  112.

 9. Wiebel, S. R. et al, "Characterization, Treatment, and Disposal  of Urban Stormwater,"
    Proceedings 3rd International Conference on Water Pollution Research, 1967, p. 327.

10. Evans,  F.  L. et al,  "Treatment of  Urban Storm-Water Runoff,"  Cincinnati  Water
    Research Laboratory  Pre-Publication  Copy, January 1967.

11. "Sewer Within a Sewer," Water Works/Wastes Engineering, February 1964, p. 36 (from
    Selected Urban Stormwater  Runoff Abstracts).

12. "Combination Sewer Separated into Sanitary and Storm Sewers at Low Cost," Civil
    Engineering,  December  1967,  p.  61.

13. McPherson, M. B., "Progress  Report-ASCE Combined Sewer Separation Project," Civil
    Engineering,  December  1967,  p.  61.

14. Koelzer, V. A. et  al, "The Chicagoland Deep  Tunnel Project," The Metropolitan
    Sanitary District  of Greater Chicago, September 1968.

15. Cellini,  W.  F. et al, "Underflow Plan  for Pollution and  Flood  Control in the Chicago
    Metropolitan Area," Paper presented  at  the EPA-WQO Symposium  on Storm and
    Combined  Sewer Overflows, Chicago, Illinois, June 22-23, 1970.


                                       117

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16.  Gregory, J.  H. et al, "Intercepting Sewers and  Storm Stand-By Tanks at Columbus,
     Ohio," ASCE Proceedings,  October 1933, p. 8.

17.  Waller, D. H., "One City's Approach to the Problem of Combined Sewer Overflows,"
     Water and Sewage  Works,  March  1967, p.  113.

18.  Him, W.  C., "Providing  Primary Treatment  for Storm Sewage Overflows," Wastes
     Engineering,  September  1962.

19.  "Research and  Development  Programs," FWPCA,  August 1968.

20.  "Milwaukee Seeks to Solve Pollution Problems," Civil Engineering, September 1967,
     p. 79.

21.  Romer, H. and Klashman, L. M.,  "The Influence of Combined Sewers on  Pollution
     Control,"  Public  Works,  October  1961,  p.  129.

22.  Simpson,  G. D.,  "Treatment of Combined  Sewer Overflows and Surface Water at
     Cleveland, Ohio,"  Technical Paper,  41st Conference, WPCF, September  1968.

23.  Dunbar, D.  D. and Henry, J. G.,  "Pollution  Control Measures for Stormwaters and
     Combined Sewer  Overflows," JWPCF, January 1966,  p. 9.

24.  Gameson,  A.  L.  H.  and   Davidson,  R.   N.,  "Storm  Water  Investigations  at
     Northampton,"  Institute  Sewage Purification Journal, 1963  (from Selected Urban
     Stormwater  Runoff Abstracts).

25.  Eliassen, R., "Coliform Aftergrowth in Chlorinated Storm Overflow,"  Journal of the
     Sanitary Engineering Division, ASCE, April  1968, p. 371.

26.  Board of Engineers (S. A. Greeley  et al) "Planning Study of Sewage Treatment Plant
     to the Year 2000," August 1964.

27.  "Rainfall Frequency Atlas of the United States," U.S. Weather Bureau Technical Paper
     No.  40, January  1963.

28.  Kiefer,  C.  J. and Chu,  H.  H.,  "Synthetic  Storm Pattern," Journal of Hydraulics
     Division, ASCE, Vol. 83, August  1957.

29.  Horner, W. W. and Jens, S. W., "Surface Runoff Determination from Rainfall Without
     Using Coefficients,"  Transactions,  ASCE, Vol.  107, 1942.

30.  "Design and Construction of Sanitary Sewers," ASCE MOP No. 37, New York, 1960.

31.  Allen and Taylor, "The  Salt-Velocity Method  of Water Measurement," Mechanical
     Engineering, ASME, Vol. 46, 1938,  p. 13-16.

32.  Gnoat, B. F., "Chemi-hydrometry and Its Application of Testing  of Hydroelectric
     Generators,"  Transactions of ASCE, Vol. 80,  1915,  p. 951-1305.

33.  Anon., "Fluorometry in Studies of Pollution and Movement of Fluids," Fluorometry
     Reviews Ace. No. 9941,  February  1968.
                                       118

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34.  Whitney, W. H. and Wilson, G. G., "Effluent Distribution  Studies on the  Miramichi
     and Restigouche Estuaries."

35.  Fewerstein,  D.  L.  and  Selleck,  R.  E.,  "Fluorescent  Tracers  for  Dispersion
     Measurements," Journal of the Sanitary Engineering Division, ASCE, Vol. 89, No.
     SA-4,  Proc.  Papers 3586,  August 1963, p.  1-21.

36.  Replagle et al, "Flow Measurements with Fluorescent Tracers," ASCE, Proc. 92 (Hy-5,
     No. 4895), September 1966, p. 1-15.

37.  Barnwell, E. L., "Multiple  Tracers Establish Waterflood Flow Behavior," Oil and Gas
     Journal, Vol. 64, N-28, 1966,  p. 76-79.

38.  Cederwall, K.  and  Hansen, J.,  "Tracer Studies  on Dilution and Residence Time  in
     Receiving Waters,"  Water  Research  Pergamon Press,  Vol.  2,  1968,  p.  297-310.

39.  Cederwall, K. and Hansen,  J., "Dispersion Studies by Means  of Tracers," (In Swedish),
     Vag-Och  Vattenbygganen,  No.  1-2.

40.  Cederwall, K. and Hansen, J., "Surface Water Studies by Means of Parallel Injected
     Tracers," (In Swedish) Vag-Och Vattenbygganen, No. 10.

41.  Kilpatrick,  F.  A.,   "Flow   Calibration  by  Dye Dilution   Measurements,"  Civil
     Engineering, Vol. 28, 74-76F,  1968.

42.  Agg, A. R., Mitchell, N. T., and Mitchell, G. E.,  "Use  of Lithium  as a Tracer for
     Measuring Rates of Flow  of Water and Sewage," Water  Pollution  Research  Labs,
     Stevenage, England, Ind.  Sewage Purif.   J.  Proc., 1961,  p.  240-5.

43.  Spencer,  E.  A. et al,  "Flow  Measurement  by Salt Dilution Method," /. Ind. Water
     Eng.,  Vol.  14,  215-35,  1960.

44.  "Selection and  Handling a Radio Tracer for  Study Sewage Distribution,"  Ind. Eng.
     Chem., 50, 210-211,  1958.

45.  Burgece, S. G. et al, "Determination of Flow Characteristics in Sewage Works Plants,"
     Sewage Purif.   J.  Proc., P+3,  206-15, 1957.

46.  Simpson, E. S. et al,  "Radio Tracer Experiments in the Mohawk  River, New York
     to Study Sewage Path and  Dilution," Geophysical Union, 39, 427-33, 1958.

47.  Montens, A.,  "The  Use  of Radioactive  Isotopes for  Water Flow and Velocity
     Measurements, Precautions and Possibilities of Use,"  Wasserfach, 93, 427-33, 1958.

48.  Truesdale, G. A., "Measurement of Sewage Flow with Radio Active  Tracers," Water
     and Sanitary  Eng., 4, 93-8,  1953.

49.  Montens, A.,  "The  Use  of Radioactive  Isotopes for  Water Flow and Velocity
     Measurements," Proc. 2nd Radio  Isotope Conf., Oxford 2, Phys. Sciences and Ind.
     App.,  169-80, 1954.

50.  Meek, R. L., Indianapolis Makes a Sewage Analysis, "Flow Velocities by Electrometric
     Determination of CaCl2,"  Am. City,  43,  (1), 96-8,  1948.

                                        119

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                                  SECTION X

                                 APPENDICES

Appendix                                                                 Page

   A       GEOLOGICAL AND OTHER NATURAL CONDITIONS  	      125
            Introduction	      125
            Geologic Setting  	      125
            Principal Unconsolidated Formations  	      126
            Artificial Fills   	      126
            Bedrock   	      127
            Hydrology  	      129
            Tunneling	      130
            Figure A-1: Generalized Geologic Map  	      134
            Figure A-2: Contours of Bedrock Surface 	      135

   B       LIST OF PERTINENT STUDIES AND REPORTS REVIEWED	      137

   C       INVESTIGATION OF RAINFALL  RUNOFF RELATIONSHIPS. ..      139
            Rainfall Data   	      139
            Peak Rate  of Overflow	      139
            Volume of Overflow	      140

   D       MONITORING EQUIPMENT, INSTRUMENTS, AND PROCEDURES     145
            Discussion of Facilities and Operating Procedures  	      145
            Descriptions of Principal Equipment and Instruments	      145
            Lithium Chloride Flow Measurement  	      148
            Monitoring Practices	      150
            Figure D-1: Monitoring Equipment Diagram  	      152
            Figure D-2: Electric Power Supply and Triggering System
                       Diagram  	      153
            Figure D-3: Sampling Components	      154
            Figure D-4: Rain Gauge	      155

   E       MONITORED WASTEWATER FLOWS AND CHARACTERISTICS .      157
            Comparison of  Representative Storms	      157
          o Bacteriological Quality of Storm Wastewater  	      159
            Waste Loadings from the Monitored Sewer Districts	      160
            Total Waste Load in Storm Water Runoff	      161
            Comparison of  Flow Rate Measurements	      163
            Tables E-1
            through E-3:   Characteristics of Dry-Weather Flow for
                          Combined and Separated Sewer Districts	      165
            Table E-4:      Characteristics of Storm Runoff in Sewer
                          District Good Hope Run	      168
            Table E-5:      Waste Loadings in Combined Sewer Overflow
                          and Separated Storm Water Discharge	      169
            Table E-6:      Total Waste Loadings Generated by
                          Different Storms	      170
                                     121

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Appendix

   E
Table E-7:
             Figures E-1
             and E-2:
             Figures E-3
             through E-7:
             Figures E-8
             and E-9:
             Figures E-10
             through E-13:
             Figure E-14:

             Figures E-15
             through E-22:
             Figures E-23
             and E-24:
             Figures E-25
             through E-27:
             Figures E-28
             and E-29:
             Figure E-30:
Comparison of Actual Total Flow
Measurement and Volume Obtained by
Hydrograph Analysis  	
              Characteristics of Dry-Weather Flow
              in Combined and Separated Sewer
              Districts  	
              Characteristics of Combined and
              Separated Sewer Flows for Storms of
              Various Intensities and Durations   . .
              Characteristics of Sewer Flow during
              Consecutive Storms in Combined Sewer
              District G-4	
                                                                  Page
                                                                               171
                                                                               172
                                                                               174
                                                                               179
              Quality and Quantity of Runoff for
              Storms of Various Intensities,
              Durations and Intervals of
              Occurrence  	
              Representative Bacteriological Data
              for Combined Sewer Overflow	
                                                    181

                                                    185
              Waste Loadings Associated with
              Storm of Various Intensities,
              Durations and Intervals of
              Occurrence  	
              Correlations between COD and
              Suspended Solids Loadings and
              Total Rainfall  	
                                                                               186
                                                                               194
               Representative Rainfall and Runoff
               Measurements for Storms of Various
               Intensities, Durations and
               Intervals of Occurrence  	
              Correlations between Water
              Quality Parameters for Various
              Sewer Districts	
              Comparison of Flow Measurement
              Techniques for Combined Sewer
              Overflows   	
                                                    196



                                                    199


                                                    201
                                 122

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Appendix                                                                     Page

   F        ULTRA-HIGH-RATE FILTRATION		     203
              Introduction	     203
             Theoretical Background  	     203
             Considerations for Practical Application  	     209
             Description of Laboratory System  	     210
             Discussion of Laboratory Procedures and Data	     213
             Table F-1:     Characteristics of Fiberglass Plug
                            Filter Beds  	     224
             Table F-2:     Summary of Filter Cartridge
                            Configurations	       225
             Table F-3:     Characteristics of Media Used in the
                            Tri-Media Filters	       226
             Table F-4
             and F-5:       Filtration Study Data Summary for
                            Fiberglass and Tri-Media Filters  	       227
              Figure F-1:     Schematic Diagram of Filtration
                            System	       229
              Figure F-2
             through F-7:   Results of Fiberglass Filter Evaluation	       230
              Figure F-8
             through F-10:  Results of Tri-Media Filter Evaluation	       236
              Figure F-11:   Upflow Filter Performance	       239
              Figure F-12:   Filtration System Components   	       240

   G        KINGMAN LAKE PROJECT 	       241
                                        123

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                                    APPENDIX  A

               GEOLOGICAL AND OTHER  NATURAL  CONDITIONS

                                     Introduction

Information  on the  geologic and other  natural conditions is essential to a complete
evaluation  of the  various  possible approaches to the abatement of pollution caused by
the inadequacies of combined sewers, including the feasibility of tunneling beneath  the
City of Washington to provide for storage of combined overflows.

Data were obtained from  published geologic  reports, from engineering  reports  prepared
under  the  auspices of  the Metropolitan  Area  Rapid Transit Authority,  and from verbal
communication  with personnel from the Authority. The published geologic data are fairly
broad in coverage, although sufficiently detailed to provide  information helpful in forming
conclusions in regard  to the feasibility of tunneling. The previously-mentioned engineering
reports are extremely detailed and provide an abundance of  data concerning the soils,
bedrock, and rock mechanics along certain restricted areas for the purpose of underground
tunneling for rapid transit. Although somewhat restricted as to area-wide application, the
data included in these reports provide enough  coverage to be representative of the  overall
Washington area.

                                   Geologic Setting

The District  of Columbia  lies  within  portions of  two  physiographic provinces;  the
southeastern  portion  is located within  the Coastal  Plain  Province, which consists  of
relatively flat-lying sediments overlying deep  bedrock,  and the northwestern portion is
in the Piedmont Province, which in general is characterized by a thin layer of overburden
covering crystalline bedrock. The Fall  Line separating the two  provinces extends roughly
southwest  from Blair Park in the northeast through  Farragut Square and on toward  the
Pentagon.  Figure A-1 presents the generalized geology of the  District  of  Columbia.

Previous subsurface investigations  throughout  the District have resulted in grouping  the
materials into five major  categories:  bedrock, Cretaceous  sediments, Pleistocene  terrace
deposits,  recent river alluvium, and drainage  channels  and man-made fills. These major
categories  of materials in  various  parts  of the  District are  found in the following five
vertical profiles:

     1.   Recent alluvium over bedrock or Pleistocene  terrace deposits,

     2.   Overburden of Pleistocene terrace and Cretaceous coastal plain soils above deep
          bedrock,

     3.   Comparatively thick cover of  Pleistocene terrace and Cretaceous coastal plain
          soils above deep bedrock,

     4.   Thin  to  moderately thick  cover of Cretaceous coastal plain materials above
          decomposed  rock and  bedrock,

     5    Relatively thin  cover of  man-made  fill and  decomposed rock and  bedrock at
          shallow  to moderate depths.
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                         Principal Unconsolidated  Formations

Cretaceous Sediments

Lower Cretaceous sediments belonging to the  Potomac group overlie weathered bedrock
throughout  most of the  downtown  area  of Washington. These sediments  dip  gently to
the southeast, thickening in that direction. In general, they vary in lithology from weathered
soft clayey  materials to  dense  sand,  silt, and  gravel.  In other areas  along the Atlantic
Coastal  Plain, the Potomac group is overlain by upper Cretaceous and Tertiary sediments.
However,  in downtown  Washington, these younger formations plus a considerable thickness
of the  Potomac  group  have been removed  by past erosion. The sediments occur over
sufficient  areas and at  elevations appropriate  for  tunnel storage.

Pleistocene Terrace  Deposits

Pleistocene terrace  deposits are  a succession of river deposits, which generally overlie the
Cretaceous sediments or  decomposed rock. They consist of  a  heterogeneous mixture of
interbedded sandy  clays, sand,  and gravelly sands.

Previous investigations  have determined that the terraces occur  at  several  characteristic
elevations in the  Washington area, e.g. the "25-foot  terrace", "50-foot terrace", and the
"90-foot terrace". The  terraces characteristically show a change in gradation (in vertical
profile)  from  coarse-grained soils at their base to fine-grained  sands, silts,  and clays at
shallower  depths.  In  general, the  Pleistocene deposits occur  at  elevations which are
considered too high for  storage tunnels.

Recent  Alluvium

In comparison to the other unconsolidated formations in the Washington  area, the recent
alluvium is relatively restricted in areal extent.  It occurs primarily along the Potomac River
as far west as the mouth  of  Rock  Creek, and along the flats bordering the Anacostia
River. The alluvial  material consists of fine-grained organic sand and silty to sandy clay
with lenses  of peat, and may have  a thickness of  as much as 25 feet.

                                    Artificial  Fills

Cutting  and  filling of  irregular natural topography has been quite extensive throughout
the Washington area. Reference to old maps indicates that extensive filling has taken place
along the low  areas bordering the Potomac and Anacostia  Rivers, and in East Potomac
Park, National  Airport, the Navy  Yard,  and the Southwest Mall area. In  addition, the
drainage systems  of the Tiber and St. James Creeks and of Slash Run, which were  originally
located  in downtown Washington, have  been  covered with  fill.

Several  hills composed of Pleistocene terrace materials have been removed and the material
utilized  to fill nearby low areas. Extensive cuts and fills have been made along Connecticut
Avenue  north of  Rock Creek. Due to the lack of continuity of the fills and to the elevation
at which  they  occur, they are not considered suitable  of  tunneling.
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                                       Bedrock

Bedrock in the Washington area consists of crystalline metamorphic  schists and  gneisses
of Paleozoic age. It  originated in  upgrading by  metamorphism  of wide areas of sandy
and clayey sediments to form the lithologic complex known as the Wissahickon formation,
which  is a part of  the  extensive band of crystalline rocks that extend from New  England
to Alabama. The general category is schistose gneiss, which is  essentially a metamorphosed
sedimentary rock with zones of various mineral compositions. In many areas of Washington,
rock  is  overlain  by  compact  residual  soil   which  is  derived  from  weathering  and
decomposition  of the  underlying parent rock.  Northwest of the Fall Line, remnants  of
residual soil over 60  feet thick have been encountered, while southeast of the Fall  Line
erosion has removed  much  of this material  leaving an average thickness of only five  feet.

General Depths of Bedrock

The  bedrock  surface  southeast of the Fall  Line  dips southeastward at  a  rate  of
approximately  60-125  feet  per mile,  thus occurring  at  increasing  depths  toward the
southeast.  In the area  of the Anacostia River, it occurs between 300  and  400 feet below
mean sea  level. Northwest  of the Fall  Line, bedrock begins to outcrop at the  surface,
although in many areas it is  overlain by a cover of unconsolidated material. In this  area,
bedrock generally occurs between the surface and a depth of about  75 feet.  Figure A-2
depicts the general  configuration of the bedrock surface underlying the City of Washington.

Depth  of  Rock Weathering

A study of the  logs of  bore holes drilled  for the Metropolitan Area Transit Authority
indicates that  the  upper surface of the bedrock  generally is weathered to some extent.
The  extent of weathering is  largely dependent on rock  type and on the frequency  of
jointing. The logs indicate the general  depth of weathering to be on  the order of 5  feet,
although weathered thicknesses  up  to   17  feet were  noted in several of the borings.

Rock Types

Through subsurface investigations, three interfingered  general bedrock types have  been
identified  along Connecticut  Avenue. These include schistose gneiss,  chlorite  schist, and
quartz-diorite gneiss; these  are described  below,  since each  has different characteristics
in regard  to  tunnel  construction. These  rock  types are  considered  to  be generally
representative  of the rock  and  conditions underlying  Washington.

     Schistose  Gneiss

The  schistose gneiss  includes  three rocks of distinctive mineral composition: hornblende
gneiss,  quartz-hornblende gneiss, and   quartz-biotite gneiss.  The  hornblende  gneiss  is
characterized by its dark color and high content of hornblende crystals,  combined  with
lesser amounts of quartz and  feldspar. Compared with the other two rock types, schistose
gneiss  is more subject  to weathering and lower in compressive strength  and modulus  of
elasticity. The quartz-hornblende gneiss is distinguished by  its "salt and pepper" appearance,
and  has the highest  compressive strength and  elastic modulus of the schistose gneisses.
The  quartz-biotite  gneiss is similar in  character to the quartz-hornblende gneiss, but has
slightly less compressive  strength and  modulus of  elasticity.
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     Chlorite Schist

The  chlorite schist is a gray-green to dark green rock, which corresponds to the soapstone
that  has been previously mapped from outcrops northwest of the Fall Line. The occurrence
of talc and the presence of joint  planes  in  which the chlorite schist has weathered to
clay  make the  formation structurally the weakest of the bedrock  types.  It has been
encountered in the valley of Rock Creek and in other areas  lying to the north.  Because
of the weakness of the chlorite schist, tunnels would probably require structural  support
whenever  this rock type  is encountered. The existing data indicate that this  rock type
is  of relatively limited  extent.

     Quartz-Diorite Gneiss

The  quartz-diorite  gneiss  (also  referred to  as granite  gneiss  or biotite  gneiss)  is  a
light-colored, coarse-grained gneiss with prominent flakes of biotite  mica. Eighty to ninety
percent of the rock is composed of feldspar  and quartz. It has  been  encountered north
of Klingle Creek,  along  Connecticut Avenue. In general, the quartz-diorite gneiss is  the
most structurally favorable bedrock from the standpoint of tunnel construction. It is  the
strongest and least weathered of the bedrock types and has the highest compressive strength
and  modulus of elasticity. Tunnels constucted in this rock type would  probably require
the  least  amount of  structural support.

Structure  of  Bedrock

     Faults and Folds

The  crystalline bedrock floor  underlying the Coastal Plain sediments has been folded and
faulted to some extent during the  geologic past. Since early  Cretaceous time, much  of
the region has been uplifted and depressed many times, accompanied  by folding and faulting
of the bedrock surface.  However, due to the thickness (and  in some cases, partial removal
of the overlying sediments),  data  on the directional trend and amount of movement  of
these folds and  faults are extremely difficult  to obtain. The predominant trend of these
movements and resultant structures has been along northeast-south-west axes, although
localized  variations,  both in  trend and amount, do exist. Several  faults in  bedrock and
the overlying sediments have been  observed in the  northwestern part  of Washington, but
the  displacements  appear small and the faults short. One fault, which  was exposed in
a trench  on 18th Street near  California Avenue, showed a displacement of 40 feet where
Potomac  group  sediments and crystalline bedrock had been thrust in contact  with each
other. Another  fault, on  Adams Mill  Road,  has a  vertical displacement of  only 8 feet.

     Joints and  Foliation

Previous investigations have been made in regard to determining the general foliation pattern
and  the primary and secondary jointing pattern of the bedrock underlying  Washington.
Foliation  is a layering within a rock caused by segregation of various constituent minerals
due  to metamorphism. It is an important factor to consider in regard to tunnel construction
in  that rock breakage may be controlled by the attitude of  foliations.  Joints are fractures
or partings  which  interrupt  the  physical continuity of a  rock  mass. The  attitude and
frequency of joints are extremely important  criteria in the construction of tunnels, and
zones of intense jointing are areas which may require special structural treatment. A detailed
examination of outcrop  in Rock Creek  Park was made by R. E. Fellows in 1950. Another
investigation made by the Metropolitan Area Transit Authority along Connecticut Avenue


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utilized bore hole  photography to determine the attitude of foliation and jointing. The
results of both investigations  show a good correlation of attitudes and indicate a definite
consistency throughout the study areas, with little effect from lithologic variations. Based
on the results of the above-mentioned  investigations, the prinicipal conclusions regarding
the attitude of  foliation  and jointing  are as follows:

     1.    The general  foliation  pattern trends directionally between  the true north and
          N20°E, and dips at angles from the horizontal between 45° and 75°, with an
          average angle of  60° to the northwest.

     2.    The primary or major jointing pattern trends directionally between  I\I70°W and
          IM80°W, with the joint  surface  dipping to the  northeast between 45° and 75°
          from the horizontal.

     3.    The secondary jointing  pattern  trends directionally between N20°  and N40°E,
          with  dips ranging between 30° and 60° to the southeast.

     Frequency  of  Secondary Openings

For the purpose of this study, secondary openings are considered to be joints which are
defined as fractures or partings which  interrupt  the  physical continuity of a rock  mass.
Joint frequency is  a criterion by which the quality of  a rock  mass can  be judged; the
greater the frequency of joints, the lower  the quality of the rock mass. In brief, frequency
is  based  on the number of joints occurring within a given  interval of rock core or  bore
hole,  computed on the basis  of  joints  per foot. Frequency of joints was studied during
the Metropolitan Area Transit Authority investigations,  which included the  use of  bore
hole  photographic  logs  and  of  core samples recovered from the bore  holes. The logs
indicated  a frequency of  joints of one for every two feet of depth.  Examination of core
samples showed a frequency  range of  1.3 to  1.9 joints per  foot  of depth.  Concentrations
of closely spaced joints in broken zones were omitted  in making the frequency counts.
It  should  be assumed that  localized  shear  zones  with more  intense jointing may be
encountered, particularly in contact zones between different rock  types. In regard to tunnel
concentration, zones  of intense jointing might necessitate structural support or sealing off
of the zone to prevent inflow of ground water.

                                      Hydrology

Present and  Potential  Ground-Water Use

Ground water in the Washington  area  is  obtained from both the unconsolidated Coastal
Plain  sediments and from the crystalline rock of the Piedmont  sediments and from the
crystalline rock of the Piedmont province. In general, the upper  portion of the Coastal
Plain  sediments are  clayey  and contain few highly productive aquifers; the older and deeper
strata are sandier and furnish moderate  yields to wells. As of 1960, approximately 2 million
gallons per day were being pumped  from wells located within Washington; this is  lower
than  the  pumpage  rates of earlier years. Most of the  well water pumped in 1960 was
from  wells located at the railroad terminal and at other industrial and commercial  sites
in  the area  east of  North and  South Capitol  Streets. Since the Piedmont section of
Washington is  largely  residential   and is supplied  with surface water, very  little ground
water is utilized there. However, ground-water studies of nearby Montgomery  and Howard
Counties  in  Maryland indicate that  the  crystalline  rock of the  Piedmont is capable of
yielding  as much as  180  gallons per minute per well.


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It  is estimated that several additional  million gallons  per day of ground water can  be
withdrawn  from  the aquifers underlying Washington without  appreciably affecting the
present  hydrologic balance.  The  general water  supply for Washington  is from surface
sources, in particular the Potomac River, and is considered adequate for present and future
demands.  However, serious  consideration  must  be given  to protecting the  valuable
ground-water resource  from pollution and depletion, in  case further demands and changes
in  the water budget necessitate  its use.

Ground-Water Levels

Ground-water levels in the Washington area are  dependent  on several factors, such  as
seasonal changes of infiltration, presence of storm sewers to carry water away, temporary
or permanent pumping associated  with construction, and variation  in  river levels. Three
observation  wells  used  by the U.  S. Geological Survey  indicate that  the typical  yearly
variation,  from  a  high in  February or  March to  a low in August  or September,  is
approximately 5 feet.  A study of well  data  and  water  levels  in the borings made by the
Metropolitan Area  Transit Authority shows that  the ground water  level in  Washington
generally occurs at depths between 16 and 38  feet.

Permeability  of  Rock  and Unconsolidated  Sediments

Permeability  tests performed on  the  various lithologies encountered  indicated that,  in
general, the overall permeability decreases with  depth and increasing age  of the deposit,
although local exceptions to  this should be expected.

The  overall  media  permeability  coefficients for the  various  lithologies are as follows:

     1.   Pleistocene sands  and  gravelly sands   5 x  10'4 feet/minute (fpm)
     2.   Cretaceous sands and  gravelly sands   3 x 10~4 fpm
     3.   Decomposed  rock   1  x 10"^ fpm
     4.   Bedrock of all types   4 x  10'°  fpm

                                      Tunneling

Types of Tunnels

Two general tunnel types, earth and rock, have been considered for the purpose of storage.
The  earth tunnel,  which would be located in the area of coastal  plain sediments,  would
require a complete lining.  It is anticipated that the rock tunnel type would be constructed
in  areas where depth  to  bedrock  is not too great. This type would probably require a
minimum  of lining and  structural  support.

Certain desirable geological criteria reguarding the feasibility of rock tunneling have been
established  as follows:

     1.   Rock type capable  of  being  tunneled  with a minimum of  structural  support.

     2.   Bedrock  with a minimum number  of shear and fault zones, which would require
         additional structural support.

     3.   Bedrock  of high stability and relative insensitivity to tectonic disturbances.
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     4.    Bedrock of  low porosity  and permeability, to minimize the amount of water
          seepage  into tunnels.

     5.    Location below the water table, to prevent contamination of ground  water.

     6.    Sufficient depth, to avoid any effects of overlying structures or nearby existing
          tunnels.

     7.    Construction in fresh  unweathered  rock.

     8.    Location as  shallow as possible,  yet conforming to  the  above criteria, to keep
          the  economics of construction and operation at a minimum

Undesirable conditions for  rock tunneling  are as follows:

     1.    Bedrock types with thick or  irregular zones of  weathering.

     2.    Bedrock susceptible to  rapid weathering.

     3.    Rock  types  of  high permeability.

     4.    Areas  of variable rock types.

     5.    Easily deformable bedrock.

     6.    Bedrock that has been  subject to much faulting and shearing.

     7.    Unstable areas subject to tectonic disturbances.

Experience has shown  that the rock types underlying the Washington area tend to become
less weathered with  increasing depth.  In addition, as depth increases, secondary openings
become tighter  and occur with less frequency. Tunnels  constructed  for the storage of
the combined flow will probably  be located at  such  a depth  that most of the weathered
zones will be avoided.

Existing Tunnels

     Earth Tunnel

An earth tunnel was recently constructed in southeast Washington for the District Sanitary
Engineering Department. It  is a  12-foot diameter sewer tunnel extending from L and Half
Streets, S.E. to  the District pumping station at the Navy Yard. The tunnel was excavated
through recent  alluvium  and terrace  deposits utilizing  a  shield-driving method.  During
construction  of  the tunnel, dewatering was provided  by deep wells spaced at minimum
intervals of 300 ft. Although the  quantity  pumped was small, it was  felt that sloughing
of cohesionless  sand  was significantly  reduced.

     Rock Tunnel

A rock tunnel was completed in 1966 for  the National  Park Service on Rock Creek and
Potomac Parkway. The tunnel is located near the Zoo and about 1/2 mile from Connecticut
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Avenue.  It is 780  feet long with a 30-foot diameter,  and extends through a rock ridge
at a distance of 80 to 100 feet from ground surface to tunnel base. The weathered condition
of the rock encountered during construction necessitated that a concrete  lining  be  used
for the  entire  length. Problems from heavy  overbreak  in  the rock occurred during
construction. Seepage  of  ground  water caused  little difficulty,  except  where bore holes
had not  been grouted prior to construction to provide storage of the combined sewer
flows,  because  most of the  construction  will be in massive  unweathered bedrock.

A more  typical example  of  rock tunneling was encountered  in  the construction of the
Lydecker Water Tunnel (1888-1902). This tunnel extends from  Georgetown Reservoir to
MacMillan  Park Reservoir, and runs at depths ranging  from-60 to 170 feet. The tunnel
has a horseshoe-shaped section  and is brick-lined for  most of  its length; however, the
section underlying  Rock Creek is circular and  steel supported.  Except for some minor
cracks  and  bulges  that developed  near  the Georgetown end of the  tunnel  (which
subsequently needed additional  support),  no evidence has been reported  of swelling or
breaking  rock.

Rock Drillability

Laboratory tests, performed  on  the  different rock types  for the purpose of estimating
the practicability of using  tunnel  excavation machines  in the  Washington  area, measured
various factors relating to rock hardness and strength. A combination of  rebound hardness
and abrasion  hardness,  known as "total  hardness", is thought to be the most closely related
to machine drillability. Past  performance  indicates that  rock  with total hardness values
less than  120 has been successfully  drilled by machines  presently in use. The  results of
the tests  are summarized  in the  following tabulation:

                                 Compressive        Modulus  of       Total
                                  Strength          Elasticity       Hardness
                                    p.s.i.              p.s.i.

      Chlorite Schist                5,000            2 x 106         20-30
      Schistose Gneiss              10,000            5 x 106            90
      Quartz-diorite Gneiss         15,000            8 x 106        110 130


It appears that  the chlorite  schist and  schistose  gneiss can be  quite easily tunneled by
the machines  now  in  use. On the other hand,  the quartz-diorite gneiss would probably
present difficulty with  respect to maintenance,  drilling  progress, and cost.

Estimates of  the rate of drilling, based on laboratory tests and  on a measurement index
known as "Reed"  drillability,  indicate the rate of mechanical  boring  in feet  per hour.
The   following   rates  have been   estimated   for   the  three  general  rock  types:
quartz-diorite-gneiss   3 ft/hr.; schistose gneiss  3-1/2   4-1/2  ft/hr.; chlorite schist   8
10 ft/hr.

Feasibility of Tunneling

Based on  existing geologic literature and the Transit  Authority investigations, tunnels for
storage of combined sewer  flows appear to  be feasible. The  bedrock geology of  the
Washington  area in general  meets most  of  the  criteria necessary for successful  rock
tunneling. Although there are areas where the condition of the bedrock will require much
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additional  structural  support,  most of the bedrock should be capable of being tunneled
with a minimum of lining and structural support.  It is probable  that the principal mode
of  support  would   be  a   combination  of   rock  bolting  and  several   layers  of
pneumatically-applied  "shotcrete"  covering the roof area of the tunnel. Because of the
low permeability of the bedrock, seepage  of ground water will probably be insignificant
except in areas where the rock has been intensely sheared. In these cases, the shear zones
will have to be sealed to  prevent  the inflow of  large  quantities of ground water into
the tunnel. In  general, the Washington area is relatively stable tectonically; therefore, no
particular  problems are anticipated  in regard  to rock deformation and  faulting  due to
tectonic  activity.

Earth tunnels  are  considered  feasible from a  geologic standpoint. At  this stage of the
investigation, the  best  sediments in the Washington area in which to construct lined-earth
tunnels  appear to be  the more dense Cretaceous  clays, sands, and  gravels. They are
considered best because of their greater horizontal continuity and  their occurrence at more
suitable  elevations.  Even though earth tunnels are feasible geologically, the fact that a
complete lining is required may inhibit  their use for sub-surface  storage,  for economic
reasons.
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DISTRICT  OF   COLUMBIA

GENERALIZED GEOLOGIC  MAP
                                                                                                                                            LEGEND
                                                                                                                                  PRIMARILY ALLUVIUM AND ARTIFICIAL FILL
                                                                                                                                  UNDIFFERENTIATED CRETACEOUS, TERTIARY AND
                                                                                                                                  QUATERNARY FORMATIONS CONSISTING OF
                                                                                                                                  CLAY, SILT, SAND A?4D GRAVEL


                                                                                                                                  RIVER TERRACE DEPOSITS CONSISTING OF
                                                                                                                                  GRAVEL, SAND AND LOAM
                                                                                                                                  PRIMARILY CRETACEOUS CLAY, SAND AND GRAVEL
                                                                                                                                  MASSIVE LIGHT GRAY, COARSE-TEXTURED GRANITE
                                                                                                                                  GRANITE GNEISS WITH LAYERS OF SCHISTOSE
                                                                                                                                  GRANITES, GNEISS AND SILICEOUS MICA SCHISTS
                                                                                                                                  1500  0  1500 3000 4500  6000

                                                                                                                                         SCALE IN FEET
                                                                                                                                             FIGURE A-l

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CO
Ul
                           DISTRICT  OF  COLUMBIA

                       CONTOURS  OF  BEDROCK  SURFACE
                                                                                                                  1500 0 1500 3000 4500 6000


                                                                                                                      SCALE IN  FEET
                                                                                                                         FIGURE A-2

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                                 APPENDIX B

         A  LIST OF PERTINENT STUDIES AND REPORTS  REVIEWED

 1. Metcalf  and  Eddy, "Report Upon Investigation of Sewerage System",  1955.

 2. Board of Engineers (Greeley, S. A., et al), "Report to District of Columbia Department
    of Sanitary Engineering on  Improvements to Sewerage Systems", 1957.

 3. Greeley, S. A., et al,  "Report  to District  of  Columbia Department of Sanitary
    Engineering on  Improvement to Sewage Treatment Plant",  1964.

 4. Metcalf and Eddy, Engineers, "A General Plan for Development of the Water Pollution
    Control  1969-1972),  (1969).

 5. Moorehead, G. J., "Overflows from Combined Sewers in Washington, D.C.," JWPCF,
    July 1961, p.  711.

 6. Johnson, C. F.,  "Equipment, Methods, and Results from Washington, D.C., Combined
    Sewer Overflow Studies", JWPCF, July 1961, p.  721.

 7. The Potomac Interceptor Symbol  of  Metropolitan  Cooperation.

 8. Project  C. Improvements  to the Sewerage System of the Nation's Capital.

 9. Storm Sewer Preparation  Program.

10. Water Pollution Control Plant of the District of Columbia,  1967.

11. Eddy-Gregory-Greeley Report, 1933.

12. Sherman-Horner  Report, 1935.
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                                    APPENDIX C

           INVESTIGATION  OF  RAINFALL   RUNOFF RELATIONSHIPS

                                    Rainfall Data

Rainfall  data specific  to the Washington,  D.C.  area were  used in this investigation.
Intensity-duration-frequency relationships have been formulated and plotted in a previous
study using rainfall  data collected during a 60-year period from 1894  to  1954. These
relationships  are  defined in the following equation for return frequencies from 2 years
to 100  years.
       'avg   (td + b) c

     where:

        t^ = duration of storm corresponding to a period of maximum rain-
             fall, minutes

       'avg = avera9e intensity during particular duration, in./hr.

     a, b, c = constants for particular return frequencies

In addition, a plot of these relationships has been updated by the Special Studies Branch
of the Office of Hydrology to reflect additional data collected at the  National Airport
for 1951-1969.  These updated relationships have only been plotted and not formulated
in the form  of equation (C-1).

                               Peak  Rate of Overflow

The  rational  method  was used to determine the peak rate of runoff in each sewer district
and  employed  the  following  equation:

       Q = CIA

     where:
                                  I
       Q = rate of runoff in cu.ft./sec.
       C = runoff coefficient
        I = rainfall intensity in in./hr.
       A = drainage area in acres

The  areas used  were the net sewage-producing  areas of each  basin. An  average runoff
coefficient was determined for each sewer district from zoning maps and runoff coefficients
applicable to each  type of zoning. This required planimetering the maps of the Zoning
Regulations of  the  District of Columbia  (effective May 12, 1958} to determine the area
occupied by each type of zoning. Coefficients for individual types of zoning were provided
by Washington,  D.C.  The overall coefficient for  each drainage basin was then determined
by a summation of the  products of the  appropriate average coefficient for  each type of
zoning multiplied by the fraction of the products of the appropriate average coefficient
for each type  of zoning multiplied by the fraction of the total  area occupied by that
type.
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Different intensities were used in equation  (C-2) together with a constant area and runoff
coefficient to determine the rate for runoff produced in each district for different storm
return frequencies. The  intensity used for each storm was the average intensity in equation
(C-1) which corresponded  to the period  of maximum  rainfall  equal to  the time  of
concentration of  each district.

The rational method determines the peak rate of runoff, not the peak rate of overflow.
To determine this, a cursory examination was made of the hydraulic characteristics, control
structures, and average  dry-weather flow at each point of overflow. The rate of flow not
overflowing, but  continuing on in the  sewer  system was subtracted  from the peak rate
of  runoff to determine the peak  rate  of  overflow. At overflow points with complete
diversion  of all flow, the rate of sewage  flow had to  be added to determine peak overflow
rates. The specific information relative to capacity of interceptors, operation  of diversion
structures, etc.  was obtained from the District  officials, as well  as  from data  included
in previous reports. Table 5 of the main report  lists the peak rate of overflow at various
diversion  structures.

                                 Volume of Overflow

Hyetograph  Method    Volume of  Runoff

The volume of the  surface runoff of  rainfall  from a  particular  area  is determined by
subtracting from  the total  amount  of precipitation the losses due  to interception by
vegetation,  infiltration   into  permeable soils,  retention  in surface  depressions, and
evaporation. Of  these,  infiltration and retention in depressions are the only losses of
significance in  urban drainage. Numerous runoff coefficients accounting  for the combined
effect  of these  losses have  been  widely reported; however,  the  use of  these  coefficients
calls for  extensive judgment because the coefficient will vary throughout the  duration
of  the  storm.  It  is more precise  to  account for these  losses separately and  to  examine
their variability through time.

The methododogy employed to account for these losses involves the development of
hyetographs. Using differential and integral calculus, the equation for the hyetograph is
deriued from the equation  (C-1) to  be as follows:
                                                                  (C-3a)
                                             '  —                 (C-3b)
                      where:

                        tj, = time before the peak intensity, minutes

                        tg = time after the peak intensity, minutes

                        i[j = instantaneous intensity before the peak intensity, in./hr.

                        ia = instantaneous intensity after the peak intensity, in./hr.

                        r  = portion of any duration of maximum rainfall occurring before
                           the peak intensity
                           Note: tb = rtd,     ta   (l-r)td

                     a,b,c   constants from equation (C-2)



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A study (28) of the storms occurring in the Chicago area showed that r in equation  B-2
has a weighted average value of 3/8. A detailed examination of twelve consecutive months
of rainfall  as recorded at the  Washington  National  Airport Station indicates that a value
of 3/8  is  reasonable  for the Washington,  D.C. area. Hyetographs for the relevant storm
frequencies were  developed on  the basis  of this value  and of the values for a, b, and
c in equation (C-1).  As an example.  Figure 5 in the main report is the hyetograph  for
various rainfall  frequencies.

Research  (29) indicates that the capacity  which a soil exhibits for infiltration varies little
with surface slope and depends primarily  on soil porosity, ground cover, and antecedent
rainfall.  Infiltration  capacity  curves have been developed for various soil and surface
conditions, and two of the mostly commonly used curves are shown in  Figure 6 of  the
main report.

The capacity  for infiltration is relatively high at the beginning of precipitation and decreases
rapidly to a rather definite minimum value.  During  periods when the rate of precipitation
is less than the infiltration capacity, all precipitation is  infiltrated; when precipitation is
greater  than  the  infiltration  capacity,  excess runoff is  produced  in an amount equal  to
the difference between  the precipitation rate and infiltration  capacity. Consequently,  an
analysis  of  runoff requires  the  simultaneous  examination  of precipitation  rates and
infiltration capacities as they vary  through the duration  of  the storm.

Figure  7  of  the main report is  a  graph of the accumulated  mass of rainfall and  the
accumulated  mass of infiltration  for residential type pervious surfaces versus time from
beginning  of  significant rainfall. For storms in which the precipitation rate is initially  less
than the infiltration capacity, it is reasonable to assume the  same amount of  infiltration
will  occur  as  if the infiltration capacity was exceeded, but at some later time in the course
of the storm  Therefore, the time of the start of excess is found by shifting the accumulated
mass of infiltration curve along the time  axis until it is tangent to the accumulated mass
of rainfall curve. The actual  mass infiltrated follows the trend  of the accumulated mass
of rainfall  from  zero  time to  the point of tangency, and from there it follows the offset
curve of accumulated mass of infiltration  up to the point when infiltration again equals
the rate of precipitation. To define the latter point, the infiltration capacity curve is plotted
with  the  hyetograph  but at a  time-offset equal to the offset  of the accumulated mass
of infiltration curve. The point at which  infiltration again equals precipitation  is defined
as the second intersection of their curves. This procedure is illustrated  in Figure 8 of
the  main  report.

After the  precipitation  rate  again  drops  below the infiltration capacity, the deficit is
satisfied in part  by  infiltration from  runoff traveling overland. It  is conservative,  but
reasonable, to assume that for an urban area of moderate  grade and intense development
such as the Northeast Boundary  Trunk Sewer  basin, the time  of overland  travel on a
pervious surface is  so short  that this  type of infiltration is  insignificant. On this basis,
the rainfall in excess  of  infiltration  is defined as the difference  between the accumulated
mass of the rainfall curve and the actual accumulated mass infiltration curve at the point
when the  rate of precipitation equals, for the second time, the infiltration capacity. The
rainfall  in  excess of  infiltration is  shown  in  Figure  5 of the  main report.

In this study, the rainfall in  excess of  infiltration  was determined for pervious surfaces
characteristic of residential and commercial-industrial  areas.  It is assumed in this  study
that infiltration is negligible for impervious surfaces and that runoff from an  impervious
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onto a pervious surface  is insignificant, or at  least the effect of such is negligible. A past
study  by  the D.C.  Department  of  Sanitary Engineering  provides  a  sound basis  for
determining the area  of  pervious and  impervious surfaces. In the study, the pervious and
impervious areas of typical  blocks of the city  were reported as  follows:

             Block Type                      Pervious               Impervious

     Residential, single house                54.1  percent             45.9 percent
     Residential, row  house                 35.8 percent             64.2 percent
     Commercial, neighborhood             25.8 percent             74.2 percent

The  overall surface characteristics  of  the drainage basins were determined by assuming
that  zoning categories R-1 and R-2 correspond to the single  house  residential block type;
R-3, R-4, and R-5 correspond to  row house  residential  block type; C-1, C-2, C-M, and
M correspond to neighborhood and commerical  block type;  park area is totally pervious;
and  C-3  and  C-4  are totally impervious.  On  this basis, the  percent impervious,  percent
residential-type pervious, and percent  commercial-type pervious  was determined for each
sewer district.

It should be noted that  any hyetograph is asymptotic to the time axis. However, in this
study the  hyetograph was  not extended beyond the point at which rainfall intensity is
less than 0.2 inches/hour.  For pervious surfaces,  the minimum infiltration is greater than
0.2 inches/hour and  there  is  no need to examine rainfall past this point. Nevertheless,
prior to the peak of a storm the mass  of rainfall preceding an intensity of 0.2 inches/hour
may be  significant. For impervious surfaces, the total amount of  precipitation for each
rainfall  frequency  examined  was  the 24-hour  duration  value  read from the  updated
Washington,  D.C.  intensity-duration-frequency curves  published by  the  Special  Studies
Branch of the Office of Hydrology of the U.  S. Weather  Bureau.
         o
A significant volume of the rainfall in excess of infiltration is retained in surface depressions,
and  it  either evaporates  or infiltrates  after the storm subsides. Observations made during
periods of heavy rainfall  for the flat topography of Chicago suggest that the overall average
depth  of depression  storage is 0.25 inches on pervious areas and  0.06  inches on paved
areas (5).  In  a  widely  accepted design manual  (30), various investigators have observed
that  in urban areas of moderate grade the overall average depth  of surface depressions
is about  0.05 inches  for impervious surfaces and about 0.10 inches for pervious surfaces.
The  values reported in the design manual were assumed to apply to the Washington, D.C.
area  and were subtracted  from the mass of  rainfall in excess  of infiltration.

The  application to a large drainage area  of rainfall data collected at one point  outside
the area  requires  careful interpretation of two  phenomena:

     a.   The difference in prevailing  physical  conditions  at two separate, but  proximate,
          locations may  result in  different  extreme rainfall  data.

     b.   Average  depth of rainfall over a large area is  less than maximum point  rainfall.

As for the  former, the atmospheric forces of extreme  storms are  greater than the local
effects of terrain  and thermal patterns in  the Washington area, and there should be no
difference  in  extreme rainfall  data  (i.e. intensity versus frequency) at two separate sites
in the  area. To  account  for the latter, a correction factor of 98 percent was extrapolated
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from  the area-depth  relationship used by  the  D.C.  Department of Sanitary  Engineering.
The  volume  of  runoff  from each drainage basin  is determined by multiplying the  mass
of rainfall  (less abstractions) by the appropriate surface area, summing, and reducing by
the appropriate  percent value  to  account for the depth-area  relationship.

Hydrograph  Routing    Volume of Overflow

The hyetograph  method provides reliable values for the volume of runoff from any sewer
district; however, this value may differ from  the  volume of overflow. To  determine the
volume of overflow,  a  method of hydrograph routing  was used.

For hydrograph routing studies, the  hydrographs  obtained  by the  rational method  were
then further  simplified by treating them as triangular hydrographs with their peaks located
at  the  time  of  concentration  of  each   drainage  basin.  Some   of   the  critical
time-of-concentration values were obtained from the District officials,  while the remaining
were  calculated  by considering the drainage area characteristics of  each  drainage district.

A time offset method of routing was utilized to route the hydrographs down the interceptor
sewer to ascertain the cumulative effect at  any point along the interceptor. This permitted
development of  a  volume and  peak rate relationship. A velocity of three feet per second
was  assumed along the interceptor, and the appropriate hydrographs from  the tributary
districts  were plotted. Each drainage district hydrograph was offset an amount equal to
the period of time required to reach the point in  question.  The resulting hydrograph was
then  found  by  summing  up the ordinates of the  individual  hydrographs at  the required
points.

The  hydrograph developed  from  hydrograph routing was compared  with the volume of
runoff determined by the hyetograph method. Using a heuristic procedure, the two types
of information were  combined  to develop a synthetic hydrograph equal  in volume to the
runoff determined by the hyetograph method but smoothed and extended to follow the
general shape of actual hydrographs. The dry-weather flow was added  to the  synthetic
hydrograph to provide a plot of flow  rate  versus  time at  each point  of  overflow

To determine the volume of  overflow, a cursory examination was  made at each point
of overflow. This  examination practically duplicated the examination made to determine
the peak rate of overflow, i.e. interceptor capacity and type of diversion structure operation
were   accounted for. Table  5 lists the  volume  of  overflow (by  point  of overflow)
corresponding to four  different storm frequencies.
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                                    APPENDIX D

         MONITORING EQUIPMENT,  INSTRUMENTS, AND PROCEDURES

                   Discussion  of  Facilities and Operating  Procedure

At  each  monitoring site, two  fenced metal sheds, 400 to 800 feet apart, were erected
along the sewer trunk line in the vicinity  of the overflow point of the monitored sewer
district. The upstream  shed  was set up as the lithium chloride  release station and the
downstream shed  as  the sample collection station. Each pair of  stations was integrated
electrically into an operating system by an underground conduit installed in the sewer.

During each  storm,  the system was actuated by the back  pressure of a bubbler system
installed  at the manhole near  the  lithium chloride release station. Lithium chloride was
injected as a tracer for accurate  measurement  of  the  unsteady storm discharges in the
sewers. With the lithium chloride continuously  released at a specified metering rate into
the sewer, wastewater  samples  were collected  intermittently at predetermined sampling
intervals  varying according to  the duration  of storm. All the collected  samples  were
refrigerated at  3°C  until they  were ready for  analysis. Discharge flows were computed
on  the basis of the lithium concentration detected  in the  collected samples and on
application of the sample mass-conservation relationship. Major equipment and instruments
installed  at each site are shown in Figure D-1 as a schematic flow  diagram.

                 Descriptions of Principal Equipment  and  Instruments

Lithium  Chloride Release  Station

The lithium chloride release station included a continuously-operated air bubbling system,
a lithium  metering system, and an  electricity triggering  system  A metal shed 6'4" x 3'4"
x 6'11"  high housed the  equipment and  instruments.  To provide additional  protection,
a transformer-cage type of structure with  a 9-gauge cyclone fence on four sides and top
was constructed  outside the metal  shed.

     Air-Bubbling System

The air-bubbling system consisted  of an air pump, a  rotameter, a pressure regulator, a
mercury  pressure switch, and a  stainless steel bubbling-tube  assembly. Air from the pump
continuously bubbled at the bottom  of the  sewer through the pressure regulator,  flow
rotameter, and  the 1/4"-stainless steel tubing system. The back pressure  of the bubbling
system actuated  a  mercury  pressure switch, which sends proper signals to the  relay of
the electrical triggering system. During  a  storm an increase of the water depth in the
sewer activated the mercury pressure switch which,  through the relay, triggered the circuits
for the lithium chloride metering  system  and  the sample  collection  system.

     Lithium Chloride  Metering System

The lithium chloride metering  system consisted of a metering pump,  a vacuum  breaker,
and  a  polyethylene  piping assembly. The  metering pump was a piston-diaphragm pump
with positive displacement, with output adjustable by  turning the handwheel  which in
turn sets the length of  the stroke.  Maximum theoretical metering rates were 11.9 gallons
per hour for the pump  used at the  B-4 Sewer District monitoring station and 26.0 gallons
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per hour for the pumps used at the other sites. The initial setting of each metering pump
was determined by the expected intensity of rainfall  and by the maximum dry-weather
flow.  The major  moving parts of the metering pump were kept in an oil bath constantly.
The  level  of the oil  in the gear box and compression reservoir was always maintained
at 3/4" below the top.

The vacuum  breaker was an anti-siphon fixture (Watts Model  No. 288A) installed for the
prevention of back-siphonage of lithium  chloride through  the pump  head after pumping
action stopped.  It contains a  light-weight  disc-float,  which  opened and  closed the
atmospheric vent according to the pressure  downstream of the outlet of the metering
pump. The minimum  negative pressure head  required  in the discharge  line was 6 inches;
at each monitoring site, this requirement was met  all  the time. The vacuum breaker was
located above the possible highest  level  of the lithium chloride in the storage tanks. In
order to prevent caking of lithium chloride  residue in the pump, a water-rinse line was
attached to the piping ahead  of the  inlet to the  metering pump. The lithium chloride
injection line downstream of the vacuum breaker was  1/2"-diameter polyethylene piping.
At each  lithium  release station, one electric clock wired  into the storm time  operating
circuit provided an accurate  estimate of total storm  operation time.

     Electricity Triggering  System

The Electricity Triggering equipment included one magnetic contactor, two manual motor
starters, underground  conduit,  and liquid-tight junction boxes, as shown  in Figure D-2.
The magnetic contactor provided a safe and  automatic connection  for  the time-operated
circuits. The  magnet coil was wired  to be energized by  the current through the pressure
switch.

The entire assembly was housed  in a water-tight enclosure on the panelboard in the lithium
chloride   release  station.  Also on  this panelboard  were  manual  starters   used  for
supplementary  control of the lithium metering pump  and water-level  recording systems.

Underground conduit  was installed  to integrate the operations of the lithium release and
sample  collection systems; this consisted  of a 3-conductor,  neoprene-jacketed  cable,
pre-assembled in  a  1-1/2"-diameter polyethylene pipe. The conduit was fastened along
the center top of the sewer with  power-charged   Ramset studs and EMT strips.

Flow  Depth  Recording System

At one of the sampling sites in a combined sewer district, an electronic flow-depth recording
system  was installed.  Integrated with the bubbler tubing  assembly, the  flow recording
instruments included a process pressure-to-current transmitter and an electronic strip chart
recorder.

The process pressure-to-current transmitter was an electronic instrument operating on the
principle of force balance. With the  bellows as the pressure element,  the transmitter
produced  an  electrical output signal  in milliamps.  The monitoring  range  of the pressure
was fully  adjustable between  zero  and the  maximum pressure, which in turn could be
adjusted  between  15  and  150  inches of water. In the  present instance, the transmitter
was calibrated  for a  pressure  range 0-100 inches  of  water.
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The water-level recorder was a 3" x 6" strip-chart electronic recorder. It accepted electrical
analog signals representing pressure as input, recorded the  input on a 4" strip chart, and
displayed  the value on a vertical indicating  scale. The input signal ranged between 4 and
20 milliamps DC. An internal power supply (117 volts AC) provided operating  power
for the transmitter.  The  accuracy  of the recorder was ±0.5  percent  of  the  range, and
repeatability  was ±0.2 percent of  the range. Recording chart speed was 7/8" per hour,
and the useful length of each roll  of chart was sufficient to permit continuous operation
for more  than a month.

Sample Collection System

The   sample  collection  system  consisted  of  a  submersible  pump,  a  refrigerated
vacuum-charged sampler, a wastewater retention tank, a portable vacuum pump, and the
piping system  associated  with wastewater flow.  During  a  storm  the sample collection
system and the lithium chloride release station were triggered by the increased back-pressure
of the bubbler  line  resulting  from the increased depth  of combined  sewer overflow or
separated  storm water discharge. The  wastewater was pumped to the surface continuously
by a  submersible  pump anchored  onto the floor of the sewer and flowed through the
wastewater retention tank (retention time  normally  less than one minute). The sample
was  collected by  the vacuum-charged sampler according  to  a predetermined sampling
interval. The wastewater retention  tank, the refrigerated  sampler, and the piping all were
housed in a  7' x 5'3" x 6'6"  metal  shed, protected  by a  9-gauge cyclone fence around
its four sides and above  its top.

     Submersible Pump

The submersible pump was a  heavy-duty, manually-controlled  sewage pump.  It could be
operated for long  periods with the motor housing out of water, without damage. In view
of the impacts generated  by the hydraulic surge  and the heavy solids flowing down the
sewer  during  a  storm, a  solid,  rigid  anchorage  for  the submersible pump was designed
and constructed. To provide additional protection against large pieces of  solid waste, an
expanded  metal cage was installed for the containment of the pump. The legs  of the
pump  were fastened onto the bottom plate of the prefabricated cage with three  1/2-inch
machine bolts, and the cage was anchored  onto the bottom of the sewer with four 1/2-inch
diameter Rawl plugs. To  furnish additional  stability for the anchorage, angle  irons were
installed to brace the rigid pipe extending from the  outlet  of the submersible pump. The
capacity of the  pump was 60 to 80  gallons  per minute, depending on the pumping head
required at  the different  sites.

    Automated Sampler

The sampler  installed at  each site was an  automated sampling device equipped with a
portable vacuum pump and an electric timer to adjust the sampling interval to the desired
period (5  minutes minimum). Twenty-four bottles, each  with  an individual sampling line
and the control switch, were furnished  for each sampler  and installed in a  refrigerated
enclosure. The  intake ends  of sampling  lines (sampling head) were  in the wastewater
retention  tank, and  the sample was drawn into the  bottle by vacuum when  the control
switch was released by a tripper arm operated in conjunction with the timer. Photographs
of the sampling components  are presented  in Figure D-3.
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Rain Gauges

The rain gauges were spring-driven, weighing-recording instruments, with 12 inches of range
and a 24-hour time scale. The precipitation was measured in a prebalanced collection system
by a weighing  mechanism,  which guided the  pen to trace  on a paper chart. The chart
drive was spring-wound, and  it rotated a cylinder  on which the chart paper was held.
The accuracy of the rain gauges  in the first traverse (0" to 6") was ±0.03", and ±0.06"
in the  second traverse  (6"  to 12").

A dashpot  was provided to  minimize irregularities  in  the  chart  trace. In view of  the
requirements for truly representative records and to protect against vandalism  the gauges
were installed on  the  roof  of the public schools in the  vicinity of the sampling points.
Their locations  were:   1) Francis Junior High  School,  at IN and  25th Streets, NW;  2)
Chamberlain Vocational  High School, at 14th and Potomac Avenue, SE; and 3) Anacostia
Senior  High  School, at  R and  16th Streets, SE.

Each of the rain gauges was fastened to a  solid foundation, and the base was carefully
leveled. To  minimize possible damage from  snow drifts  or floods, each gauge was set up
on a wooden platform  15  inches above the roof. For each rain gauge, windbreakers  of
2" x 12" x  1" white pine were installed to provide additional stability for the measurement
of rainfall,  as illustrated  in  Figure  D-4.

                         Lithium Chloride  Flow  Measurement

General  Procedures and Principles

The  lithium dilution  procedure  provides  an  accurate  and  simple  technique for the
measurement of wastewater  flows which may  be applied when:

     1.   Flow measurement devices do not  exist,

     2.   Temporary installation  of  flow measurement devices is  difficult, and

     3.   Suitable  conditions  for application  exist in the wastewater  system

The  lithium dilution  procedure was a modification of the long-applied  salt  dilution
procedure. The use of a lithium  salt improves the technique  because  the  background of
lithium  in wastewater is usually low,  and because lithium concentrations at fractional parts
per million  levels  can  be accurately and conveniently determined by atomic  absorption
or flame emission spectroscopy.
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The technique involves preparing  a lithium  salt  at  a  known concentration and  then
delivering to the  wastewater stream at a continuous precise rate. At a point downstream
where  the lithium  salt has become homogeneously mixed  with the  flow of wastewater,
the wastewater is sampled and the  concentration of lithium is determined. The flow of
wastewater  is then calculated as:
                       Ci     Co
         where:

         Qw  = the flow rate of wastewater in the sewer, in gallons per minute (gpm)

         QI  = the metering rate of the lithium chloride solution, in gpm

         C-|  = the lithium concentration in the lithium chloride solution, in milligrams/
                liter (mg/L)

         C2  = the lithium concentration in the collected sample in mg/L, and

         Co  = the lithium concentration in the raw wastewater, in mg/L

Since repeated analyses showed that the lithium concentration  in the  raw wastewater was
consistently at  undetectable  level.  Equation D-1  was simplified by eliminating  Co,  as
follows:
                 Qw =  Ql x
                                 C2

          which rearranges to:


                 Qw +  Q-|  =  Q-]  x	


However, during a storm the metering rate of lithium chloride (Q-|) is negligible compared
to the wastewater flow rate (Qw), and thus it can be eliminated from the left-hand term
of Equation  2 without affecting  the  accuracy of subsequent calculations. This permits
further  simplification of  the equation  to:
         Qw  = Q!  x
                       C1
Precautions
The  preparation  of  the  lithium salt  solution requires a high  degree of mixing to insure
that  the lithium  is homgeneously  dispersed. Because of the density of the salt solution,
stratification can occur, if  mixing is  inadequate. Once the  solution  is prepared, it will
remain  homogeneous.

Mixing in the wastewater stream after the lithium solution is added must adequately achieve
a  homogeneous  dispersion  of  lithium  throughout  the wastewater  stream  before  the


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downstream sample is taken. If the wastewater stream is essentially in laminar flow  the
salt dilution  procedure  cannot be employed.

Application to D.C. Combined Sewer Study

Lithium chloride solutions varying in strength from 60,000 to 78,000 mg/L were purchased
from  the  Foote Mineral Company. The actual lithium concentration  in each batch was
determined by ROY F. WESTON personnel using  an atomic absorption spectrometer. The
lithium chloride solution was introduced into the sewers (by means of previously calibrated
pumps) at flow rates as high as 260 milliliters per minute. Lithium chloride solution volumes
were determined before and  after each  dosing period, to serve as  a check on the dosing
rate. Since lithium is detectable  in concentrations as low as 0.005 mg/L, flows as high
as 1,000,000 gallons  per  minute could be measured with reasonable accuracy.

                                Monitoring Practices

Storm-monitoring activity  was triggered automatically by the increase  of  depth  of water
in  the   sewer.   Lithium   chloride   release,  submersible  pump  operation,  and the
sample-collection system were started by this initial impulse. However, a time lag of 5-10
minutes was  built  into the program for the start of actual sampling, to give enough time
for the injected lithium chloride to mix with the wastewater and to flow  to the downstream
manhole. The operational  metering  rate for lithium chloride solution was calculated from
the storage tank  levels  before and  after release, and  from  electric clock measurements
of initiation  and  completion of release.

After each monitored storm, the collected samples were immediately brought to the ROY
F. WESTON  laboratory in  West Chester,  Pennsylvania  for analysis.  The  characteristics
determined for each sample  included: BOD, COD, settleable solids, total solids, volatile
solids, suspended  solids, volatile suspended solids, lithium chloride, total  coliform fecal
coliform,  and fecal streptococci. Total  phosphate,  total nitrogen, and  other  nutrient
analyses were performed by ROY F. WESTON personnel at Baltimore's  Back River Sewage
Treatment Plant.

The lithium concentration was analyzed  in an atomic absorption spectrometer. All analyses
of the  other chemical  and  physical characteristics  were conducted  according  to the
appropriate procedures in   "Standard  Methods  for  the Examination  of Water and
Wastewater",  Twelfth Edition,  1967.  The  bacteriological  analyses  were basically  in
accordance with the membrane  filter technique  suggested in "Standard Methods", with
various  equipment  and  procedural   improvements  as  recommended  by  the  filter
manufacturer.

After each storm  operation,  the lithium chloride release  lines,  the metering-pump head,
the wastewater retention tank, the sample  collection  piping, and the sampling lines were
rinsed clean with tap water. The area around the submersible pump was cleaned of debris,
rags, and large solids. Before the systems were set up for the next storm  all  equipment
and instruments were turned on by  hand  to check  for  proper functioning.
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During the  monitoring  program,  several operating problems were encountered, the most
significant of  which were:

     1.   Difficulties in Pumping Wastewater Up from the Sewer-The submersible pump
         anchored to the bottom of the sewer was often clogged by solid wastes (such
         as cans, rags,  wire, wood  chips, tree stems,  gravel,  sand,  etc.)  and stopped
         working.  There were also some pump stoppages during  low-intensity  storms,
         probably  because  of insufficient water depth  in  the  sewer.

     2.   Physical Damage to Equipment  Installed in the Sewer-During intense  storms,
         heavy  solid wastes  (such as tires, concrete slabs, 55-gallon  drums,  mattresses,
         automobile  radiators,  chains, etc.) slammed into the protective  cages of the
         submersible pumps  and caused  extensive damage to various equipment items.
         Bubbler lines were  broken  and torn loose; the  protective cage  was severely
         deformed and even  disintegrated; pump  braces were sheared off; pumps were
         washed away  in the  sewer; and the electric conduit was pulled out of its fastening
         studs.

     3.   Flooding of  Lithium Chloride  Release Station  at Rose Park Playground-This
         station was sunk half way into the ground, at the  request of  the local residents.
         Consequently, the lower part of the structure was  inundated by  excess storm
         water  runoff. This  flooding caused minor damage to  the bubbler instruments,
         the  lithium chloride  release  system  and the pressure-to-current transmitter. This
         problem was  overcome by  reinstalling the equipment above grade.

The equipment  malfunctions  and physical damage described above prevented complete
coverage of all  the storms  that  occurred  during the monitoring period.
                                       151

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-------
                                                                              FIGURE  D-2

                                                            ELECTRIC POWER SUPPLY AND TRIGGERING SYSTEM
                                      14>-IOO AMPS SERVICE

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                                                                                                                                          (HUBBEL #7736)
                                                                                                                                                                  D-2

-------
                         FIGURE  D-3
                    SAMPLING COMPONENTS
REFRIGERATED AUTOMATIC SAMPLER
         INSIDE OF SAMPLER
                                   PLATE SWITCHES OF SAMPLER
   WASTEWATER RETENTION
      TANK AND PIPING
154
D-3

-------
         FIGURE  D-4
        RAIN  GAUGE
RAIN GAUGE AND WIND BAFFLE
             155
D-4

-------
                                   APPENDIX E

          MONITORED WASTEWATER FLOWS AND CHARACTERISTICS

                        Comparison of Representative Storms

The  characteristics  of the combined sewer overflows and of the separated storm water
discharges  generated  by  representative  storms  are  described  herein, according to the
duration and  intensity  of the  storms monitored.

A detailed  examination  of some graphs reveals an apparent discrepancy, at times, between
rainfall  intensity and flow rate. For example, flow may be  decreasing while it is still raining
at a significant rate. Inconsistencies such as this reflect the non-uniform spatial and temporal
distribution of rainfall over the drainage basin. Although rainfall  was measured at a location
closest  to  the sampling point in each of the districts, the rainfall  intensity  may vary
considerably between that measured at the point  of sample collection and that which
is actually  falling in  upper areas of the drainage basin.

Dry-Weather Conditions

In order to provide  a  more accurate definition of the pollution problem of  combined
sewer overflows,  a  24-hour dry-weather flow study was conducted for Sewer  District G-4
on September 22,  1969.  The time variations of the  characteristics and of the flow rate
of the  dry-weather flow  from  this combined sewer  area are presented in Table E-1 and
in  Figure E-1. The range and mean value of each of the waste constituents in  dry-weather
sewage  are presented in  Table  E-2. The characteristics  of the dry-weather flow were
consistent  with those expected for municipal sewage.

The  dry-weather  flow  for  Good  Hope  Run Separated  Storm Sewer  District was also
monitored; a  very  small  flow  of significantly polluted water was observed.  Quality and
flow data for a 24-hour dry-weather flow study are  shown in  Table  E-3 and Figure E-2.
Hydraulically, the  variation  of flow was minor. The  biochemical oxygen demand was
generally between 10 and 20 mg/L; comparative chemical oxygen  demand concentrations
were 40 to 100  mg/L. The bacteriological analyses  show that the mean values of total
coliform and fecal  coliform  were, respectively,  24,000  counts/100 ml and  21,000
counts/100 ml.

Whereas the dry-weather  flow from the  combined sewer  district  exhibited characteristics
which were expected, the flow from the separated storm sewer  district indicated relatively
high BOD,  COD, and fecal  coliform levels. The BOD's  and COD s  could be explained
by decaying organics in  catch basins, inlets, manholes, and deposition in the  pipe. The
fecal coliform level is less than  one percent of  the corresponding value in the combined
sewer district, and  is  an indicator that either some sanitary sewage or animal  fecal  matter
is entering the storm sewer.

Short-Duration Storms

The  data derived from the samples collected for the storms on  June 8 and June 15, 1969
indicate the combined sewer overflow quality and quantity in Sewer District G-4  for storms
of short duration. Figures E-3 and  E-4 show the starting time, the duration, and the total
rainfall  of  these  storms.  Because samples were  collected  only  during the period of high
                                        157

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flow  in  the sewer (the monitoring  equipment automatically  shuts-off when the flow
subsides), the fact that  samples were not obtained indicates that the flow rate is quite
low  at the  end points of the graphs,  with  corresponding concentrations  of pollutants.
The  total rainfall of each storm  was the same, 0.7  inches, but  the peak flow rate  during
the storm of June 8, 1969 was much  higher than that of June 15, 1969. The characteristics
(other than  the settleable solids concentration) of the combined sewer overflow generated
by these two storms were almost identical because both storms occurred during the same
season and both had comparable waste accumulation times, as measured by the dry-weather
period before precipitation.

For  the short intense storms, as shown in Figures E-4  and E-5, the concentration of each
waste constituent was  observed to increase with the discharge rate in the sewer; the peak
concentrations of  many  waste constituents were  concurrent with the peak flow.

The  concentrations were significantly  high  and  remained so  throughout  most of the
monitoring  period. For  example, for the  intense storm  of June 8,  1969,  the flow rate
was  relatively constant during the 30-minute storm discharge period, but the concentrations
of pollutants peaked in the early period of discharge and  decreased to approximately one
half  of the  peak value after two thirds  of the discharge period had elapsed. The observed
peak values for biochemical oxygen  demand, chemical  oxygen  demand, and suspended
solids were  405 mg/L, 1,358  mg/L, and 1,268 mg/L, respectively.  The fraction of the
fixed or inorganic solids was about one half of the total  suspended solids, and  this
essentially   constant  relationship  reflected  the  composition  of   surface flushings.
Characteristically, the ratio of  COD to  BODs in the wastewater during this  short  storm
period varied  between 3.0 and 20.

Long-Duration, High-Intensity  Storms

The  time variation of the quality and  quantity of wastewater generated by a  long-duration,
high-intensity  storm at Sewer District G-4 is indicated by the data for the storm on August
2, 1969  (Figure E-6). This shows that the flow rate of the wastewater generated by this
long, intense storm is much higher than  that of short storms. However, the concentrations
of various constituents were  observed to be lower, which is an  anticipated  result of high
dilution by  storm water.

Similar results were observed at  Sewer District B-4, as shown in  Figure E-7. In general,
the concentrations of specific waste constituents measured at District B-4 were lower than
those at  District  G-4.  This  may be explained by the  fact that higher sewer flows were
required  before sampling could be triggered.

Concentration data in Figures E-3 and E-6  show that  chemical oxygen  demand  and
suspended solids  concentrations of wastewater  from a long, intense  storm  are reduced
to approximately  one third of the comparable values for a short,  intense storm  The
biochemical  oxygen demands for the long, intense storm wastewater were about one seventh
of that in short-storm wastewater. This also implies that a higher fraction of surface material
was eroded by the long intense storm. However, the ratio  of COD to BOD5 was essentially
the same as that for short-storm wastewater.

Consecutive  Storms

The  characteristics and quantities  of  wastewater generated by consecutive storms can be
represented  by the data of the four storms during July 27-28, 1969, as presented in Figures


                                       158

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E-8 and  E-9. The initial flushing effect was observed in all  cases, even  when the storms
were only a few hours apart. However, the average concentrations of specific contaminants
were observed  to follow a decreasing  trend with consecutive  storms. For example, the
average concentration  of chemical oxygen demand (COD) decreased from 307  mg/L for
the first storm  to  154 mg/L  for the fourth storm  This decrease may be attributed to
the reduction of waste material accumulation on the  surface and in the collection system.
The ratio of COD to  BODs was essentially {he same as the comparable ratios for  short
storms and  for  long-duration,  high-intensity storms.  The characteristics  of long-duration,
low-intensity storm wastewater probably  will be similar to that observed for consecutive
storms.
I

     Separated  Storm  Water Discharge

Nine storms, of varying size, were monitored at the Good Hope Run Sewer District. Table
E-4 and Figures E-10, E-11,  E-12  and E-13  illustrate  the  quality and quantity of the
runoffs from a short  intense  storm a long intense  storm  and two consecutive storms.
The average organic and nutrient concentrations in separated storm water discharges were
observed  to  be approximately one third  of  those  in combined  sewers,  but the solids
concentrations  (especially non-volatile solids and settleable solids) were much higher than
those  in  combined sewer overflow. However, this phenomenon is attributed to the
differences in the urban  development  on  land surfaces in  the monitored areas.

In general, the  time variation in characteristics of wastewater from separated storm sewers
is  very similar  to that from combined  sewers. These figures also show the effects of the
intensity, duration,  and  frequency  of rainfall on wastewater  characteristics. When the
interval between storms is short, the accumulation of contaminants on the surface is less,
and storm water is less contaminated.

One significant difference observed  for separated storm sewer discharge  is the broader
range of COD  to 6005 ratio  (1.8 to 32).  The higher ratio probably reflects a significant
level of  chemically  oxidizable  inorganic  material introduced by erosion.

                     Bacteriological  Quality of Storm  Wastewater

Combined Sewer

The  bacteriological examinations were  made on selected individual samples. The range of
variation  and the mean values of different bacteria  species are summarized in Table 9
in the body  of the report. As presented  in Figure E-14, the bacteriological counts varied
with the  flow  rate  of combined  sewer overflow during each storm  The initial flushing
also  had  a  significant effect  on various  bacteria counts.

The mean values for total and  fecal  coliforms were, respectively, 2,800,000 and 2,400,000
microorganisms/100 ml.

Separated Storm Sewer

The variation of bacteriological data for  the separated storm sewer discharge was similar
to the variation in the combined sewer discharge. Bacteria counts were high at the beginning
of the storm and then decreased as the storm progressed. For instance, the average bacteria
counts in the  early part of the storm  runoff on August 9,  1969  were 1,340,000/100
                                         159

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ml, 1,300,000/100 ml, and 31,000/100 ml, respectively for total coliform, fecal coliform,
and  fecal  streptococci,  whereas  in  the  later  part of the  storm  they  averaged only
540,000/100 ml, 160,000/100 ml, and  17,400/100  ml, respectively.

Bacteriological  examinations  were made for  selected samples, and their results indicated
that microorganisms  were present in storm runoff  in fairly significant amounts although
less than  in combined sewage as cited  in Table 9.  The mean values of total and fecal
coliforms   in   separated   storm   sewer   discharge  were   600,000   and   310,000
microorganisms/100  ml.

                Waste  Loadings from  the Monitored  Sewer Districts

Waste  loading during a storm is  the total  waste material  discharged, as pounds per unit
time, and is computed from  the  measured flow rate and the concentration  of  each waste
constituent. Expression  of the  waste  loading  in  terms  of pounds of  specific waste
constituent  per minute  provides an  integrated assessment of the pollution potential
associated with the wastewater generated by different storms. The range and mean value
of waste  loadings  from  the  monitored storms and from  the dry-weather  flow in Sewer
District G-4 are summarized  in Table  E-5.

Waste  Loading Associated  with Combined Sewer Overflow

The variation  in waste  loadings of combined sewer overflow  was  found  to be  highly
dependent on the fluctuation of the flow rate in the sewer, which changed with  the rainfall
intensity during each storm.  For  an impulse-type short storm, the waste loading reached
the peak value immediately and decreased very  rapidly with time  (see Figure  E-15). For
a  long intense  storm  (with  more  than  one  discharge peak)  the  loadings  of  various
constituents varied with  the flow rate  during the initial peak as anticipated (see  Figure
E-16). When a  second peak occurred, the  loadings  increased with discharge only through
the first few minutes and then dropped rapidly. Thus, most waste materials were carried
by  the  initial flushing and  scouring of the  sewer. Waste loadings carried by the secondary
flushing in a prolonged  storm were  limited.

The waste-loading  time-variations in  combined  sewer  overflow  associated  with  the
consecutive storms are presented together with the flow rate and the rainfall data in Figures
E-17 and  E-18. As anticipated from flow and concentration data, an initial impulse loading
was always observed  for the short intense storms even though they were only a few hours
apart. Also as anticipated, the magnitude of the initial loading was found to be proportional
to the  length  of the dry-weather period between  the  storms. The organic loading after
the initial flushing of each storm  was almost always low;  for instance, the COD loading
at the end of  each  consecutive  storm  was  between 20 and 60 pounds per  minute on
the monitored  areas, while the peak loadings varied between  105 and 346 pounds per
minute. This implies that a certain base value may exist for the average organic loading
in combined sewer overflow  in each sewer  district.

The mean waste loading of the dry-weather  flow (sanitary sewage from District G-4) was
calculated  to  demonstrate  the relationship between the pollution loads  of dry-  and
wet-weather flows. Because of the significant increase in flow rates  during wet weather,
the pollution load during such a time  may be as much as three orders of magnitude higher.
                                       160

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Waste  Loading Associated with  Separated  Storm  Water Discharge

The waste loadings contained in separated  storm water discharges varied with time in the
same manner as combined sewer overflows. Generally, the peak organic loading in separated
storm water discharges was lower than in combined sewer overflow, but  the peak solids
loading was higher  (see  Figures E-19, E-20, E-21  and  E-22).  However, these deviations
may be  attributed to the difference in  surface runoff  characteristics  of the monitored
sewer districts. Silt was found to be the dominant factor in  storm  water discharges from
the  Good  Hope  Run Sewer  District.

                      Total Waste  Load in Storm Water  Runoff

The pollution  constituents  found  in  storm   water  runoff  constitute  inputs to  the
environment or disruptions of  the  environment. These  include:

     1.    Depositions on the surface from air  pollution,

     2.    Depositions on highways  from vehicular traffic  or dust  control  activities,

     3.    Practiced depositions from such activities as plant fertilization or insect control,

     4.    Natural  degradation for flora and fauna,

     5.    Soil erosion, and

     6.    Air  pollutants  washed from  air  during  rainfall.

The waste  load in a particular  storms depends upon: 1) the amount of material which
has  accumulated or developed on surfaces  since the last storm  and 2) the  efficiency of
the  washing action  accomplished by the storm

If the storm  waters  are transported  through  combined  sewers,  materials which  have
accumulated between storms may be  flushed  from the sewer. Any attempt to predict
waste loads which will be generated by a specific storm must  be based upon knowledge
of the inputs to the  drainage area and the washing  efficiency that the storm will develop.
Waste  loadings generated by  storms in combined  and in separated storm sewer districts
are presented in Table E-6. The total waste loading generated  by each storm was computed
by  integrating  the waste-loading time  relationship of  each storm  Since  the total waste
loading carried  by each  storm  could be a function of  intensity of rainfall, quantity of
rainfall, variation of  the  surface  runoff characteristics, duration of the dry-weather period
before the  storm, and factors related  to surface  deposition, it  would be  very difficult
to  derive any  definitive correlation between  any  type  of total waste loading and the
variables mentioned  above. Examination of the data indicates that depositions from  air
pollution are very important in waste generation, because the waste loading is appreciably
larger for a  storm  interval of even a  few days (that is, larger than  for a one-day or shorter
interval). The major source of the rather rapid accumulation of materials is logically from
air  pollution; other sources are  catch  basins,  inlet boxes, and street  sweepings.

Two storms which provide  a  good comparison occurred on  June 8  and  15, 1969 in
combined Sewer District G-4 (refer to Figures  E-3 and E-4). Rainfall  in each of the two
storms was the same (0.7 inches), the dry-weather period before each storm was about
                                        161

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the same  (6-7  days), and  the storms were one week apart, which should eliminate any
seasonal differences. Also, the dry-weather flow  should have been the same since both
storms occurred in the  afternoon  of the  same day of the week.  In addition to this, the
characteristics of the rainfall event preceding  the June 8th storm  were approximately the
same  as those during the June 8th storm. However,  the maximum intensities of the two
storms were different, being 4.0  inches per hour  on  June 8 and  2.5  inches per hour on
June  15. The more  intense storm produced about twice the  waste load, as measured by
chemical oxygen demand. Maximum storm intensity and waste loading appear to correlate,
which suggests that depositions to  be carried away by the  storm flow were equal and
that the different results  were due to  washing  efficiency.  A potential  fallacy in this
reasoning is related to depositions on surfaces. Depositions which existed before the more
intense storm may have been twice as  large.  The  number of  days of dry weather is not
in itself  an adequate criterion for  estimating the deposition on  a  given  area  from air
pollution. Wind direction and velocity as related to pollution sources are potentially more
important.

Examination of the data  in Table E-6 shows  that  there are general trends which  are
influenced  by the length of  dry-weather periods, total rainfall, and rainfall intensity. The
variations of the total loadings of COD and suspended  solids with total rainfall of each
storm  are presented in  Figures E-23 and  E-24. The relationships  were fitted to the data
using the method  of least  squares. Although the results tend to be inconclusive and there
is considerable data scattering, Figures E-23 and E-24 show a  recognizable difference
between the separated and the combined sewer districts; however, they do not show the
consistent  pattern that  might have been expected for the two combined  sewer districts.
Despite the inconsistencies in the available data, an attempt  has  been made to  establish
a correlation between various parameters. The average correlation  between the total COD
loading and total rainfall for Sewer District G-4 can  be derived from  Figure E-23, as follows:

     L =  1,000 x e1-47F     , with 0.5>   F >  3.0

     where     L  =  total  COD  loading, in pounds per storm, and

               F  =  total  rainfall  of the  storms,  in  inches

Similarly an  average suspended solids correlation can be derived:

     S = 600 x e°-44F     , with  0.5>  F  >   3.0

     where     S =  total suspended solids  loading, in  pounds per storm

The  variation of runoff with the progress of the storm showed  a reasonably consistent
relationship to the change in  rainfall intensity. Figures E-25, E-26,  and E-27 depict typical
variations  of wastewater depth  in the  sewer, rainfall intensity, and  wastewater flow as
the storm  progresses; these  plots  show the  respective  effects of  a short intense storm,
a long intense  storm, and  consecutive storms in a combined  sewer district. Rainfall and
runoff data were also compared to develop the coefficient used in the calculation of volume
of storm runoff.

In order to generalize the  quality of both combined sewer overflow and separated storm
water  discharge,  the concentrations of  different wastewater quality  parameters were
compared and correlated. A comparison between BOD^ and COD  is shown in Figure E-28,
                                        162

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in which the relationships were fitted to the data by inspection. The ratios between average
BOD5 and average COD are 0.20,  0.14, and 0.11 for Sewer Districts G-4, B-4, and Good
Hope Run,  respectively. This implies that the organic materials  in separated storm water
discharge  do not degrade as rapidly or as  completely  as the organic materials in combined
sewer overflow. The average ratio of 6005 to COD for the combined sewer overflow
from  Sewer District B-4 falls between the ratio for combined sewer overflow from Sewer
District G-4 and the ratio  for the separated storm water discharge  from the Good Hope
Run District, possibly because the combined sewer overflow monitored at Sewer  District
B-4 was more highly diluted by  storm runoff than was the combined sewer overflow in
District G-4. As shown in Figure E-29, the  correlation (developed by fitting the relationships
to the data by inspection) between  volatile suspended solids and total suspended solids
averaged  0.50, 0.30, and  0.052, respectively, for  G-4,  B-4, and Good Hope  Run. This
indicates that the  organic proportion of  the solids  varied in much the same  manner as
the BOD5-to-COD  ratio for  the wastewater  collected at the different  sewer districts. The
ratios of  the  volatile suspended  solids to total suspended solids also indicate that most
of the solids  contained in storm runoff  are non-volatile silt and  sand.

The  results  of the various comparisons  and correlations indicate that there are definite
overall trends  within these  relationships; however,  they  are very  loose.  Although it is
believed that a  relationship could be developed for surface characteristics and depositions
to relate to waste  loading characteristics, sufficient data were not collected to  define this
relationship.

                       Comparison  of Flow Rate Measurements

Use of the steady-state formula and flow  depth  measurement has been the basic approach
of many engineers to estimation of the flow rate  of storm runoff.  This method  may be
valid  for  the  flow in streams or rivers, where flow  variations generally are  gradual.  The
flows of interest in the current study, however, vary drastically with time, especially during
the surge period of a storm. Thus, a formula for  calculation based on steady-state flow
was considered not applicable. The lithium dilution tracer method as a  direct measurement
technique was selected, therefore, as the primary flow measurement  method in  this study.

Tracer dilution  methods  are  recognized as  reliable  and  practical  flow measurement
techniques in both laboratory and industrial operations. Application of the lithium dilution
method to  a variety of  industrial wastewater  stream  flow measurements by  ROY  F.
WESTON  has shown  an accuracy  of ±4 percent  (6). A  detailed outline of the lithium
chloride flow measurement  technique  is presented  in Appendix D.

For purposes of comparison, flow estimations were  made at Sewer District G-4 by assuming
steady-state conditions (Manning equation) and  measuring the depth  of flow. A plot of
the "depth" method versus the reference  lithium chloride method is  shown in Figure E-30.
Although  a detailed  statistical evaluation was not made,  the data were  observed to  be
a general cluster around the 45° line of exact correlation. The maximum predicted gravity
flow  using  the Manning  equation  (n  =  0.015, s = 0.0459 ft/ft, Diam = 5.5  feet) is
approximately  280,000 gpm.

It is  felt  that  the variability in  the flow rate estimated  by depth measurements is due
to the lack of applicability of the steady state flow formula to the estimation of storm
runoff.  However, the depth-of-flow measuring instrument may  have malfunctioned (leak
in the line,  insufficient air pressure etc.)  even though this was not detected.  Nevertheless,
                                         163

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the tracer  method  may  introduce some errors into the results  unless feed rates, remote
operations, degree  of  mixing,  and concentration of tracer  during  storage are carefully
checked or controlled.  Besides this, the tracer method gives no indication of flow between
samples.

In order to verify the unit hydrograph approach to the estimation of total runoff discharge,
the flow data generated by the  lithium chloride dilution method in District G-4 for various
monitored  storms were compared with unit hydrographs constructed for the same storms.

The actual  total discharge of each storm was determined by integrating the measured flow
rates with time, with peak rates taken directly from the field data. The unit  hydrograph
methodology was discussed in a  preceding section and in Appendix C. Table E-7  summarizes
the results  of this  comparison.  For each storm compared,  the total measured runoff was
within  ten  percent of  the amount established  from the corresponding unit hydrograph.
                                        164

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         Sampling
           Date
       Sept. 22, 1969
O)
01
       Sept. 23, 1969
Schedule
 Time
Sampling
 Interval
 minutes
10:50 a.m.
11:48 a.m.
12:46 p.m.
1:44 p.m.
2:42 p.m.
3:40 p.m.
4:38 p.m.
5:36 p.m.
6:34 p.m.
7:32 p.m.
8:30 p.m.
9:28 p.m.
10:26 p.m.
11:24 p.m.
12:22 a.m.
1:20 a.m.
2: 18 a.m.
3:16a.m.
4:14 a.m.
5:12 a.m.
6:10a.m.
7:08 a.m.
8:06 a.m.
9:04 a.m.
10:02 a.m.
11:00 a.m.
11:58 a.m.
58
58
58
58
58
58
58
58
58
58
58
58
58
58
58
58
58
58
58
58
58
58
58
58
58
58
58
                                                                                 Table E-1

                                                              Dry Weather Flow For Combined Sewer District G-4


Flow
gpm
1,000
1,000
940
955
900
882
940
985
1,000
1,015
985
955
940
711
872
604
542
516
477
438
457
542
780
1,156
940
956
928


£H

6.5
6.7
6.7
6.6
6.8
6.8
6.8
6.6
6.4
6.7
6.6
6.8
6.4
6.4
6.6
6.6
6.6
6.7
6.8
6.6
6.4
6.4
6.8
6.7
6.8
6.6
6.7


COD
mg/L
360
340
330
360
360
370
420
440
400
510
560
490
430
340
320
320
320
260
170
184
275
255
357
418
439
337
306


BOD
mg/L
204
119
....
108
111
128
126
135
117
171
192
183
153
117
188
—
84
71
49
54
58
86
103
91
168
123
105

Total
Solids
mg/L
680
540
610
570
830
540
600
650
550
680
660
720
680
580
650
610
610
740
470
550
780
540
570
610
620
590
540
Total
Volatile
Solids
mg/L
330
160
180
180
210
210
200
230
300
250
280
300
290
200
250
260
220
230
210
220
760
180
300
240
240
200
190

Suspended
Solids
mg/L
170
130
130
170
170
190
190
210
170
240
220
260
200
160
190
190
190
200
90
120
240
200
160
180
160
110
100
Volatile
Suspended
Solids
mg/L
130
130
120
156
170
182
182
190
168
230
178
230
154
160
174
168
190
200
88
120
20C
180
140
156
158
110
90

Settleable
Solids
mg/L
90
30
22
70
88
110
90
102
50
100
100
140
60
60
110
130
118
160
50
100
200
168
92
70
12



-------
  Waste Constituents. ma/L
Chemical Oxygen Demand
Biochemical Oxygen Demand
Total Solids
Total Volatile Solids
Suspended Solids
Volatile Suspended Solids
Settleable Solids
Total Phosphate
Total Nitrogen
Orthophosphate
Ammonia Nitrogen
pH
                                           Table E-2

                               Characteristics of Dry-Weather Flow
Combined Sewer District G-4
 "Range          A/lean
170-560
 49 - 204
470 - 830
 30 - 760
 90 - 260
 88 - 230
 12-300
   358
   120
   621
   243
   176
   161
    95
               Separate Storm Sewer in
                  Good Hope Run
                   Sewer District
Range
10- 184
8- 58
456-1,950
158-1,780
20 - 260
0- 64
2- 180
Mean
69
18
639
345
68
28
47
 6.4-6.8
6.6
6.6-6.1
6.35
Total Coliform, counts/100 ml

Fecal Coliform, counts/100 ml

Fecal Streptococcus, counts/100 ml
                3,900,000

                2,900,000

                  64,000
                              24,000

                              21,000

                                 800

-------
                                                                                 Table E-3

                                                Storm Sewer Dry-Weather Flow for Separated Sewer District - Good Hope Run
      Location of Sampling Site - 17th St. - Minnesota Ave. S.E.
      Drainage Area - 264 acres
        Sampling
          Date
      Sept. 22, 1969
O)
      Sept. 23, 1969
Schedule
  Time
 3:15 p.m.
 4:15 p.m.
 5:15 p.m.
 6:15 p.m.
 7:15 p.m.
 8:15 p.m.
 9:15 p.m.
10:15 p.m.
11:15 p.m.

12:15 a.m.
 1:15 a.m.
 2:15 a.m.
 3:15 a.m.
 4:15 a.m.
 5:15 a.m.
 6:15 a.m.
 7:15 a.m.
 8:15a.m.
 9:15 a.m.
10:15 a.m.
                          12:15 p.m.
                           1:15 p.m.
                           2:15 p.m.
                           3:15 p.m.
Sampling
 Interval
 minutes
   60
   60
   60
   60
   60
   60
   60
   60
   60

   60
   60
   60
   60
   60
   60
   60
   60
   60
   60
   60
   60
   60
   60
   60
   60


Flow
gpm
92.0
90.0
86.0
83.7
116.0
90.0
90.0
90.0
90.0
88.1
90.0
91.0
91.0
91.0
89.2
91.0
92.0
92.0
138.0
92.0
109.0
88.0
88.0
91.0
89.0


PH

6.5
6.4
6.4
6.4
6.4
6.4
6.4
6.3
6.4
6.4
6.4
6.4
6.4
6.5
6.2
6.2
6.2
6.1
6.2
6.2
6.2
6.4
6.4
6.4
6.6


COD
mg/L
41
82
51
	
10
61
42
71
61
61
51
82
82
82
51
82
51
51
82
184
102
71
71
102
102


BOD
mg/L
37
—
13
11
10
8
8
13
9
12
20
14
17
12
11
18
15
31
19
58
22
18
18
16
20

Total
Solids
mg/L
730
630
630
590
640
610
540
620
550
560
560
1,950
534
550
564
560
514
630
456
920
470
464
546
554
610
Total
Volatile
Solids
mg/L
240
300
310
230
270
180
190
280
290
280
320
1,780
264
334
314
308
192
270
232
764
250
158
296
308
258

Suspended
Solids
mg/L
170
60
60
70
260
130
50
80
200
90
52
60
68
52
60
28
30
98
30
46
40
20
32
36
30
Volatile
Suspended
Solids
mg/L
50
40
34
30
64
50
10
50
64
60
44
18
40
6
0
14
10
18
20
16
20
0
22
16
10

Settleable
Solids
mg/L
50
16
12
34
180
62
14
32
152
42
50
40
50
6
20
14
2
90
22
46
20
20
12
36
12

-------
                                                                                                      Table E-4

                                                                             Characteristics of Storm Runoff in Sewer District Good Hope Run
Location of Sampling Site • 17-Minn. and 16 S.E.

	Storm	
                                       Total
                                      Rainfall
                                       inches

                                        1.6
     Date
                       Time
 July 28
 1:20-2:00 p.m.
July 28
5:00-5:30 p.m.
                                        0.20
August 2
8:17-9:30 p.m.
                                        2.9
August 9
9:20-9:45 p.m.
                                        1.5
                                    Sampling
                                     Interval
                                     minutes
                                                         5
                                                         5
                                                         5
                                                         5
                                                         5
                                                         5
                                                         5
                                                         5
                                                         5
                                                         5
                                                         5
                                                         5
                                                        10
                                                        10
                                                        10
                                                        10
                                                        35
                                                        10
                                                        10
                                                        10
                                                        30
                                                       10
                                                       10
                                                       10
                                                       10
                                                       10
                                                       10
                                                       10
                                                       10
                                                       10
                                                       10
                                                       10
                                                       10
                                                       10
                                                       10
                                                       10
                                                       10
                                                       10
                                                       10
                                                       10
                                                       10
                                                       40
                                                       10
                                                       10
                                                       10
                                                       20


Flow
gpm
21,000
65,600
75,000
57,900
47,700
43,300
57,900
15,400
12,500
10,200
7,900
6,090
4,570
5,000
3,740
3,620
4,770
2,020
2,625
2,190
3,180
1,140
2,020
2,500
4,040
2,640
3,600
4,200
3,090
1,640
2,020
34,400
16,800
10,100
5,660
4,400
3,520
2,470
1,960
1,995
1,601
1,410
1.340
2,205
2,030
50,000
16,150
7,500
5,000
2,860


_EH

6.2
6.2
6.1
6.0
6.1
6.0
6.0
6.2
6.2
6.3
6.2
6.3
6.4
6.3
6.6
6.8
6.9
7.0
6.3
7.0
7.0
7.1
7.0

6.9
7.0
7.1
7.1
7.1
7.2
7.1
6.3
6.3
6.2
6.2
6.5
6.6
6.8
6.9
7.0
7.0
7.0
7.1
6.3
6.3
6.1
6.2
6.1
6.2
6.2


COD
mg/L
430
400
280
170
310
300
370
240
230
210
210
230
150
120
140
120
58
48
67
77
67
29
58
96
77
77
48
106
86
77
38
400
259
216
140
184
119
108
140
129
65
86
54
180
200
160
390
270
180
150


BOD
mg/L
13
15
11
16
15
15
5
8
13
15
16
4
15
17
14
14
12
4
4
5
8
3
4
6
7
5
5
5
5
4
3
16
12
36
16
36
17
12
31
13
40
14
17
20
29
19
28
20
16
17

Total
Solids
mg/L
14,600
12,560
6,638
5,830
10,002
10,632
10,242
8,676
7,198
6,092
4,898
4,598
3,908
2,898
2,310
1,670
1,454
1,140
770
944
776
778
578
488
446
530
1,070
1,842
1,580
1,984
1,240
10,346
6,626
4,290
3,318
2,478
1,836
1,090
1,290
1,342
680
1,130
910
458
1,094
2,374
13,590
10,674
5,462
3,988
Total
Volatile
Solids
mg/L
912
996
278
268
600
484
512
488
460
390
288
378
284
228
200
110
136
136
138
136
76
142
90
90
154
96
120
136
84
12
106
538
368
250
226
188
130
40
184
178
164
200
72
190
272
126
826
604
248
260

Suspended
Solids
mg/L
9,600
11,200
6,050
5,520
9,020
10,010
9,170
8,150
5,560
5,900
4,620
3,920
3,140
2,160
1,920
1,020
1,160
640
480
720
480
520
380
320
300
340
920
1,500
1,300
1,740
980
9,568
6,560
4,210
2,610
1,200
1,550
1,278
910
840
200
548
416
100
1,000
2,020
11.28C
8,50C
5,100
3,400
Volatile
Suspended
Solids
mg/L
880
860
60
40
430
370
380
410
460
210
180
280
300
180
200
50
100
120
100
120

100
100
100
120
100
120
180
160
180
140
524
210
250
50
70
60
232
60
20
0
40
12
10
80
92
720
450
150
150

Settleable
Solids
mg/L
6,756
7,640
3,330
2,660
6,528
6,906
5,702
6,662
2,912
2,332
2,530
3,616
2,792
1,016
1,036
360
524
—
__
396
280
200
248
144
192
157
472
812
708
964
496
5,353
4,760
2,370
1,290
710
1,050
490
662
700
40
400
268
80
280
396
460
1,676
1,640
1,212
Total P
 mg/L

  4.5
  2.8
  1.5
  1.8
  2.4
  2.0
  2.6
  1.6
  1.8
  2.2
  2.0
  1.6
  1.6
  1.5
  1.4
  2.1
  1.0
  1.0
  0.5
  1.0
  1.0
  0.4

  0.3
  0.4
  0.4
  1.8
  1.0
  0.8
  0.4
  0.2
  0.?

  2.0
  1.8
  1.5
  1.0
  1.0
  1.0
  1.0
  1.0
  1.4
  0.4
  0.2
  0.4

  1.4
  1.0
  1.0
  1.4
  1.0
  1.0
  0.6
Total N
 mg/L

  4.0
  2.8
  2.5
  2.5
  4.0
  2.5
  3.0
  2.5
  2.0
  3.2
  3.0
  2.0
  2.2
  1.8
  2.0
  2.0
  1.6
  1.4
  1.5
  2.4
  1.2
  1.6
  2.0
  1.6
  1.4
  3.4
  1.2
  1.2
  1.2
  1.2
  1.0

  4.0
  4.0
  2.5
  2.0
  2.0
  1.5
  2.0
  1.6
  1.0
  1.0
  1.0
  0.6

   1.4
   1.2
  0.3
   1.6
   1.4
   1.0
   0.8

-------
                                                      Table E-5
                                      Waste Loadings in Combined Sewer Overflow and
                                             Separated Storm Water Discharge
05
CO
    Waste Constituents


Chemical Oxygen Demand

Biochemical Oxygen Demand

Total Solids

Total Volatile Solids

Suspended Solids

Volatile Suspended Solids

Settleable Solids

Total Phosphate

Total Nitrogen
                                              Combined Sewer Overflow
                                               from Sewer District G-4
(Ibs./min.)
Range Mean
0.2-1,359
0.6
10.4
3.0
7.3
1.5
3.4
0.0
0.1
-298
- 2,552
-876
- 2,268
-652
- 1 ,996
- 38.75
-15.37
157.4
28.3
419.9
125 .4
322.7
85.8
165.7
1.82
1.56
    Separated Storm Water
  Discharge from Good Hope
      Run Sewer District
         (Ibs./min.)
    Range           Mean
  0.2-219            19.0

<0.1-8.7             1.7

  3.7 - 6,872         333.0

  0.2 - 545            23.8

  0.9-6,128         293.0

<0.1 -471            16.5

<0.1 -4,180          10.2

<0.1 -1.53             .09

<0.1 -1.5              .11

-------
                                                                                   Table E-6

                                                                 Total Waste Loadings Generated by Different Storms
                            Storm
           Date
           1969
Combined Sewer District G-4

  May 19
  May 20
  June 8
  June 15
  July 6
  July 27
  July 28
  July 28
  July 28
  August 2
  August 9
  August 9
  August 19

Combined Sewer District B-4

  June 1
  June 2
  June 3
  July 27
  August 2
  August 3
  August 9

Separate Sewer District -
  Good Hope Run

  July 28
  July 28
  August 2
  August 9
  August 9
  August 10
  September 17
Time
               Total
               Rainfall
1:42- 1:45 a.m.
11:42-1 1:49 p.m.
5:50- 6:03 p.m.
2:20- 2:40 p.m.
7:40- 8:20 p.m.
11:35-12:14a.m.
2:30- 2:52 a.m.
11:30-1 1:45 a.m.
1:20- 2:00 p.m.
8:05- 9: 15 p.m.
9:20- 9:37 p.m.
11:20-1 1:30 p.m.
6:40- 6:53 p.m.
7:25- 7:45 p.m.
7:45- 8:05 p.m.
12:25-12:40 a.m.
11:35-1 1:55 p.m.
8:10- 9:00 p.m.
10:30-1 1:40 p.m.
11:22-1 1:37 p.m.
1:20- 2:00 p.m.
5:00- 5:30 p.m.
8:17- 9: 30 p.m.
9:20- 9:45 p.m.
11:00-1 1:30 p.m.
12:25-12:45 a.m.
8:20-10: 00 p.m.
0.4"
0.6"
0.7"
0.7"
0.4"
2.1"
0.6"
0.6"
1.3"
2.8"
1.1"
1.6"
1.35"
1.4"
0.9"
0.95"
1.3"
3.9"
0.4"
1.6"
1.6"
0.2"
2.9"
1.1"
0.8"
0.65"
0.6"
                                                                    COD
                               5,423
                                155
                               2,474
                               3,749
                                193
                                178
                               1,906
                                            BOD
            Total
 Total      Volatile
Solids      Solids
                                                                                                           Total Loadings, pounds
Suspended
  Solids
 Volatile
Suspended
  Solids
Settleable
  Solids
Total
  P
1 'oofl 0
1 ,9£U.U
2,890.0
1,415.0
838 0
Otju.vs
9,538.0
2,009.0
2,696.0
3,109.0
44,815.0
7,624.0
673.0
3,213.0
T/ \J
152
1 Oi
894
302
160
1,554
326
526
390
10,109
1,272
115
354
R ORQ
\jf\j*)*y
3,947
2,410
1,304
26^886
4,777
5,539
7,895
101,817
29,176
2,476
14,218
2 309
£.rtj\jy
2,250
1,130
637
10,951
2,075
2,071
1,379
24,010
10,136
736
3,569
4 294
^f AOt
2,521
1,328
1,060
20J01
3,187
3,844
6,431
75,657
18,374
2,061
11,667
l'fi34
1 ,UOt
1,390
473
561
4,877
974
1,200
1,506
14,399
4,635
289
1,089
*J/ I
fifi?
UU/
880
1,007
14,374
2,107
2,969
4,434
61,705
3,331
153
9,052

11.13
5.75
37.89
9.11
13.40
25.61
421.44
59.99
5.11
13.30

20.52
5.19
104.18
13.66
18.21
23.90
382.48
88.02
4.43
61.29
3,120.0
155.0
137.5
866.0
4,608.0
280.0
5,848.0
316
28
29
85
1,309
105
1,063
6,335
345
405
2,694
18,831
454
14,692
1,392
166
170
	
3,671
252
4,041
4,306
78
73
2,004
18,145
444
13,469
1,249
40
13
1,011
2,709
156
3,722
4,205
48
38
1,822
16,162
39
886
                                                                                                                      7.86
                                                                                                                     21.87
                                                                                                                    222.72

                                                                                                                     14.18
                                                                          15.37
                                                                          15.41
                                                                          74.84

                                                                          10.63
252
10
160
388
16
40
208
160,253
2,167
57,556
81,193
425
1,884
15980
9,415
215
3,180
4,709
76
359
1.841
142,958
1,732
55,000
68,150
272
1,737
143R3
6,621
268
2,604
3,679
3
56
1 9R7
90,845
924
30,503
9,021
148
433
sru-*
41.60
1.37
13.47
20.03
0.93
1.83

54.69
3.06
25.91
18.01
0.90
1.16


-------
                             Table  E-7

         Comparison of Actual Total Flow Measurement and
               Volume Obtained by Hydrograph Analysis

                      Actual Measurement             Volume From
    Storm            __	Volume	         Hydrograph Analysis
                        million gallons              million gallons

                    Combined Sewer District G-4:

July 27-28,  1969             4.36                       3.93
11:35p.m.-0:14a.m.

July 28,1969                 2.43                       3.22
 1:28 p.m.  2:03 p.m.

August 2, 1969              21.10                      20.20
 8:05 p.m.-9:10 p.m.

July 6, 1969                 0.12                       0.19
 7:40 p.m. - 8:20 p.m.

July 28, 1969                1.09                       0.96
 2:30 a.m.-2:52 a.m.

                    Combined Sewer District B-4:

August 2, 1969               4.40                       5.12
 8:10 p.m. -9:00 p.m.
                                171

-------
         FIGURE  E-1
         DRY  WEATHER  FLOW IN COMBINED SEWER  DISTRICT G-4
                                 SEPTEMBER 22.  1969 110 50 >«) DRY REtTHER FLO*
  .200 _
  1.000 _
3  600 -
   200 -
                                       10    12     14    16    18    20    22    24
                                 SEPTEMBER 22.  1969 (10:50 AN) OR* WEATHER FLOW
           250
              0246
                                      10    12    i4    16    IB
                                             TIDE .HOURS'
                                                                20    22    24    26    28
                                         172
                                                                                                     E-1

-------
   FIGURE   E-2

 DRY WEATHER  FLOW  IN GOOD  HOPE RUN  SEPARATED  STORM  SEWER
                         SEPTEMBER 22-23,1969 (3:15 PM) DRI HEATHER FLOK
 2,000-



 i.aoo



 1,600-



 1.400-



~l,200-
\


~.000 -
   400-



   200-



    0-
            0246
                                     10    12     U   16


                                        TIME (HOURS)
                                                              20    22    24    26
                          SEPTEMBER 22-23, 1969 (3:15 PM) DRV HEATHER FLOW
  160 -



  140 -




  120 '



 IlOO


 §
 ^80



 360 '



   40 '



   20'



    0
            0246
                                      10    12    14    16

                                         TIME (HOURS)
                                                               20    22    24    26
                                             173
                                                                                                  E-2

-------
          FIGURE  E-3
          SHORT  INTENSE STORM IN COMBINED  SEWER DISTRICT G-4
                                    IIME I.  IBM (9:50 M) 13 Ml. - 0.7"
20,000-
       2,000-
10,000" j
       i.ooo-
   0-1
              2.000
            £ 1.000
                                      10                  20

                                                TIDE (MINUTES)

                                         JUNE 8, 1969 (550 W) 13 III. - 0.7"
                                                                                              1.25
                                               174
E-3

-------
        FIGURE   E-4


        LOW   INTENSITY  STORM  IN  COMBINED   SEWER   DISTRICT  G-4
        i

        i
        a
        g
                                     JUNE 15,  1969 (2:00 PI) 40 UN.   0.7'
 2,000 -
 .1,000 -
                                                 TIKE (MINUTES)
                                      JUNE 15, 1969 (2:00  PI) 40 UN. - 0.7"
  10.000 -
= 5,000 -
                                                 TIME (MINUTES)
                                         175
                                                                                                    E-4

-------
      FIGURE   E-5
      SHORT INTENSE  STORM IN COMBINED  SEWER DISTRICT  B-4
      100 -i  § i.ooo
       50-
        0.
180,000-1    600-1  1,500
150,000-
120,000-
;90,000-
 60, 000-
 30. 000-
     0-1
           500-
400-
300-
           200-
           100-
     1,250
1,000
                                   JUNE I, 1969 7:25 PM 22 MIN.  1.4"
                                      10          15         20


                                             TIME (MINUTES)
                                                                                30
                                                IUNE I, 1969 (7:25 PM) 22 MIN   1.4"
                                         10          15          20
                                                TIME  (MINUTES)
                                                               25         30
                                          176
                                                                                      E-5

-------
               FIGURE  E-6
               LONG  INTENSE STORM IN  COMBINED SEWER  DISTRICT G-4
  600,
  500-
  400-
  300-
i 200-
   100-
                                                                                     660,000 GPM
                                           HUGUST 2, 1969 (8: OS PN) 65MIN.  -2.8
    0-"-  0
                                                   40        50

                                                     TIME (MINUTES)
 100 -
     ll.OOO
 5D-
     p  500
  0 J
                                         AUCOST 2,  1969(8:05 PM)65MIK.   2.8"
                     10         20         30
                                                   40          50

                                                    TIME (MINUTES)
                                                   177
                                                                                                          E-6

-------
                        FIGURE   E-7

                        LONG  INTENSE  STORM IN COMBINED SEWER DISTRICT  B-4

                                                          AUGUST 2. 1969 (B 10 PM) 50 HIM  - 3.9"
                    200-
                     150-
                     100-
                     50-
                     0 -1
                           100 -
                            J5 -
                            50 -
                            25 -
                                                          10          15         20
                                                                TIKE (MINUTES)
                                                1320,000
                                                                       AUGUST 2, I9G9 (8:10 PH) 50 MIN  - 3.9"
200 000-

I
100 000-
          oj    o
              500
                                     10         15
                                                         20         25
                                                               TIKE (HINUTES)
                                                                              30         35         40          45         50
                                                        178
                                                                                                                    E-7

-------
    FIGURE   E-8
    CONSECUTIVE  STORMS   IN   COMBINED   SEWER  DISTRICT   G-4
                                JULY  27-28, 1969
                        1.820
                                 JULY 27.1969 (I!:35 PH) 39HIN.-2.1''
    150,000 -    I5QO
    125,000  -
    100.000 -
  4
  £  75.000 -
     50,000 -
     25,000 -
                                     20        30        40

                                        TIME (MINUTES)


                                   JULY 28, 1969 (2:30 AM) 22 DIN.  0.6"
500 -
f
250 -
     ion,ooo-
     50.000-
                                              179
                                                                                             E-8

-------
          FIGURE  E-9

          CONSECUTIVE   STORMS  IN   COMBINED  SEWER   DISTRICT   G-4

                                       JULY 28, 1969
                                        IULT 28, 1969 (11:30 AH) 15 DIN  - 0.6"
  100.000 -
i 50.000
                                         JULY 28. 1969 (I 28 PN) 35 MIN   1.3"
                                               180
E-9

-------
    FIGURE  E-10
    SHORT   INTENSE  STORM   IN  SEPARATED   SEWER   DISTRICT
                                       AUGUST 9. 1969 (9:20 PM) 25 MIN.-I.5"
12,000-1
10.000-
 8 000-
 6.000-
 4 000"
 2,000-
    0-1
        1,000-
         600-
      3 400-
         200-
                    0          20
                                        40         60
                                               TIKE CHINUTES)
                                                                                    120
                                       AUCUST 9.  1969 (9:20 PM) 25 MIN.-l
 50,000-
 40,000-
!=30,DOO-
 20.000-
         1.000-
          aoo-
        ^ 600-
           400-
  10.000-    200-
      0-1     0-1
               15,000
                12,500
                                                 TIME (MINUTES)
                                            181
E-10

-------
            FIGURE   E-11
            LONG INTENSE  STORM  IN SEPARATED  SEWER  DISTRICT
100 —i   I 000 —i   10.000
      -  500 -
  30,000-
  20.000.

  Ci
  g


  10.000-
          1.500.
          1.000-
           500-
                  15,000
                  10,000
                  5.000
                                AUGUST 2  1969 (8  17PM) I  HO.  13 KIN -2.9"
                             34.400
                                             TIME (HINUUi)
                                          AUGUST 2. 1969 (6 17 PM)  I Hft. 13 MIN   2.9"
                                                                        100        120
                                               TIME (MINUTES)
                                            182
                                                                                                   E-11

-------
                FIGURE  E-12
                CONSECUTIVE   STORMS  IN   SEPARATED   SEWER  DISTRICT
                                    JULY  28, 1969  1:20  PM
 10.000 -1  14.
 50.000    10.000
                                                            I DO       120       HO
                                                         TIKE (MINUTES)
                                                                                        160        I BO        200
                                                   Kill 28. 1969 (1'20 PM) 40 MIN  - I.I
 .400-r  700 T   14
1.000
4
                                                           100        120
                                                       TIME (MINUTES)
                                                                             140       160        180        200
                                                  183
E-12

-------
                      FIGURE  E-13
                      CONSECUTIVE   STORMS  IN  SEPARATED   SEWER   DISTRICT
                                          JULY 28,  1969   5:00  PM
           6.000
          ' 4.000
         51.000
               I"

               i
               - 20
                                                      IUIT 2!. 1969 (5 00 PI) 30 KINS  - 0 20
                                                           40        50
                                                            TIKE I III NOTES)
                                                      IU11 26. 1969 (5 00 Pll) 30 MINS - 0 ZO' '
ft
^ 1 000
          £600
                                                           40         SO
                                                            TIKE llimiTES)
                                                     184
E-13

-------
   FIGURE   E-14
   REPRESENTATIVE  BACTERIOLOGICAL  DATA   FOR   COMBINED  SEWER OVERFLOW
   IN  WASHINGTON,   D.C.
  62.500-
" 37.500
3 25.000
  12.500
g
I 2.1
                                                                         1UU 21. 1969 (11:30 I.II ) 15 IIH.   0 I
                40,000
               -30.000
                10.000
                                                       20        25
                                                       TIME (MINUTES)
                                                                    (11:35 P.I.)   39 DIN. - 2 I"
                                               30       40
                                             TIME (MIKUTES)
                                                  185
                                                                                                      E-14

-------
    FIGURE  E-15
    WASTE  LOADING ASSOCIATED  WITH SHORT  INTENSE STORM IN
    COMBINED  SEWER  DISTRICT G-4
24-,  240
20 -
15 -
                           10          15
                                   TIME (MINUTES)
                            1UNE 8 1969 (5:50 PM) 13 KINS. - 0.7"
                                      15         20

                                  TIKE (MINUTES)
                                    186
E-15

-------
FIGURE  E-16
WASTE LOADING ASSOCIATED WITH  LONG INTENSE STORM  IN COMBINED SEWER DISTRICT G-4
                                                »UGUST 2,  1969 (8:95 PH) 65 MINS - 2.9"
       • 2,4
       ± 1.290
                                                               50
                                                      TIME (MINUTES)
                                               AUGUST 2, 1999 (9:05 PM) 79 BINS. -2.8"
                           19        29       39
                                                               50       60
                                                       TI«E (MINUTES)
                                                     187
E-16

-------
FIGURE  E-17

WASTE LOADING ASSOCIATED WITH CONSECUTIVE STORMS IN COMBINED SEWED DISTRICT G-4
             JULY 27, 1969 . CUMULATIVE  RAINFALL, FLOW  RATE,  COO
                                                             - 0 6 '
                                                                                                           111   900
                                                                                                                                                  E-17

-------
  FIGURE   E-IS
  WASTE  LOADING ASSOCIATED WITH CONSECUTIVE STORMS IN COMBINED SEWER DISTRICT G 4
JULY 27,  1969 .  SUSPENDED  SOLIDS,  TOTAL  VOLATILE  SOLIDS,  VOLATILE  SUSPENDED SOLIDS.
                                                                              15 KINS  - 0
                                                                                                                                                                           E-18

-------
FIGURE  E-19
WASTE LOADING  ASSOCIATED WITH SHORT INTENSE STORM IN SEPARATED SEWER DISTRICT
                                            45       BO       75
                                                TIKE (IIIIIIITES)
                                                                              105      120
        2  0-,  35.000-,  ,n
                                                             AUGUST 9. 1969 (9:10 P «.) <5 KIN  -15
            -20.000-
                              15       30       15       60       15       90        IDS       liO
                                         190
E-19

-------
   FIGURE  E-20
   WASTE   LOADING  ASSOCIATED   WITH  LONG   INTENSE  STORM   IN  SEPARATED  SEWER  DISTRICT
28 000-.  l«o_,   I
                        34.400
                                                                                  • UGOST 2. 1963 (B I) P M I  73 SitN   - 2 90
                       ID       20         30       40        50
1600 -i    160
                                                                                       •OCOST 2  1969 (8 17 P «  II. HIM  -i  31
                                               0        50
                                               TIME (HIHUTES)
                                                                                                            I 0      !2D
                                                      191
                                                                                                                   E-20

-------
CO
ro
3 HI
3
                                                                       FIGURE E-21
                                                                       WASTE LOADING  ASSOCIATED  WITH CONSECUTIVE  STORMS  IN  SEPARATED  SEWER  DISTRICT
                                                                                      JULY 28, 1969 - CUMULATIVE  RAINFALL,  FLOW RATE,  COD
                                                                                                                                                             E-21

-------
                                            40 HIHS  - 1.6 INCHES
CO
CO
                                                                  FIGURE  E-22


                                                                  WASTE  LOADING  ASSOCIATED  WITH  CONSECUTIVE  STORMS  IN SEPARATED SEWER DISTRICT


                                                           JULY 28, 1969  TOTAL  SOLIDS;  SUSPENDED SOLIDS, TOTAL  VOLATILE  SOLIDS, VOLATILE  SUSPENDED  SOLIDS
                                                                                                                                                         E-22

-------
FIGURE  E-23
CORRELATION  BETWEEN COD  WASTE  LOADING AND  TOTAL RAINFALL
  100. 000

  70. 000
  GO 000
  50 000

  .10.000

  jO. 000


  20. 000
   10.000

    7.000
    6,000
    5,000

    4,000

    3.000


    2,000
    1 .000

     700
     GOO
     500

     400

     300


     200
     100
COMBINED  SEWER DISTRICT B-4   (—  •)
COMBINED  SEWER DISTRICT G-4   (	  •)
SEPARATE  SEWER DISTRICT GOOD  HOPE RUN  (-
- -A)
             A/
                  0.5
                            1.0
                                      1.5        2.0        2.5

                                       TOTAL RAINFALL ( INCHES)
                          3.0
                                     3.5
                                              4.0
                                          194

-------
FIGURE E-24
CORRELATION BETWEEN SUSPENDED SOLIDS WASTE LOADING
AND TOTAL RAINFALL
200 000
100, 000
70 000
60,000
GO, 01)0
40, onn
30, 000
20, 000
1 10,000
o
1 —
co
\
£ 7.000
" 6,000
CO
- 5,000
— 1
4,000
a
LU
E 3,000
O_
CO
to
2, 000
1,000
700
600
500
400
300
20
100











•


'/
J*



jt










(
A
/
/
/
/
• / /
•/
k^
/ A
/
•
>
x^
/
r

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m


A
/
/
/
/
/
/
/
/
/
/
/ •
/
/
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/
/
•



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/
/
/
/





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SUSPENDS
r n MR i H F r
COMBINE!
. SEPAR.AT






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/





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s







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D SOLIDS
SEWER DISTRICT B-4 (— ^— • )
SEWER DISTRICT G-4 ( 	 •)
SEWER DISTRICT GOOD HOPE RUN ( 	










^r u












• -A)

I
s
0 0.5 .0 .5 2.0 2.5 3.0 3.5 4.0
TOTAL RAINFALL (INCHES)
E-24

-------
     FIGURE  E-25
     REPRESENTATIVE RAINFALL AND RUNOFF MEASUREMENTS FOR
     SHORT INTENSE STORM IN COMBINED SEWER DISTRICT G-4
                   (SQNVSnOHi Nl HdO) MOId 33VM3S Q]NI9W03
i	r
                                                  T
•••• CBH/S3H3NI)
                                        JO A1ISN31NI
                  	(S3HONI) H3M3S  Nl Hld30 MOU
                                196
                                                                        E-25

-------
FIGURE E-26
REPRESENTATIVE RAINFALL AND RUNOFF MEASUREMENTS FOR
LONG INTENSE STORM IN COMBINED SEWER DISTRICT G-4
         '(SQNVSfiOHi N! WdD) Mdld 33VM3S Q]NI8WOO
      ••••• Cm l  S3H3NI) 11VJNIVU JO  AHSN31NI
           	 (S3HONI) H3M3S Nl  Hid3Q M01J
                            197
                                                                  E-26

-------
    FIGURE  E-27


    REPRESENTATIVE RAINFALL AND RUNOFF MEASUREMENTS


FOR  CONSECUTIVE STORMS IN COMBINED  SEWER DISTRICT G-4
                                                           "***:
                                                              •
                                                          •••• —
             •••• ('8H/S3H3ND 11VJNIVM dO AilSNBiNI
             	(S3HONI) H3M3S Nl Hid3fl MOU

             	1	1	
                    .(Nd9) MOld 33VM3S Q3NI8W03
                            198
                                                                   E-27

-------
6D
50
40
s
1 30
20
10
0
NOTE: LINES OF
FIGURE E-28
CORRELATION BETWEEN BOD AND COD
COMBINED SEWER DISTRICT B 4



•
X
J**^ •
0
600
500
400
-1
•
= 300
t
200
IDD
0
IDO
90
80
70
60
3 50
0
"~ 30
20
10
BEJ

m
'
'. «.. s
^



/
•
m


^



.






IOD 200 300 400
CID (HE'D
COMBINED SEVER DISTRICT G-4





'3r*P




•
#£•''




'>"




.
jX**""^ •
• .



'
/^
'•



^





^





•




^

•

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COD (MS/L)
SEPARATE STORM SEVER DISTRICT









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^^
:
"





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/
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.




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^

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^







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500
BOO
lm 2DO 300 400 500 600 100 300 900
COD (MC LI
,T FIT 199 E-28

-------
                  FIGURE E-29
                  CORRELATION RETWEEN SUSFENDfD SOLIDS AND  VOLATILE SUSPENDED SOLIDS
                                                      COKBtltD UVCB DiSTIICT 8 t
                                                               n SEDER QlSIEiCT H •
|  NOTE  LINES OF BEST FIT
                                                   200
E-29

-------
FIGURE E-30
COMPARISON OF FLOW MEASUREMENT TECHNIQUES FOR COMBINED SEWER OVERFLOWS
LOW
, uuu
7on

RQfl
400
300
200
100
70
50
40
30
20
10
7
5
3
1
















































































/



















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•

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V
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(
















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2 3457 10 20 30 40 50 70 100 200 300 400 500 700 1,000
                       FLOW RATE MEASURED WITH LITHIUM TRACING (GPM IN THOUSANDS)
                                                                               E-30
                                       201

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                                    APPENDIX F

                          ULTRA-HIGH-RATE  FILTRATION

                                     Introduction

High-rate  filtration has been extensively  applied for the removal of suspended impuritites
from  raw water  or  wastewater, especially when the impurities are primarily non-volatile
discrete particulates, such as the wastewater from steel mills. In combined sewer overflow
and separated  sewer discharge, large fractions of the suspended  waste constituents  are
recognized to be non-volatile discrete solids; thus, high-rate filtration may be an effective
treatment method.  Despite the  many studies that  have  been undertaken, the status of
filtration  development  is still in transition  from an  art to a science. The practical design
parameters for the filtration process to treat a specific wastewater must still be determined
from  results of specific laboratory or pilot-scale investigations. Moreover, ultra-high-rates
of filtration (greater than 15 gpm  per  square foot) must be applied in order to cope
economically  with the unique  hydraulic characteristics of the combined sewer overflow
or separated sewer discharge-high discharges within  a short-time period. This adds another
dimension of uncertainty  to the development of a feasible filtration process to treat the
excess urban  wastewater derived from  intense storms. Therefore, a filtration  study was
conducted with  the following  objectives:

     1.    To  evaluate  the applicability  of ultra-high-rate filtration to the treatment of
          combined sewer overflows,

     2.    To  determine the flocculation effects of chemical  additives on the  solids and
          organic material removal  and

     3.    To provide a conceptual design basis for pilot-scale or full-scale treatment units.

The principal  process  variables evaluated in the laboratory program were:

     1.    Filter media, including type, depth, size  and arrangement;
     2.    Filtration  rates;
     3.    Effects  of addition of  flocculants and flocculant aids;
     4.    Variation  of  solids concentration in the  wastewater;
     5.    Backwash rate and quantity;
     6.    Air-scouring  rate, duration, and  sequence in the backwash procedure;
     7.    Effluent quality characteristics, including suspended solids, COD, total five-day
          BOD, and soluble five-day BOD.  (Soluble BOD$ was measured by performing
          BOD5 analyses upon the filtrate produced by vacuum filtration of the wastewater
          sample passed  through  a  diatomaceous  earth  filter);
     8.    Length  of filter run; and
     9.    Head loss requirements.

                         Theoretical  Background

The basis for this discussion  of technical background  was a comprehensive review of the
technical  literature  on removal mechanisms  in the filtration process,  analysis of filter
performance,  and considerations  for practical filter applications.
                                         203

-------
Particle Removal Mechanisms

The  possible mechanisms for the removal  of particulate material from water by filtration
through porous  media may be categorized into two types: physical and chemical removal
mechanisms.

     Physical  Removal

Physical   removal   mechanisms  include:  1)   straining,  2)  sedimentation,  3)  inertial
impingement and centrifugal collection, 4)  Brownian movement, 5) physical contact caused
by the convergence of fluid streamlines, and  6) diffusion of particulate  materials. They
are all dependent in varying  degrees  on different physical  and operation variables such
as size of the media, size of  the  particulates, filtration rate,  temperature, etc.

Straining: Straining  (or direct sieving) has been considered as the  primary mechanism to
remove suspended  solids in the traditional sand-filtration  process.  The probability of
removal for suspended  solids by straining, Ps, was  defined  as:

                          Ps~e>

in which  D and d are, respectively, the diameters of the suspended particle and the sand.

Sedimentation: The ability of the void spaces in a rapid sand filter to act  as settling
basins  was first  postulated by  Hazen.  Stanley  found that the sand  filter can be expected
to remove particulates which are one-twentieth the diameter of the particles removed by
a settling  process at the same hydraulic loading. It has also been found that the removal
increases  with the  square  of  the particulate  size and  the difference  in density between
the particle and the fluid. Increases in filtration rate and  the fluid viscosity may impair
the  particle  removal rate. Particle growth by  flocculation  within  the pores of a filter
increases  the  effectiveness of the  straining and sedimentation  removal mechanisms.  The
mean velocity gradient affects  the  rate of flocculation  in the filter and the  total amount
of flocculation produced is proportional to the  product  of mean velocity gradient  and
average detention  time.

Inertial Impingement: As the  suspension  flows around the filter  media  with continual
changes of  direction, the momentum associated  with  the  inertial  force  may cause  the
particles  to impinge  on  the  surface  of  the filter  media. Chen describes  the probability
of impingement for the air  flow through a fibrous medium as:
                            pD2v
                   where:
                        PJ is the probability of impingement,
                        D is the diameter of the particle,
                        p is the density of the particle,
                        v is the particle velocity,
                        f is the fluid viscosity, and
                        d is the diameter of the filter medium fibers.
                                         204

-------
Brownian Movement: This removal mechanism is not too significant in rapid sand filtration.
It would  provide the contact between the particulates and the surface of the filter media,
but would have little effect for the particles larger than two microns, based on theoretical
calculations.

Physical Contact: Physical contact between the particles and the surface of the filter media
will  be generated as a  result of convergence of the fluid streamlines. Stein proposed the
following relationship:

                 P  „  21
                 PC     d3

            where:

                 Pc is the probability of removal of a suspended particle,
                 D is the diameter of the particle, and
                  d is the diameter of the filter medium grains.

Diffusion: The diffusion of suspended particles into the "dead spaces" of the filter medium
was  proposed  as a  removal  mechanism  by  Hunter and Alexander. The dead spaces are
those regions where the fluid flow is essentially zero. The colloidal particles diffuse across
the  stream-line driven  by the  particle concentration  gradient. Because  of the tendency
to migrate to  the  regions of low shear, the colloidal particle concentration in  the dead
space  may become  considerably higher  than that in the ambient fluid.

     Chemical  Removal

Review of filter performance in the treatment of  uncoagulated and coagulated suspensions
indicated  that the  physical  removal mechanisms are inadequate to  expain the entire
filtration  process. Thus,  chemical removal  mechanisms were postulated. Basically, these
all stem  from  the  electric charges on the  surface  of particles.

All the electrostatic charges on  the  surface of  the particles in  water  are  derived from
one  or more of the following sources:  1} ionization of molecules at the particle surface,
2) imperfections of the  crystal lattice, 3) direct chemical reaction with specific ions in
the  water, and 4)  physical  adsorption of  ions  from the water  solution. The  principal
chemical  removal  mechanisms  are discussed in the following paragraphs.

Electrokinetic  Effects:  From  observations of suspension penetration in filter beds, different
investigators  have concluded  that  the  electrokinetic forces were the  primary  removal
mechanism for charged particles. Additional  support for  this conclusion was found from
filter bed examinations which showed the floe had no preference for horizontal surfaces
or pore interstices.  Using positively  pre-charged  media. Hunter and Alexander were able
to improve the filter efficiency for negatively-charged clay particles. O'Melia and Crapps
found that the floe suspensions with zeta potential  ranging from low negative to high
positive would allow little bed penetration  in  sand  filters; they also suggested that rapid
sand filtration  could be chemically controlled  through the influence of  specific chemicals
on the adsorption  of  particulates to the filter  media.
                                         205

-------
Van der Waal  Forces: These are molecular cohesive forces between particles. The intensity
increases drastically as the particles approach each other. Between two atoms, these forces
are proportional to r^, where r is the distance between the two atoms. For large multi-atom
particles, the Van der Waal forces are  proportional to r'3. Mackrles contended that these
attractive  forces  were  not affected by  the electrokinetic  nature  of the  particles  but
depended  almost completely  on  their  density.

Mathematical  Relationships

Many different mathematical models  have been  developed  to  describe the  behavior of
filtration through granular media for the  removal  of suspended solids from water. Iwasaki
first formulated the  filtration phenomenon in terms  of a first-order equation  as:


       ff=-Xc                                                         (F-D

     where:

       c  is concentration of suspended solids,
       I   is depth of filter layer from top  surface, and
       X  is impediment modulus, or filter coefficient.

Iwasaki  suggested another relationship  to express the removal of suspended solids as the
increase of  deposition onto  each  layer:

        3c _     I  da
        dl  ~  ~ v  3t                                                      

     where:

       a  is the specific deposit on the filter,
       t  is the filtration time, and
       v  is filtration rate.

These two equations have been  widely used in  filtration studies for  many years. Although
other researchers have  applied  these equations to evaluate  filtration behavior,  no basic
modifications  have been made.

The filter coefficient, X, varies with the  filtration time,  t, due to progressive clogging of
the filter  pores, and  may be  defined by  the specific deposit,a, as suggested by Iwasaki:

       X = X0 + ka                                                        (F_3)

     where:

       X    is initial filter coefficient, and
       k°   is constant.
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Ives later suggested another equation  to describe  the  variation  of the filter coefficient,
X, with the  specific  deposit, a, as
                          Po - a                                               (F-4)

     where:

       P0   is the porosity of clean bed, and
       0    is a filtration parameter.

In Inves1 formula,  the  increase of the interstitial velocity  and the reduction  of  available
grain surface  area  near the  end  of  filter run  were considered.

Sholji  generalized the  Ives equation  based  on his theoretical and experimental analyses
and  expressed the filter coefficient  in terms of different  operation  variables as:


           x~vaVv"                                                    (F-5)

   where:

      v        is   approach velocity of filtration,
      do       is   geometric mean size of media,
      M        is   dynamic viscosity of influent fluid, and
      a1/t>1,ci, are  constants.

However, Fox and Cleasby found that Ives' equation could not adequately describe the
behavior of filtration of  hydrous ferric floe suspensions,  but they did verify the initial
linear relationship ofX versus t. The failure to fit the experimental data with Ives'  equation
could  be attributed to  the electric potential associated with the hydrous floe, which was
not  considered  in the derivation of  the equation. Recently, Deb suggested a new set of
filtration equations which have  incorporated the  unsteady component of local  variation
of suspension concentrations with time into the non-dimensional forms. Specifically,

            1~ps    9a  = xc                                             (F-7)
          c0(Po - a>  91
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     where:

               c
         c = —  , dimensionless concentration ratio                    (F-8)
         ~    co
              \f
         _t_ = — t, dimensionless time value                            (F-9)


         I  = —  , dimensionless depth                                (F-10)
              L

         co is initial concentration of suspended solids,

         L is total depth of filter bed, and

         ps is porosity of deposited material.


The  filtration behavior of unsized  Fuller's earth could be defined satisfactorily. However,
the application of this  model to the removal of flocculated material was not considered.

Considering  the probabilistic  nature of  particle  transport and attachment to a granular
medium, Hsiung proposed a new filter  performance prediction theory based on a "Random
Walk"  analogy.  If  P  represents the probability  of penetration of a unit of filter depth
by a particle, the  probability of a particle moving down to depth I at time t will be:
The  total number of  particles deposited between I  and  l+ 1 can  be represented  by:

       Am  ~ P (I: vt, p) Qc0 At                                       (F-12)

Then,  from equation  (F-2),  the  following  can be derived:

       |f-  vAt ~P(I: vt,p) vc0At                                     (F-13)


       t   ff~P(l:vt'P>


Equation  (F-I3)  indicates  that  the particle  removal per unit depth  of  filter could be
characterized by  a  probability  function.  Based  on  the Chi-square distribution,  Hsiung
proposed a deposit index,  U, to  translate filtration performance data  for practical  design.
This probability  theory application  permits description  of the  random nature  of the
suspension, of the filter media,  and of the transport and removal mechanisms (including
both physical and chemical  mechanisms)  in a relatively  practical  and simple formula.
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                        Considerations  For Practical Application

Filtration efficiency  is a function of many design variables:  filtration rate, media size,
filter depth, and  the properties of  the suspension. With the use of the deposit index,
U, in the "random walk" analogy, Hsiumg also studied the relationship between different
design varables for high-rate filtration, and found that any increase in filtration rate must
be accompanied by a decrease of grain size in order to produce the same effluent quality.
On the other hand, he also  pointed out  that the grain size of the meia should be increased
in order to provide comparable filtration results for the same influent at a higher filtration
rate  at the same  allowable head  loss.  Two  types  of  performance curves were  proposed
for evaluation  of various  ranges of  grain  size,  flow rate,  and influent suspended  solids
concentration;  one based  on  required  effluent quality and  other on terminal  head loss.

For  the multi-media filter, Conley  and Hsiumg  showed the  application  of the random
walk analogy by  using  an  equivalent grain size, de,  as:

          de = xi di + x2 d2 + x3 d3                                    (F-14)

     where:

          xt. x2, and x3 are the percentages by volume of individual
          media, and

          dj, d2, and d3 are the mean grain size of individual media,
          respectively.

Hudson and Hsuing suggested the following relationship for head loss and filtration time:

                            L0.5t
        L    O          O     xj 1 Q                                      \r~~IOj

      where:

          Ht is head loss at filtration  time t, and
          Ho is head loss at beginning of filtration
             through a clean bed.

Thus, the  head  requirement  will  increase  with  filtration rate and  initial suspension
concentration very rapidly. Accordinq to the relationship between the depth of filter, L,
and  the lumped data of G (G  = v0-2*3  d°-62t) it is suggested that, for the same filtration
efficiency and  same  length of filter  run, the  filter bed depth requirement increases with
the  filtration  rate.

Therefore, in order  to  facilitate ultra-high-rates of filtration, (v>15 gpm/sq.ft.), the filter
bed  must be deep, the  total  head available must be high, and the size of the filter media
must not be too small. However,  for an influent containing a high  solids  concentration,
such  as combined sewage, the grain size of the media cannot afford to be too large either.

In various types  of  filter  applications, the  arrangement of media is still an art. Oeben
et al found that the reverse-graded  filter will permit decreasing  the  head requirement or
increasing the  filter  run. Upflow with  deep  depth of sand  has been  applied to facilitate
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utilization  of  the entire filter bed. Mixed-media filters  were reported as being able to
provide longer filter runs or better effluent  quality than regular sand filters.  Filter  media
made of fiberglass were also  reported  to  have potential application for ultra-high-rate
filtration when the suspended solids concentration is high  in the influent.

The  backwash after  each  filter  run  has gradually attracted  the attention of various
researchers. In general, it was found that the air scouring would  improve the backwash
efficiency and reduce the backwash  water  requirements. The air may be introduced at
the same time as the low-rate backwash water,  but generally the  air scouring is applied
in alternation  with water at  3-5  cfm for 5 minutes every cycle.

For  the treatment of steel  mill  industrial wastewater, ultra-high-rate filtration  has been
applied.  The  filtration  rate  could be  as  high  as 20  gpm/sq.ft. with  influent  solids
concentration  of  50  mg/L. Some deep-bed pressure filter applications  for  steel mill
wastewater treatment reported similar  results.

                          Description of  Laboratory System

Three independent laboratory  filtration systems, identical except for the filter media, were
constructed for this program. As shown on the schematic diagram (Figure F-1), the principal
components were  the filter  column, storage tank, transmission facilities, flocculant supply
system, and various controls and  safeguards. Photographs of these principal  components
are shown  in  Figure  F-2.

Filter Column

A filter column was  required  with associated instrumentation to monitor and/or control
filtration rate, operating pressure, total  head loss, and fluid temperature. The column had
to have adequate  strength to  withstand  elevated pressures, adequate depth for deep bed
filtration, and easy disassembly for the  purpose  of  changing or modifying the filter bed.

Initially, each  system included a  glass column as described below  (a  second  column was
subsequently  provided for  the fiberglass system  when a  new form of fiberglass medium
was introduced). The  column is a 9-foot, jointed, glass pipe with a four-inch inside diameter
(Figure F-1). Enclosed at the top by a one-inch thick PVC plate, the column will withstand
internal pressures  up  to 35 psig. The underdrain also consists of a one-inch thick PVC
plate, perforated with 30 to  40  evenly-distributed 1/2- and  1/4-inch holes. Mechanical
joints consisting of cast  iron flanges and Teflon gaskets are located 60, 74, and 86 inches
above  the  underdrain, connecting the four  sections of conical pipe.  The underdrain is
attached to the bottom section of the column so that one or more sections may be removed
from the frame, retaining the media while making it accessible for purposes of replacement
or modification. The maximum available depth for a fluidized  granular bed during backwash
is 92 inches.

The  top section  of the column is a cross tee, with 2-inch diameter branches. When the
column is operated as a downflow filter,  the wastewater enters through one of the branches
and  exits  through the underdrain. The other  branch  of the  cross accommodates the
backwash effluent, as well as filter effluent when the apparatus is used for upflow operation.

Midway through  the  study, when a  new form  of  fiberglass  medium was introduced, a
special filter column,  constructed by  Owens-Corning Fiberglas Corporation, was installed
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in the system to accommodate the new fiberglas-reinforced-plastic (FRP) cartridges. This
new column is constructed of plexiglass in five sections. Each end section contains a splash
plate, a perforated baffle and  1/2-inch pipe connections. The three intermediate sections
each can accommodate cartridges of 12 to 24  inches in depth. The total available depth
for the fiberglass medium is 60  inches, and no space is required for backwash expansion.
Taps located at each end of each section of the column permit multi-depth sampling and
measurement of head loss distribution with depth. Fabrication of the column is such that
it may  be inserted  in  place of  the glass column without disruption  or major alteration
of the appurtenant piping.  Consequently, the appurtenant piping and  instrumentation are
the  same for  both types of  columns.

Filtration rate is controlled by a constant-pressure differential  flow controller located on
the effluent line and capable of maintaining a constant flow as  long as there is a constant
pressure on the downstream side of the controller. Flow can be regulated and automatically
controlled  between 0.4 and 4.4  gallons per minute, with a minimum pressure differential
of 6 psi across the controller. Filtration rate and  backwash rate are measured by a rotameter
located in-line between the filter and the flow  controller.

Pressure taps are located at the  top of the filter and at the underdrain, and a  precision
pressure gage  is connected to  either end  (depending upon whether the  filter is operated
downflow  or  upflow)  to monitor influent  pressure.

Head loss  across the filter bed  is measured directly with a mercury manometer having
an upper limit of 66 inches of mercury. The temperature of the wastewater in the  glass
filter column  is measured  with  a dial-type thermometer located  67  inches above the
underdrain in a tee-section of the filter column.

The filter bed is backwashed with tap water  supplied by a connection below the underdrain.
Air  scouring of the bed may be  used  in  the  backwash process. The  air supply is also
connected  to a  tap located   below  the underdrain. Distribution of the  air bubbles is
accomplished  by the underdrain and by the supporting gravel  layer of granular beds. Air
pressure may  be regulated  at any level  to 35 psig. An air relief valve is connected  to
the  top  of the filter to permit evacuation  of accumulated air  in the filter column  prior
to bringing the  filter up  to operating pressure. Filtered water samples are  collected  from
the  sampling  valve downstream  of the  flow controller.

Storage Tank

Storage of sufficient capacity  was required to provide for the maximum anticipated volume
of wastewater  which the system may process in a single filter run.

The storage tank  has  a gross capacity  of 1,120 gallons and  is capable of sustaining a
filtration  rate of  15 gpm per  square  foot for  12 hours, or a filtration rate of 50 gpm
per  square foot for 3-1/2  hours.  The fiberglass-lined  wooden  tank  is 5 feet square and
7 feet deep, and  is enclosed  on top by wooden hatches and insulated on the  sides and
bottom by 5 inches of fiberglass insulation. A thermostat-controlled 2,000-watt immersion
heater compensates for heat loss to maintain the desired water temperature. The wastewater
is continuously  mixed by an  electric, propeller-type mixer suspended over the  center of
the  tank.
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Transmission Facilities

Transmission facilities between the storage tank and  the filter were required to  deliver
the wastewater over the desired  ranges of  flow and pressure without materially  affecting
its quality.

Wastewater is transmitted by a centrifugal pump from the storage tank through a 1/2-inch
PVC pipe to  the filter. At an operating pressure of 35 psig at the filter, the pump delivers
more than 10 gpm.  System pressure is controlled  by a back-pressure relief valve located
on the pump throttle line.  All pump discharge in excess of the filtration rate is returned
to the tank.  The small (1/2-inch diameter) transmission  line was chosen to minimize the
settling  of solids without  excessive head  loss due to friction.

Flocculant Supply

Separate systems were  required for  the  simultaneous  injection  of the  flocculant and
flocculant aid in the transmission line so as  to avoid contact between  the chemicals before
mixing with  the  wastewater.

Each  injection  system consists of  a  metering pump which feeds a PVC injection  nozzle
strategically located  in the transmission line near the filter (Figure F-1). Mixing is achieved
by three mechanisms: turbulence induced by the projection  of the nozzle into  the flow
of the wastewater, turbulence occurring at three to six  elbows between the injection point
and  the  filter,  and  longitudinal  mixing in  non-laminar  pipe  flow.

System  Controls  and Safeguards

Coordination and protection of the filtration system  is provided by the devices listed  below.

     Safeguards

  Pressure regulator  ahead  of filter.
  Low water-level auto-shutoff for  tank heater and mixer, with alarm and warning light.

     Monitors

  Tank water-level indicator.
  Pressure gauges on filter  and backwash  air  and  water lines.
•  Flow meters  for air and  water.
  Thermometer on  filter column.

     Controls

  Back-pressure relief valve on transmission line.
  Flow controller.
  Pressure Regulators for air  and  backwash water.
  Theremostat on  tank  heater.
  Purgemeter with needle  valve for air scour.
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                    Discussion  of Laboratory  Procedures and  Data

Outline of  Laboratory Investigation

The purpose of  the  laboratory  investigation was to evaluate the technical feasibility of
ultra-high-rate  filtration  for the treatment  of  combined  sewer overflow.  Minimum
performance levels could not be prescribed, because the state of the art would not support
such  assumptions with  any  degree  of confidence.   Consequently, a more generalized
approach  was applied to the investigation.

Technical feasibility depends primarily on  three broad  conditions: 1)  filtration capacity,
2) effluent  quality, 3) operating efficiency. These conditions were evaluated  in  terms of
filtration  rate and duration  of filter run; removal of 6005, COD, and suspended  solids;
and  quantity of filtrate required for backwashing.                               !

Three types of filters were operated at rates of 15 or more gallons per minute per  square
foot, utilizing a simulated wastewater and  both inorganic and polyelectrolyte flocculants.
Three filters, with different types of filter media and filter-bed arrangements, were evaluated
in this  study:

     1.    A  newly-developed fiberglass filter medium previously  untested in application
          to high-rate filtration of combined sewer overflow, provided by Owens-Corning
          Fiberglas Corporation.

     2.    A deep-bed  tri-media  filter specially designed for this application, provided by
          Neptune-Microfloc Corporation.

     3.    A  garnet bed  operated as an upflow filter.

Alum was used as the inorganic flocculant and Rohm & Haas Primafloc C5 as the cationic
polyelectrolyte flocculant.

Filter  runs  were  also conducted with excess  activated sludge added both to  use  as a
flocculant and to exploit its biosorptive capacity in an attempt to effect significant removal
of soluble BOD.

The study was  conducted  within a two-phase framework. The first  phase consisted of
a series of runs to determine a suitable flocculant for each  filter. Separate runs were made
with:

     1.    Plain wastewater  (no flocculant  dosage).
     2.    Wastewater plus alum.
     3.    Wastewater plus alum and  Rohm & Haas Primafloc C5.
     4.    Wastewater plus activated  sludge.

These runs were performed  at the lower end of the range of filtration  rates to be covered,
i.e.,  at  10 and  15 gallons  per  minute  per square foot  (gpm/sq.ft.).

The second  phase  of the study  consisted of a  series  of runs designed to evaluate the
performance of  each filter over various  ranges of filtration  rate  and  suspended solids
concentration.  In each case, the flocculant used  was the one found to  be most suitable
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to each filter as determined  in the first phase of the study. The use of air scouring and
agitation was  evaluated  as an aid to  backwashing of clogged filters in an attempt  to
economize  on backwash requirements.

Laboratory System Design and Operation

     Process and System  Parameters

Wastewater  characteristics  which  were controlled   and/or  observed  were:  size  and
concentration of suspended solids,  6005 and COD concentrations, and  temperature. The
operating variables were: filtration rate, pressure, backwash rate and quantity, air-scouring
rate  and duration, and flocculant dosage. The design  variables included the type,  depth,
size, and arrangement of filter media.

Three  identical  independent  filtration systems  were  constructed  at  laboratory  scale,  as
shown in the schematic flow  diagram, Figure F-1. The description  in the preceding section
of this appendix is  typical of each  system exclusive of the filter media.

     Characteristics of Wastewater  Feed

The  combined  sewer overflow  used  in this  study  was a  simulated  combined  sewer
wastewater, composed  of diluted  raw domestic  sewage and  silt.  A  wastewater with
suspended solids and  BOD5 concentrations  of 400 mg/L and 40  mg/L, respectively, was
desired for the  purpose  of uniformity  in the  flocculant evaluation  and for some other
comparisons. The intended procedure  for synthesis of the waste was to dilute the domestic
sewage with fresh water to  attain  the  desired 6005 concentration  and then to add a
slurry  of silt to the  diluted sewage  to bring  the suspended  solids concentration  to the
desired level. However, the character  of the domestic sewage was too variable to  permit
determination  of an  appropriate  dilution  ratio;  therefore,  the  wastewater formulation
became largely  a matter of  adjusting the suspended  solids  concentration.

Soil  was oven-dried at 250°C and then pulverized. A slurry of the resulting silt was prepared
at a concentration  of 100 grams per liter.  After thorough mixing (at least 10 minutes)
the  slurry  was  allowed to settle for one minute. The  supernatnat was then used (at a
suspended  solids concentration  of   30,000  mg/L)  to  adjust  the suspended  solids
concentration  of the simulated wastewater.

Sewage was delivered  to  the laboratory by truck from a local  sewage treatment plant.
Several loads were  anaerobic upon delivery,  and on  at least one occasion, the pH was
a high as 10 (pH affects flocculant action and the attachment of solids to the filter medium,
the  fiberglass being  especially  sensitive  to  pH  variation).

Large  particles   in the sewage  were removed during  the formulation of the wastewater,
to prevent  subsequent clogging of pumps, transmission lines,  regulators, and valves. Most
of this solid matter consisted of gravel and  grease which was retained in a residual  sludge
in the delivery  truck. Attempts to  flush this material from the tank truck before loading
with  sewage  at the treatment plant  were  unsuccessful. The problem  was resolved by
pumping the first 50-100  gallons from  the truck into 55-gallon drums.  The sewage was
passed through  a wire cloth-lined  basket to remove  the large but less dense solids. The
effect  of this screening procedure was basically the same as that of a  grit chamber  except
that  large buoyant solids  were also  removed.
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Substantially different suspended solids and BOD5 concentrations were encountered when
the three storage tanks were filled one at a time from the truck. This difference  was
attributed to  the density  stratification  of solids in the tank truck during transport. It
was therefore necessary to fill  all three tanks simultaneously so as to obtain uniform
wastewater characteristics. This was  achieved by pumping  from the truck into a small
dosing tank which drained into all three  storage tanks.

     Filter Media

Fiberglass Filter-Two  basic forms of fiberglass were utilized in this study: fiberglass plugs
and  fiberglass-reinforced-plastic  (FRP)  cartridges. Several  configurations of each  form,
differing in  depth, density, fiber diameter, fiber orientation, density stratification,  and
combination  with granular media, were tested.

The  fiberglass plugs were  cut from  laminated fiberglass boards, with the fibers sharing
a common alignment (either parallel or perpendicular to the direction of fluid flow). Plugs
with  parallel fiber orientation were  3"  long  and slightly  more  than  4" in diameter so
that  they fit tightly inside the 4"  glass column.  Insertion of the plugs inside the column
required approximately 5  percent compression of the  medium  Plugs with perpendicular
fiber  orientation were  actually  disc-shaped, having a 4" diameter and a 5/8"  thickness.
The  disc  were used for one run only and were found  to  be unsuitable because of high
resistance to flow.

The first seven runs were performed on  beds consisting of plugs in layers of two densitites.
The upper layer in all cases had a density of 5 Ibs. per cu.ft., although the layer thickness
and fiber diameter varied  among the  runs. The lower layer, also  varying in thickness  and
fiber  orientation, was  in all cases 10  Ibs.  per  cu.ft. The compositon of the bed for each
test run is presented  in Table  F-1.

Each  of the first five  runs was  attended by a media-collapse phenomenon, wherein  the
individual plugs were  observed  to collapse inward  and  to  separate from  the  glass wall
of the filter column. At the termination of each run,  the collapsed plugs were no longer
suitable for use, because  backwashing did  not  restore  the  original structure of the plug.
Two subsequent runs were performed  on beds 3"  shallower than those of the earlier runs.
The collapse phenomenon  was not evident in these runs, but recycling on the same medium
was not attempted. On several occasions (including Runs 6 and 7), the plugs were displaced
by the  backwash  water.

Runs 8 through 16 were  performed  on FRP cartridges, fiberglass modules consisting of
an inner core of  fibers bonded  to a rigid resinous casing.  This  form  was introduced in
an attempt to circumvent the collapsing phenomenon  observed with the fiberglass plugs
and to achieve more effective  backwashing. Two densities of fiberglass medium were tested
in the FRP cartridge  form.

Each  cartridge had a 4"-square cross  section. The 5 Ibs/cu.ft. cartridges were  24" deep,
and the  denser  medium was  10"  deep.

Five  cartridge configurations  were tested. Three  cycles (Runs 8  through 10)  were made
on Configuration  A, which consisted of  48" of 5 Ibs/cu.ft. material with .00150 fiber
diameter over 10" of  10 Ibs/cu.ft., .00050 material. Two attempts were made  at running
on Configuration B, which consisted solely of a 10" depth of 10  Ibs/cu.ft. cartridge; both
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attempts were unsuccessful  because  of excessive  head loss, and no effluent samples were
collected nor measurements taken. Cartridge Configuration C was the first dual-media filter
utilizing fiberglass. It consisted of 10" of 10 Ibs/cu.ft. material, 24" of 5 Ibs/cu.ft. (.00150)
material, and a cover layer  of 6"  of coarse and 6" of fine garnet. The garnet was chosen
for its high specific gravity to  permit high backwash rates  without necessitating special
measures for preventing loss of media. The filter performance was the same as Configuration
B  and is  not reported in  the  results  of the study. In  Configuration  D, the garnet was
replaced  by  coarse  anthracite,  and the  performance was more  satisfactory  (Run  11).
Configuration E was used in five cycles (Runs 12 through 16); the only distinction between
Configurations  D and  E was in  the  fiber diameter of the 5  Ibs/cu.ft. material. The latter
contained .00110 fibers, and the former  contained .00150 diameter fibers. The anthracite
was contained in a 4"-diameter PVC pipe covered with a perforated  plate to prevent loss
of media  during backwash.

The  collapse problem appears to have been  solved  by  the use of  the FRP  cartridges,
although internal splitting of the medium  may be another manifestation of the same basic
circumstance.

A  summary of cartridge configurations for which  runs are analyzed in this report appears
in  Table F-2.

Tri-Media  Filter-The tri-media filter consisted of  an  anthracite-sand-garnet bed  on a 12"
gravel and  coarse garnet base. The depth, grain sizes, and specific gravities of the various
constituents are listed  in Table F-3.

The gravel  and garnet were placed  in 3" layers. After placing 25" of the intermediate-sand,
fine-garnet mixture, the bed was  backwashed and 1" of media was syphoned  from the
surface. Similarly,  after placement of  about  40"  of   anthracite,  the bed  was again
backwashed and 4" of media syphoned  off the surface.  After an initial trial run, which
lasted only  15  minutes, the anthracite depth  was decreased  to 30" by syphoning off the
top of the surface. After Run 5, the anthracite depth was increased to 36" in an attempt
to improve effluent quality. The depth was again decreased  to 30" after Run  10, when
the bed was repacked  after a  failure  of the glass column.

Dp-Flow Filter~The up-flow filter contained a 48" garnet bed on a 12" gravel, coarse-garnet
base identical  to that  of tri-media filter.  The  garnet  bed  consisted basically of two  grain
sizes (0.707  mm and  1.19 mm) in equal volumes,  except  for the  first run, when the
bed was composed of  the  finer grain size only.

     Results of  Filter  Runs

Methods and Criteria of Evaluation-The effluent quality aspect of filter performance was
evaluated  in terms of the percentage removal  of 6005,  COD, and suspended solids from
the raw wastewater; the effects of differences in  concentrations of these materials in the
raw wastewater were also considered. Soluble 6005 was monitored  for the purposes of
characterizing the wastewater and evaluating the usefulness of activated  sludge as a soluble
6005  removal agent.  Raw wastewater samples were collected from the pump throttle
lines at the storage tanks.  Filtrate  samples were  taken  from the sampling valve located
downstream from the flow controller.  Streaming  current and  pH were measured  on a
majority  of the samples.
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The capacity evaluation was based upon filtration rate and length of filter run. The length
of run as reported herein does not necessarily refer to the actual duration of filter operation.
Time  designated  as  "T^"  is the time to the  point at which head loss equalled 15  psi.
The Jength of run characterized by  a  breakthrough of  suspended solids is designated by
"Tb"  and  is defined as the time  to the  midpoint of a breakthrough. The breakthrough
was taken  as a significant upturn  in the effluent concentration from a lower stable state.
This definition was  preferred to  the  more traditional  definition based on a percentage
increase  in concentration,  because it  is more characteristic of the filter and  is  less of  a
reflection of an imposed effluent  criterion. The length  of run is  assumed to be the lesser
of T-|5 and Tj-,. Consequently, the average effluent concentration (and percent  removal)
is  computed  from the analytical  results of samples jtaken prior to breakthrough or head
loss in excess of 15 psi. Therefore,  TI-, tends to  be a conservative estimate of run time;
backwash requirements (based on actual  backwash and filtrate volumes) also  tend  to be
conservative.

The backwash requirements were  evaluated independently  of the other parameters as  the
search for an economic backwashing procedure was carried  out. Backwash  requirements
are expressed as percent of filtrate volume and as gallons  of backwash water required
per pound of solids  removed from the  wastewater during the  run.

Fiberglass Filter Flocculant  Evaluation  (Runs 1, 3, 5, 6)-The performance of the fiberglass
filter  was not enhanced by the  use  of flocculants.  Four filter runs at 15 gpm per sq.ft.
were  compared  in this evaluation  (Figure F-3 and  F-4); Run  1 was made with plain
wastewater (no flocculant was added);  Run 3 with a dosage of 150 mg/L of alum injected
continuously in-line;  Run 5 with  Primafloc C5 (4 mg/L), a cationic polyelectrolyte, used
in  addition to the alum;  and Run 6 with 50 mg/L of activated sludge added to  the
wastewater.

The effluent quality  of the run  with plain wastewater was superior to that of each of
the comparable  runs. With the apparent exception of BOD5 removal in the alum-C5 run,
the removal  of  COD, 6605, and suspended solids was  unexcelled by any of  the runs
utilizing  a flocculant. However, the influent BOD5 concentration for the plain run was
suspiciously low with respect to the influent COD concentration (Table  F-4). While  the
ratio  of  COD to  BQD$ concentration for the plain  1.8 to 4.0,  the ratio in  Run 1 was
about 38.  (In all of the subsequent runs  the COD/BOD5 ratio was still below 5.5 except
in Run 11, where the ratio was 42.) Apparently there was an erroneous influent BOD^
measurement in the  case of Run 1 and   11.  If  in fact the influent BOD5  in the plain
run were of the order of 100 mg/L (giving a COD to BOD5 ratio of 7.5), then the degree
of removal would amount to  95 percent. On the basis of effluent quality, the plain and
the alum-C5 runs were significantly more effective. Of the two, the plain run was considered
to  be  better because  of greater  COD removal and longer run  time.

Breakthrough of suspended solids was observed  in  each of the four runs. The time to
breakthrough (TD) was nearly 85 percent  longer in the case of the alum and the  activated
sludge runs as compared to the 3-hour plain run. However,  the  35 percent higher solids
and 140 percent higher COD of  the  influent  of the plain  run  undoubtedly contributed
significantly to the shorter run time.

The apparent deficiency in  run time is not considered  to  be of  sufficient importance to
outweigh the substantially higher  effluent quality  obtained from  the plain  run.  All
subsequent runs on the fiberglass  filter were performed without benefit  of flocculant or
flocculant  aid.

                                         217

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Efflect  of Solids Concentration  (Runs  8 and  14)-Two  runs  at 25  gpm/sq.ft., with
wastewaters having high  and low suspended solids  concentrations are depicted  in  Figure
F-5  in  terms  of head  loss  (Runs 8  and  14).  The  rate  of  increase in  head loss was
approximately 7 times greater for the run with the higher  solids. The non-soluble BOD$
was the same  for each wastewater (approximately  40 mg/L), but the COD concentration
was higher for the low solids run. Therefore,  the higher rate of head loss is attributable
to the higher  solids concentration  rather  than  to  higher  organic  content.

Filtration  Rate (Runs 15, 13, and 12)-Three filter runs at 15, 35, and 50 gpm per square
foot, show a sharply  reduced run time at  the two  higher rates (see Table F-4 and Figure
F-6). The run time  at the  lower  of the three  rates was 2  hours  (T-J5 = 122  minutes),
while at rates of 35 and 50 gpm  per square foot,  the run times dropped to less than
one-half hour  (T-J5  = 28 and  25 minutes, respectively).

Effluent quality was lower at the higher filtration  rates also, but to a lesser extent. COD
removal showed the greatest reduction of the  three effluent  parameters evaluated. The
removal of COD at 15  gpm per square foot averaged 78  percent, whereas removals at
the higher filtration  rates were 52 percent and 64 percent.  Suspended solids removal
dropped from  95 percent to 87-91  percent, and 6005 removal dropped from 72  percent
at 15 gpm/sq.ft. to 58-68 percent at 35  and 50  gpm/sq.ft.

A significant change in filter performance occurs between 15 and  35 gpm per square foot.
The  performance levels at the two  higher rates  were very  nearly the same, and the runs
were very  short. It  should  be pointed out that all  three  runs  were performed  on the
same fiberglass cartridges, but in  order of decreasing filtration rate. Thus, the shorter run
times for the higher rates cannot be attributed to solids retained in the bed from previous
runs.

Fiber Backwash-A unique feature of the  fiberglass medium  undergoing  backwash is that
the medium remains unexpended. Consequently, the solids,  wherever they may be lodged
in the bed, must  be forced through the medium  through which  they have penetrated
during the filtration cycle. Unlike a  fluidized granular bed, the fiberglass retains the ability
to trap  solids during the backwash cycle  and to impede their passage, thereby limiting
backwash  efficiency. The solids, wherever they may be lodged in  the bed, must  be forced
back through  the medium which  they have penetrated during the filtration cycle. This
limitation may be partially offset by providing some mechanism for releasing solid particles
so entrapped. The mechanism chosen for study was air agitation. Air was discharged through
the bed, both  alternating with  and  concurrent with backwash water, and the process was
repeated until  the backwash  effluent remained  clear at high backwash rates. The alternating
discharge  method  was the more  effective technique.

Due  to  the high porosity and compressibility of the fiberglass medium  fiber reorientation
is possible. An extreme case  of  such distortion occurs when fiberglass plugs collapse during
filtration.  The media collapse phenomenon,  in all  cases,  was  observed  to  occur in a
progression from the upstream plug to successive  plugs in  a downstream  direction. The
plugs collapsed  anisotropically  inward, normal to  the  planes  of  laminations.

The  probable  mechanism by which collapsing occurs  is  basically  that  as the  filter run
progresses, a layer of solids builds up  near the  upstream  face  of the plug or directly on
the  upstream   face,  thereby creating a  sharp  pressure  differential  within   the  plug.
Simultaneously,  as wastewater seeps between  the plug and  the glass  wall of the column,
                                        218

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the flow  acquires a  radial  component, and another layer of  solids builds up within the
plug,  concentric to the column. The pressure differential then increases until  failure occurs
in the direction  of the weakest  plane. This process recurs in each successive plug.

Backwash requirements of the plug-type medium ranged from 6.5 percent to  14.5 percent
of the filtrate volume for first-run beds, or 13 to 41 gallons per pound of solids retained
(Table F-4). Backwashing of a second-run bed required 41 percent of the filtrate, or nearly
90  gallons per pound  of solids.

Backwashing of fiberglass plugs was  not effective. Although the collapsed plugs partially
recovered their  original shape  after the run terminated,  the basic weakness  of the plugs
remained, probably due to  broken fibers. Only  one  recycle was attempted on plugs. Runs
3 and 4 constituted  the first and  second runs on one set of plugs. However, the first
run was terminated on the basis of head loss before all the plugs had collapsed. When
the second cycle began, the weakened plugs again  collapsed almost immediately, but the
remaining plugs were effective for  1-1/4 hours,  at which  time breakthrough occurred.

In addition  to  the problem  of media collapse,  the  plug-form  of fiberglass was shown to
be  susceptible  to  dislodging during backwash.  This usually occurred in the  denser layer
of the bed, and all the plugs above it were displaced  upward.

The use of  FRP cartridges, to avoid the media collapse phenomenon and to enhance the
washability  of  the bed, was largely successful. The bonding of the outer fibers to the
casing apparently prevented the build-up of the forces which are presumed to have caused
the plugs  to collapse, and the medium  also was held firmly in place during backwashing.
In a  few  of the cartridges, however,  internal  splits, which were visible at  the surface,
developed. These less extreme fiber reorientations  were relatively small, the largest opening
being less  than 1/4  inch wide  and approximately one  inch  long. The depth was  not
measured, but  obviously did not extend through the entire depth  of the cartridge. The
split appeared  to  be the result  of  a weakness in  the fabrication  of the medium

The backwash requirements for the cartridge were  not very different from those for the
plugs, and they ranged from 3.6  percent to 22 percent of the  filtrate volume,  or 11 to
43  gallons per pound  of solids  retained  (Table  F-4). However, backwash  requirements
decreased  with  successive cycles.  For example, only  3.6 percent of the filtrate was required
to backwash the medium after its fifth filtration cycle. This indicates an  increasing degree
of fiber reorientation  and that  increased quantities of  backwash water flows  through
channels or  "corridors" of high permeability. The  degree to which the agitating air bubbles
contribute  to such  channeling effects  was not  estimated, but the effectiveness of  air
agitation in loosening bound solids  was repeatedly demonstrated.

The effectiveness of air agitation is shown in Figures F-7 and F-8. Five cycles are depicted
in terms of  head loss  and the  removal  of suspended solids, 6005, and COD. The initial
head  loss  increased from 3.5 psi to 7.5 psi between Cycle  1  and Cycle 5, at a filtration
rate of  50 gpm per  square foot.  (The effect  of subsequent cycles on the  initial  head
loss was lessened somewhat by the difference in  influent suspended solids concentration,
since  a  higher concentration  was associated  with the  earlier cycle.)  The  removals of
suspended solids, BOD^, and COD were not greatly affected by repeated cycles, although
a slight decline in percentage removal appears to be related to the difference in influent
concentrations.
                                         219

-------
Tri-Media Filter Runs-Flocculant Evaluation  (Runs 1, 3, 4, 5)-The combination of alum
and  Primafloc  C5 was found to be the most suitable of the flocculants tested in terms
of both  effluent quality and  length of filter run. The flocculant  evaluation was based
upon four runs at 10 pgm/sq.ft.: Run 1  with  plain synthetic wastewater. Run 3 with
an alum dosage of 150 mg/L, Run 4 with the same dosage of alum plus 4 mg/L of Primafloc
C5,  and  Run  5 with activated sludge at  a concentration of  55 mg/L.

The  alum-C5 run did not demonstrate the highest degree of removal of either suspended
solids, BODs, or COD, nor did any other flocculant exhibit consistent removal superiority.
As may  be seen in  Figure  F-9  and Table F-5, the alum C5 combination  was generally
the second best of the flocculants with respect  to effluent quality. Suspended solids removal
in excess of 90 percent was achieved in  the alum C5 run, and  was second only to the
98 percent  removal  in  the  laum run.  The BOD5  removal of  nearly 60 percent for this
run was  exceeded only  in Run 1 (plain wastewater), for which removal averaged slightly
less  than 70  percent; COD removal  was 40  percent. The  alum-C5 combination  was
considered to be the best avialable alternative, largely on the basis of greater length of
filter run, which  was 80 to 400 percent longer than the others. Head loss  of  15 psi was
reached after  3-1/4  hours.

Effect of Suspended  Solids Concentration (Runs 4, 6, 10)--The effect of influent suspended
solids  concentration  on filter performance was demonstrated by Runs 4 and  10 (Figure
F-10 and Table F-5), with  influent solids concentrations of 410 mg/L and 2,420 mg/L
respectively, and COD and  BOD5 concentrations approximately the same  in  both  runs.
The  run  with the lower  solids concentration  (No.  4) was  nearly 90 percent longer than
Run   10.

Run  6 also  appears to show the effect of the organic content of the wastewater (Figure
F-10). The  wastewater  used in Run 6 had a  lower suspended solids concentration than
either of the  other  runs, but  had a much higher organic content-200 mg/L 6005 and
560  mg/L COD in  Run 6, versus 25  mg/L  6005 and  160 mg/L COD in Runs 4 and
10. The  effect of the higher  organic  content was a 50 percent shorter run time than
that  in the high-solids run  (Run 10).

Filtration Rate (Run 8)-Operation of the tri-media  filter at rates in excess of 10 gpm/sq.ft.
proved to be unsatisfactory with  respect to effluent quality and  length of run. Although
performance  was erratic at  rates above 10 gpm/sq.ft., Figure F-11 illustrates a typical
performance for Run 8 at 20 gpm/sq.ft. This run lasted less than one hour, and the removal
of suspended solids, 6005, and COD declined typically as the run progressed. The average
suspended solids concentration in the filter effluent was 240 mg/L (50 percent removal),
while removal  of COD  and BOD5 each averaged  approximately 30  percent.

Backwash Requirements-The normal backwash requirements of the tri-media  filter were
12 percent to 25 percent of the filtrate, or 40 to 75 gallons per pound of solids retained
(Table F-5).  However, frequently  more backwash  was required  (up to 250 gallons per
pound of solids) because of two factors:  1) fibrous solids clinging to the surface of the
bed  during  backwash, and 2)  difficulties  in fluidizing the bed. The fibrous solids could
be removed only by expanding the bed to the overflow level. Failure of the bed to break
up readily  resulted in the entire sand and anthracite layers being lifted without fluidizing.
The  anthracite  layer  was particularly difficult to break up, and the problem was usually
caused by the accumulation  of a layer of tiny air bubbles at the sand-anthracite interface.
                                        220

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Upflow Filter Runs-The  upflow filter was limited  to  a maximum  filtration rate of 15
gpm per square  foot, because the bed (a garnet medium) would fluidize at higher rates.
Nine runs were  performed  at  5,  10 and 15  gpm  per  square  foot  (Table  F-6).

Flocculant Evaluation-The  use of flocculants did  not appear to have  a beneficial effect
upon effluent quality at either 15 or  10 gpm per square foot.  Run 1,  with no flocculant
addition, was terminated because  of excessive head loss (15 psi)  after less than 1-1/4 hours;
only 60 percent removal of suspended  solids was achieved.

Since a more  rapid head-loss buildup was anticipated with a flocculant added, the garnet
bed was modified after the first run. Fifty percent of the fine garnet  medium (by volume)
was replaced by a garnet sand  of slightly larger grain size. This  was effective in increasing
the length of  run, and head loss did not again reach 15 psi in any  run until much later
in the study when the bed depth was  increased.

The second  run  (at 15 gpm  per square foot) was made with an alum dosage of 150 mg/L.
Compared with the first run, the performance was only slightly better. The percent removal
of suspended solids was about the same, with the influent solids concentration about 40
percent lower and the  effluent concentration correspondingly  low. The 6005 removal
was about the same and the COD removal  (75 percent) was double  that of  the first run.

Two subsequent runs at  15 gpm per square foot  were made  with  different dosages of
alum and Primafloc  C5 polyelectrolyte.  In both cases, the removals of suspended solids,
6005,  and  COD  were  all  less than one-half the  corresponding removal in Run 1.

The  consistently poor performance  of the upflow filter at  15  gpm  per square foot  and
the ineffectiveness of flocculant  addition seemed to indicate that a  lower filtration rate
was appropriate. This was reinforced by the knowledge that at 15 gpm  per square foot
the bed was on the verge of expansion. The flocculant evaluation  was repeated at a filtration
rate of  10 gpm  per  square  foot;  in  this  series, a run with activated sludge as a flocculant
was also included.

In general, the filter performance did  not improve at the lower filtration rate. Runs with
plain wastewater and with the combination of alum and Primafloc C5 were slightly better
at 10 gpm per square foot than at 15 gpm per square foot. However, the  effluent suspended
solids concentration never  dropped  below 100 mg/L, nor did  the removal exceed  80
percent. The maximum  BOD^  and COD removals were 75 percent. A  final run at 5 gpm
per square foot with the addition of alum was not substantially  better in terms of effluent
quality.

Filter performance at 5, 10, and  15 gpm per square foot is shown  in Figure F-12. The
runs at 15  and  5 gpm per square  foot (Runs 2 and 9) were  both made with  an alum
dosage of 150 mg/L, and the run at  10 gpm per square foot was made  with no flocculant
added.  Runs 2 and 9 were  characterized by steadily decreasing  removal efficiencies; thus,
the average  concentrations are strongly affected by the  length of run. On the other hand,
Run 6, with plain wastewater, exhibited relatively  constant removal  efficiencies.

The  reduced fluid velocity  in the filter  column above the garnet bed  was not sufficient
to keep all  of the solids in suspension  in  the filter effluent.  Consequently, the solids
concentration  continuously increased in this portion of the column. Filter effluent samples
taken from  a valve  downstream  from the  column  were not truly  representative of  the
                                        221

-------
filter  effluent.  Only when the  solids concentration  in  the  column reached  such  a level
that the overflow concentration equalled the filtrate concentration would  the data  be
representative. Thus, the effluent concentrations were actually higher than the data indicate.

Backwashing the upflow filter was a formidable task;  almost  always, the bed was so bound
up  with solids  within the gravel  layer that the entire bed was lifted as a solid plug when
backwashing was attempted. The most  successful  technique was to  backwash at  a low
rate (less  than 15  gpm per  square foot)  to  remove fine solids from  the  upper  portion
of  the bed.  Air was then introduced at a pressure of 25 psig, and a drain  valve at the
bottom of the filter was opened with the filter  under pressure, resulting in  a very rapid
downflow. The high velocity  downflow stripped accumulated solids from the lower portion
of  the bed.  This procedure  generally had  to be repeated six or more times before the
bed could be backwashed by  the more normal procedure.

Backwash  requirements generally amounted to  13 to 18 percent of the filtrate volume.
However,  these figures  are of limited value  in  that  the filter runs were not terminated
due to head loss or turbidity breakthrough. Effluent quality was  so consistently poor
that the filter  runs were terminated at the  convenience  of the  operator.

Filter  Runs With Activated Sludge-One  run was performed  on each filter  with activated
sludge as  a flocculant and as  a potential removal agent  for  soluble  6005. (Run  6 in
the fiberglass filter  series. Run 5  in the  tri-media series, and Run 5 in  the upflow filter
series.) In  no case was thaactivated sludge determined to be the most  suitable flocculant,
nor did the sludge  have a noticeably detrimental effect on effluent quality or  length  of
filter  run   (see  Tables  F-4, F-5,  and F-6).  No significant removal  of  soluble 8005 was
observed.  In fact, the soluble BOD5 decreased by  only  1  mg/L on  the average for each
run with  activated  sludge. (Average reductions  of zero to  30 mg/L  were observed for
other  runs, by comparison.

Summary  of Findings

The laboratory test program indicated that ultra-high-rate filtration, at  rates of 15 or more
gallons per minute per square foot, is  a technically feasible process  for the removal  of
suspended solids and associated non-soluble BOD from combined sewer overflow. Of the
three  filter systems  tested, the fiberglass filters performed best, achieving at least 90 percent
removal of suspended solids and 70 percent removal of non-soluble  BOD5  at filtration
rates  of  15-30 gpm/sq.ft. and with  filter runs  of 1 to 3 hours duration. The addition
of flocculants and flocculant aids was not effective in  improving the performance of the
fiberglass  filters. Comparable effluent quality  was not achieved in the tri-media filter runs
at filter rates above  10 gpm/sq.ft. Upflow filtration through a garnet bed was unsatisfactory,
largely on the  basis of poor effluent quality.

Soluble BOD removal  was negligible in all three  filter systems, even with the addition
of activated  sludge to the influent wastewater.  The non-soluble organic content  of the
influent wastewater appeared to  have a  greater impact on head-loss  building than did the
suspended  solids  content.
                                        222

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From the  results  of these observations, it  can be concluded that  an improved effluent
quality  (i.e. lower concentrations of suspended solids, BOD^ and COD) could be obtained
from  the fiberglass  filter  by:

     1.    increasing  total  bed  depth
     2.    increasing  media density  in the  bottom  layer
     3.    optimizing  density gradation

A  multi-  or  graded-density fiberglass bed  is needed to retain large solids and  to permit
the passage of smaller solids so as  to  make the most  efficient use  of pore space and
avoid premature clogging at the shallower  depths of the  bed. Turbidity of effluent from
the fiberglass filter  was due  to very fine  particulates, and  it is believed that  a bottom
density  in excess of 15 Ibs/cu.ft. could reduce effluent concentrations  of suspended solids
to less  than  40 mg/L.

The economic feasibility of fiberglass filter process for ultra-high-rate  filtration may depend
on extending the  useful life of the fibergalss medium beyond the limits indicated by the
laboratory tests.  Improvement  of the  backwash  operations  through modification of
underdrain design, staged  removal of backwash  effluent, the use of  air scouring during
backwash, and  development of  improved  fiberglass bed designs and  fiberglass  filter
regeneration  techniques appeared to be promising approaches to extension  of filter life.
                                         223

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                                      Table F-1
                      Characteristics of Fiberglass Plug Filter Beds
                                                               1
            Upper Layer, 5 Ibs./cu.ft.
Run          Layer          Fiber
No.        Thickness      Diameter
             inches
inches
                 Lower Layer, 10 Ibs./cu.ft.
                  Layer             Fiber
                Thickness         Diameter
inches
inches
Total
Depth
inches
1
2
3-4
5
6
7
48
54
54
54
51
51
.0011
.0015
.0011
.0011
.0011
.0011
12
6
6
6
6
6
.0005
.00052
.0005
.0005
.0005
.0005
60
60
60
60
57
57
1
 All fibers aligned parallel to flow unless otherwise noted.
-Fibers aligned perpendicular to flow.
                                       224

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                Table F-2



Summary of Filter Cartridge Configurations
                                  Fiber Diameter
Configuration

Configuration A (Run Nos. 8-10)
Upper Layer
Lower Layer
Configuration D (Run No. 11)
Upper Layer
K> Middle Layer
ui Lower Layer
Configuration E (Run Nos. 12-16)
Upper Layer
Middle Layer
Lower Layer
Medium

— .
Anthracite
Fiberglass
Fiberglass
Anthracite
Fiberglass
Fiberglass
Depth
inches
48
48
18
24
10
18
24
10
or Grain Size
1 Clinches
150
50
coarse
150
50
coarse
110
50
Density
Ibs/cu.ft.
5
10
5
10
,5
10

-------
                           Table F-3

              Characteristics of Media Used in the
                       Tri-Media Filters

                                                 Grain          Specific
     Material               Layer Depth             Size           Gravity
                             inches

Anthracite                   30-36           2.00-2.83 mm         1.6
Mixed:  Sand                  15             0.50-1.00 mm         2.6
        Fine Garnet             9             0.35-1.00 mm         4.2
Coarse Garnet                   3             1.41-4.00 mm         4.2
Fine Gravel                      3             4.00-8.00 mm         2.6
Medium Gravel                  3             5/16-5/8 inch         2.6
Coarse Gravel                    3               1-2 inches           2.6
                            226

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                                                                                                                                              Table F-4
                                                                                                                                   Filtration Study Data Summary
                                                                                                                                           Fiberglass Filter
ro
Run No.
Nominal Flow per Unit Area, gpm/sq.ft.
Flocculant Dosage
Alum, mg/L
Primafloc C5, mg/L
Activated Sludge, mg/L
Sutpended Solids
Influent, mg/L
Effluent, mg/L
Percent Removal
BOD5
Influent, mg/L
Effluent, mg/L
Percent Removal
Soluble BOD5
n u , "W
P B 1
COD
Influent, mg/L
Effluent. mg/L
Percent Removal
pH
Influent
Effluent
Length of Filter Run, minutes
Head Lots
Initial psi
Final, psi
Filtrate Volume (actual), gallons
Backwash (actual)
Volume, gallons
Volume as Percent of Filtrate.
Volume per Pound of Solids Retained, gal/lb.
Influent Pressure, psig
Actual Run Terminated By:


Cycle
Form
— 1
15

0
0
0

670
10
98

19
5
72




7SO
68
91

6.8
7.0
187b

1.4
7.9
299.4
21.1
7.0
13.0
24
Media-
Collapse


	
Plugs
_2
15

0
0
0

465
51
89

58
32
45




214
118
45

6.7
6.8
149b

1.4
8.2
248.8
	
	
27
Media-
Collapse
and
Head Loss

	
Plugs
_3
15

ISO
0
0

500
60
88

97
34
65




288
112
«1

7.1
6.8
**b.K

0.9
15-0
463.5
30.1
6.5
17.9
25
Media-
Collapse
and
Head Loo

1st of 2
Plugs
_4
15

150
0
0

632
32
95

62
14
78




250
58
77

7.0
6.9
75b

1.7
9.1
173.7
71.2
41.0
88.4
25
Media-
Collapse
and
Head Loss

2nd of 2
Plu«s
_5
15

150
4
0

580
6
99

124
6
95

18
6
65

220
44
80

6.8
6.9
"«b

0.4
8.4
217.2
14.2
6.6
15.2
25
Media-
Collapse,
Head Lots,
and
Turbidity
	
Plugs
_6
15

0
0
50

506
73
84

110
23
77

12
11
10
320
144
55

6.8
6.8
330,,

0.5
9.3
510.9
73.8
14 5
40.8
25
Turbidity
{no collapse)


	
Plugs
_7
25

0
0
0

232
46
80

87
58
53

32
30
3
296
148
50

7.2
7.2
210,

0.8
6.9
590.0
	
.........
24
Shortage
of
Synthetic
Wntewanr
(DO collapse)
	
Plugs
J
25

0
0
0

176
26
85

105
85
19

67
54
19
350
178
49

6.8
6.8
220

2.2
15.0
544.6
	
	
21
Head Loss


1st of 3
FRP
J)
35

0
0
0

560
56
90

98
61
37

145)
(45)
0
410
287
30

6.9
7.0
28

5.3
15.0
160.3


25
Head Loss


2nd of 3
FRP
JIO
25

0
0
0

242
24
90

95
58
39

43
(43)
0
400
208
48

6.8
6.7
62

5.4
15.0
234.2
	
	
24
Head Loss


3rd of 3
FRP
VI
30

0
0
0

680
48
93

4
1
71

0
0

170
60
65

7.4
7.6
'So

2.1
9.3
234.9
51.2
21 8
43.2
23
Head Loss


	
FRP
!2
50

0
0
0

1,000
90
91

86
36
58

20
15
25
343
123
64

7.0
7.1
25

3.4
15.0
126.1
15.1
11.9

IB
Turbidity
and
Head Loss


1st of 5
FRP
13
35

0
0
0

760
99
87

48
15
68

13
1 1
B
212
102
52

7.2
7.3
28

3.5
15.0
1D2.3
9.2
9.0
16.3
21
Turbidity
and
Head Loss


2nd of 5
FRP
H
25

0
0
0

840
42
95

45
10
77

8
7
11

243
61
75

6.9
7.1
52

1.9
15.0
183.8
1X3
7 j
iO.9
22
Head Loss


3rd of S
FRP
16
15

0
0
0

888
44
95

96
27
72

1 1
18

435
78
82

7.1
7.1
122

0.4
15.0
201.2
15.9
79

28
Head Lost


4th of 5
FRP

S





334
40
B8

22
9
58
5
5


91
46
49

7.0
7.0
52

7.4
15.0
350.6
12.7
3.6
14.7
19
Head Loss


SThofS
FftP
          b w b 15 = Breakthrough of Suspended Solids.

-------
                                                                                                                                Table F 5
                                                                                                                      Filtration Study Data Summary
                                                                                                                             Tri-M«di» Filter
NJ
Run No,

Nominal Flow per Unit Am, gpm/eq.ft.

Flocculenl Dotage
  Alum, mg/L
  Primafloc C5. mg/L
  Activated Sludge. mg/L

Suspended Solids
  Influent. mg/L
  Effluent, mg/L
  Percent R«movil

B005
  Influent. mg/L
  Effluent, mg/L
  Percent Remove!

Soluble BOD6
  Influent, mg/L
  EHIuent, mo/L
  Percent Removel

COD
  Influent, mg/L
  Effluent, mg/L
  Percent Removel

pH
  Influent
  Effluent
	 1
10
0
0
0
390
23
94
31
10
68

	


110

6.8
6.8
_2
15
75
0
0
440
42
90
47
23
52



137
70
49
6.7
6.9
_3
10
150
0
0
418
8
98
40
18
54
._._...
	
— 	
108
77
29
7.0
7.0
4
10
150
4
0
410
29
93
25
11
57

	
	
107
65
39
6.9
6.9
_B
10
0
0
55
475
101
79
66
37
44
19
16
6
339
207
39
6.8
6.9
_6
10
150
4
0
218
87
60
196
137
30
103
(103)
0
560
431
23
6.8
6.9
-1
15
150
4
0
158
96
39
159
102
36
110
(110)
0
670
456
20
7.0
7.0
_a
20
150
4
0
528
243
54
89
60
33
69
46
33
360
256
29
6.7
6.7
_9
6
150
4
0
188
113
40
111
58
48
50
20
60
340
156
54
7.0
6.7
JLQ
10
150
4
0
2,420
436
82
19
8
59
1
3
19
162
32
80
7.1
7.2
11
10
0
0
0
620
112
82
5
1
83
1
0
100
120
80
37
7.9
7.8
12
20
150
4
0
640
173
68
29
16
48
11
6
41
172
69
60
7.0
6.5
11
16
150
4
0
640
90
86
42
8
80
9
5
48
2S3
56
78
7.0
6.4
J4.
10
160
4
0
720
161
79
65
4
94
IS
4
76
232
51
78
7.0
6.0
Jt
20
0
4
0
334
37
89
22
9
57
6
4
20
91
36
60
7.0
7.0
              Length of Filter Run, minutes

              Heed Lou
                Initial. p«i
                Final, pv

              Filtrate Volume (actual), gallon!

              BackwB* (actual)
                Volume, gallons
                Volume as Percent of Filtrate
                Volume per Pound of Solids Retained, gal./lb.

              Actual Run Terminated By:
                                                                   46
                                                      1.5
                                                     15.0
                                                     51.8
                                                     13.8
                                                     26.6
                                                     87
                                                                                42
 2.3
1S.O
                                                                  67.6
12.0
17.8
54
                                                                                              75
 1.4
15.0
                                                                                87.2
21.9
25.2
73
                                                                                                          198
  1.4
15.0
                                                                                            ?08.3
26.0
12.5
40
                                                                                                                     111
 1.3
 9.1
                                                                                                        91.1
20.8
22.8
                                                                                                                                 54
  1.3
 15.0
                                                                                                                    61.6
 17.5
 28.4
248
                                                                                                                                              38
 1.6
15.0
                                                                                                                                                            57
 3.1
15.0
                                                                                                                                             123.2
             16.5
             13.4
             61
                                                                                                                                                                      120
0.7
3.0
                                                                                                                                                         61.2
                                                 11.2
                                                177
                                                                                                                                                                    105b
 1.4
13.2
                                                                                                                                                                    102.0
1.5
3.3
                                                                                                                                                                                 102.0
                                   15.3
                                   15.0
                                   37
 2.7
15.0
                                                                                                                                                                                                33.1
                                      8.2
                                     24.9
                                     81
                                                                                                                                                                                                                           13
 2.2
15.0
                                                                                                                                                                                                              17.2
                                         6.6
                                        32.0
                                        71
                                                                                                                                                                                                                                        21
 1.6
16.0
                                                                                                                                                                                                                           22.0
                                         7.4
                                        33.5
                                        71
                                                                                                                                                                                                                                                      24
 4.4
16.0
                                                                                                                                                                                                                                        61.7
                                          9.1
                                         17.6
                                         71
                                                               Heed Loss     Head Loss     Head Loss    Head Loss   Turbidity   Head Loss    Head Loss     Heed LOB  Turbidity  Turbidity     Turbidity     Head Loet     Head Lose    Hied Lou     Heed Lot*
             D • Breakthrough of Suspended Solids.

-------
                                                                    FIGURE  F-l
                                                                    SCHEMATIC  DIAGRAM  OF  FILTRATION   SYSTEM
                      WASTEWATER
                      STORAGE TANK
                                                                                                                    FILTER
                                                                                                                    COLUMN
PRECISION
PRESSURE GUAGE
   BACKWASH WASTE OR  UPFLW FILTRATE
  THERMOSTAT
Ni
CO
 TEMP.
 SENSOR
MSTEMTER
LEVEL
INDICATOR
(lANMETER)
                                          On
              PURGEMETEfl
                            PRESSURE
                            DIFFERENTIAL
                            REGULATOR
                                                                                                               LIQUID LINE
                                                                                                 	  AIR LINE
                                                                                                 	  ELECTRICAL LINE
                                                 F-l

-------
       FIGURE  F-2
       FIBERGLASS FILTER:  FLOCCULANT EVALUATION ( RUNS  1,3,5,6
                 -HEAD   LOSS  AND  SUSPENDED  SOLIDS  REMOVAL
  t   HEAD LOSS
                                          FILTRATION TIME. MINUTES

                                         (FILTRATION RATE = 15 GPH SF)
    SUSPENDED SOLIDS REMOVAL
90
                                                                      • PLAIN
                                                                      A ALUM (150 MG Ll + PRIMAFLOC C5 (4 MG L)
                                                                      • ALUM (150 MG L)
                                                                      # ACTIVATED SLUDGE (50 MG Li
                               120
                                      150
                                              160
                                                      210
                                                             240
                                                                     270
                                                                            300
                                                                                    330
                                                                                           360
                                                                                                   390
                                          FILTRATION TIME  MINUTES

                                         (FILTRATION RATE - 15 CPM SFI
                                              230
F-2

-------
      FIGURE  F-3
      FIBERGLASS FILTER: FLOCCULANT  EVALUATION ( RUNS   1,3,5,6 )

                              BOD   AND  COD   REMOVALS

C.  BOD5 REMOVAL
                                                                          « PLAIN
                                                                          A ALUM (150 MG/L) + PRIMAFLOC C5 (4 MG L)
                                                                            ALUM (150 MG'L)
                                                                          * ACTUATED SLUDGE (50 MG L)
                                            FILTRATION TIME, MINUTES

                                          (FILTRATION RATE = I5GPM SF)
0.   COD REMOVAL
                                                                           A  ALUM (150 MG.-L) 4- PRIMAFLOC C5  M MG L)
                                                                           •  ALUU (150 MG/L)
                                                                           *  ACTIVATED SLUDGE (50 MG L)
                                         150       180      210

                                             FILTRATION TIME. MINUTES

                                           (FILTRATION RATE   15 GPM SF)
                                               231
                                                                                                                   F-3

-------
FIGURE  F-4
FIBERGLASS FILTER:  EFFECT OF INFLUENT SOLIDS CONCENTRATION
            ON HEAD REQUIREMENT  (RUNS 8 , 14)
                                               So =INFLUENT SUSPENDED
                                                    SOLIDS CONCENTRATION
                                               So =840 HG/L
                                               So =180 MG/L
                           FILTRATION TIME, MINUTES

                       (FILRATION RATE   25 GPM/SQ.  FT.)
                                                                  F-4
                           232

-------
                          FIGURE   F-5
                          FIBERGLASS  FILTER: PERFORMANCE  AT  15-50 GPM/SQ.  FT.
       PERFORMANCE AT 50 GPM/SQ.  FT.  (RUN  NO. 12)
    PERFORMANCE AT 35 GPM/SQ.  FT. (RUN NO.  13|
INFLUENT QUALITY:
• SUSPENDEU SOLIUS - 1.000 MG;L
A 6005-a6 MG L
*COD-340 MG/L
                                                                                               100
                               0               30
                                 FILTRATION TIME. MINUTES
INFLUENT QUALITY:
• SUSPENDED SOLIDS =160 MG  L
A BOD5 = 48 MG/L
# COD =210 MG/L

16
15
H
                            0               30
                             FILTRATION TIME. MINUTES
                                           PERFORMANCE AT 15 GPM/SQ.  FT.  (RUN NO. 15)
                                      100
                                     '50
                                     -40



                                                          HEAD
                                                          LOSS



                                                       INFLUENT DUALITY:
                                                       • SUSPENDED SOLIDS = 890 MG/L
                                                       A BOD5 = 96 MG/L
                                                       * COD = 435
                                                        60      9D        120

                                                       FILTRATION TIME, MINUTES
                                                                                 150
                                                          233
                                                    F-5

-------
FIGURE F-6
FIBERGLASS FILTER: FIVE CYCLES ON FRP CARTRIDGES
HEAD LOSS AND SUSPENDED SOLIDS REMOVAL
A HEAD LOSS
CICLC
IMC.CPI.'SF
I15 milUIES



15


CO
0.



2
o
1
50
25




i


/
/
/ ,
i

2
35
21



/
/

/
/
/



3
25
52






i
/

\
/


f
1
1
/
'





/










4
15
122










/
/







/
/







/
/
f







/
/






/
/
/








'









5
50
50

i





^







/
/
|/





^
/
/









0 30 60 90 120 150 160 210 240 270 300 330 360
FILTRATION TIME, MINUTES
B SUSPENDED SOLIDS REMOVAL
CYCLE
(UTE.GPH/SF
INFL.CQNC.tHGA
100
BO
BO
70
^60
UJ
«50
a
u
S40
30
20
10
0
\
50
1000

A
J








2
35
760

n
\








3
25
B40


































4
15
888




/









f





















































5
50
334


_











^^^









-•— -1








0 30 BO 90 120 150 160 210 240 270 300 330
FILTRATION TINE. MINUTES
234











360
F-6

-------
            FIGURE  F-7
            FIBERGLASS FILTER: FIVE  CYCLES ON  FRP CARTRIDGES
                         BOD5  AND  COD   REMOVALS
C. B005 REMOVAL
CYCLE
RATE. GPM/SF
INFL. CONC. CMG/L)
100
90
80
70
i 60
j
" 50
UJ
CJ
LL4
=-40
30
20
10
0
1
50
86




\
N;





2
35
48




X,






3
25
45














^








^








4
15
96


k
A. — ,















































0 30 60 90 120 ISO 180 210 240 2










5
50
22



k
v
X,









^^










,- 	





0 300 330 36
                                      FILTRATION TIME, MINUTES
D COD REMOVAL
CYCLE
RftTE . GPM/SF
NFL CONC. (KG/LI
100
90
80
70
LLJ
^ 50
LJJ
CJ
§ 40
30
20
10
0
1
50
343




.X






2
35
212





1















3
25
243






1


















^
^









*+*






4
15
435


•—

1







-"^-~- .









1 	 	 	 u









— * 	 '








i








•^







5
50
31


1 	

\









/
V







/
/





30 60 90 120 150 180 210 240 270 300 330 3
                                      FILTRATION TIME, MINUTES
                                     235
F-7

-------
                         FIGURE   F-8

                         TRI-MEDIA  FILTER:  FLOCCULANT  EVALUATION  {  RUNS 1,3,4,5  )
>   mi LOSS
                                                                               SumiDED SOLIDS IEIOIH
                                   • Pill I
                                   • ILUI (ISO IC/L)
                                   A ILDI (ISO IC/L) < PIIIIFLOC
                                                     CS (4 IE/L)
                                     ICTIIITED ILUOGE (55 IC/L)
                60      BO     IZO      ISO
                     FIITR«TIO« HIE. HIIIIITES
                     (FUTRITIOI RITE  "  10 CPI/SF)
              •  PLUM
              •  ILUI (150 1C  L>
              A  HUH (ISO 11!  L) 4 PHIimOC
                                 CS  (4 11! L)
              *  ICIIVIIED SLUDCE (Si  11! L)
    00      120       ISO
 FILTRATION  TIKE.  HIKUTES
(FILTRITIOK  RITE = 10  CPU SF)
                                                                                                                           100
                                     C  BODj REIDVU
                                                                       •  PLAII
                                                                       •  ILUI (ISO  IC/L)
                                                                       A  ILUI (ISO  II/L) 4 milFLOC
                                                                                          CS (4 1C L)
                                                                          ICTIIITEO  SLUDCE (SS 1C LI
                                                          FILTRITIO» THE.  IHUTES
                                                        (FILTRITIOI I1TE = ID GPI SF)
                                                             236
                                                                                                                                             F-8

-------
      FIGURE F-9
      TRI-MEDIA FILTER:  EFFECT OF INFLUENT SOLIDS CONCENTRATION
               ON HEAD REQUIREMENT  (RUN   4, 6, 10)
20
                                            So - INFLUENT SUSPENDED SOLIDS
                                                CONCENTRATION
                                            So = 220 MG/L
                                            So= 410 IG/L
                                            So - 2,420 MG/L
                         FILTRATION  TIME,MINUTES

                     (FILTRATION RATE  = 10  GPM/SF)
                              237
                                                                      F-9

-------
          FIGURE  F-10
          TRI-MEDIA FILTER: PERFORMANCE AT 20 GPM/5Q. FT. (RUN  8)
INFLUENT QUALITY:
• SUSPENDED SOLIDS = 530 MG/L
ABOD5 = 89 MG/L
#COD =360 MG/L
                                           FILTRATION TIME, MINUTES
                                 238
                                                                           F-10

-------
                        FIGURE   F-ll
                        UPFLOW FILTER:  PERFORMANCE  AT 5,10,AND  15  GPM/SQ.FT.
PERFORMANCE AT 15 GPM/ SQ. FT.  (RUN 2)
                            PERFORMANCE AT 10 GPM/SQ. FT. (RUN  6)
               INFLUENT QUALITY:
               I SUSPENDED SOLIDS = 420 MG/L
                   ;=4I MG/L
              * COD =160 H/L
                                                  100
            FILTRATION TIME, MINUTES
                                     12°
                                                  = 50
                                                  i40
                                                   30
                                                   20
                                                      INFLUENT QUALITY:
                                                      • SUSPENDED SOLIDS =560 MG/L
                                                      A BOD5 = 94 MG/L
                                                      4i COD =260 MG/L
                                                             30
                                                                                                                          -  I :
                                       90      120      150      180


                                         FILTRATION TIME,  MINUTES
                                                                                                              210
                                                                                                                      240
                                           PERFORMANCE AT 5 GPM/SQ. FT. (RUN 9]
  100


   90


   80


   70


   60

i
£  so


1  40


   30


   20


   10

                                                         \
                                             INFLUENT QUALITY:

                                             • SUSPENDED SOLIDS = 870 MG/L
                                             A BOD5 = B7 MG/L
                                             * COD = 330 MG/L
                                                    30       60       90      120
                                                     FILTRATION  TIME, MINUTES
                                                         239
                                                                                                                         f"

-------
                       FIGURE  F.I2
              FILTRATION SYSTEM COMPONENTS
 WASTE STORAGE TANK
WASTE FEED PUMPS
                                     SAFEGUARD DEVICES
FILTER COLUMN
                            240
                    F-12

-------
                                    APPENDIX G

                             KINGMAN  LAKE  PROJECT

                                      Summary

This conceptual engineering study concerns the reclamation of combined sewer overflows
and  utilization of the reclaimed waters in a major water-oriented recreational facility for
the  District  of Columbia.  The investigation encompasses a comprehensive solution  of
environmental  problems by proposing  multi-use objectives and  facilities.

Principal objectives of the project included: 1)  evaluation of rainfall runoff relationships
for sizing of storage and treatment plant capacities; 2) confirmation of treatment feasibility
using filtration and an activated carbon process; and 3) development of  sufficient data
for preliminary design  purposes.

Laboratory studies not  only  demonstrated process feasibility, but showed the need for
including flocculation and sedimentation for removal of minute particles, together with
chlorine   and  iodine   addition   for   maximum  disinfection.   The  recommended
storage/treatment   plan   provides  for  a  175  million  gallon  storage   basin,   a  50
million-gallon-per-day reclamation  facility  and two 46-acre swimming and boating lakes.

Cost effectiveness (Cost/Benefit Ratio) of the project,  as  envisioned, has been indicated
to be  1.6 at  an estimated  total project  cost of $45,200,000, and an estimated  annual
operating cost of $1,777,000.  Implementation  of the proposed plan would not only provide
a least-cost alternative over single-purpose  projects to attain identical objectives, but would
also  reduce the annual pollution now discharged by the Northeast Boundary Trunk Sewer
by approximately 99 percent.

This report was submitted in  fulfillment of Program  No. 11023  FIX under Contract No.
14-12-829 between the  Federal Water Quality Administration and Roy F. Weston, Inc.

                                     Conclusions

It is the considered  opinion  of  Roy F.  Weston, Inc. that this project  in its entirety is
both technically and  economically feasible. It is possible for the Federal Government to
demonstrate that wastewater and waste land can be reclaimed for the use and advancement
of society, and that a total environmental approach to the problem  of  pollution  can be
effective.

Combined Sewer Overflow

  1.  The project conceived as a result of  the study  would be  the  largest control and
     treatment works for combined sewer overflows in the United States and would elevate
     the  effluent quality above all  other  existing  or  planned combined sewer overflow
     projects.

  2.  The Northeast Boundary  Trunk Sewer serves approximately one third of the combined
     sewer  area of the District of Columbia.
                                        241

-------
  3. The methodology developed for this study provides a reasonably accurate definition
    of  the  quantity, quality, and  variability of overflow from the Northeast Boundary
    Trunk Sewer.

  4. The annual discharge of BODs in the overflow from the Northeast Boundary Trunk
    Sewer accounts for over 25 percent  of the recommended allowable waste loading
    to  the Potomac River in the Washington metropolitan area.  Even the storm  that is
    expected to occur with a  frequency  of four times or more per year  results  in a
    BOD loading  of over twice the recommended allowable daily loading for discharges
    from all waste treatment facilities  in the metropolitan Washington area. The recent
    Potomac Enforcement  Conference held 21  and 22 May  1970  required that these
    recommended  allowable loadings be further reduced.

  5. The impact of BOD loading in  the overflow on dissolved oxygen levels is more serious
    than the 25 percent value reflects, due to the combined effect of long  residence
    times of estuarine waters and the true form of overflows occurring at discrete impact
    loadings.

Storage  Alternatives

  6. Storage  is an  essential element of any plan  for the abatement of pollution from the
    Northeast Boundary  Trunk Sewer,  because of the extremely high  overflow rates.

  7. Locating a surface  storage basin in  the vicinity of Kingman  Lake  is feasible  and
    desirable since all  overflow can be collected there without extensive modifications
    and without pumping, and  also  because much of the area is undeveloped, indicating
    the release of open space for a storage basin is possible. The estimated cost for surface
    storage was $14.3 million as compared to $33.4 million for comparable mined storage.

  8. Preliminary soils investigation  indicates that the construction of a  storage basin  in
    the lower section of  Kingman Lake  is technically feasible.

  9. The tunnel storage  concept is applicable to the Northeast Boundary Trunk Sewer
    and has the decided advantage  of providing surcharge relief of the existing sewer
    system.

Treatment Alternatives

10. Different  levels  of benefits  are associated with  each capacity of  a wastewater
    reclamation  facility;  these  include  allowable bather  load,  probability   of  not
    overflowing the storage basin,  and the additional  storage capacity provided by the
    plant's  operating during the period of the  storm.

11. A  literature evaluation disclosed that  there are some promising alternatives to those
    unit processes investigated  in  this study; however,  confirmation  work  is  necessary
    before  any one can  be applied totally to the  Kingman  Lake Project.  Included  in
    this listing are fiberglass  filtration media  and  microstraining  for  suspended solids
    removal, U-tube aerators for aeration, and ozonation for odor control and disinfection.

12. The use of iodine in conjunction with chlorine will  provide  effective disinfection
    of  viruses as  well  as  bacteria  in the  swimming lake.
                                        242

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 13.  The use of chlorine in the swimming lake will  prevent  excessive algae growth,  but
     there may be an algae problem in the fishing-boating  lake, which does not otherwise
     require chlorination.

 14.  The recommended standards  for the influent to the swimming lake are: pH    7.5
     to 8.0; BOD   5.0 mg/L; Suspended  Solids -15.0 mg/L; Total Phosphorus   0.05 to
     1.0 mg/L; Free Chlorine   1.0 mg/L; Free Iodine   1.0 mg/L; Fecal Coliform   200
     per  100 ml.

 Laboratory Investigative Program

 15.  Coagulation-Sedimentation  followed  by  multi-media filtration, activated  carbon
     adsorption,  and disinfection will produce an  effluent which meets the water quality
     criteria objectives for swimming and fishing.

 16.  Filtration through  fiberglass was shown to be  an  effective method for removal  of
     suspended solids; however, significant development work is required prior to any major
     facility application.

 Soils Investigation

 17.  Construction of a  storage basin with vertical walls to a  depth  of minus 40 feet is
     feasible.

 18.  Construction of a storage  basin with  sloping  side walls is undesirable because of the
     restrictions on side slopes,  the period of construction, and the relatively small storage
     capacity  available.

 19.  Construction cost estimates indicate that significant economics can be effected through
     use of the  slurry wall  construction  method  rather than the conventional approach
     using sheeting  and bracing.

 20.  The foundations for all structures must extend to the sand and gravel  layer or to
     the underlying stiff clay.  For shallow structures, it will generally be most economic
     to provide pile foundations extending to these strata. The deeper structures can be
     founded  directly  on the  above-mentioned strata  or may  be  constructed on  pile
     foundations.

21.  Problems  concerning general  side grading, seepage, and other work associated with
     raising the fishing  and  swimming  lakes to elevation  +3.5 feet  are not anticipated.

Selection of Alternative

22.  The alternative scheme  evaluated to  have the highest cost effectiveness encompasses
     a  storage basin capacity of 175 million gallons and a reclamation plant  capacity of
     50  million gallons  per  day.

23.  The alternative  scheme selected will  provide:

     a.    Ninety-nine percent reduction of annual pollution load from  Northeast Boundary
          Trunk Sewer, eighty percent reduction of pollution from a storm with a two-year
          recurrence frequency, and sixty-one percent reduction of pollution from a storm
          with  a five-year recurrence frequency.

                                         243

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     b.   Effective storage capacity  to contain  a storm with a recurrence frequency of
         1.2 years.

     c.   A ninety-six percent probability that  the reclamation facility will draw down
         the storage basin prior to the recurrence of a second storm overflow (the volume
         of which  would exceed the remaining volume in  the  storage  basin).

     d.   Sufficient treatment plant capacity  to support a maximum of 30,000 bathers
         per day  in  the  swimming lake.

24.  The covering  of the storage basin with  a  parking  roof is justified  on the basis of
     comparable land acquisition and development costs and estimated annual revenues.

25.  The total project cost estimate of $45,200,000 compares extremely well with benefits
     estimated at $72,755,000.

26.  Operating costs are estimated to be $1,777,000  per year.  Included  in the operating
     costs are:  administration, labor, maintenance, utilities,  chemicals, make-up  carbon,
     fuel oil, and  an operating  contingency.

                                  Recommendations

1.   Demonstrate how the treatment  of combined sewer overflows can serve additional
     beneficial uses.

2.   Demonstrate how the FEDERAL  GOVERNMENT  can  approach the total solution
     to  environmental  problems.

3.   Design and construct a  175,000,000-gallon  storage facility, a 50,000,000-gallon per
     day water-reclamation facility,  and the associated swimming, boating, fishing, and
     parking facilities.

4.   Continue to investigate and gather additional data to refine this  report and estimate
     prior to and during  the engineering design  and construction  phases  of this project.

5.   Provide sufficient space  within  the water-reclamation plant and establish a field test
     facility to demonstrate new and promising  processes for improving the treatment of
     combined sewer overflows.
                                        244

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    A ccessiori1 Number
                               Snbj-e.ct Field & Group
                                                     SELECTED  WATER RESOURCES ABSTRACTS
                                                            INPUT  TRANSACTION  FORM
    Organization
                ROY F. WESTON, West Chester, Pennsylvania
    Title
                COMBINED SEWER OVERFLOW ABATEMENT ALTERNATIVES:
                WASHINGTON, D.C.
10
Authors)

  Buckingham, Phillip L.
  Shin, ChiaS.
  Ryan, James G.
  Lee, James A.
  Kane, John K.
16
    Project Designation
                                                   EPA, WOO Contract No. 14-12-403
                                         21  Note
22
     Citation
23
     Descriptors (Starred First)
         *Storm Runoff, *0verflow, * Flow Measurement, Underground Storage, *Filtration, Design Storm,
         Depth-Area-Duration Analysis, Rainfall-Runoff Relationships, Organic Loading, Treatment Facilities,
         Tunnel Design, Reservoir Design, Sewers, Capital Costs, Annual Costs, Comparative Costs, Geology,
         Tracers, Analysis, Sludge, Hydrology.
 25
Identifiers (Starred First)


     *Combined Sewers, *Storm Water, Potomac River, District of Columbia
27
Abstract
     Objectives of the project were:  1) define the characteristics of combined sewer overflow; 2) investigate
  the feasibility of high-rate filtration for treatment of combined sewer overflow; and 3) develop and evaluate
  alternative methods of solution.

     Investigative activities included: review of pertinent reports and technical literature; field monitoring
  of combined sewer overflows and separated storm water discharges at three sites; laboratory studies of
  ultra-high-rate filtration of combined sewer overflow; hydrological analysis; and evaluation of feasible
  alternatives (based on conceptual designs, preliminary  cost estimates, and other factors).

     Reservoir Storage, Treatment at Overflow Points, Conveyance Tunnels and Mined Storage, and Sewer
  Separation were the approaches considered sufficiently promising for detailed evaluation.  Tunnels and
  Mined Storage with treatment at the Blue Plains plant  and at Kingman Lake after subsidence of the storm
  is recommended.  Estimated capital costs (based on the 15-year storm) are $318,000,000 with annual
  operation and maintenance costs of $3,500,000. This approach also was preferable to the others on the
  basis of systematic evaluation of reliability, flexibility, public convenience and other non-quantifiable
  factors.

Abstractor
                                  Institution
                                                      ROY F. WESTON
                                                     SEND TO:  WATER RESOURCES SCIENTIFIC INFORMATION CENTER
                                                             U.S. DEPARTMENT OF THE INTERIOR
                                                             WASHINGTON. D. C. 20240
                                                                                         « SPO: 1969-359-339

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Continued from inside front cover....
11022 	 08/67

11023 	 09/67

11020	12/67

11023 	 05/68

11031	08/68
11030 DNS 01/69
11020 DIH 06/69
11020 DES 06/69
11020 	 06/69
11020 EXV 07/69

11020 DIG 08/69
11023 DPI 08/69
11020 DGZ 10/69
11020¥EKO 10/69
11020 	 10/69
11024 FKN 11/69

11020 DWF 12/69
11000 	 01/70

,11020 FKI 01/70

11024 DOK 02/70
11023 FDD 03/70

11024 DMS 05/70

11023 EVO 06/70
11024 	 06/70
11034 FKL 07/70
11022 DMU 07/70
11024 EJC 07/70

11020 	 08/70
11022 DMU 08/70

11023 	 08/70
11023 FIX 08/70
11024 EXF 08/70
 Phase  I  - Feasibility  of  a Periodic  Flushing System for
 Combined Sewer  Cleaning
 Demonstrate  Feasibility of the  Use of  Ultrasonic Filtration
 in Treating  the Overflows  from  Combined  and/or Storm Sewers
 Problems  of  Combined Sewer Facilities  and Overflows, 1967
 (WP-20-11)
 Feasibility  of  a Stabilization-Retention Basin in Lake Erie
 at Cleveland, Ohio
 The Beneficial  Use of  Storm Water
 Water Pollution Aspects of  Urban Runoff,  (WP-20-15)
 Improved  Sealants for  Infiltration Control,  (WP-20-18)
 Selected Urban  Storm Water  Runoff Abstracts,  (WP-20-21)
 Sewer Infiltration Reduction by Zone Pumping,  (DAST-9)
 Strainer/Filter Treatment of Combined  Sewer  Overflows,
 (WP-20-16)
Polymers for Sewer Flow Control, (WP-20-22)
Rapid-Flow Filter for  Sewer Overflows
Design of a Combined Sewer Fluidic Regulator,  (DAST-13)
Combined Sewer  Separation Using Pressure  Sewers,  (ORD-4)
Crazed Resin Filtration of Combined Sewer Overflows, (DAST-4)
Stream Pollution and Abatement from Combined  Sewer Overflows •
Bucyrus,  Ohio,  (DAST-32)
Control of Pollution by Underwater Storage
Storm and Combined Sewer Demonstration Projects  -
January 1970
Dissolved Air Flotation Treatment of Combined  Sewer
Overflows, (WP-20-17)
Proposed Combined Sewer Control by Electrode Potential
Rotary Vibratory Fine Screening of Combined  Sewer Overflows,
 (DAST-5)
Engineering Investigation of Sewer Overflow Problem -
Roanoke,  Virginia
Microstraining and Disinfection of Combined  Sewer Overflows
Combined Sewer Overflow Abatement Technology
 Storm Water Pollution from Urban Land Activity
 Combined Sewer Regulator Overflow Facilities
 Selected Urban  Storm Water Abstracts, July 1968  -
 June 1970
 Combined Sewer  Overflow Seminar Papers
 Combined Sewer Regulation and Management  - A Manual of
Practice
Retention Basin Control of  Combined Sewer Overflows
 Conceptual Engineering Report - Kingman  Lake Project
 Combined  Sewer  Overflow Abatement Alternatives -
 Washington, D.C.

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