EPA-R2-73-139
JANUARY 1973             Environmental Protection Technology Series
The Beneficial  Use
of Storm Water
                                     Office of Research and Monitoring

                                     U.S. Environmental Protection Agency

                                     Washington, O.C. 20460

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

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

This report has been assigned to the ENVIRONMENTAL
PROTECTION   TECHNOLOGY   series.    This   series
describes   research   performed  to  develop  and
demonstrate   instrumentation,    equipment    and
methodology  to  repair  or  prevent environmental
degradation from point and  non-point  sources  of
pollution.  This work provides the new or improved
technology  required for the control and treatment
of pollution sources to meet environmental quality
standards.

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                                         EPA-R2-73-139
                                         January 1973
         THE BENEFICIAL USE

           OF STORM WATER
                 By

            C.  W. Mallory
       Contract No. 68-01-0173
          Project 11030 DNK
           Project Officer

            Sidney Beeman
     Municipal Technology Branch
   Environmental Protection Agency
       Washington, B.C. 20460
            Prepared for

  OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
       WASHINGTON, D.C. 20460

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                EPA Review Notice
This report has been reviewed by 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.
                        11

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                             ABSTRACT
This report covers work originally performed by Hittman Associates in
1967 and 1968 under Contract No. 14-12-20 for the then Federal Water
Pollution Control Administration.  Only a limited number of copies of
the report covering this work were produced  at that time.  The purpose
of this report is to make this information available for general distribution.

A  system study was conducted to determine the technical and economic
feasibility of using small storage reservoirs  throughout an urban com-
munity as-a means of storm water pollution control.  Facilities were pro-
vided to treat the water prior to release or to provide sub-potable or
potable water for use in the community.   A conventional  approach to
controlling storm water pollution was defined for comparative purposes.

The study considered an 1140-acre watershed located in the new city  of
Columbia,  Maryland.   Regression analysis techniques were  used to
develop hydrologic models for predicting storm runoff following develop-
ment.  Special water quality classifications were defined for the use of
treated storm water and estimates were made of the water demands as
a function of quality.  Design and cost- data were developed parametri-
cally for storage,  treatment facilities, distribution systems, andopera-
tion and maintenance as inputs to the system  analysis model.

Computerized system analysis was used to select the optimal  combina-
tions Of reservoir locations, type of treatment, and type of reuse on a
least cost per day basis.  Alternatives were  ranked and the  optimal
practical solution determined considering the constraints on  land use
imposed by existing development plans.

As a result of this work, it  was determined that the use of local storage
and treatment does represent a feasible and economical method for storm
water pollution control. Further, the use of  the treated water can sup-
ply a large portion of the fresh water  demands of a typical urban  resi-
dential community.

A  demonstration program was planned and subsequently implemented by
the State of Maryland and the  Environmental Protection Agency to eval-
uate erosion and sediment control practices on a 200-acre watershed in
Columbia,  Maryland.   The  project includes a three-and-one-half-acre
lake,  evaluation of cleaning and sediment handling methods, and sampling
and gaging stations to monitor changes in water quality  and hydrology
during development.
                                 111

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                             CONTENTS
Section
 I
 II
 III
 IV
 V
 VI
 VII
 VIII
 IX
 X
 XI
 XII
 XIII

 XIV

 XV

 XVI
 XVII
 XVIII
 XIX
 XX
 XXI
 XXII
Abstract
List of Figures
List of Tables
Conclusions
Recommendations
Introduction
Storm Water Hydrology
Water Quality and Demands
Storm Water Quality
Storm Water Storage
Treatment Methods
Reuse Distribution Systems
System  Model
System  Model Outputs and Optimization
Development of Conceptual Designs
Local Collection,  Storage, and Treatment of
Storm Water for  Potable Reuse
Local Collection,  Storage, and Treatment of
Storm Water for  Sub-Potable Reuse
Local Collection,  Storage, and Treatment of
Storm Water for  Pollution Control
Conventional Storm Water Treatment System
Economic Comparison
Secondary Benefits
Demonstration Program
Acknowledgements
References
Appendices
Page
 iii
 vi
 ix
  1
  5
  7
 15
 41
 57
 65
 97
103
111
131
143

147

159

171
177
185
193
205
213
215
219
                                 v

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                            FIGURES
No.                                                          Pa§e

 1        Complete Water System Incorporating Local
          Storage, Treatment,  and Reuse of Stormwater         8

 2        Location Map of Columbia,  Maryland                 11

 3        Wilde Lake Watershed - Sub-Water shed Map          14

 4        Increased Yield vs. Fraction Impervious              20

 5        Increased Yield vs. Rainfall Volume                  21

 6        Routing Method - Linear Storage Reservoir Model     25

 7        Derivation of Flow-Duration-Frequency Curve
          for Five-Year  Storm  Runoff                         27

 8        Effect of Impervious Fraction (I) on Five-Year
          Storm Runoff                                       28

 9        Effect of Lag Time (m) on Five-Year Storm Runoff    29

10        Average Runoff Rate vs. Storm Duration              30

11        Maximum Storm Volumes                            31

12        Actual Daily Volume vs. Return Period
          Wilde Lake                                         33

13        Calculated Daily Volume vs. Return Period -
          Wilde Lake Watershed                               34

14        Work Sheet - Typical Sub-Watershed Land Use
          Tabulation and Imperviousness Factor Calculation     35

15        One-Year Daily Hydrograph for Sub-Watershed
          No.  6                                              38

16        Wilde Lake Watershed - Service Areas               52

17        Work Sheet - Typical Sub-Watershed Land Use
          Tabulation and Water Demand Calculation             53

18        Summary of Water Demands                         55
                                VI

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                        FIGURES (Continued)
No.                                                            Page

 19     Storage vs. Yield Example of Residual Mass
        Tabulation Analysis Sub-Watershed No.  8                70

 20     Storage vs. Yield -  Comparison of Rippl Method
        and Residual Mass Tabulation, Sub-Watershed No. 4     71

 21     Storage Yield Characteristic vs.  Proportion of
        Demand Used for Sprinkling Lawns                      75

 22     Storage/Sprinkling Use Characteristic vs.  Yield,
        Sub-Watershed No.  16                                  76

 23     Storage/Yield Characteristic vs. Reliability             79

 24     Storage/Reliability Relationship vs. Average
        Daily Demand                                          80

 25     Tube Settler - Principles of Operation                   85

 26     Required  Volume vs. Overflow Rate for Removal
        of 10-Micron Silt Particle Under Ideal Conditions         87

 27     Rainfall Intensity-Frequency-Duration Curves,
        Howard County, Maryland                              89

 28     Storage/Pretreatment Rate Combinations vs.
        Spill Percentages                                      91

 29     Pretreatment Rate/Spill Percentage Relationships
        vs. Storage                                            92

 30     Storage/Reliability Characteristics vs. Yield,
        Sub-Watershed No.  16                                  94

 31     Class "AA" Treatment Systems                         98

 32     Distribution System Map - Wilde Lake Watershed        104

 33     Wilde Lake Drainage Area Sub-Watershed Flow
        Pattern                                               112

 34     Table of Net  Benefits   Computer Run A                132

 35     Table of Capital Cost   Computer Run A                134
                                vu

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                       FIGURES (Continued)



No.                                                           Page

 36     Table of Daily Cost   Computer Run A                   135

 37     Table of Benefits - Computer Run A                     137

 38     Table of Net Benefits of Combinations of
        Watersheds, Reuse   Computer Run A                   139

 39     Table of Net Benefits of Combinations of
        Watersheds, No Reuse - Computer Run A                140

 40     Potable Reuse System Location Plan                     148

 41     Potable Reuse System Flow Diagram                    151

 42     Sub-Potable Reuse System -  Location Plan               160

 43     Sub-Potable Reuse System Flow Diagram -
        Class "B" Treatment                                   163

 44     Sub-Potable Reuse System Flow Diagram
        Class "C" Treatment                                   164

 45     Local Pollution Control System  Location Plan          172

 46     Plan  of Conventional Treatment System                  178

 47     Conventional System Treatment Basin                   180

 48     Net Benefits vs. Value of Treated Water                 189

 49     Basins Used for Hydrograph Damping Investigation       195

 50     Runoff at Point A                                       196

 51     Runoff at Point B                                       197

 52     Local Storage Pond in Natural Setting                    201

 53     Local Storage Pond in Wooded Park Setting              202

 54     Local Storage Pond in Recreation Area Setting           203
                                Vlll

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                              TABLES

No.                                                             Page

  1       The Wilde Lake Watershed, Columbia,  Maryland         13

  2       Final Regression Equation Coefficients                   17

  3       Typical Monthly Rainfall Totals,  Baltimore
         Customs House, 1900-1950                             36

  4       Calculated One-Year Storm Volumes for Wilde
         Lake Sub-Watersheds                                   39

  5       Distribution of Residential Water Use, After Reid        48

  6       Distribution of Residential Water Use - Revised          48

  7       Maximum Concentration of Selected Pollutants
         by Reuse Category                                     50

  8       Reported Storm Water Pollutant Concentrations          5f>

  9       Principal Indices of Storm Water Pollution               58

 10       Expected Maximum Pollutant Concentrations For
         Storm Water in Wilde Lake Watershed                   61

 11       Effluent Standards for Water Discharged into
         Wilde Lake                                             63

 12       Storm Water Storage Reservoir  Construction Types      66

 13       Example of Residual Mass Tabulation - Sub-
         Watershed No.  8                                        68

 14       Ratio of Sprinkling Use During Selected Period to
         Average Sprinkling Use                                 72

 15       Example of Modified Residual Mass Tabulation
         Storage vs.  Proportion of Demand Used for
         Sprinkling Lawns                                       73

 16       Example of Modified Residual Mass Tabulation
         Storage vs. Reliability                                  77

 17       Settling Velocities of Selected Particles, after
         Hazen                                                  82
                                  IX

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                       TABLES (Continued)
No.
                                                               Page
 18        Minimum Sedimentation Basin Area Requirements
           for Selected Particles, Sub-Watershed No. 14         83

 19        Expected Quantity of Runoff in Excess of Selected
           Storm Volumes                                      90

 20        Proposed Treatment Processes                       99

 21        Construction Costs for Service Connections and
           Internal Plumbing for Sub-Potable Reuse            106

 22        Construction Cost vs. Service Area   Distribution
           System                                            108

 23        Construction Costs vs. Service Area-Transmission
           Lines                                             109

 24        Expected Maximum  Volume of One-Year Storms     114

 25        Expected Available Supply from Storage             115

 26        Total Annual Runoff vs. Sub-Watershed             116

 27        Collection Areas - Computer Run A                 123

 28        Collection Areas   Computer Run B                 124

 29        Collection Areas - Computer Run C                 125

 30        Combination of Areas - Computer Run A            126

 31        Combination of Areas - Computer Run B            127

 32        Combination of Areas - Computer Run C            128

 33        Potable  Reuse System Storage Reservoir
           Collection Areas                                   147

 34        Local,  Collection,  Storage,  and Treatment of
           Storm Water for Potable Reuse - Conceptual
           Design                                            149

 35        Potable  Water Requirements,  Total Storm Water
           Runoff,  and Amount Supplied                       153

 36        Local Collection,  Storage, and Treatment of  Storm
           Water for Potable Reuse - Design and Construction
           Costs                                             156

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                        TABLES (Continued)
No.                                                             Page
 37        Local Collection,  Storage,  and Treatment of Storm
           Water for Potable Reuse  - Annual Operating and
           Maintenance Costs                                   157

 38        Sub-Potable Reuse System Storage Reservoir
           Collection Areas                                     159

 39        Local Collection,  Storage,  and Treatment of
           Storm Water for Sub-Potable Reuse - Conceptual
           Design                                               162

 40        Sub-Potable Water Requirements,  Total Storm
           Water Runoff, and Amount Supplied                    166

 41        Local Collection,  Storage,  and Treatment of Storm
           Water for Sub-Potable Reuse Design  and
           Construction Costs                                   167

 42        Effect of  Distribution System on Capital Costs         168

 43        Local Collection,  Storage, and Treatment of Storm
           Water for Sub-Potable Reuse - Annual Operation
           and Maintenance Costs                               169

 44        Local Collection,  Storage,  and Treatment of Storm
           Water for Pollution Control Runoff by Sub-Water shed
           and Pretreatment Unit with Pretreatment and
           Reservoir Capacities                                173

 45        Local Collection,  Storage,  and Treatment of Storm
           Water for Water Pollution Control  Design and
           Construction Costs                                   175

 46        Local Collection,  Storage,  and Treatment of Storm
           Water for Water Pollution Control - Annual Operation
           and Maintenance Costs                               176

 47        Design  Requirements for Conventional Treatment
           Plant                                                177

 48        Particle Removal with Conventional Treatment Basin  182

 49        Design  and  Construction  Costs - Conventional
           Treatment System                                   183
                                 XI

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TABLES (Continued)
                                            e
No.                                                            Page

50         Economic Comparison of Pollution Control
           Systems                                             186

51         Benefit/Cost Analysis of Water Supply and
           Pollution Control Alternatives                        187
         XII

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                             SECTION I

                           CONCLUSIONS
Based  on this system study, it was determined that the use of small
storage basins dispersed throughout an urban community for the control
of storm water pollution was technically feasible and economically attrac-
tive compared to other alternatives.  Further,  the  storm water collected
in these basins could be  treated to provide approximately half the water
demands of a typical urban residential  community.  In addition, a number
of secondary benefits could be derived  through  the use of this approach.

Four types of systems for the control of storm water pollution and for
supplying water were defined for evaluation  purposes.  These were:

1.    Use of local storage basins with treatment to body contact
      recreation standards for release downstream.

2.    Use of local storage, basins  with treatment to sub-potable
      quality for reuse with separate distribution systems.

3.    Use of local storage basins  with treatment to potable
      quality for distribution through existing water distribution
      systems.

4.    Use of a large basin to collect storm water from interceptors
      and pumping stations with conventional treatment systems.

The comparative costs and performance characteristics of the four
systems are summarized as follows:

                          (1)         (2)           (3)         (4)
Initial Costs ($)      $830,000  2,598,000*  1,445,000  1,315,000
Fixed  Costs  ($/day)       119        373          207        189
Operation and
   Maintenance ($/day)      55        151          194         68
Daily Costs ($/day)        174        524          401        257
Amount of Water
   Supplied (gal/day)        0    556,000      460,000           0
Value  of Water ($/day)      0        207          250           0
Net Operating Costs
   ($/day)                 174        317          151        257
Cost per Year ($/yr)  63,400    115,800       55,200     93,000
Cost per Acre/Year
   ($/acre/yr)              55.25     104.30        48.05      81.71
Cost per Dwelling Unit
   ($/D.U.)                 16.88      30.82        14.68      24.97

   -'-'Includes water distribution system at$.l, 562, 000

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The other major« conclusions from this study are as follows:

1.     A system of 10 small reservoirs dispersed throughout
      an 1140-acre watershed was found to provide storage
      capacity to receive in excess of 90  percent of the runoff
      of storms  with a one year return interval without encroach-
      ment upon the existing land  development plan.

2.     The same  effectiveness could be  obtained with a lesser
      number of larger reservoirs at a reduced  cost, if areas
      for the collection and storage of storm water were provided
      in the initial land development planning.

3.     The amount of storm water  that can be collected and treated
      could provide up to 52.5 percent  of the water demands of a
      typical urban residential development.  The most economical
      method of  distributing the treated storm water would be to
      treat the water to potable  quality and inject the water into
      existing water distribution systems.

4.     Water treated to sub-potable water quality could provide
      up to 46. 5  percent of the water demands of a typical urban
      residential area; however, the cost of providing a second
      distribution system for the sub-potable water would be
      much greater than the cost of treating to potable water
      quality for distribution through existing systems.

5.     Treatment to sub-potable  quality for reuse could be eco-
      nomically  attractive in those cases where  a large demand
      for sub-potable water exists for a few industrial or com-
      mercial establishments, and the  cost of separate distribution
      systems can be reduced.

6.     The use of small earthen dams for the construction of storm
      retention ponds is by far the least-cost alternative.  The cost
      of constructed storage facilities of other types is generally
      prohibitively expensive.

7.     The small reservoirs used to collect storm water will also be
      effective in controlling the excess runoff resulting from urban-
      ization. With proper design, the runoff hydrographs can be
      maintained near those  of a natural area.

8.     The ideal  time to introduce  storm retention ponds is prior to
      development of the area and to use  the ponds  to control the
      erosion and sediment generated by  construction.

9.     Using retention ponds for storm water management and for
      sediment and pollution control will  materially assist in the
      preservation of ecology in urban areas.

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10.    The use of collected storm water in sewered communities
      could reduce nutrient releases since the water could be
      effectively diverted to treatment facilities having nutrient
      removal capabilities.

11.    The use of storm retention ponds could be used for the
      separation of combined sewers in  selected situations.

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                             SECTION II

                        RECOMMENDATIONS


It is recommended that storm retention ponds be considered in the plan-
ning of the storm drainage facilities for new community development and
in modifications of the storm drainage systems  in existing communities.
The ponds will provide an effective means of removing sediment and
dampen the peak storm water flows resulting from urbanization.  The
availability of storage will reduce the capacity and costs of other drain-
ange and treatment systems.

It is recommended that storm retention ponds be introduced prior to
initial grading of the development site.  This will provide a means of
trapping the large quantities of sediment generated by construction.
Following construction,  the  ponds should  be cleaned and used as part
of the  permanent system for storm water management  and pollution
control.

It is recommended that demonstration projects be conducted to provide
information on the  design, application,  operation,  and  maintenance of
storm retention structures.   Emphasis should be placed on methods of
cleaning and maintaining the ponds since the acceptability of this approach
will depend upon maintaining the  ponds  in an aesthetically acceptable con-
dition  at reasonable costs.   These projects  should also consider methods
for the handling, processing, and disposal of sediment removed from the
ponds.

It is recommended that demonstration projects be conducted to develop
design and operating criteria for the application of storm retention ponds
as a method of storm water management.  Design and performance infor-
mation should be obtained on relationships among pond levels,  surface
area,  intensity of storm events,  and the quantity and quality of water
released.  This should also  include demonstration of retention  structures
operating in a series-parallel arrangement to define interactions and
design and performance criteria  for systems incorporating a number of
retention structures.

It is recommended that a demonstration project be undertaken to deter-
mine the feasibility of treating storm water  for various reuse applications.
In this project,  the emphasis should be placed on the development and
demonstration of a water treatment system  capable of reliably  treating
water  to a quality suitable for distribution in existing water  supply dis-
tribution systems.   The treatment system should be automated for un-
attended operation  and should have features for monitoring and auto-
matic  shutdown if water quality is not suitable for supply.

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                             SECTION III

                           INTRODUCTION
GENERAL
Simply stated,  the local storage,  treatment,  and reuse of storm water
is a concept for the control of storm water pollution in which the storm
water  runoff is collected in small storage basins dispersed throughout
an urban area, treated to remove pollutants, and further treated for use.
With this concept,  the benefits derived from the use of storm water
are used to offset the  cost of effecting pollution  control of storm water.
This final report on "The Beneficial Use of Storm Water" contains a
description of the system study, design, and evaluation of the local
storage, treatment, and reuse of storm water and the analysis of the
economic and technical feasibility of this concept.

The system study is based on the new city of Columbia, Maryland, and
specifically Wilde  Lake and  its associated watershed which is located
in the  first village of Columbia.   Wilde  Lake is  an artificial lake con-
structed in  1966,  surrounded by apartments, townhouses, and individual
residences, now approaching completion.  This study is further based
on the land  development plans for this area,  established lot boundaries,
and other physical, aesthetic, and sociologic requirements existing
within the area.  The  objective of this study has been to develop systems
that could control the  storm water pollution of Wilde Lake and to perform
a comparative evaluation of  the performance and economic  aspects of
these systems.
USE OF SYSTEM ANALYSIS

In order to subject the local storage,  treatment,  and reuse of storm
water to comprehensive examination,  system analysis techniques were
used.  This required the development of models to describe the various
subsystems and compilation of generalized input  data to define the design,
economic, and performance parameters involved.  The subsystems that
comprise the overall system andthe interrelationship to the characteristics
of the study area and other utility systems are shown diagramatically on
Figure  1.  Rainfall and water from a public water supply are inputs to
the system and evapotranspiration,  soil percolation,  surface drainage
out of the watershed,  consumptive uses, and sanitary sewer flow are
outputs.  The principal parts of the overall  system considered in the
analysis are:

      Storm Water Storage

      Storm Water Pretreatment

      Final Treatment

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                   EVAPO- TRANSPIRATION
            RAINFALL (P) .
CO
                                             STORM WATER
                                             COLLECTING
                                               SYSTEM
                                                           EFFECTIVE
                                                            RUNOFF
(QE)
          STORM WATER
           STORAGE
STORM  v
YIELD (Q )_
  STORM WATER
  PRETREATMENT
                                                    NET    c
                                                    YIELD (CT)
                                             OVERFLOW TO    „
                                           SURFACE DRAINAGE (L )
         OVERFLOW TO    ,
       SURFACE DRAINAGE (L )
 E-XCESS WATER TO
SURFACE DRAINAGE (LY)
                                      PUBLIC SUPPLY
                                    MAKEUP WATER (QM)
                                                                                      TREATED WATER
                                                                                         USES
                                      WASTE TREATED
                                      WATER
                                                                                        CONSUMPTION (CN)
                                                                    PUBLIC SUPPLY
                                                                    DEMAND (QP) -
                      PUBLIC SUPPLY USES
                                                                                                                    (WP)
                                                                                                      WASTE PUBLIC
                                                                                                      WATER
                                            FINAL
                                          TREATMENT
                                             TREATED
                                             WATER (Q1)
                                                                                                                              LOSSES TO SANITARY
                                                                                                                              SEWER (WY)
                                                                                                                                   (WY)
                                                                SANITARY SEWER
                                                                 COLLECTING
                                                                   SYSTEM
                                                                                                                                               SEWER
                                             FLOW (WT)
                                                                                      CONSUMPTION (C)
                          Figure  1.   Complete  Water System Incorporating Local Storage,  Treatment,
                                                            and Reuse of  Storm Water

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      Treated Water Storage

      Treated Water Uses

Following development,  the  system models were then applied using the
data and characteristics of the Wilde Lake watershed in Columbia,
Maryland.   The formulation of the models and the .results from1 applying
these models to a specific watershed are  contained in this report.  It
is noted that the methodology and the models used in this study are gen-
eralized and can be adapted  to a variety of situations.

The objective function used in the formulation of the  system model is
described as follows:

      Water released to surface drainage from the Local Storage,
      Treatment,  and Reuse of Storm Water System shall meet or
      exceed stated effluent  standards, and;

      This condition will be  achieved at the lowest net system  cost.

This function is subject to all applicable  physical, technological, legal,
and institutional constraints, as described in the following sections.
The term "lowest net system cost" is understood to be interchangeable
with the term "highest net system benefit" and is defined as:

      min(SC  + aSCf -SB )                                (1)
         \    a       i      a/

or,  stated differently

                       - aSC-)                                (2)
              a      a

where:

      C     =     marginal annual operating and maintenance costs
       cL

      Cf    =     marginal fixed construction and project costs

      B     =     marginal annual benefits
       3.

      a     -     capital recovery factor

Equation 2 is described as the "net benefit function" and subsequent
discussion will be in terms of maximizing this function.  The capital
recovery factor used in Equation  2 is defined  as:


      a     =     - L_ -                                   (3)

                 1   (1 + i)m

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where:

      i      -     annual rate of interest or cost of capital

      m     =     period of amortization


SITE  SELECTION

Early in the formulation of the Storm. Water Reuse program, it became
apparent that the new city of Columbia,  Maryland, offered several unique
advantages as a study  site for the systems analysis.  The Storm Water
Reuse concept is specifically directed to urbanized areas where  water
runoff can be clearly identified as a source of water pollution.  In order
to perform a systems  analysis in such an  area,  the physical character-
istics of the area must be known in some detail,  including hydrologic
factors,  land uses, population densities, etc.   Since the method of anal-
ysis was to be kept generalized wherever  feasible, a study  area was
deliberately selected where gage data were not available for rainfall and
runoff.   The requirements that led to the close examination of Columbia,
however, were those related to the planned demonstration of the concept
following analysis.

Columbia is a completely planned new town being developed by Howard
Research and Development Corporation of Baltimore,  Maryland,  an affil-
iate of the Rouse Company, on a 27 square mile  site in Howard County,
Maryland (Figure 2).  Designed for a 1980 population of 110, 000 people,
Columbia is midway between Baltimore and Washington astride the busy
Northeast Corridor.   Construction started in 1966 and the first residents
moved into  the city in June 1967.  By the first anniversary  of the arrival
of these residents, more than 5000 people were living in  the community
and construction was proceeding on schedule.   The complete town will
consist of nine villages with  each village  made  up of a number of  neigh-
borhoods.  A principal feature of the Columbia plan is the extensive use
of water as a focal point  for the activities of the  community.  The town
 site includes portions of  the Little Patuxent,  Middle  Patuxent,  and
 Patuxent river basins, and five man-made lakes totaling  over 500 acres
 of water surface are scheduled.   Two of these,  Lake Kittamaqundi and
Wilde Lake, are already in existence.

The availability  of the complete Columbia plan permits the  conduct of
 a systems study of the Storm Water  Reuse concept in an area which is
not  yet  fully developed.   If this study is based on the planned charac-
teristics of the area after development, a demonstration  program can
be conducted which will fully evaluate the results of the systems analysis
 while taking advantage of the reduced costs  of concurrent construction
 Since the entire  area  is being developed by one organization, coordi-
nation and cooperation are greatly enhanced. Another fortunate feature
 of Columbia is the integration  of many different types of  land  use
 including low to high density residential development, numerous type's
                                  10

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Figure 2.  Location Map of Columbia,  Maryland
                          11

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of commercial uses,  and various industrial uses.   In some areas of
Columbia,  a wide variety of these uses can be found in a single water-
shed.  As a result, the influence of various land uses on storm water
quality and quantity as well as the accompanying possibilities for reuse
can be evaluated in the  systems study and subsequent demonstration.
WILDE LAKE WATERSHED

In order to simplify hydrologic aspects of the systems study as well as
to create an easily definable  water quality objective, it was decided to
perform the study on the drainage area of one of the artificial lakes. Of
the two lakes which would be available for the demonstration program,
only one, Wilde Lake,  had a  drainage area substantially within the
Columbia project. Furthermore, a great diversity of land use exists in
the Wilde Lake watershed.  Construction in the watershed is scheduled
for completion before 1970, permitting concurrent construction of dem-
onstration facilities, followed almost immediately by  operation of these
facilities in a fully developed area.

The Wilde Lake watershed consists of 1140 acres, or about 1.8 square
miles. Other information concerning the lake and its watershed is listed
in Table 1. Figure 3 is a map of the area, showing a number of sub-
watersheds which were used  in the hydrologic analysis reported in Sec-
tion IV.

With the cooperation and assistance of Howard Research and Development
Corporation, the  Wilde  Lake  watershed was chosen as  the site for  the sys-
tems analysis effort of the Storm Water Reuse program,  and the south-
west quadrant of  the watershed was identified as the tentative  site of a
first-phase demonstration facility following satisfactory completion of
the systems analysis.   To permit  evaluation of various storm water re-
use concepts in as many configurations as possible, the study watershed
was divided into 22 sub-watersheds.  These were delineated by natural
ridge lines wherever possible,  permitting the runoff from each area to
be collected at a  single point.
                                 12

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TABLE 1.  THE WILDE LAKE WATERSHED, COLUMBIA,  MARYLAND
Watershed Area
Planned Population
No. Dwelling Units
Planned Land Use  - Columbia
      Open Space
      Single Family Res. - Low Density
      Single Family Res. - Medium Density
      Town  houses
      Garden Apartments
      Mid-rise Apartments
      Employment Centers
      School Sites
      Public Rights-of-way
            Total - Columbia
Expected Land Use - Outside Columbia
      Open Space
      Single Family Res. - Low Density
      Public Rights-of-way
            Total - Outside Columbia
Wilde Lake  Water  Surface Area
Estimated Maximum Capacity
Fraction Impervious Construction
      in Watershed
     1, 140   Acres
    12, 254   Persons
     3, 757
147. 6
 13. 3
185. 8
114. 8
 66. 6
  4. 9
 24. 8
 37. 7
115. 8
711. 3
             Acres
             Acres
             Acres
             Acres
             Acres
             Acres
             Acres
             Acres
             Acres
             Acres
       194. 5 Acres
       191. 0 Acres
        22. 1 Acres
       407. 6 Acres
        21.1 Acres
48, 200, 000   Gallons

          0. 22
                                 13

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\
      LEGEND
  WILDE LAKE
  WATERSHED
7 SUB-WATERSHEDS -
                                                                         FWPCA Contract No.l4-]2-20
                                                                          WltDE LAKE WATERSHED
                                                                             Columbia, Md.
        Figure 3.  Wilde Lake Watershed -  Sub-Water shed Map

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                             SECTION IV

                    STORM WATER HYDROLOGY
As one of the initial phases of the Storm Water Reuse project,  it was
necessary to develop methods of adequately describing the storm water
flow characteristics of the Wilde Lake drainage area.  Two different
types of hydrologic data were required:

      A continuous daily runoff hydrograph from each of the
      sub-water sheds in the basin

      Peak flows in each sub-watershed as a function of
      rainfall recurrence interval

The  first of these was needed to estimate the total volume of water
available for reservoir storage and reuse for any time interval, and
the second to estimate sedimentation efficiency and system operation
during large storms.  Methods were required for obtaining both types
of data without benefit of gaged  stream flow records at Wilde Lake.

•Fortunately, many methods  exist for calculating peak flows from
drainage areas lacking stream flow data.  There are, however, few
methods which can be applied to the development of a daily runoff
hydrograph in an area where basic hydrologic data are unavailable.
Since this  problem was the first to be approached and required consid-
erable effort for solution,  it will be discussed in detail in the following
sections.
AVAILABLE METHODS FOR CALCULATING CONTINUOUS RUNOFF
HYDROGRAPHS

The method to  be  used in the derivation of a runoff hydrograph for the
sub-watersheds of  Wilde Lake had to satisfy the following requirements:

1.    It had to provide  a continuous hydrograph of daily runoff
      volumes for each sub-watershed and be applicable to the
      variety  of impervious conditions of the watersheds.

2.    It had to be a fairly simple method requiring a minimum  of
      data input and a minimum amount of time spent in its
      development.

3.    It had to be derivable without any basic hydrologic data
      except land use and rainfall.

For small rural watersheds such  as Wilde Lake,  there  exists no
standard simple method of providing a runoff model that would  satisfy
these requirements.  To develop such a method would have required
                                 15

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more effort than could have been justified under this project since the
selection of runoff values satisfied only a; small part of the project goals.
Therefore   several existing approaches to the solution of similar prob-
lems were examined with the purpose of selectingthebest suited approach
and modifying.it as necessary.

Each of the methods that were examined has been used in the past to
estimate runoff volumes and uses as one  of the input parameters a
rainfall record for the drainage area.  The following approaches were
considered.
Unit Hydrograph

This involves calculating for a drainage area the hydrograph that would
be produced by one unit of  "effective precipitation'  (actual rainfall minus
infiltration and other losses)  occurring during a specific period of
time  (1).  This  unit  hydrograph is then used to calculate the runoff
hydrograph from any distribution of effective rainfall.  On small drain-
age basins,  the time intervals which would be required for rainfall
input would be measured in minutes.  The calculation of effective pre-
cipitation from actual precipitation would require a knowledge of infil-
tration losses during each  rainfall at any time of the year.


Linear Storage Reservoir Models

This computer method, which has been employed by the U. S.  Department
of Agriculture (2),  utilizes  routings of effective precipitation  through
linear storage reservoirs  with a built-in lag time.   This method gives
excellent results for individual storms,  but also requires short-time
interval  inputs as well as infiltration knowledge to calculate effective
precipitation.


Digital Simulation Models

Several models  of this type exist with many variations. The basic prob-
lem with them, however, is that they  require a great deal of detailed
input information to describe  the watershed.


Regression Models

This method takes  a dependent variable  and one or more independent
variables and derives the coefficients relating the variables so that the
variation between the observed dependent variable and the calculated
dependent variable is at a minimum.  Regression equations involving
rainfall and runoff have been used in past hydrologic studies in areas
where gaged data exist.  However,  it  is possible to derive a regression
equation for a gaged watershed and apply it to another ungaged area so
long as the areas are physically and hydrologically similar.
                                 16

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It was decided that the adoption of some form of regression model
would probably be the most fruitful approach.  The procedure that was
chosen was to select  from the Maryland area another  watershed that
had the same physical and hydrologic conditions as the Wilde Lake area
and had at least five years of rainfall and runoff data.   A regression
analysis could then be performed on this watershed and the results
applied to Wilde Lake.

The advantage of this approach is that a detailed knowledge of infiltration
and soil conditions is not required since the  overall effects of such
parameters are indicated by the regression coefficients.  The regression
model does not have to present an exact cause-effect relationship between
variables as long as its predictive ability is  good and the variable rela-
tionship is reasonable.
DEVELOPMENT OF REGRESSION MODELS

After examining the available runoff data in the Maryland area, only
one watershed was located having physical characteristics similar to
those of Wilde Lake.  This watershed,  on the West Branch of Herring
Run in Baltimore County, is of the same approximate size and shape,
has the same topographic features, and is located in the same geologic
zone as the Wilde Lake drainage area.   For these reasons it is ideally
suited for the derivation of a rainfall-runoff model which could then be
applied to Wilde Lake with modifications to account for varying percent-
ages of imperviousness in the sub-watersheds.

A number of regression models were tested including models in which
the effect of antecedent precipitation on runoff and the seasonal variations
of base flow were considered.   The model found  to provide  the best
correlations with actual data consisted of a third order polynomial
shown in Table 2.

     TABLE 2. FINAL REGRESSION EQUATION COEFFICIENTS

      Q..    =    A + BRt + CRt2 + DR..3                       (4)

                     Regression Coefficients             Correlation
               A	B	C	D	   R        R2

Yearly      0.5247    3.016    1.187    -0.168     0.858    0.736

Seasonal
  Winter     0.885      3.449    0.808     0.099     0.756    0.572
  Spring     0.625      2.044    1.917    -0.419     0.874    0.764
  Summer    0.269      1.849    1.969    -0.260     0.974    0.949
  Fall        0.353      1.297    4.591     -1.389     0.927    0.859

      R.    =    rainfall in inches/day
      Q.    =    runoff in cfs-days/mile2-day
                                  17

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APPLICATION OF THE REGRESSION MODEL TO WILDE LAKE

Although the Herring Run and Wilde Lake areas are similar in most
respects, the  sub-watersheds of Wilde Lake will have a variety of
impervious percentages after development.  Past studies of the effects
of urbanization on runoff (3) have shown that an increase in impervious
cover will decrease  the lag time between peak rainfall and runoff,
increase the peak runoff rate, and increase the runoff yield  per unit
area.  It is only this last effect  which will affect the derived runoff
model in this case,  since the areas  are  too small for lag time changes
to be important on a daily flow basis,  and the peak flows will only affect
the pipe sizings.

It was therefore necessary to develop a  procedure for modifying the
model to take  into account a full range of impervious conditions. This
involves several  assumptions:

1.    For the  Herring Run area, which is 11.9 percent impervious,
      equations can be derived representing unit flow from both the
      completely pervious and completely impervious portions of
      the basin.

2.    The yield from the completely impervious portions will be less
      than 100 percent of the rain that falls on them,  since some
      water will flow from impervious surfaces to pervious  surfaces
      where it will be lost to infiltration.

3.    While this percentage will actually vary, an average value
      can be calculated and used in the equations.

These assumptions were used in the derivation of the following equation,
which is fully  described in Appendix A:
                 A + KXI'R. +(^i-')[(B-KXI)R. + CR.2 + DR.3]   (5)
where:
      Qi    -     runoff/unit area from any Wilde Lake watershed on
                 the ithday

      K     =     conversion factor between in. /day and cfs/mi2 = 26. 88

      X     -     fraction of rainfall actually running off impervious
                 areas

      I      =     fraction imperviousness (Herring Run = 0. 119)

      :'     =     fraction imperviousness of any Wilde Lake watershed

      R^    =     rainfall on the fth day

A, B, C, D   -     regression coefficients derived previously

-------
The only unknown in this equation is X, the percentage of runoff from
impervious areas. To obtain a value, the results of a study of effects
of urbanization on runoff from selected Texas watersheds were used (3).
By relating increased runoff to increased imperviousness on the same
watershed, the following equation was derived:


      •     -     QI  1         1-1
                 "R
                  n      1(1
where;
      Qj    =     runoff volume (as calculated by the equation given in
                 Appendix A) for an area with an impervious fraction of I

      R     =     rainfall volume

By taking individual storm  data and calculating Qj, a value of X can be
calculated for each storm,  and these values can be averaged over all
storms.   The value of X thus obtained is:

      X     =     0.8586

Using this value in the equation for Q-, the final equation for runoff on
the Wilde Lake watersheds becomes:


Q. = A+Ri [23. 08I'+g^)(B-2. 77)] +R.2 [C^jj+Ri3 [D(^)]      (7)

Separate equations for each sub-watershed and for each season can be
derived by using the appropriate values of I1 and the regression coef-
ficients A, B, C, and D,  and from these equations the continuous runoff
hydrograph can be calculated using a daily rainfall input.

To illustrate the actual effects of imperviousness on the runoff yield
per unit  area, an equation can be developed giving the percent increase
in unit yield of an area with a fraction imperviousness  of I' over the
natural area (0 impervious fraction).
                  lOOT
      P     =     TTTTT - - - LJ1T (Appendix A)        (8)
                   \: i; - KXI+B+CR.+DR.
                   K.              i     i


where P = percent increase in yield over the natural state.  Figures 4
and 5 show, respectively, P versus I' for different values of R^ and P
versus Ri for different  values of I'.  The results of the Texas study on
effects of urbanization are also indicated in Figure  4.  It can be seen
that for every value of I', the precipitation values between about 0. 2 inch
and 1. 0 inch have the greatest effects on P. This would be expected
                                 19

-------
 700
                                                                  R=0.50"
                                                                 = 1.00"
                                                                    R = 0.25'
                                                                  = 2.00"
                                                                     = 3.00"
               0.10
0.20        0.30       0.40
     Fraction Impervious
0.50        0.60
Figure 4.  Increased Yield vs. Fraction Impervious
                               20

-------
700
600
 s
 D
-*-
 D
z

 
-------
since during small rainstorms the pervious areas would contribute very
little runoff, and during heavy rains, the pervious areas would eventually
contribute large volumes because the infiltration capacity would be
exceeded.
SENSITIVITY ANALYSIS

As one method of testing the usefulness of the final modified regression
equation,  a sensitivity analysis was made of the equation coefficients.
Such an analysis indicates how sensitive the calculated values of runoff
are to minor variations in these coefficients and also provides a measure
of the reliability of the equation over the range of rainfall values.  To
perform the type of sensitivity analysis required,  the  regression equa-
tion was partially  differentiated in the terms  of  each coefficient, and
the resulting differential equations were used to calculate the change in
runoff as a function of the  change in coefficients.  This was done for
both the upper and lower limits of the imperviousness parameter.

It was determined that the final regression equation is not abnormally
affected by coefficient changes, and throughout the  rainfall range the
equation remains  stable.
STORM HYDROGRAPH AND PEAK FLOW MODEL DEVELOPMENT

In order to calculate the expected peak flows for a storm of any recur-
rence interval, a method was desired which could use the rainfall
intensity-duration-frequency curves for Howard County as a basic
input.  Although the standard procedure for this type of calculation is
to use the Rational Method with an appropriate runoff coefficient for
each watershed, a more sophisticated approach which would provide
more detailed information was selected.  This approach, mentioned
previously,  involves the routing of a rainfall hyetograph through a
linear storage reservoir model to obtain a complete storm hydrograph.
It has been used with great success by the U. S. Department of Agricul-
ture in analyzing storm runoff  from small agricultural watersheds (2),
and it required only minor changes to be  adapted to this  study.

As the first step in this analysis,  the Howard County rainfall curves
were fitted to an equation relating the intensity of rainfall, the duration
of rainfall, and the return period  of the storm.  This equation,  in a
standard form, is:

                 2QOT0.176
           ~     	i—1~                                     (9)
                 (t + 25)1' *-
                                  22

-------
where:

      i      =    intensity (inches/hour)

      T     =    return period (years)

      t      =    duration of rainfall (minutes)

Using this equation,  rainfall hyetographs for a 60-minute storm with
return periods on one, two, five, and ten years were synthesized.
These hyetographs were developed  with the following conditions:

1.    For each storm, the intensity of rainfall for any duration
      from five minutes to 60 minutes is identical to the intensity
      calculated by the rainfall equation.

2.    The hyetograph is approximately symmetric about the peak
      intensity.

3.    The minimum time interval for calculating intensities
      is five minutes.

In addition to these conditions,  the  60-minute  storm volume is only
slightly less than the volume of a 24-hour storm of the same return
period,  and therefore is  analogous to the daily rainfall and runoff
volumes used in the  regression analysis.

The linear storage reservoir model,  which calculates the runoff hydro-
graph,  requires effective  precipitation as an input.   Since effective
precipitation is simply the rainfall  hyetograph minus any losses due
to infiltration or surface storage,  a method was needed to alter the
hyetograph to include these  losses.  This was done by using an infil-
tration  equation for the  losses on the pervious portion of a watershed
and by assuming the  rainfall on the impervious portion is entirely
available for runoff.   The chosen infiltration equation was one originally
derived by Horton  (4) which had been used in a Johns Hopkins University
study of the rainfall  in runoff processes (5) and for which values of infil-
tration  coefficients had been calculated for the Baltimore area.  The
steps involved in changing the original hyetograph are summarized in
the following equations, which were applied to the  hyetograph for each
interval of At:
      PPer
PT    -f = PT    -  ff + It - f Yl-e~at]il         (10)
 Imp       Imp   L o  \ c   o/\       /J         v   '
where:

      f      =     infiltration loss = f + (f - f Vl-e~at\
                                    o  ( c   o)(      )

      f      =     initial infiltration rate (inches/hour)  = 2.5
                                  23

-------
     f     =     final infiltration rate (inches/hour) = 1.5
      c
     a     =     exponential decay constant (hour~ )  = 0. 7

     p    =     effective rainfall on pervious areas
       Per
     P    =     rainfall on impervious areas = original hyetograph
       Imp


                 0whenf>Plmp
      PEff

where:

      ?_,.,, -     final effective precipitation hyetograph
       -hit!
      I     =     fraction imperviousness of the watershed

The resulting effective precipitation hyetograph has been applied as _
input  to a linear storage reservoir model of the runoff process.  This
model uses the following continuity equation as its basis:

                 q + q     S9 ~ S
      I.    =      *   2  +  2A,  1                              (13)
      i            2         At

where:

      I.    =     average inflow rate for time period At(cfs)

      q     =     outflow rate (cfs)

      S     =     storage volume (feet^)

      At   -     time increment between times 1 and 2, seconds

The effect of storage  on the outflow depends on the physical properties
of the entire  drainage area and on the volume of storage.   Normally
the storage will impart a time delay to the outflow with respect to the
inflow into the basin.  This concept is expressed by the equation:
where M is the basin storage coefficient, which may be considered to
be equal to the lag time (2).

In order to obtain the best estimates of peak flow, timing, and hydro-
graph shape, investigations have shown that two routings of the rainfall
                                 24

-------
through half of the indicated storage are required, where the output
from the first reservoir becomes the input to the second.
h

s - s
bl 2
Q! = h

q - S
S2 ~2
«2,

      Figure 6.  Routing Method - Linear Storage Reservoir Model
From the two preceding equations and the double-routing technique,
a single equation can be derived to take effective precipitation as the
input to the first reservoir and calculate the output from the  second
reservoir.

This final equation for routing the effective precipitation is:
      Q;
         VP   + 9P
          Eff.     Eff.
J
                                                               (15)
where:
      m

      At
runoff in cfs/acre during the i^ time interval

lag time (minutes)

time interval (minutes)
Using a computer,  the effective precipitation hyetographs for each storm
return period, and for a range of imperviousness from 0.1 to 0.5, were
used as input to the routing equation.  Various lag times from 4 minutes
to 20 minutes were  assumed and a total of 48 hydrographs representing
each combination of return period, imperviousness, and lag time  was
obtained as output.

These data were then  reduced by calculating for each hydrograph the
maximum average flow for durations from five minutes to 60 minutes,
or in equation form:

      Q,    =    Max [ZyQ/d| , where d = duration in minutes   (16)

The resulting values of QJ, plotted against duration (for every combina-
tion of lag time,  imperviousness,  and return period),  provided a set
of curves that are analogous to the rainfall intensity-duration-frequency
                                  25

-------
curves.  The evolution of these runoff curves is summarized in graph-
ical form in Figure 7,  and the effects of all the parameters on Q can be
seen in Figures  8 through 10.

In order  to more easily use the  data that these curves represent, an
equation  was graphically fitted to all of the points for durations up to
30 minutes.  This equation related all of the parameters,  eliminating
the need for interpolation between the original curves and allowing a
rapid determination of peak flows for any sub -watershed.  The equation
which follows has a multiple correlation coefficient of 0. 98 when
compared to the original data points.
      Qd    =     8T


                 0. 955T0' 033I(2. 482-0. 129m+0. 010m2-0. 00033m3)

where:

      m    =     lag time (minutes)       4<_ m < 20

      d     -     duration (minutes)       5< d <_ 30

      T     =     return period (years)    1< T < 10

      I      =     impervious fraction     0. !<_ I < 0. 5

By applying this equation to the sub -water sheds, storm flow determina-
tions could be made for any storm up to 10 years in magnitude,  and
the results of these determinations and their application to sedimenta-
tion requirements are described in a subsequent section.

As a final application of this storm hydrograph analysis, the volumes  of
the individual hydrographs were calculated and plotted against impervi-
ousness and return period.   These runoff volumes  represent approxi-
mately the maximum runoff volumes of a 24-hour storm for each return
period  since  the original 60-minute rainfall hyetograph volume was
almost identical to the 24-hour rainfall volume.  A graph of storm vol-
umes is shown in Figure 11.


COMPARISON OF REGRESSION MODEL AND  STORM HYDROGRAPH
MODEL

Since two entirely different, techniques were  used to analyze storm water
runoff,  a comparison was made of the results  of the two.  Because both
methods ultimately calculated the volumes of runoff,  storm volumes
were chosen as the basis for comparison.
                                 26

-------
                                              (5)
                                         = 5, I =0.1, m = 12
                                              (1)  Intensity - duration-frequency
                                                  curve for a five-year storm
                                                  rainfall

                                              (2)  Synthesized hyetograph

                                              (3)  Effective precipitation hyetograph

                                              (4)  Runoff hydrograph for area with
                                                  12 minute lag time
Flow-duration-frequency curve
for five-year storm runoff
10   15   20    25   30   35   40  45   50    55  60   65   70  75

                   Time (minutes)
   Figure 7.  Derivation of Flow-Duration-Frequency Curve
                   for Five-Year Storm Runoff

-------
O
cti
03
<-n
O
K
 O
 a
 txO
 cfl
 d
 s
 'x
 a!
                                                Lag Time = 8 minutes
                  10
20
  30          40

Time (minutes)
50
   Figure 8.  Effect of Impervious Fraction (I) on Five-Year Storm Runoff
                                     28

-------
o>
SH
O
Cti
K

-------
CO
o
         CD
         S-i
         O
         cfl
        n!

        K
O

§  2
K

0)
bo
CO
                                                              Fraction Impervious 1-0.3

                                                                      Lag Time m = 4
                     10
                             15
                                      20
                                      25       30       35       40

                                             Duration (minutes)
                                                                                 45
                                                                                  50
                                                                                                   55
                                                                                                            60
                              Figure 10.  Average Runoff Rate vs.  Storm Duration

-------
     0.04
o
cti

ao

a
s
3
.— <
O
a
JH
O
 x
 cti
     0.03 —
0.02 	
     0.01  —
                    0. 1
                          0.2        0.3        0,4


                          Fraction Impervious
                                                                0. 5
                Figure  11.  Maximum Storm Volumes
                                    31

-------
A five-year computer calculation of daily flows for the Wilde Lake water-
shed, as determined by the regression model, was examined and a fre-
quency distribution of the runoff was plotted.  This was then converted
to  a plot of daily flow versus return period as shown in Figure 12.  To
calculate the volumes of storms using the hydrograph approach,  curves
similar to those in Figure 11 were employed, using a fraction impervi-
ousness  of 0. 22.   This provided storm volumes for storms with return
periods of one, two, five, and ten years,  which could be  compared to
the corresponding volumes in Figure 12.

A plot of storm volumes calculated by both methods is given in Figure 13.
It can be seen that the different techniques gave approximately the same
results  with a maximum difference of only eight percent for a two-year
storm.
INPUT TO THE SYSTEM ANALYSIS

In order to use the final regression equation (Equation 7) to calculate con-
tinuous runoff hydrographs for each of the Wilde Lake sub-watersheds,
it was necessary to first determine the fraction imperviousness of each
watershed.  Since land  use data were readily available for the Columbia
project,  a tabulation was made of the acreage that was to  be devoted to
each type of land use in every sub-watershed. A factor was applied to
each use to represent the percent imperviousness estimated for that type
of use.   By multiplying the impervious  factor by the number of acres and
summing for all land uses,  the total number of pervious and impervious
acres could be obtained.

For the portions  of watersheds that were situated outside  the Columbia
boundaries, a similar procedure was followed.   In this case, either ex-
isting land uses or zoning maps were used to tabulate the  land uses. The
same impervious factors were applied to the  non-Columbia acreage as
were used for similar uses in the Columbia project.

Figure  14 is an actual tabulation of land uses, residence units, popula-
tion, and imperviousnesses for sub-watershed number 17.  The same
tabulation was prepared for all other watersheds and the overall imper-
viousness (shown in the last line of Figure 14) was used as I in Equation 7.

The only additional data required to calculate runoff hydrographs were
daily precipitation  for the Wilde  Lake area.   After examining monthly
precipitation data from four rain gages in the vicinity of Columbia, it
could be seen that the Friendship Airport weather station  data agreed
most closely with the monthly rainfall calculated for Columbia by  the
Thiessen method.  Therefore,  five years of daily rainfall data were
obtained from Friendship Airport to be used as input to the regression
model.

-------
              cd
              P
                    30
                                                                                  Estimated
              CD
              G
              O
              i—i
              i—i
              03
              bo

              S
              o
                    25
                    20
              0)
              a
              i — i
              o
                    15
CO
CO
10
                                                              ,
                                                                       ,
                                                            ,
                                                         4        567

                                                              Return Period (years)
                                                                                          10
                           Figure  12.  Calculated Daily Volume vs. Return Period - Wilde Lake

-------
     30
 TO  25

 G
 O
i—<
•—i
 cfl

 ttD

 c
 O



3  20
 a
 3
    15
O
-}->

co
    10
                                            Calculated by Regression Analysis
                                            Calculated by Hydrograph Analysis
                                          4567


                                            Return Period (years)
10
                 Figure 13.  Calculated Daily Volume vs.  Return Period

                                    Wilde Lake Watershed

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Project 3519
SUB-DRAINAGE AREA
   DATA SHEET
Coll. Area No.  j f

COLUMBIA PROJECT
NON-COLUMBIA

LAND USE
OPEN SPACE
Single Family -
Low Density
Single Family -
Medium Density
Town- Houses
Garden Apartments
Mid-Rise
Apartments
Employment
Centers
School Sites
Public
Rights-of-way
OPEN SPACE
Single Family -
Low Density
Public
Rights-of-way
COLUMBIA TOTAL
NON-COLUMBIA
TOTAL
AREA TOTAL
AREA
(Ac.)
10.7

12.5
4.9
6.8
3.6
7.4
2.5
95
O.I


579
O.I
58.0
UNITS/
Ac.
RESID.
UNITS
POPUL./
UNIT
POPUL.

1.2
4.0
11,0
17.0
28.O

50
54
116
101
4.0
4.0
3.5
2:5
2.5

200
189
290
253

1.2



321

321
4.0



932
t|V
932
%
IMPERV.
o.o
7.0
I6.O
33.O
2O.O ;
22.Q
IOQO
18.0
85,0
o;o
,7.0
8.5
37.7

37.6
IMPERV.
AREA
(Ac.) •
,
/
E.O
1.6
'\A
O.8
i
7.4
0.5
8.1



21.8

21.8
        Figure 14.  Work Sheet - Typical Sub-Watershed Land
        Use Tabulation and Imperviousness Factor Calculation
                                   35

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These data were first altered to more closely represent the long-term
precipitation record at Friendship Airport.  To perform the  alteration,
a simple normalization technique was used which preserved the histor-
ical time distribution of rainfall, but which changed the daily volume of
rainfall on a random basis.  This alteration eliminated the extremely dry
or wet months, which on the average would be unlikely to occur in a given
five-year period, without eliminating most daily extremes  or greatly
changing yearly totals.  The procedure used involved the following data
input:

1.    A set of 30  monthly rainfall totals to represent typical  monthly
      rainfalls expected.  These were obtained from a 50-year dis-
      tribution of monthly precipitation at the Baltimore Customs
      House.  These values are shown in Table 3.

2.    The continuous daily rainfall  record for Friendship Airport
      expressed in inches for the five-year period 1960 through 1964.


        TABLE 3.  TYPICAL MONTHLY RAINFALL TOTALS
             BALTIMORE  CUSTOMS HOUSE, 1900-1950
Month

    1
    2
    3
    4
    5
    6
    7
    8
    9
   10
   11
   12
   13
   14
   15
Total Monthly
 Precipitation
   (inches)

     0.40
     0. 69
     0.92
     1. 18
     1.40
     1. 52
     1.71
     1. 85
     2. 00
     2. 15
     2. 29
     2.41
     2. 59
     2. 71
     2.90
Month

  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
Total Monthly
 Precipitation
   (inches)

      3. 05
      3.21
      3.41
      4.
      5.
      5.
        60
        80
4. 01
4. 28
4. 50
  80
  10
  50
      6. 00
      6. 65
      7. 45
     10. 70
A computer program was used to take each month's daily rainfall data
and sum these data to give the total monthly rainfall.  This monthly value
(Mi) was compared to the set  of 30 typical monthly values and the month
that was closest to Mi numerically was chosen. (This can be called Ti. )
The difference between  Mt and T--  was calculated and M;  was increased
or decreased by this amount so that  it equaled Ti.  The adjustment was
done in the following manner:

1.     If Mi was greater than Ti, one  day during the month was chosen
      at random and 0. 01 inch of rainfall was subtracted. (If that day
                                 36

-------
      had no rainfall, then another day was chosen. )  This was done
      repeatedly until M. = T..

2.    If Mi was less than Tj_,  one day during the month was chosen
      at random and 0. 01 inch of rainfall was added.  (Once again,
      only days on which rainfall actually occurred were changed.)
      This was done repeatedly until M. = T..

As a numerical example of this, assume that for January 1962 a total of
5. 02 inches of rain fell according to the sum of the first 31 daily volumes.
It is found by comparison to the  30 typical monthly values that the typical
month which is numerically the closest to 5. 02  inches is one with 5. 10
inches of rain.  This value therefore represents T..

      T.  - M.    =   0.08 inch                                   (18)

Since MI is  less than TI, the  0. 08 inch must be added to the daily rain-
fall during the month of  January 1955. A day on which rainfall occurred
would be picked at random and 0.01 inch would  be  added to the rainfall
data for this day.  This  procedure would have to be done 8 times until
the original 5. 02 inches  of January rainfall would equal 5.10 inches.

This procedure was followed  for each of the 60  months in the five-year
record and the adjusted  daily precipitation was  then used as the input to
the regression model.   The computer was used to output daily runoff
values (neglecting base flow) for each sub-watershed and combination of
watersheds.   A typical year's output for one of  the sub-watersheds,  in-
cluding coefficients,  is shown in Figure 15.

It should be noted that the five years of rainfall data, when compared to
the long-term record, consist of one very wet year, three dry years,
and one average year.  The occurrence  of below average precipitation
during three years should provide a conservative input to an economic
study of storm water reuse.
STORM VOLUMES

To provide the estimates of one-year storm volumes for different water-
sheds, the results of the hydrograph analysis were employed. For every
sub-watershed, the values of imperviousness and size were used to ob-
tain from Figure 11 the  total volumes of a one-year storm.  These values
were  then tabulated and  are presented in Table 4.  The application of
these volumes to the  sizing of reservoir ponds and sedimentation facili-
ties will be  discussed in a subsequent section.


GAGING AND SAMPLING

As a part of this program, a gaging and sampling station was established
in the Wilde Lake watershed.   The results of this work  are  contained in
Appendix B.
                                 37

-------
OJ
co
RUN— OFF
DATA RUN NO.
iGRESSION COEFFICIENTS
A a
JAN
FEB
MAR
APR
MAY
JUNE
JULY
AUG
SEPT
UCT
NOV
DEC

I
2
3
4
5
6
7
a
?
10
IT
12
13
14
IS
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
O.O
o.~o
0,0
0.0
0.0
0.0
0 .0
O.O
0.0
O.T>
0.0
0.0
JAN.
0-V59













O. 53
0.05


0.62
0.05


O.O3


0.27





6.6134 0.
6 . 61 3 4 0".
6.6134 0.
5.4347 I".
5.4347 1.
5.4347 1.
5.2710 1 .
5.2T10 1.
5.2710 1.
4.S080 3.
4.8080 3.
4.8080 3.
FEB. MAR.
O.O5 O.09

0.95
0.10 0.06

0.04

0.70 0 .66



0.17
0.02 0.12
0 .09



0.32 0 .39
0.18

0.12
0.46 0.54
0 .29 0.12

0.34
0.02

0 .09 0.04


0 .64
= 6
C
6777
6777
6777
60"78
6078
6078
6515
6515
6515
8510
8510
8510
APR.
0.01







0.23
0.67

0.46
I .03


0.16





0.09


0.02
0 . 14

0.21
0.03


AREH
O
0.0827
0.0827
0.0827
-OV35T9
-0.3519
-0.3519
-0.2183
- 0 . 21 83
-0.2183
-f. 1654
-1. 1654
-1 .165*
MAY
0.25
0.02



0.12
0.32

0.34

0.44
0.04













0.22


O.C4


- 0.1078 SCT.7*
A












JUNE JULY
0.09

OV07 OV26

~
0.36
O'i02
0.10
XT. 77 0.01
0.02


0.13 0.21
1 .29 0.08
0.02
0.90
0.07

-•

0.51

0 .05
I .39
0.46
0.02
0.22

0.01
0.02

                                                                                          AREA  =
                                                                                                      0 . 1078
                                                                                               AUG.
                                                                                               0.42
                                                                                               avis
IT. 06""
0.04
                                                                                               0.04
                                                                                               0.23
                                                                                               0.06
                                                                                               1.15
                                                                                               0.49
                                                                                               0.36
                                                                                                       SEPT.
                                                                                                        0.03
                                                                                                        0.98
                                                                                                        0.01
                                                                                                        0 .03
                                                                                                         0.05
                                                                                                         0 .02
                                                                                                                 OCT.
                                                                                                                 0.15
                                                                                                                 0 ,06
                                                                                                                  0 . 80
                                                                                                                  1 .89
                                                                                                                  0.02
                                                                                                                          NOV.
                                                                                                                           0 .27
                                                                                                                           0 .07
                                                                                                                           O.,07
                                                                                                                          ~.P .04
                                                                                                                           0.06
                                                                                                                           0.15
                                                                                                                           0 .57
o-. t o
,-o.o;6
0 jt>6
0.45
                                     .0.08
                                     0^42
                                     0.44
                                     0.07
                                    <0. 13
                                                                                                                                    "0.07
                                                                                                                  0.01
                                    Figure 15.  One-Year Daily Hydarograph for Sub-Water shed  No.  6

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TABLE 4.  CALCULATED ONE YEAR STORM VOLUMES
        FOR WILDE LAKE SUB-WATERSHEDS
Storm Volume
Watershed (Million Gallons)
1 0.461
2 0.586
3 0.530
4 0.342
5 0.530
6 1.104
7 0.803
8 0.626
9 1.460
10 1.258
11 0.854
Watershed
12
13
14
15
16
17
18
19
20
21
22
Storm Volume
(Million Gallons)
0.594
0.697
1.030
0.236
0. 782
1.130
0. 290
0. 924
1.203
0.690
0. 358
                          39

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                             SECTION V

                  WATER QUALITY AND DEMANDS


Storm runoff has been stored and reused locally within the catchment
area for centuries.  Many island communities, such as Gibralter, Guam,
and Bermuda,  have been entirely dependent on local efforts to maximize
this type of water resource to supply their needs.   The Department of
Agriculture published handbooks to assist farmers  in constructing farm
cisterns as supplementary water supplies.  In contrast to water falling
on clean and well-maintained, frequently impervious  catchments,  the
storm runoff from a typical urban area has  acquired heavy pollutant
loads before it enters a storm water collection system.  In addition to
discharging large quantities of pollutant  into natural watercourses,
storm runoff is sometimes permitted  to enter combined sewer systems
or may accidentally enter sanitary sewers through  leaks, improper con-
nections, etc. , where it causes  overflows and further increases stream
pollution.

The reuse of urban runoff as a supplementary water resource presents
a number of problems, detailed elsewhere in this report.  It is clear that
the treatment of storm water to  drinking water quality is potentially a
difficult and expensive task.  Section VIII discusses the treatment prob-
lem in some detail.  Since many possible water uses  do not require
drinking water quality,  an investigation was made of applications of sub-
potable water within an urban community.  A literature search was made
to discover other applications of storm water to sub-potable reuse.  No
local  reuse of  storm water was reported in the literature surveyed, but
numerous  applications of sub-potable  water systems, including reclaimed
wastewater, were reported (6, 1, 8, 10, 13, 20, 21, 22).  Next, the kinds of
reuse available in the Columbia  area were investigated and listed.  The
various types of reuse were categorized into four water quality classes
and criteria developed for estimating  the total demand in each. Finally,
demands were calculated for the Wilde Lake watershed and each of its
component sub-watersheds.

A literature survey has been made of  previously reported efforts to re-
cover a wide variety of waste and  sub-potable waters for distribution to
uses that would otherwise be supplied by public potable water systems.
This search was made to determine previous technical  success with such
projects but, more particularly,  to determine levels  of demand for vari-
ous types of reuse and to discover whether public acceptance  of such
systems was achieved.  The largest portion of reported applications was
devoted to use  of reclaimed wastewater, normally from the municipal
wastewater treatment plant.  Although this involves a water resource
somewhat more difficult to treat  and probably much more unlikely  to win
widespread acceptance, published experience has been  summarized to
permit an examination of a more severe case than the one under study.
                                  41

-------
-WATER RECLAMATION'

 TKe expression "wastewater reclamation" is used to overcome ptfblie
 aesthetic- or, more properly, semantic - objections to the term  "sewage
.treatment" (6).,  In a broad sense, "wastewater reclamation  is defined
 as'.ih'e purposeful upgrading of the quality of sewage, rendering it reus-
 able by agriculture,  industry, or the public (11). Planned wastewater
-reclamation has been practiced for over 30 years.   All the basic use
 categories  except drinking water supply are being directly served by
 reclaimed waters.  Even though the  present quantity of reclaimed waste-
 water being used is still rather small, planned reclamation appears to
 be on the threshold of becoming a major consideration in the augmenta-
 tion of water resources (9).

 Wastewater reclamation falls into two categories:- incidental and planned.
 Waste treatment plants discharging into fresh waters provide incidental
 reclamation in that the effluent may  be used again.  On the other hand,
.planned  reclamation involves the production of water suitable for direct
 application to a beneficial use.   Treatment facilities are financed and
 constructed specifically for this purpose (9).

 Reclamation of wastewater may be directed toward any of the following
 applications:

       Specialized industrial uses

       Crop and  domestic'irrigation

       Recreational lakes;and  ponds

       Ground water recharge

      Non-potable domestic uses,  e.g., toilet flushing (6)

 A brief summary of reported experience in each of these areas  of use
 follows.
 INDUSTRIAL USES

 -Direct use of treated municipal wastewaters by industry is presently
 small, but the increasing number of undertakings attest to the enormous
 potential that exists (13). .Most of the recirculation by industry has been
 limited to using industrial wastewater for cooling purposes and a few have
 virtually closed systems requiring only small amounts of  makeup  water
 (24)  Mining, metallurgical,  and allied industries located  in arid regions
 of the United States have pioneered the reclamation of wastewater and
 many large industrial plants find it desirable to treat and  reuse  waste-
 water because of significant financial savings (10).  The literature  reports
 that more than 150 industries located in 38 states are reclaiming indus-
 trial wastewater (10).  Two well-known examples are Bethlehem Steel
                                  42

-------
Company's plant at Sparrow's Point, Maryland, which uses effluent from
Baltimore's domestic sewage treatment plant (13),  and the Kaiser Steel
Company at Fontana,  California,  which reclaims industrial and domes-
tic wastes from'its own plant (6).

The  quantities of water used by industry may often  be radically reduced
by proper reuse.  The steel industry offers the best example of this. At
the Kaiser Steel Plant at  Fontana, the net use of water has been reduced
to 1000 gallons per ton of steel.  This is a substantial saying when com-
pared to the national average of 65, 000  gallons per ton of steel. Not only
will  the reuse of water affect the  total quantity of water used,  but  reused
water can often be purchased at a considerably lower cost (23; see also
15-22).
AGRICULTURAL USES

Irrigation requires more water than any other use (24). Methods of irri-
gation with reclaimed water include:  flooding,  spraying or sprinkling,
ridge and furrow, and subsurface irrigation.  Although most state health
standards do not permit the use of sewage for truck farming regardless
of the degree  of treatment, treated effluent  can be used on cotton, beets,
vegetables grown for seed production, pasture crops,  and woodlands (13).
Crop irrigation has been used as an aid to disposal of community wastes,
with irrigation being merely incidental to the disposal operation.   At
Fresno, California, the city sewage farm takes the place of a secondary
treatment plant that would be needed to sufficiently clean the wastewater
for disposal to a canal or stream (10).

RECREATIONAL USES

One of the outstanding examples  of recreational use of reclaimed waste-
water is the installation at  Golden Gate Park in San Francisco.   This
activated sludge plant is providing an effluent which is chlorinated and
used for maintaining the level of decorative  lakes and the irrigation of
pastures, grass, and gardens. Irrigation of golf courses using reclaimed
wastewater has increased in recent years.  The Marine bases at El Toro
and  Pendleton,  California, are examples.  At El Cajon, near Palo Alto,
California, there are semipublic courses now under construction which
will use sewage effluent for irrigation.  It has been shown that golf
courses employing sewage  effluent are able  to maintain themselves  with-
out additional fertilization (10).

A reclamation project has been undertaken by the Santee County Water
District in San Diego County, California, which provides for the develop-
ment of a series of artificial  lakes fed by the effluent of a standard acti-
vated sludge sewage treatment plant. There are four lakes, two of which
are open to the public for recreational uses. Swimming is currently not
permitted, and catching fish for human consumption is not allowed.  How-
ever, a recreational  area is provided, via use of reclaimed wastewater,
in an area which affords little attraction of this type (13).
                                 43

-------
 GROUND WATER. RECHARGE

 Replenishment of ground waters through artificial recharge has been
 given considerable attention.  In many areas,  ground water levels have
 been rapidly falling and are not being restored through natural means.
 Annual water replacement may lag behind withdrawals due to the slow
 movement rate of ground water and limited opportunities for  surface
 waters to penetrate the earth's surface.  Waters suitable for artificial
 recharge may be classified generally as flood waters, industrial wastes,
 and  municipal sewage effluents (13).

 Numerous methods are used in artificial  recharge operations. The old-
 est and still most common technique is the utilization of holding basins.
 A second method is the use of a modified stream bed. A stream chan-
 nel is  widened and  treated by a combination of methods to increase the
 percolation rate  (13).  Ditches and furrows may also be  used. The basic
 arrangements are contour,  lateral, and branching types. Where slopes
 are  relatively uniform, flooding provides an economical means of  re-
 charge.  Another recharge method is the pumping of water through in-
 jection wells  directly into porous  strata (13, 16).

 The  Whittier  Narrows water reclamation project in Los  Angeles County,
 California,  is an example of ground water recharge  potential (12).  The
 object of this project is to conserve and assist in restoring the Water
 resources of the agricultural area of Southern California.  Treated sew-
 age  is distributed into spreading ponds.  The reclaimed  waters then per-
 colate through to the ground  water aquifers and are eventually used in
 the irrigation of  agricultural lands.  Operation of the Whittier Narrows
 plant is being closely watched by various agencies interested  in public
 health, education,  pollution control, and  industry (13).


 DOMESTIC USES

 Domestic uses of reclaimed  wastewater are generally limited to lawn
 watering and toilet flushing with a few notable  exceptions.  These excep-
 tions are relatively recent developments.  Some of the domestic uses
 reported are:

 1.    Sites of Grand Canyon National Park, where treated domestic
      wastewater was first used in the park in 1926 for toilet  flushing,
      lawn sprinkling,  cooling water,  and boiler feedwater at the
      power plant.

2.    Pomona, California, where  municipal sewage plant effluent
     has been used for domestic irrigation of lawns and gardens
     in a suburban home development since 1929.
3.

      1931.
San Diego State Teachers College,  California, where sewage
effluent was first used for lawn and shrubbery irrigation in
                                 44

-------
4.     Golden Gate Park,  San Francisco,  California, which was men-
      tioned earlier, first used activated sludge plant effluent in 1932
      for lawn watering and  maintaining water levels in some of the
      park lakes (6).

A pilot plant in Tucson, Arizona, has demonstrated that potable water may
be made from municipal waste treatment effluent.  The process is auto-
matic and uses effluent from an  activated sludge process, followed by
softening,  flocculation, filtration,  demineralization, and carbon absorp-
tion (14).

A more 'striking example is  the experience of Chanute,  Kansas. In 1956,
when drought dried up the local water supply, effluent from the city's
secondary treatment plant was diverted to the water supply reservoir.
Treated  wastewater was recycled through the city 8 to 15 times during
a five-month period under the  supervision of public health authorities
(8,14).
DUAL SYSTEMS

For situations where domestic water requirements can be partially met
by a nearby source of reasonably clean water,  a dual water system may
be used.  Dual water systems can be defined as those involving distribu-
tion of two grades of water to consumers through independent pipe net-
works (7).

The idea of dual water systems for  domestic supply received consider-
ation in the United States as early as 1894.  At first, universal adoption
of the concept was not advocated.  It was urged, however:

      "Where there is a supply of naturally pure water  sufficient to
      meet culinary and drinking requirements, it (should) be sup-
      plied through a separate system,  leaving the larger require-
      ments to be furnished  from the nearest, cheapest source of
      reasonably clean water"  (7)

The water of  Coalinga, a city of 6300 located in South Central California,
is highly mineralized and unsatisfactory for drinking purposes and most
home uses.  Because of the  poor quality of this supply, softer  water  is
shipped to Coalinga from Armona, California,  by railroad car.  Since
1931, this water has been distributed to the homes through a system
constructed in parallel with  the hard water system.  The hard  water
supply is  disinfected for safety reasons.  Thus, Coalinga has been
operating a dual water system for-over 35 years (7).

Avalon, a town  on Catalina Island offshore from Los Angeles,  operates
a dual water system.  This system  has been in operation since 1914. A
fresh water distribution system  supplies water for drinking,  cooking,
and bathing.   A salt water system supplies ocean water for fire protec-
tion and sanitary purposes.  It appears that the operation of this system
will continue due to the shortage of  fresh water on the  island (7).
                                 45

-------
Another example of a dual water system is the one in operation at the
University of Wisconsin since sometime prior to 1913.  The University
draws water from Lake Mendota which is treated and pumped to the
buildings and used for showers,  laboratories, air conditioning, fire pro-
tection, boilers,and  other  uses not involving human consumption. Drinking
water is purchased from the city of Madison and supplied to the same
buildings through a separate distribution system (7).

For public health reasons,  community-wide distribution of biologically
safe and unsafe  waters through a dual system  cannot be  seriously con-
sidered.  If the  question of dual water systems is  examined  on the con-
dition that both supplies are safe for drinking  purposes, then the  concept
appears worthy  of study.   The two supplies are  usually termed "potable'
and "sub-potable" (7).

The sub-potable supply should be maintained at  a quality level such  that
occasional inadvertent use for drinking  purposes will not result in harm
to the consumer.  The supply must be free from harmful biologic forms
and toxic  chemicals.  Elements  of the sub-potable  system that furnishes
water for normal and fire  fighting demands must provide hydraulic capac-
ity for fire flows plus the  coincident draft for  toilet flushing, irrigation,
and other domestic and industrial uses.
 PROBLEMS AFFECTING PUBLIC ACCEPTANCE

 The literature is essentially silent on public reaction to the aesthetics of
 wastewater reclamation and dual water systems.  It can be observed,
 however, that the public has accepted existing projects.  Even though
 this acceptance has occurred, the aesthetics of  reclamation are still con-
 sidered an important factor (9).

 Hundreds of U. S. cities draw their water from inland streams. They are
 in fact,  using the diluted sewage effluent of upstream cities. Although the
 presence of such pollution is  generally known, consumer acceptance of the
 water does not appear to be appreciably reduced. Dilution and time appear
 to dissipate  aesthetic objections. An assumed public aversion to the con-
 cept of direct wastewater reclamation has been  a major deterrent to ex-
 pansion of this practice (9).

 When  dual water systems are mentioned,  objections regarding health
 hazards are raised.  These objections arise from associating the  word
  dual   with the hazardous combination of potable and contaminated water
 (7). Early in the development of dual water systems, it was established
 that the most serious difficulty in operating such systems "will be found
 in the proper regulation of the use of purified water" (7)    It was felt
 that some customers would use the pure water for other than intended
 uses,  while  others, either carelessly or to avoid cost, would not  use
 it at all.
                                 46

-------
Conversely,  the two water supplies in existing dual water systems are
both safe for drinking purposes.  The "potable" supply is maintained at
an excellent quality,  suitable in all respects for drinking, cooking, and
bathing.  The "sub-potable"  supply,  inferior in chemical quality but
equal in safety, is  suitable for, waste transport, lawn and garden irrigation,
street flushing, fire protection, and other uses not requiring water of
high quality.  Each dwelling served by a dual water system  requires  two
service lines  and two  meters (7).

The difference between treatment systems for water reuse and wastewater
treatment for disposal to streams  seems to be one of degree rather than
of kind.  At least no sharp distinction is evident in the literature. Streams
and lakes are natural  systems for  bio-treatment.  Their water is often
reused several times  before discharge to the sea.  Present public  accep-
tance of "natural" processes is considered greater than  acceptance of
engineering processes (4).


REUSE CLASSIFICATIONS

Storm water was considered as a potential water source for  every  level
of water use existing within  the Wilde Lake area.  Although each discrete
use has its own unique water quality requirement or standard,  an estimate
will be made to draw the various uses into a limited number of categories,
simplifying further analysis.  Whenever a group of use types is defined
as  one category, the water quality standard  selected for that category
must meet the requirements of each use considered.

Water use can be broadly described as being either residential, commer-
cial,  industrial,  or public.  Table  5 lists various types of  residential
water uses, with approximate percentages of total consumption. Linaweaver
et al.  collected data  from more than 3000 residences in public metered
water and public sewer areas of the eastern United States and analyzed
that data in terms of residential consumption not including sprinkling use
and sprinkling use  alone .(26).  All areas studied in the eastern U.S.
averaged 56. 7 gallons per capita per day for nonsprinkling residential
use.  The thirteen  local areas studied ranged from 42. 9 to 71. 1 gallons
per capita per day  (27).   Examination of similarities between areas
studied by Linaweaver and the Wilde Lake region of Columbia led to the
selection of 61.5 gallons per capita per day  as an estimate of water con-
sumption within the, dwelling unit.

Sprinkling use was  conclusively correlated,  in the Linaweaver work, to
the irrigable area associated with  the dwelling unit and the local deficiency
between potential evapotranspiration and summer precipitation (28). Three
areas were located within the immediate vicinity of Columbia for which
data were available, known as Glenmont, English Manor, and Northwest
Branch Estates.  All are served by the  Washington Suburban Sanitary
Commission and are comprised of homes similar in value and lot size
to those in Columbia.  Average annual sprinkling use,  as computed by
Linaweaver, divided by average irrigable area for each  of these locations
                                  47

-------
resulted in sprinkling usages ranging from 253 gallons per day per acre
to 921 gallons per day per acre (27).  In order to arrive at a value for
estimating demand in Columbia, these three areas were averaged,  and
the mean was found to be 518 gallons per day per acre.  Table  5 was
revised  with slight regrouping of uses,  due to certain uses sharing
common plumbing fixtures,  making separation unfeasible.  The revised
table is shown as Table 6.

            TABLE 5.  DISTRIBUTION  OF RESIDENTIAL
                  WATER  USE. AFTER REID (25)	
Toilet flushing

Bathing

Dishwashing

Drinking and other kitchen

Laundering

Lawn sprinkling

Auto washing
                        % of Total

                           28

                           23

                           4

                           3

                           10

                           29

                           3
   Gal/Capita/Day

         24.0

         20. 0

          3. 75

          2. 75

          8.5

         25. 0

          2.5
            TABLE 6.  DISTRIBUTION OF RESIDENTIAL
                      WATER USE  - REVISED
 Quality
  AA
              Use

Human consumption, food prepa-
ration, general kitchen use
   Gal/         Gal/
Capita/Day   Day/Ac re

    6. 5
  A      Bathing, laundering,  auto washing

  B      Lawn sprinkling

  C      Toilet flushing
                                        31. 0
                                        24. 0
                                                     518.0
 The water quality considerations shown in Table 6 have been assigned in
 decreasing order to quality level.  Water quality Class "AA" is defined
 as meeting the U.S. Public Health Service Drinking Water Standards and
 is intended for all potable water uses (29).  Class  "A" is virtually identi-
 cal to Class "AA" except for taste and odor considerations not important
 in water which will not actually be consumed or used in food preparation.
 Class   B  has somewhat more lenient requirements,  particularly with
 respect to suspended solids, except that it must be disinfected to the
                                 48

-------
same standard as Class "AA, " thus providing safety for accidental inges-
tion.  Class "C, " also disinfected, has little more than a suspended  solids
limit and minimal requirements for corrosivity.   Specific limits on var-
ious quality parameters are shown in Table 7.

Commercial water use might contain  all of the use categories discussed
above in addition to air conditioning  loads and other miscellaneous com-
mercial uses.  In all cases, the water demands of each commercial  user
must be evaluated with respect to the four water quality levels described
above and defined in Table 7.  Particular types of commercial use vary
widely not only in the  specific uses involved, but in the relative magnitude
of each of them.

Industrial uses fall, to a great degree,  into the same type of breakdown
as commercial uses.  Additionally, industry frequently has large demands
for process water,  whose required quality varies from very low to sub-
stantially higher than potable water quality, depending on the  industry
and the process employed.  In order to compute demands for  each water
quality,  a particular industry must be analyzed in detail to determine its
requirements by quality level.  In the study area, the Wilde Lake water-
shed of Columbia,  no process-water-using industry is contemplated,
making this type of analysis unnecessary in the present study.

Public water uses include applications such as street cleaning,  sewer
flushing, fire protection,  and snow melting.  Street cleaning and sewer
flushing account  for very little water  use on a long-term basis, compared
to the available supply. Providing water for fire protection implies  that
high flows will be available from a system of very high reliability.  Fire
insurance rating bureaus normally insist that the required fire flows for
a community like Columbia be available entirely from elevated storage,
independent of pumping capacity.  The lowest requirement in  the Wilde
Lake watershed applies to  the detached single family residential areas,
where 120, 000 gallons of storage must be continuously available. In
order to consider a number of separate systems,  each of them must have
the full fire flow capability.  Furthermore,  the area under study is  al-
ready served by  the Howard County Metropolitan Commission with a con-
ventional public water supply system  designed  to provide  necessary fire
flows.  For these reasons, fire flows were not considered as possible uses
of the storm water within the local reuse concept.  Another public use
considered was the  flushing of streets following snowfalls  to melt and
remove accumulated snow.  This is nonconsumptive use from the stand-
point of the storm water system, since the runoff returns  to the  storage
facility.  This type  of snow removal is confined to those occasions when
pavement temperature is above 40°F  and air temperature  is at least 30°F,
to prevent refreezing of the water as ice.  The flushing must also be
done at a time when the pavement will have the opportunity of drying
prior to the next freezing  cycle, effectively preventing use of the tech-
nique at any time except under bright sunlight. Unfortunately,  the circum-
stances which permit the use of water flushing of snow usually result in
rapid melting of the snow without flushing.  The water required on the
infrequent occasions when  this procedure is indicated is considered to  be
a negligible amount.
                                 49

-------
  TABLE 7.  MAXIMUM CONCENTRATION OF
SELECTED POLLUTANTS BY REUSE CATEGORY
                            Required Water Quality*
                            Maximum Concentration
      Constituent
 (mg/i unless indicated)

 Alkyl benzene sulfonate
 Ammonia (NH^)
 Arsenic
 Barium
 Cadmium
 Calcium
 Carbon chloroform extract
 Chloride
 Chromium (hexavalent)
 Copper
 Cyanide
 Fluoride
 Iron
 Lead
 Magnesium
 Magnesium+Sodium sulfate
 Manganese
 Nitrate (as
 Oxygen,  dissolved (minimum)
 Phenolic compounds (as phenols)
 Selenium
 Silver
 Sulfate
 Total solids .
 Zinc
 BOD (5-day) mg/4
 Coliform (MPN per 100 m 4)
 pH (units)
 Color (units)
 Turbidity (units)
 Suspended solids
 Phosphates
 Volatile suspended solids

 *Based upon maximum concentrations.allowed by the USPHS, the World
  Health Organization, and the Water Quality Standards of the State of
  Maryland.

--Higher suspended solids are permitted by various water quality stan-
  dards.   Limit based on sediment control and water contact recreation.
AA
0.5
0.5
0.01
1.0
0.01
75
0.2
250
0.05
1.0
0.01
1.5
0. 3
0.05
50
500
0. 05
45
5.0
0.001
0.01
0.05
250
500
5.0
1
7.0
15
0-3
	
1.0
A
0. 5
0. 5
0. 05
1.0
0.01
75
0.2
250
0.05
1.0
0. 2
3.0
0. 3
0. 1
150
500
0. 1
50
5. 0
0.002
0.05
0.05
250
500
15
70
6.0
20
3-8
	
1.0
B
0. 5
0.5
0. 05
1.0
0.01
75
0. 2
250
0.05
1.5
0.2
3.0
0.3
0.1
150
1000
0. 5
50
4.0
0.002
0. 05
0. 05
400
500
15
240
6.0
30
8-15
1 r\ •-'•' "•''
j_ \j '\-- 'I-*
1.0
c
0. 5
0. 5
Of 05
1.0
0.01
75
0.2
250
0.05
1.5
0.2
3.0
0. 3
0.1
150
1000
0.5
50
4.0
0.002
0.05
0.05
400
500
15
240
6.0
30
15-20
30**
1.0
                       50

-------
DISTRIBUTION OF DEMANDS

In order to permit evaluation of various levels of treatment for each of
the sub-watersheds and combinations of sub-watersheds,  the water de-
mands were tabulated,  by water quality class,  for each sub-watershed.
The boundaries of the sub-watersheds were revised slightly for this
tabulation in order that the area of computation be similar to that which
would actually be  serviced by a discrete distribution system within the
sub-watershed. Figure 16 shows the distribution areas,  divided by
broken lines,  except  for the sub-watersheds lying wholly  outside the
Columbia project, where the natural drainage lines will continue to de-
fine the areas.  A second  tabulation was made  of land uses within the
revised sub-watersheds,  analogous to that  shown previously as  Figure 14.
This tabulation, shown as Figure 17,  also  lists irrigable  area,  defined
as the difference between  total area and impervious area, excepting  open
space.  This is the approximate area of all lawns,  gardens, and school
grounds  which are likely  to be irrigated by lawn sprinklers during the
summer.

The usage coefficients  described earlier for each of the water  quality
classes are applied to the appropriate parameters and residential water
use is computed for each quality level.  Other  demands,  including, com-
mercial and  institutional  uses,  are estimated  individually for each instal-
lation and listed on the sheet.  Residential and other demands can be
totalled to yield water demand by water quality class for the sub-watershed.
This operation was performed on each sub-watershed in the entire drainage
area to evaluate total demands.  Prior to assembling this information for
input to the systems  analysis computer program, however,  the demands
listed for Class "B"  uses, lawn  sprinkling, were derated. The storage
requirements associated  with several patterns of water demand were
evaluated.  It was found that the nonuniform behavior of sprinkling de-
mands would place a  significant  requirement on reservoir size.  Since
other sources  of supply would be required  during certain  periods, an
analysis was performed to determine the extent to which sprinkling de-
mands could be met with  reservoirs  of reasonable size.

It was determined that  when sprinkling demands were satisfied with an
87. 5 percent reliability and  the balance of  the demand with a 100 percent
reliability,  the reservoir  requirement was essentially independent of the
fraction of total demand which was composed of sprinkling uses.  In  other
words,  sprinkling demands are interchangeable with other demands, pro-
vided no more than 87. 5 percent of the sprinkling use is satisfied by the
system.   The balance of the demands would be supplied from the public
water system through a makeup water connection.   As a result of this
analysis, sprinkling demands in the watershed were reduced to 87. 5 per-
cent of their original value,  then treated on the same basis as  other,
uniform  demands  with respect to storage requirements.   The  methods
used in  making this analysis are described in  Section VII.

Examination of the water use categories indicates that eight possible com-
binations of water use exist.  This includes all possible combinations of
the lower three quality classes,  as well as all  four classes together.
                                 51

-------
CJ1
                                                                                                     LEGEND
                                                                                                 WILDE LAKE
                                                                                                 WATERSHED
                                                                                                / SERVICE AREA
                                                                                                 BOUNDARIES
                                      Figure  16.  Wilde  Lake Watershed -  Service Areas

-------
Project 3519
SUB-DRAINAGE AREA
   DATA SHEET
                               Distr. Area No.



u
LU
•— >
o
Q£
Q-
co
— \
0
U



, <
Zffl
i=
0
u



LAND USE
OPEN SPACE
Single Family -
Low Density
Single Family -
Medium Density
Town- Houses
Garden Apartments
Mid-Rise
Apartments
Employment
Centers
School Sites
Public
Rights-of-way
OPEN SPACE
Single Family -
Low Density
Public
Rights-of-way
COLUMBIA TOTAL
NON-COLUMBIA
TOTAL
AREA TOTAL
AREA
(Ac.}
IO.7

12.5
4.9
6.8
3.6
14.

9.5



62O

62O
UNITS/
Ac.

1.2
4.0
II.O
I7.O
28.0




1.2




RESID.
UNITS


50
54
116
IOI






321

321
POPUL./
UNIT

4.0
4.0
3.5
2.5
2.5




4.0




POPUL.


2OO
189
29O
253






932

932
%
IMPERV.
o.o
7.0
I6.O
33.0
2OD
22.0
IOO.O
I8.O
85.O
0.0
7,O
85.O
45.O

45. 0
IMPERV.
AREA
(Ac.)


2.0
1.6
1.4
Q8
I4.O

8.1



27.9

27.9
 OTHER
 DEMANDS
       ESTIMATED WATER DEMANDS (AVG. DAY)
       POPULATION X  6.5 G/D/Person  (AA)  =
       POPULATION X 31.0 G/D/Person  (A)
       = 23.4 Ac. X 518.0 G/D/Acre   (B)
       POPULATION X 24.0 G/D/Person  (C)

ESTIMATED DEMAND OF  WILDE (AA)
LAKE VILLAGE GREEN  SHOP-
PING CENTERx  LIBRARYxAND
COMMUNITY  CENTER.
                                DEMAND
                                 (G/D)


                              12X120
                              22x370

                                3x800
                                 400
                                8x750
     Figure 17.  Work Sheet - Typical Sub-Watershed Land Use
            Tabulation and Water Demand Calculation
                            53

-------
It was assumed that,  should potable water be produced, there would be
no incentive for separating plumbing systems, therefore all demands
would be connected to a single system.  In all the other cases, where
sub-potable water is being produced, the  plumbing systems constructed
for sub-potable water distribution might be connected to any combina-
tion of fixtures.

The water demands computed for each sub-watershed,  after derating of
the Class "B" demand as discussed above, were combined into each of
the possible use combinations and displayed on a table.  This table was
input to the computer program to serve as the basis for evaluating vari-
ous alternate reuse systems.  A printout  of this table appears as Figure
18.
                               54

-------
                                                              ****  OUTPUT  ****
                                                  ***«•   WATER   DEMANDS  _ BY.	SFRVIf.E _LEVF1	****
WATERSHED
              AA
1 	
2
3
4
_5
6
7
8
9
10
11
12
_L3 	
14
±5
16
JJ 	
18
19
20
2J 	
22
	 550.0
550.0
210.0
1960.0
2550.0
17310.0
. -9080.0
4050.0
2730.0
45460.0
3150.0
1480.0
_234Q.Q_..
5280.0
810.0
2310.0
6060.0
1200.0
1140.0
3460.0
_. 5430.0.
1460.0
2600.0
2600.0
990.0
9180.0
12150.0
82550.0
43310.0
18230.0
13000.0
33670.0
15000.0
7070.0
11160.Q .
23500.0
3840.0
11040.0
28890. 0-
5700.0
5460.0
17800.0
25890.0
6940.0
                                      7210.0
                                      7298.0
                                      3120.0
                                      6799.0
                                      4078.0
                                     20983.0
                                     11830.0
                                      7980.0
                                     36930.0
                                      9520.0
                                     12100.0
                                      5800.0
                                     10330.0
                                     15910.0
                                      3130.0
                                     21480.0
                                     10610.0
                                      5710.0
                                     12190..Q-
                                     17590.0
                                     10560.0
                                      6210.0
 2020.0
 2020.0
  770.0
 7480.0
 9410.0
63910.0
33530.0
15060.0
10100.0
34760.0
11620.0
 5470.0
 8640.0
21690.0
 2980.0
 8540.0
22370.0
 4420.0
16280.0
20040.0
 5380.0
                                                               A,B
  9810.0_
  9898.0
  4110.0
 15979.0
 16228.0
103533.0
 55140.0_
 26210.0
 49930.0
 43190.0
 27100.0
 12870.0
 21490.Q_
 39410.0
  6970.0
 32520.0
 39500.0
 11410.0
_.17650..0__
 35390.0
 36450.0
 13150.0
A,C
4620.0
4620.0
1760.0
16660.0
21560.0
146460.0
76840^0.
33290.0
23100.0
68430.0
26620.0
12540.0
i9aoa.a
45190.0
6820.0
19580.0
51260.0
10120.0
96BO.O
34080.0
_ 45930.0 	
12320.0
A.B.C
1 1A3O.O
11918.0
4880.0
23459.0
25638.0
167443.0
88670,0
41270.0
60030*0
77950.0
38720.0-
18340.0
^Dl^fl-O
61100.0
995O.O
41060.0
61870.0
15830.0
?lfl70T0
51670.0
564<»0»0
18530.0
B,C
<)?~*n.n
9318.0
ifl^An,n
23040.0
4703fi,o
44280.0
2^72f».0
11270.0
1BQ70.0
37600.0
6HO.O
30020.0
•*2
-------
                              SECTION VI

                      STORM WATER QUALITY

In order to specify the various treatment  alternatives which might be con-
sidered in the development of the optimum system to achieve the desired
water quality requirement, it is necessary that the pollutional content of
the storm water be known to  some reasonable degree.  At the least, the
nature and approximate maximum levels of concentration of the  principal
pollutants should be known.   The first attempt towards determining these
parameters was to search published reports for analysis of urban runoff
from similar areas.   Numerous references to storm water quality were
located,  but  only a few went further than isolated,  unrelated pieces of
data (30-38).  Among the several extensive studies of storm water pollu-
tion, most failed to relate specific pollutants to conditions in the watershed
such as land use,  industry,  industrial and commercial wastes, etc.   Pol-
lutant concentrations quoted seldom included any reference to the intensity
of runoff at the  time of sampling or the hydrograph previous to the  sam-
pling time.   One of the more complete studies of storm water pollution
was performed  in Cincinnati,  Ohio, by Weibel et al. , yet it did little more
than set  up some broad ranges of pollutant concentrations for watersheds
similar to the one analyzed (31).  Table 8 summarizes the observed range
of a number  of pollutants found in storm water at a variety of locations
throughout the world.  Each of the studies used to  develop this table were
sufficiently comprehensive to exclude the possibility of a chance or "freak"
occurrence of an unrepresentative concentration of some specific pollutant.
It can be seen that many of the items vary by two or more orders of magni-
tude throughout reported experience.  It was concluded that  the literature
survey would be of little value in establishing a pollutant baseline for the
Columbia location, due to the very wide variance of reported data.  The
sections below describe the tentative listing of maximum concentrations
for expected pollutants, followed by the results of  the water quality sam-
pling station, intended to verify  the tentative data.


TENTATIVE DESCRIPTION OF  RUNOFF QUALITY

A review of the specific pollutants mentioned in various studies  led to a
classification of the parameters as shown in Table 9.

Solids

None of the studies reported  above contained any quantitative data on
floating solids.  Inlet structures are normally expected to exclude large
floating objects (boards,  tree branches, toys,  etc. ) but the existence of
open drainage channels downstream from the closed storm water collection
system permits such objects to  enter the  flow.  In addition,  leaves,  small
branches, paper or cardboard objects,  etc. ,  are commonly found in all
storm water  collection systems.  Much of the debris will eventually ab-
sorb water and  sink, joining  suspended solids, but some will remain
bouyant until it  is manually or mechanically  removed from the stream.
                                  57

-------
              TABLE 8.  REPORTED STORM WATER
                POLLUTANT CONCENTRATIONS*



Observed Range
Dissolved Solids

Suspended Solids
Volatile
Nonvolatile
BOD
COD
DO
Total Nitrogen (NO2, NO3,
Organic)
Total Phosphate
Coliform Total/100 ml
Fecal Strep/100 ml
Chlorides
30 -
154 -
26 -
38 -
119 •-
6. 9 -
18 -
6.4 -

2.3 -
0.47 -
40
median-
11 •
8, 000
228
36,250
98
292
625
3, 100
8.0

11. 8
1, 400
240, 000
20, 500
160
Number
Location^
. ' .1,. /
1 ."
6
1
.. 1
9:
2
' 1

, 3
2
4

' ' 2
  *Refs.  30,  31, 34, 35,  36,  37,  38
Oxygen Balance
Nutrients
Bacteria


Miscellaneous
  Physical and
  Chemical
  Parameters
TABLE 9.  PRINCIPAL INDICES OF
   STORM WATER POLLUTION

              Pollutant

  Floating Solids
  Suspended Solids
  Dissolved Solids

  Biochemical Oxygen Demand (BOD)
  Chemical Oxygen Demand (COD)
  Dissolved Oxygen (DO)

  Total Nitrogen (N,NO2, NOs,  etc.)

  Total Phosphorous (P, PO4, etc.)
  Coliform Group
  Fecal Streptococci

  PH
  Temperature                  >
  Oil and Grease
  Chlorides
  Pesticides
  Surfactants
                                                    Unit of Measure

                                                      Ib/day
                                                      mg/ JL
mg/ i (5-day)
mg/ H
mg/ji
mg/ !L
MPN/100 ml
MPN/100 ml

pH units
°C
mg/4
mg/A
mg/ml
mg/ IL
                                58

-------
To a degree, the nature and size of these objects will be determined by
the physical layout of the collection system.  No estimate was made for
the incidence of floating solids.

Suspended solids include all those particles so fine or so bouyant that
they are suspended in the stream.  It may include both particles which
will settle following loss of stream velocity and those which are either
colloidal or at  neutral bouyancy.  These  solids may or may not be volatile
in nature.  The volatile  solids are generally composed of various organic
substances,, both animal and vegetable in origin, which are characterized
by putrescibility and eventual decomposition into simpler, stable materials.
Volatile solids of vegetable origin may include cut  and  fallen vegetation
(leaves, grass, etc.), humus, and discarded food. Animals contribute
offal and carcasses of various sizes and stages of decomposition.  Non-
volatile suspended solids are primarily soils and general surface debris
and are inherently stable and inorganic in nature.  Analysis of runoff from
similar watersheds in the Cincinnati  study cited earlier led to the tenta-
tive assumption that, after construction is completed,  runoff from Columbia
will probably not exceed 300 mg/4 suspended solids,  60 mg/4 of which
might be volatile.

Dissolved solids may include various soluble minerals and salts, as well
as small quantities of other  organic and inorganic materials which might
be slightly soluble. Decomposition of volatile suspended solids often pro-
duces soluble organic products.  Some dissolved materials have been pre-
cipitated from the  atmosphere by the  rainfall and were dissolved before
striking the ground,  but most have entered the water as suspended solids
and have  subsequently dissolved. Many dissolved substances are of inter-
est themselves as  specific pollutants, such as chlorides, pesticides, sur-
factants,  etc.  Since these separately discussed pollutants are the only
dissolved  solids  expected to be of any interest  in the  Columbia runoff,
no limit was created for dissolved solids.

Oxygen Balance

Biochemical Oxygen Demand (BOD) is an index determined by a labora-
tory procedure for measuring the amount of oxygen consumed,  in five
days, by natural agencies in  stabilizing the volatile material in  the water.
It is a reasonable estimate of the oxygen that will be  consumed  in nature
as the various organic materials decompose.  Untreated domestic sewage
has a BOD on the order of 200 rag/A,  while Maryland Department of Water
Resources water quality criteria classify as "good" a stream having less
than 3. 5 rag/ & BOD.  It was estimated that the storm runoff might contain
up to 25. 0 mg/4 BOD.

Chemical Oxygen Demand (COD) measures the amount of oxygen consumed
under specified conditions in the oxidation of organic  and oxidizable inor-
ganic matter, corrected for the influence of chlorides. COD and BOD tend
to complement one another,  although  there is no inherent relation between
the two.  The difference is primarily one of the mechanism of oxidation.
In the present  analysis,  the BOD test is  considered more appropriate
than COD, so no  estimate was made of storm water COD.
                                 59

-------
Dissolved Oxygen (DO) measures the quantity of oxygen available in ,the
water in molecular form.  It may range from 0.0 up to saturation, which
is a function of water temperature and,  to a lesser extent, atmospheric
pressure.  Saturation levels may range, at sea level,  from 7. 1 mg/£ at
35°C to 14. 4 mg/£ at 1°C.  It can be assumed that  falling raindrops  are
100 percent saturated and that any loss  of oxygen content is a result  of  -
rising temperature or of physical contact with oxidizable contaminants,
or both. It was assumed that the DO of storm water might be as low as
0.0 mg/0.

Nutrients
Both nitrogen and phosphorous are effective nutrients and are commonly
found in water as nitrates and phosphates.  Nitrogen might  also be present
as nitrites and as dissolved or organic nitrogen,  due to the decomposition
of organic material.  The presence of either of these materials is usually
indicative of decomposing organic materials in the stream or in the water-
shed, or of the direct application of chemical fertilizers  containing these
materials to land in the watershed,  resulting in a high nutrient level of
runoff.  The presence of  these substances in excessive concentrations
contributes to algal blooms and to distortion of the ecological balance of
the receiving body of water.  It was assumed that the runoff under study
would not exceed 3.0 mg/2.  Nitrogen (measured as NOg) or 1. 0 mg/0
phosphorous (measured as
 Bacteria

 Due to the great difficulty of isolating and identifying all of the possible
 pathogenic (disease-producing) bacteria which might be present in storm
 water, it is common practice to test for presence of one  of the fecal
 bacteria and use that strain as an indicator of fecal contamination.  If
 such contamination is found to be present, it  is considered possible that
 pathogens might also be present. If no fecal bacteria  are identified, the
 presence of pathogens is considered unlikely.  The fecal  bacteria used
 most widely as an indicator is the coliform group of bacteria, particu-
 larly the  Escherichia Coli, a relatively large rod-like bacteria.  It is
 readily detected by means of any of several standard laboratory methods.
 Since coliform bacteria may be present in soil as well as humans and
 animals,  more specific indicators,  such as the fecal streptococci group,
 are sometimes used.  In all cases,  test results are reported as most
 probable  number (MPN) per 100 ml.  Since public health  considerations
 dictate that chlorination should be practiced regardless of the bacterial
 concentrations, no limit was suggested for the  probable bacterial pollution.

 Miscellaneous Physical and Chemical Parameters

 From the many parameters that could be considered under this heading
 the only ones which are expected to be of any significance in the Wilde
 Lake area are chlorides, oil,  and grease.  No quantitative  estimate
 was made for oil and grease, but it is virtually certain that runoff from
 streets,  driveways, and parking lots will include  noticeable quantities
 It is estimated that chlorides, primarily from salt used to melt snow in the
                                 60

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winter;  may range as high as 160 mg/jfc.  Table 10 lists the tentative
storm water quality description for the Wilde Lake watershed.

TABLE 10.   EXPECTED MAXIMUM  POLLUTANT CONCENTRATIONS
      .  rFOR STORM WATER IN WILDE LAKE WATERSHED
 Type

Solids
                             Pollutant

                 Floating Solids
                 Suspended Solids
                 Volatile Suspended Solids
Oxygen Balance  BOD

Nutrients        Nitrogen (N,  NO2,
Miscellaneous
  Physical and
  Chemical
  Parameters
                 Phosphorous (P,  PO.^)

                 Chlorides
                 Oil and Grease
                                          (as NO3)
                                          (as PO4)
Expected Max.
Concentration

Present
300    mg/ji
  60    mg/ H

  25    mg/1

   3. 0  mg/ JL
   1. 0  mg/A

160    mg/ i
Present
  The results of the water quality sampling program conducted in the
  Wilde  Lake watershed are contained in Appendix B.
WATER QUALITY STANDARDS FOR WILDE LAKE

The Maryland Department of Water Resources has recently adopted a
comprehensive set of water quality  standards regulating the state's
interstate and principal intrastate waters, incompliance with federal
requirements (40).  Although Wilde Lake is not specifically assigned a
minimum water quality in these standards, its intended use is clearly
consistent with the Class "C" uses outlined in the regulations — water
contact recreation, fish propagation, agricultural and industrial water
supply.  These standards make the following requirements of bodies
of water intended for Class "C" uses:

1.    Fecal coliform bacteria  less than 240 MPN/100  ml

2.    Dissolved oxygen greater than or equal to 4. 0 mg/£
      at any time, 5. 0 mg/1 monthly average

3.    pH greater than or equal to 6. 0, less than or equal
      to 8. 5

4.    Temperature less than or equal to 93 F (35 C)
                                 61

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In addition,  general requirements are made, prohibiting harmful concen-
trations of any other pollutants which might be present.  Harmful concen-
trations are to be determined in  terms of the intended uses of the body of
water which is to be protected.

A conservative interpretation of  these water quality standards and the
ability of Wilde Lake to neutralize pollutants entering it from  storm
water runoff led to  the definition of effluent  standards for all water
deliberately discharged into Wilde Lake or its tributary watercourses.
These  standards take into account the possibility of spills during severe
storms and have been further adjusted to coincide with the water quality
criteria adopted for Class  "C" water uses in the previous section.
Table 11 lists the parameters being used to  define effluent water quality
together with the maximum concentration of each.
                                  62

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              TABLE ,11.  EFFLUENT STANDARDS FOR
              WATER DISCHARG'ED INTO WILDE LAKE*
Solids   ,',  ,,,.,



Oxygen Balance

Nutrients


Bacteria

Miscellaneous
  Physical and
  Chemical
  Parameters
Floating Solids
Suspended Solids
Volatile Suspended Solids

BOD
Nitrogen (as
Phosphorous (as

Fecal Coliform
pH
Oil and Grease
Chlorides
Surfactants (ABS)
Ammonia (NHs)
Arsenic
Barium
Cadmium
Calcium
Carbon Chloroform Extract
Chromium (hexavalent)
Copper
Cyanide
Fluoride
Iron
Lead
Magnesium
Manganese
Phenolic Compounds
  (as phenols)
Selenium
Silver
Sulfate
Zinc
Color
 None
 30.0 mg/4
 None
  3.5
 50.0 mg/4
  .1.0 mg/4

240   MPN/100

  6. 0 or greater
 None
      nig/4
    5 mg/4
    5 mg/4
    05 mg/4
    0 mg/4
    01 mg/4
      rag/A
    2 mg/4
    05 mg/4

    2 mg/4
    0 mg/Ji
    3 mg/4
    1 me/^-
250
  0
  0
  0
  1
  0
200
  0
  0
  1
  0
  3
  0
  0
150
  0. 5 mg/4
  0
  0
  0
400
 15
 30
                                                     .002
                                                     . 05
                                                      05 mg/^
                                                        mg/Ji
                                                        mg/Ji
                                                     color units
 = Refs. 40 and 41
                                63

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                            SECTION VII

                      STORM WATER STORAGE
The Wilde Lake watershed of Columbia is similar to other recent sub-
urban developments in its approach to the storm drainage problem. The
natural drainage channels have been retained with their original topog-
raphy and the floodplains are used,  in part,  to satisfy the open space
requirement of the community planning concept.  The floodplains are
normally surrounded with building lots and these, in turn,  are circum-
scribed by roads.  The storm drain system  consists of many relatively
small inlet and pipe systems,  each draining independently into a flood-
plain.  After discharge, the storm water follows  natural drainage lines
to Wilde Lake.  Roads are generally located at or near the ridge lines
of the various sub-drainage areas and only a few  cases exist within the
Wilde Lake watershed where  an appreciable  amount of runoff is collected
by a single closed collection system before  discharge to  a floodplain.
CONSTRUCTION TYPES

The early planning of the Local Reuse System study provided for consid-
eration of unconventional storage facilities, such as natural or artificial
underground cavities, slip-formed vaults beneath streets,  etc., as well
as more conventional approaches to storage within the floodplain.  Exam-
ination of the drainage area indicated that significant  quantities of storm
water were not available at any place in the watershed, except at loca-
tions within the natural floodplains.  Of the  22 sub-watersheds consid-
ered,  only number 10 enters Wilde Lake as a wholly closed system with-
out having been substantially collected within a natural floodplain. When
storage is to be provided in the floodplain,  two types  were considered -
open ponds and constructed storage.  In sub-watersheds where floodplain
space is not  available,  such as number  10,  conventional constructed
storage was  considered,  along with unconventional approaches,  such as
special vaults under  roads and parking lots.  Construction costs for such
vaults were found to  be on the  order  of $0. 20/gallon of storage capacity
and maintenance  problems were considered to be severe.   Since conven-
tional constructed storage is competitive with other methods from sizes
of 50, 000 gallons upward and maintenance is facilitated by the improved
access, parametric costs for unconventional approaches were not devel-
oped and no further consideration of  them was judged necessary.

In the case of constructed storage, costs are dependent on location with
respect to existing grade. In most cases, the storage facility must be
placed below grade to permit gra.vity inflow under all conditions. Occa-
sionally,  local topography may permit  a tank to be constructed partially
or completely above  grade.  To maintain maximum flexibility, the below
grade and above grade cases were separately analyzed and costed.  Tanks
of steel and of prestressed concrete  construction were also investigated.
Open ponds were studied and the optimum combination of excavated  and
                                 65

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natural storage determined for ponds in topography similar to Columbia.
Table 12 summarizes the types of reservoir construction which were
studied and cost estimated.

              TABLE 12.  STORM WATER STORAGE .       :
                RESERVOIR CONSTRUCTION TYPES  ,         ;  ,-

    Natural Storage               Open Ponds

    Constructed Storage           Steel Tanks - Above  Grade
                                  Steel Tanks - Below  Grade
                                  Concrete  Tanks - Above Grade
                                  Concrete  Tanks   Below Grade
 SIZING CRITERIA

 The storm water storage facilities included in the Local Storage, Treat-
 ment, and Reuse of Storm Water concept function as multiple purpose
 reservoirs and,as such, are subject to several potentially conflicting
 requirements. Their basic purposes, in the order of the priority implied
 by the orientation of this study, are water quality control, water supply,
 and the creation of a pleasing and harmonious asset to the local  environ-
 ment.  As water quality control reservoirs, they are expected to be
 designed and  operated so as to prevent degradation of their contents,
 maintain sufficient release of the natural watercourse  to protect down-
 stream uses,  and possibly effect sedimentation.  The water supply use
 dictates certain relationships of storage capacity, supply, and yield,
 dependent on, among other things, the reliability with which the  yield
 must be maintained.   Finally,  the appearance of the facility must be at
 least consistent with its surroundings and might well be designed to be
 an asset to the area.  The presence of the facilities must be acceptable
 to the community and pose no particular safety hazard or nuisance.

 In studying size requirements for the local storage units,  the individual
 reservoir locations were first analyzed to determine the yield versus
 capacity relationships, assuming 100 percent reliability over the five-
 year period of the  synthetic hydrograph.  Similar analyses were performed
 to determine  relationships with 99,  98, 95,  90, and 80 percent reliability for
 the five-year period.  These analyses were performed for constant yields
 and for yields approximating the patterns of several different levels of
 lawn sprinkling use.   Next, water quality considerations were analyzed
 in terms of operating and design requirements,  and the storage  units
 studied as sedimentation basins.  Finally,  sizes and design criteria were
 developed which  met requirements imposed by all three purposes.  The
 following sections  describe in detail the development of these criteria.
                                  66

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STORAGE/YIELD CHARACTERISTICS FOR WATER SUPPLY USE

A common approach to water supply reservoir sizing problems is the Mass
Diagram or Rippl Method (42).  When performed graphically, this method
plots cumulative supply against cumulative yield so that cumulative surplus
or deficiency can be examined.  A simple graphical manipulation is suffi-
cient to measure maximum required storage directly for the time period
plotted.  The identical result may be obtained with somewhat better reso-
lution by applying the  following continuity equations to tabular data:

      Qi + Si =  D.+Si + 1                                     (19)

where:

      Q.    =    inflow on the i   day

      S.     =    storage volume at  the start of the i   day

      D.    =    yield on the  i   day

This equation may be  applied to each successive time  period throughout
the available -record, and the maximum value found for Si is the  maximum
required storage,  comparable to that found by  the graphical technique.
In order to achieve meaningful results in small watersheds subject to
large, short-term fluctuations in runoff  rates, a five-year daily synthetic
hydrograph was developed (Section IV), containing 1825 data points.  These
data were developedf or each of the 22 sub-watersheds. Each of these must be
analyzed over a wide  range of demand levels,  or yields.  This last require-
ment is made to permit an economic tradeoff between  the revenue of addi-
tional water uses and  the incremental cost of additional storage.  A prelim-
inary appraisal of  the difficulty of a  conventional mass balance  continuity
analysis of 1825 data  points for each of the watershed  yield combinations
led to investigation of alternate approaches to  the reservoir sizing
problem.

The selected method was that  of Residual Mass Tabulation,  a technique
for approximating  the result of the method described above with many
fewer calculations and in a manner much better suited to the high speed
processing characteristics of  the digital computer (42). Table  13  is a
portion of a residual mass tabulation for one of the sub-watersheds in
the Wilde Lake  area.   The two left-hand columns  list total accumulated
runoff (in cfs-days) for various periods (in days) in the synthetic record.
The first line indicates runoff for the driest day of record;  the  second
line indicates the total runoff for the driest five consecutive days of
record; the third line indicates the total for the driest 10 consecutive
days of record; etc.   For example,  the eleventh line indicates that
during the driest 60 consecutive days of  record, the total accumulated
runoff was  1. 0 cfs-day.  This listing continues until the period  listed
equals the total record,  1825 days,  and the accumulated runoff equals
the total runoff for the period,  83. 09 cfs-day in this example.  The second
                                  67

-------
                               TABLE 13.  EXAMPLE OF RESIDUAL MASS TABULATION -
                                                    SUB-WATERSHED NO.
CO
Period
(days)
1
5
10
15
20
25
30
35
40
50
60
80
100
150
200
250
300
350
400
450
500
600
700
800
900
1000
1200
1400
1600
1825
Runoff
(cfs-days)
0.0
0.0
0. 0
0.0
0.0
0. 0
0.0
0. 12
0.22
0. 37
1.00
1.54
1.70
3. 32
4, 65
7. 53
9. 97
12. 33
13.85
15. 58
10.00
23.05
29.52
33.71
39.03
43.37
52.26
61. 56
72. 27
83.09
Demand(cfs)=0. 0125
Outflow Storage
(cfs-days)
0. 0125
0.0625
0. 1250
0. 1875
0.2500
0. 3125
0. 3750
0.4375
0.5000
0. 6250
0.7500
1.0000
1.2500
1.8750
2.5000
3. 1250
3.7500
4. 3750
5.0000
5.6250
6. 2500
7. 5000
8.7500
10.0000
11.2500
12. 5000
15.0000
17 5000
20.0000
22.8120
0.0125
0.0625
0. 1250
0. 1875
0.2500
0. 3125
0. 3750
0.3175
0.2800
0.2550
-0.2500
-0. 5400
-0.4500
-1.4450
-2. 1500
-4.4050
-6.2200
-7. 9550
-8.8500
-9.9550
-11.7500
-15. 5500
-20.7700
-23.7100
-27.7800
-30.8700
-37.2600
-44.0600
-52.2700
-60.2780
Demand(cfs) = 0. 0200
Outflow Storage
(cfs-days)
0.0200
0. 1000
0.2000
0.3000
0.4000
0.5000
0. 6000
0.7000
0.8000
1.0000
1.2000
1.6000
2.0000
3.0000
4.0000
5.0000
6.0000
7.0000
8.0000
9.0000
10.0000
12.0000
14.0000
16.0000
18.0000
20.0000
24.0000
28.0000
32.0000
36. 5000"
0.0200
0. 1000
0.2000
0. 3000
0.4000
0.5000
0.6000
0. 5800
0. 5800
0. 6300
0.2000
0.0600
0.3000
-0.3200
-0.6500
-2. 5300
-3. 9700
-5.3300
-5.8500
-6. 5800
-8.0000
-11.0500
-15.5200
-17.7100
-21.0300
-23.3700
-28.2600
-33. 5600
-40.2700
-46.5900
Demand(cfs)=0. 0400
Outflow Storage
(cfs-days)
0.0400
0.2000
0.4000
0.6000
0.8000
1.0000
1.2000
1.4000
1.6000
2.0000
2.4000
3.2000
4.0000
6.0000
8.0000
10.0000
12.0000
14.0000
16.0000
18.0000
20.0000
24.0000
28.0000
32.0000
36.0000
40.0000
48.0000
56.0000
64.0000
73.0000
0.0400
0. 2000
0.4000
0. 6000
0.8000
1.0000
1.2000
1. 2800
1.3800
1. 6300
1.4000
1.6600
2. 3000
2. 6800
3. 3500
2.4700
2.0300
1.6700
2. 1500
2.4200
2.0000
0.9500
-1. 5200
-1.7100
-3. 0300
-3.3700
-4.2600
-5. 5600
-8.2700
-10.0900
Demand(cfs)=0. 0600
Outflow Storage
(cfs-days)
0.0600
0.3000
0.6000
0.9000
1.2000
1.5000
1.8000
2. 1000
2.4000
3.0000
3.6000
4.8000
6.0000
9.0000
12.0000
15.0000
18.0000
21.0000
24.0000
27.0000
30.0000
36.0000
42.0000
48.0000
54.0000
60.0000
72.0000
84. 0000
96.0000
109.5000
0.0600
0. 30,00
0.6000
0. 9000
1.2000
1.5000
1.8000
1.9800
2. 1800
2.6300
2.6000
3.2600
4.3000
5.6800
7.3500
7.4700
8.0300
8.6700
10.1500
11.4200
12.0000
12.9500
12.4800
14.2900
14.9700
16.6300
19.7400
22.4400
23.7300
26.4100
        Maximum Storage
                                            0.3750
0.6300
                        3.3500
(supply deficit)

-------
pair of columns, headed "DEMAND (CFS) = 0.0125, " show the method
of analysis for a constant yield of 0. 0125 cfs.  The column headed "OUT-
FLOW" lists the total yield for each of the periods listed in the first
column (number of days times daily yield). The column headed "STORAGE"
lists the volume drawn from storage found by  subtracting the "RUNOFF"
column from the "OUTFLOW" column.  The largest positive number in
this column is the approximate size, in cfs-day,  of the required reservoir,
given this demand.  This process is repeated  successively  with various
demands until the entire possible operating range has been explored.  In
each case, the largest positive number in the  storage column is taken as
the required reservoir size. When the "STORAGE" column  does not show
a negative entry in the last row, a supply deficit  is indicated.  That is,
the total available supply is less than the total required yield and no finite
reservoir can be constructed which would provide this yield during the
period analyzed.

After the resudual mass tabulation has been performed for a sufficient
number of yields to describe the range of possible operation, a plot is
made of yield versus storage requirement.  A typical plot is shown on
Figure  19.  In this case, the units of storage  have been converted from
cfs-day to gallons and those of yield from cfs  to gallons/day.  Since the
method used samples of various time periods  and computes storage for
the sampled periods only, the  storage  requirement found will be only an
approximation of the actual requirement.   It may be equal to the actual
requirement or, more probably,  slightly smaller.  For this reason,  the
plot shows a smooth curve  intersecting or  passing above the plotted points.
This curve  can  be taken as a continuous relationship between storage re-
quirements and yield for the period of the synthetic hydrograph used to
generate the points.  Figure 20 shows the storage/yield characteristic  of
another sub-watershed as well as the results  of a graphical RipplMethod
solution for the same area.  The correspondence between the two methods
was considered satisfactory for the purposes  of this study,  and all subse-
quent storage analyses were made by the method of residual mass tabu-
lation, using digital computers.


STORAGE/YIELD CHARACTERISTICS FOR SPRINKLING USES

The determinations  of storage requirements described  above assumed
that the demand on the storage facility,  or yield, would be constant in
terms of volume/day.  This assumption is relatively valid for  domestic
uses such as toilet flushing, bathing,  laundering, food preparation,  etc.
The only significant use which cannot be treated as a constant demand is
lawn sprinkling. In addition to its totally seasonal characteristic in many
areas of the country, the pattern of use is  highly irregular from day to
day.  In their major  study on residential water use,  Linaweaver and
others found the relationships  between the  most severe and  the average
periods of sprinkling use in a residential area near the Columbia site
(27).  These are shown in Table 14.
                                 69

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                                                Required Storage Capacity (MG)
   X
   P

   3
 '  CD rt>
SH CO
^-i >_.. i—•
P  a CD
CT ^
CD  £
w  P
 J  I
CO  ^ CO

^ ^ S"
(T)  i-=l O


S-SS
3
cr
0)
03
P Kj
   h^-
   CD
   i—'
s a

>
3
P

^
CO
(-"
CO

-------
O
bo
ctS
 s
 IT
 4)
    1.8
    1.6
    1.4
    1.2
    in

     ' U
    0.8
    0.6
    0.4
    0.2
                                     Mean Runoff =

                                  13, 121 gallons/day
                         —  Rippl Method
                            Residual Mass Tabulation
                            5000                 10,000


                                 Yield (gallons/day)
15,000
                      Figure 20.  Storage vs. Yield -

        Comparison of Rippl Method and Residual Mass Tabulation

                        Sub-Watershed Number 4
                                   71

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     TABLE 14.  RATIO OF SPRINKLING USE DURING SELECTED
     _ PERIOD TO AVERAGE SPRINKLING USE _

              Glenmont and Northwest Branch Estates,
              Washington  Suburban Sanitary Commission,
                   October 1963 to September 1965


                                 Ratio of Sprinkling Use
   Time Period                  to Average Use (27, p.  6)

   Peak Hour                            21.20

   Maximum Day                          7.17

   Maximum  92 Days                      2.16
            365 Days                      1. 00

 A continuous curve was fitted to the four data points listed by a parabolic
 regression technique,  yielding the following equation:
                                                            (20)
      RI   =    7.26d             Standard error of estimate =
                                  0. 0061; o = 0.993

 where:

      R    =    ratio between  average sprinkling use during period,
                d,  and annual  average sprinkling use

      d     =    period of  sprinkling use being studied in days

 This equation can now be used to estimate the ratio of  sprinkling use
 during the most severe period of a selected length to the average sprin-
 kling use.  When average sprinkling use levels are developed te Section V
                                                      .
        as an input to this calculation.             irrigaDie area is
tohee                    sprinkling demand patterns can be applied

                                            "u             d is
       te      -- -- d--e -^rr sr
                             72

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               TABLE 15.  EXAMPLE OF MODIFIED RESIDUAL MASS TABULATION -
              STORAGE VS.  PROPORTION OF DEMAND USED FOR SPRINKLING LAWNS
Sub-watershed #16, Demand (cfs) = 0.0232
                           (g/d)= 15,000
Period   Runoff
(days) (cfs-days)
                        0% Sprinkling
                     Outflow    Storage
                 25% Sprinkling
           Ratio     Outflow     Storage
                   100% Sprinkling
            Ratio     Outflow      Storage
1
5
10
15
20
25
30
35
40
50
60
80
100
150
200
250
300
350
0.0
0. 0
0.0
0.0
0.0
0.0
0.0
0. 10
0. 18
0. 30
0. 86
1. 30
1.46
2.89
4.05
6.70
9. 12
11.45
0.
0.
0.
0.
0.
0.
0.
0.
0.
1.
1.
1.
2.
3.
4.
5.
6.
8.
0232
1160
2320
3480
4640
5800
6960
8120
9280
1600
3920
8560
3200
4800
6400
8000
9600
1200
0. 0232
0. 1160
0. 2320
0.3480
0.4640
0.5800
0.6960
0.7120
0.7480
0.8600
0. 5320
0. 5560
0.8600
0. 5900
0. 5900
-0.9000
-2. 1600
-3. 3300
2. 565
1.807
1. 588
1.481
1.414
1. 366
1.329
1. 300
1. 276
1.238
1.209
1. 167
1. 137
1.087
1.056
1.034
1.017
1.004
0.0595
0.2096
0.3684
0. 5154
0.6561
0.7923
0.9250
1.0556
1. 1841
1.4361
1. 6829
2. 1660
2.6378
3. 7828
4.8998
5.9972
7.0783
8. 1525
0.0595
0.2096
0. 3684
0. 5154
0.6561
0.7923
0. 9250
0. 9556
1.0041
1. 1361
0. 8229
0.8660
1. 1778
0.8928
0.8498
-0.7028
-2. 0417
-3.2975
7.
4.
3.
2.
2.
2.
2.
2.
2.
1.
1.
1.
1.
1.
1.
1.
1.
1.
260
229
351
924
654
463
316
200
103
951
835
666
546
349
224
136
069
015
0. 1684
0.4906
0.7774
1.0176
1.2315
1.4285
1. 6119
1.7864
1. 9516
2.2632
2. 5543
3.0921
3. 5867
4. 6945
5. 6794
6. 5888
7.4402
8.2418
0. 1684
0.4906
0. 7774
1. 0176
1.2315
1.4285
1. 6119
1. 6864
1.7716
1. 9632
1. 6943
1. 7921
2. 1267
1.8045
1. 6294
-0. 1112
-1. 6798
-3. 2082
Maximum Storage
0.8600
1.1778
                                                                                                   2.1267

-------
sprinkling  25 percent sprinkling, and 100 percent sprinkling.   The
"RATIO" columns are determined by evaluating Equation 20 for each
time period and adjusting this ratio as follows:


      R.,   =     pR. +d-p)                                    (21)

where:

      R. ,   =    • adjusted ratio for i  period

      R.   =     ratio from Equation 20 for i  period

      p    =     fraction of use assumed as  sprinkling

These adjusted ratios are then entered in the "RATIO" columns in the
rows corresponding to the correct time period.  The tabulation proceeds
as before,  except that the "DEMAND" column is the product of the average
daily demand, the number of days in the period,  and the corresponding
adjusted ratio.  The results of this tabulation indicates significant increase
in required storage as a direct result of an increasing proportion of the
water being used to irrigate lawns.  Figure 21 presents the results of a
complete tabulation for one sub-watershed showing a family of curves for
various proportions of sprinkling use.  Figure 22 is another presentation
of the same data,  comparing sprinkling use fraction to required storage
for a range of total average daily use levels.   As discussed in  Section V.
this type of analysis was used to derive the derating factors for sprinkling
uses  used in  the study.


STORAGE /YIELD CHARACTERISTICS AS A FUNCTION OF RELIABILITY

Both the constant  use and the  sprinkling use storage characteristics invest-
gated above have been oriented toward a requirement of 100 percent reliable
operation of the storage system based on a five-year synthetic  hydrograph.
Since the Local Storage, Treatment, and Reuse of Storm Water concept
required that the system function only as a supplemental supply to a con-
ventional public water distribution system, the storage requirements asso-
ciated with various levels  of system reliability were also analyzed.  For
purposes of this analysis,  90  percent reliability is  defined as the ability of
the system to supply at least 90 percent of the total water demand in any
given year.  Once again, the residual mass tabulation was employed to deter-
mine storage/yield characteristics.  In this case, an assumption was made
that the portion of the total demand which the storage system would fail to
supply would be that occurring during the driest period. Table 1-6 is an ex-
ample of a tabulation of a sub-watershed with a 15, 000  gallon/day total de-
mand which would be either 100 percent,  98 percent, 95 percent, or 90 per-
cent supplied by the reservoir under study.   In each case, the "DEMAND11
column is reduced by the annual difference between reservoir  yield and
demand for each year or fraction thereof.   In the example given, the
                                  74

-------
 4. 0
ai
C
_0
—<
cd
O

c
O
nJ
Q,
oi
U
•a
0)
3
a"
ffi
 .3. 0
  1.0
                          10,000                  20,000

                                   Yield (Gal/day)
30, 000
        Figure 21.  Storage Yield Characteristic vs. Proportion

                  of Demand Used for Sprinkling Lawns
                                    75

-------
    4.0
    3.0
O
o
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a
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u

0)
M
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"D
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3
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-------
                 TABLE  1.6.  EXAMPLE  OF MODIFIED RESIDUAL MASS TABULATION -
                 	      STORAGE VS. RELIABILITY	
Sub-watershed #16, Demand 
-------
98 percent column is reduced by 0. 1694 cfs-day* for all time periods of
one year or less, by 2 x 0. 1694 cfs-day for time periods of two years or
less but more than one year,  etc.  A complete analysis of the  sub-water-
shed for various levels of reliability is shown in Figure 23.  The same
information is displayed in Figure 24 as the required storage as. a func-
tion of supply reliability for various levels of demand.

The previous paragraphs have summarized an investigation of storage
requirements for the 22 sub-watersheds in the Wilde Lake area, derived
as a continuous function of such variables as total demand,  proportion of
demand devoted to lawn  sprinkling,  and supply reliability.  This analysis
has indicated that storage requirements are highly nonlinear with demand,
relatively sensitive  to sprinkling uses, and highly sensitive to the avail-  ;
ability of supplemental water  from other sources.  The method of analysis
employed,  a modified residual mass tabulation technique,  was well suited
to the application of digital computer methods and produced satisfactory
results within the scope of the initial assumptions.  Since the same sim-
ulated rainfall record was applied to all sub-watersheds, little error will
be introduced by summing the cumulative  runoff columns of the tabulations
for several sub-watersheds to analyze  the characteristics of the combi-
nation.  Unfortunately,  it is necessary to  perform the complete tabulation
for each possible combination of sub-watersheds in order to determine the
storage/yield characteristic for each possible reservoir application.


WATER QUALITY CRITERIA

In providing for detention of water for any purpose,  reasonable care must
be taken to  prevent degradation of the water in storage.  In the application
under study, possibilities exist for degradation as a result of decomposition
of suspended or floating organic materials,  flushing of previously settled
solids into downstream flows, growth of algae in the case o.f open storage
facilities,  and the creation of nuisance conditions due to breeding of flies
and mosquitoes from aquatic  larvae.  Fortunately, most organic materials
found in storm water are not  readily putrescible and may be retained for
a reasonable period before appreciable decomposition occurs.   Periodic
removal of accumulated materials is normally sufficient to avoid difficulty
from this source, as well as  minimizing the possibility of flushing settled
material downstream.  Design criteria can be developed to minimize spills,
further reducing the occurrence of this problem.  Algal blooms can be con-
trolled by chemical  treatment and by the maintenance of a relatively high
throughput as a proportion of average contents,  which will serve to mini-
mize the growth of insect larvae as well.  Provision must be made  for
sufficient attention to the condition of the reservoir, such as daily inspec-
tions, to preclude the formation of a quality degradation condition,

It would be  desirable to exclude trash from the storage facility by the
installation of a mechanical trash screen at the  storm water inlet.  Such an
installation, however, would  be prone to accumulate trash and clog during
periods of high flow,  thus causing overflows and possible flood damage.'

* 0. 1694 cfs-day = '[(100 - 98)15, 000/646, 316  x 100] 365
                                 78

-------
  4. 0'
  3.0
O
c
o

-------
    3.0
                       Sub-Watershed #16
                                                              28, 140 Gal/Day
                                                              25,000 Gal/Day
ra
fi
O
i — i
i — i
nl
o
 o
 rt
 a
 aj
 O
 n!
 S-i
 O
 T3
 (U
 CT*
 0)
     2.0
      1.0
                I     I     I     I
I  /   I/
                                   50

                               Reliability (%]
                                                               20,000 Gal/Day
                                                               15,000 Gal/Day






                                                               10,000 Gal/Day




                                                                 5,000 Gal/Day
                    100
              Figure 24.  Storage/Reliability Relationship vs.
                           Average Daily Demand
                                       80

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For purposes of the system study, therefore,  it was assumed that trash
would be allowed to enter the storage facility for later manual  removal.
The outlet from this facility,  which would operate at flows much below
storm flow rates, could be screened to exclude trash from the treatment
works and downstream areas without  creating appreciable maintenance
problems.

An important aspect of water quality control along a natural watercourse
is the protection of downstream uses  through maintenance of minimum
flows.   In the case of  Wilde Lake, it was considered desirable to protect
existing stream bed ecology as well as maintain evaporation losses  in
Wilde Lake along with the release requirement imposed on the Wilde
Lake dam by the Maryland Department of Water Resources.  These fac-
tors will be taken into account in  the development of operating  criteria
in a later section.
SEDIMENTATION

The operation of the storage facility as a sedimentation basin is of inter-
est in sizing the facility. Large quantities of suspended solids must be
removed from storm water in order to meet the minimum water quality
standards described in Section V.  In order to accomplish this objective,
a reservoir may be operated as a combination storage and sedimentation
facility, or a storage facility may be followed by a separate  sedimenta-
tion device.   Sedimentation will occur whenever the velocity of the storm
flow is reduced by directing it into a structure or basin of large cross
section, compared to the stream channel.  Since the storage reservoir
will function as a sedimentation basin  regardless of its design criteria,
the first approach was to analyze the effectiveness of this type of  sedi-
mentation device.

The unhindered settling velocity of free and discrete particles suspended
in a liquid has been given (42) as:

                     Ps " P  V
      vs
where Cj^ is the Newtonian drag coefficient,  a function of particle geom-
etry, fluid characteristics,  and Reynolds number,  and where:

      V     =     particle volume

      A     =     projected area of the particle
       L*

      g     -     acceleration of gravity

      p     =     mass density of the particle

      p     =     mass density of the fluid
                                  81

-------
If a velocity, vo,is defined for a specific ideal sedimentation chamber in
the following terms:
                 Q                                              (23)
      vo    =     A

where:

      Q     =     overflow rate

      A     =     surface area of chamber

then it can be shown that:

      when  v  >v , the particle settles; and
            so
      when  v  0) solids in  significant quantities.  Hazen has calculated
the  settling velocity of various particles representative of  those found in
storm water as shown in Table 17.

               TABLE 17.   SETTLING VELOCITIES OF
               SELECTED  PARTICLES, AFTER HAZEN
               	(Ref. 48, p. 1474)	
                           Particle Diameter          Settling Rate
 Kind of Material          	(uj	            (cm/sec)

 Coarse sand                    1000                  10. 0

 Coarse sand                     200                   2. 1

 Fine sand                       100                   0. 8

 Fine sand                        60                   0.38
                                  82

-------
             . , TABLE  17.  SETTLING VELOCITIES'OF
              SELECTED PARTICLES, AFTER HAZEN
              	(Ref. 48,  p.  1474) (Continued)

                           Particle Diameter       Settling Rate
Kind of Material           	(y_)	         (cm/sec)

Fine sand                        40                  0. 21

Silt                               10                  0.015

Coarse clay                       1                  0.00015

Fine clay                         0.1,            0.0000015

Since the distribution of particle sizes is not known,  a  conservative
approach to sedimentation facility design is indicated.  Hydrologic investi-
gations reported in Section IV estimated the mean runoff rate from  sub-
watershed number 14 at approximately 29. 5 gallons per minute (gpm).  A-
range  of  mean overflow rates might be considered in design of the sedi-
mentation facility, but obviously none  can be less than  the mean runoff
rate.  Since reducing the  overflow rate tends  to reduce th'e area require-
ment for;  a given settling velocity (Equation 22),  Table  18 represents the
minimum areas where settlement can be achieved under ideal conditions
for the particles indicated.

TABLE 18.  MINIMUM SEDIMENTATION BASIN AREA REQUIREMENTS
    FOR  SELECTED PARTICLES. SUB-WATERSHED  NUMBER 14

                        Particle  Diameter    Minimum Area Requirement
Kind of Material        	(u)                   (square feet)	

Coarse sand                1000               ,             0.20

Fine sand                    100                            2. 50

Silt                    ',      10                          133.56

Coarse clay                     1                       13, 356

Fine clay                       0. 1                  1, 335, 600

In practice, the area requirements would be considerably larger since
the overflow rate would have to be greater and flow and velocity distri-
butions would be greatly different than the ideal conditions.

As a result of, this evaluation,  it was concluded that storage basins of the
 sizes  that would be feasible in most locations would .not alone produce
                                  83

-------
the desired water quality.  Although the  basins would serve to remove
most of the larger size materials, the unfavorable velocity gradients that
would exist during storm events would disturb the sedimentation process.
This  would cause  the carryover of the  smaller  particles.  For this reason,
it was determined that supplemental treatment  would be  required to re-
move the small particles.  However,  the storage pond would still provide
for the removal of a large  portion of the  solids and would reduce the
sediment handling requirements of the supplemental treatment devices.


PRETREATMENT UNIT

Alternatives to the use of conventional sedimentation basins include the
use of specialized sedimentation devices  offering high effective-to-total
surface area ratios, the application of chemical coagulants and coagulant
aids to agglomerate  small or light particles, and combinations of these
techniques.  Examination of  settling requirements for particles below
1. 0 micron in diameter led to selection of a combination approach - the
use of an advanced sedimentation  technique with chemical coagulants
and/or coagulant aids.  This  facility, combined with  chlorination of settled
water, is referred to in  later sections as the "Pretreatment" process.
All runoff captured by the  storage facility is subjected to this process,
whether  for subsequent final treatment or discharge  to the stream.

Costs for the pretreatment phase  were based on the  use  of a tube settler
as marketed by Neptune-Microfloc, Inc. , and described by Hansen and
Gulp  (46).   This device employs a series of small diameter plastic tubes
inclined  upward  approximately 60 degrees from the horizontal.   The
flocculated water  is  permitted to pass upward through the tubes at con-
trolled flow rates, typically between 3. 0  and 5. 0 gpm/square foot  of cross
sectional area.  Figure 25 illustrates the principle of operation of the tube
settler.  Water moving up  the tube at  velocity Vf contains particles having
a settling velocity vg.  The resultant velocity,  vr, tends to move the  parti-
cles toward the tube wall,  where they become trapped in a layer of parti-
cles previously removed.  A two-inch diameter tube  four feet in  length can
be operated at flow velocities as high  as  2. 84 gpm/square  foot tube area
and still permit a 10 micron  silt particle to move completely across the
tube.  The corresponding loading  on a conventional sedimentation basin is
0. 015 cm/second or 0. 221 gpm  overflow  rate per square foot of  surface
area  (Equation  22) (see Table 17).  This  comparison is based on ideal condi-
tions  and does not take into account hindered settling conditions caused by
the  concentration of  particles as they near  the sludge collection zone.  In
the  case  of plain sedimentation, basins are commonly maintained at a
minimum depth of five to eight feet to allow sufficient space above the
sludge storage  zone for hindered settling to occur in a low velocity bound-
ary zone between the top layer,  where flow is close  to average overflow
rate,  and the static bottom layer.   In the case of the tube settler,  the
steep inclination of the tubes causes the sludge  to counterflow along the
side of the tube as it accumulates, falling into  a sump below the tube
assembly.   The tube settler configuration also  requires  influent  and
                                  84

-------
        Vector Relationships for Particle in Tube, Settler
              Typical Operation of the Tube Settler
Figure 25.  Tube Settler - Principles of Operation
                         85

-------
effluent plenums to distribute the flow to the tubes and to collect it after
clarification  Figure 26 shows a comparison of the  volume of typical
sedimentation facilities designed to remove 10-micron silt particles at
various overflow rates.  The tube settler volumes include provisions
for influent flume,  influent plenum, sludge storage sump,  and effluent
plenum,  while the conventional sedimentation volumes are based on an
average  depth of 5. 0 feet to provide for sludge collection and storage.
Inside  partitions and supporting structures are included, but outside walls
are not.

Other sedimentation devices, such as tray settlers,  were investigated.
Performance characteristics fell between conventional sedimentation
and the tube settler, but sediment removal and maintenance  problems
were more severe than either of the two  techniques compared above.
PHYSICAL AND AESTHETIC  CONSIDERATIONS

Inherent in the concept of the  Local Storage,  Treatment,  and Reuse of
Storm Water- system is the close proximity of the system elements to the
properties which benefit from the system.  In addition to engineering
and economic considerations then, it is essential that the physical appear-
ance of the facilities be consistent with the immediate environment.  In
the case of Columbia,  the storage and pretreatment units must be,located
in the floodplains  to permit gravity flow through the units.  In general,
the floodplains of the  Wilde Lake watershed have been dedicatedto public
use as open space. They are typically lightly forested with  some  shrub-
bery and underbrush and are bounded on  all sides by residential land uses.
Any construction within these areas must be particularly unobtrusive in
order to achieve acceptability within the  community.   The pretreatment
units  and constructed storage can be placedbelow grade and any necessary
superstructure, i.e.,  hatchways, vents, etc. , can be dis,guised with shrub-
bery, fences, etc.  In the case of open pond storage, the design of the pond
must  insure that its appearance under all conditions of operation will be one
of an  attractive, natural pond. All construction must be confined to an area
which will permit at least a fringe of trees along the perimeter, thus avoid-
ing a  conspicuous  discontinuity in the open space.   Subsequent cost esti-
mates of constructed  storage  and pretreatment units are  based on their
installation entirely below grade, while open  pond estimates provide for
design features to insure  their acceptability.


SIZING STORAGE FOR MULTIPLE PURPOSES

Earlier paragraphs described methods for determining required storage
capacities for various conditions of water demand.   It was found that for
a given  demand with a known proportion of lawn sprinkling  uses,   the
storage requirement is a  function of the reliability of the  system  or,
stated differently, a function of the  quantity of water drawn  from  the
existing public water  supply system in  times  of dry  weather.   Water
quality considerations were found to affect operation policy more than
                                 86

-------
   1000
4)
O
•r-l

•§
O
T3
0)
fn
•iH
3
cr
0)
    100
     10
               Plain Sedimentation
                                           Tube Settler
I  I  I  I I  I
                         I   I  I  I  I I
                                    10
                                   100
                          Overflow Rate (gallons/minute)
        Figure 26.  Required Volume vs.  Overflow Rate for.
     Removal of 10-Micron Silt Particle Under Ideal Conditions
                               87

-------
design size,  since meeting the standards by sedimentation in the reser-
voir was found to be impractical.  The application of the pretreatment
step following storage does, however,  impose  a different type of yield
requirement on the storage facility,  in that it must be provided with a
constant flow for proper operation, although that flow need not be con-
tinuous.   Physical and aesthetic considerations were examined and found
to apply primarily to design criteria other than size, except that avail-
able land  may limit the maximum attainable storage in a particular
location.

Since the  operation of the pretreatment unit appears to place  a definable
size requirement on the reservoir, that requirement will be evaluated
first, then reviewed in the light of other requirements.   Based upon pre-
vious discussions, the following assumptions are made with respect to
the operation of the storage facility as a supply to the pretreatment unit:

1.    The reservoir will be operated on a fill-and-draw basis,
      storage capacity calculated as the difference between
      minimum and maximum pools.

2.    The highest proportion of total runoff feasible  must be
      actually intercepted by the reservoir and subjected to
      pretreatment.

3.    When outflow to the pretreatment unit occurs,  it must
      be at a constant controlled rate.

4.    Outflow need not occur at all times, e.g., intermittent
      operation of the pretreatment unit is permissible.

The proportion of the total runoff which is captured by the storage facility
is a function of the volume of individual storms and the probability of
available  storage coincident with the occurrence of each  storm.   Since
the reservoir is on a fill-and-draw cycle, the probability of available
storage is a  function  of both the maximum storage capacity and the draw
rate, or the  rate of operation of the pretreatment unit.  The analysis of
reservoir performance will be in terms of recurrence  intervals of storms
and it will be initially assumed that storage is  available to capture the
entire volume of some design storm.  When storms  of larger volume or
longer return interval occur, the excess  quantity will be spilled,  by-
passing the pretreatment unit.  Figure 27 shows rainfall-intensity-
duration curves for storms of various recurrence intervals in Howard
County, Maryland.  From  the definition of recurrence interval,  the fol-
lowing identity exists:
      E(n)   =                                                      (24)
where:
      E(n)   -     expected number of storms meeting or exceeding
                 conditions for a return interval T (years) occurring
                 during period P (years)
                                  88

-------
co
CO
                                                       25 year return interval
                                                       20 year return interval
                                                       10 year return interval
                                                        5 year return interval
                                                        1 year return interval
                                                      50     60     70      80
                                                       Rainfall Duration (minutes)
100
110
120
                               Figure 27.  Rainfall Intensity-Frequency-Duration Curves,
                                             Howard County,  Maryland

-------
 Rainfall-intensity-duration curves can be used to generate runoff-
 intensity-duration curves for specific watersheds, using the methodology
 outlined in Section IV. By application of probability and expectation the-
 ory to these  curves,  the quantity of runoff occurring in excess of the
 storm volume corresponding to any selected return interval  may be cal-
 culated.  Table 19 lists the results of one such analysis!

         TABLE 19.   EXPECTED QUANTITY OF RUNOFF IN
              EXCESS OF SELECTED STORM VOLUMES

          (Imperviousness - 0. 30,  m = (lag time) = 4 minutes)

               (Total annual runoff = 220, 307  gallons/acre)

         Base Storm           Expected
       Return Interval       Excess Runoff              Excess
          (years)           (gallons/acre)                (%)  '

             1                  16,160                   7.34
             5                   5,050                   2.29

            10                   3,066                   1.39
            20                   1,857                   0.84
            25                   1,584                   0.74

            50                     962                   0.44

           100                     579                   0.26


 Based on the most conservative calculation of  storm volumes and on
 intensity-frequency-duration curves calculated to be conservative with
 respect to long-term  records,  a one-year storm volume storage capa-
 bility can be expected to capture at least  92. 66 percent (100 - 7. 34) of
 the total runoff in a year.  This value is dependent, however, on the
 availability of maximum storage at the beginning of each storm, a func-
 tion of the release rate of the reservoir.

 The release rate can  be as low as the annual mean daily runoff rate orq
 When this rate  is assumed with a storage capacity equal to the volume of
 a one-year storm, analysis of the five-year synthetic hydrograph for sub-
 watershed number 6 reveals that an additional  3. 01 percent of the runoff
 can be expected to spill as a result of the occurrence of storms whose  >
 volumes, although less than  the one-year storm,  exceed available storage,
 When the release rate is increased to 2.0q, the additional percentage  of
 spill falls to  1.42 percent.  Figures 28 and 29  show the  approximate re-
lationships between various releases  or pretreatment rates and spill per-
 centages for  a range of storage capacities.  It  can be seen from these
figures that a release rate of approximately 1. 7q in combination with  a
                                 90

-------
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                  CD
                  S-,
                  cd
                  0)
                  o
                  4-J
                  GO


                  0)

                  g
                  0)
                  M
                  rt
                  ^
                  O
                     50.0
                     25. 0

                     20.0
                     10.0
                      5.0
2.0






1.0



0.7


0. 5
                      0. 2
                      0. 1
                          1.0
                             2.0                       3.0
                     Pretreatment Rate (x Mean Annual Daily Runoff)
                                                                                                           2%
                                                                                                          3%
                                                                                                      4. 0
                                           Figure 28.   Storage/Pretreatment Rate
                                             Combinations vs.  Spill Percentages

-------
                         14
                         13
                                                                                                                      0. 5 yr
                         12
CD

to
                    o
                    a
                    a
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11





10





 9
                            1.0
                                                                        _L
                                2.0                           3.0

                        Pretreatment Rate (x Mean Annual Daily Runoff)
                                                                                                                       0.7 yr
                                                                                              2.0 yr
                                                                                                                       5.0 yr
                                                                                                                   4.0
CQ
0)

a
3
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O
                                                                                              !-°yr   ^

                                                                                                       6
                                                                                                        O)

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-------
storage facility having a capacity equal to the volume of a one-year storm
will result in approximately nine  percent of the runoff being spilled with-
out treatment:  The remaining 91 percent will pass through the pretreat-
ment unit at a controlled rate.  Lowering pretreatment rate to approxi-
mately 1. Iq increases the spill to 10 percent and greatly reduces storage
requirements following the pretreatment unit where reuse is being
practiced;

It is  important to note that the water which does spill from the storage
facility does  so after passing through the storage structure where it has
been detained for sufficient time to settle the larger and heavier solids.
In view of the high  quality of the balance of the water after pretreatment
and the very  infrequent nature of the spills,  it was felt that restricting
spills to 10 percent of total runoff was a realistic  limit on the design and
operation of the storage/pretreatment system.  It would appear then, that
a reservoir sized at the one-year storm volume operated in conjunction
with a  pretreatment unit controlled at a release rate somewhat greater
than the mean runoff rate  would process storm water within the water
quality requirements of the system. A tradeoff obviously exists between
spill volume  and design criteria.   Furthermore, a system having a given
Spill performance consists of a series of complex tradeoffs between storage
capacity,  release rate, and intermediate storage following pretreatment.
Analysis of any of these tradeoffs,  however, would require a quantitative
estimate of the value of various levels of water quality,  a task outside
the scope of this  study.  Inherent in the study, however,  is a method for
inputing a value for water pollution control due to  the study of the appli-
cation  of conventional methods of pollution control to the same watershed,
reported in Section XVI.   Both studies were  directed to  the same water
quality requirement, and the 10 percent  maximum spill requirement was
made of both systems. The method employed to estimate spills  was also
common to both studies.

Having'determined the storage requirement for effective water pollution
control,  this requirement must be weighed against other reservoir pur-
poses.  Figure 30 shows the storage/yield characteristics of sub-watershed
number 16 plotted against the storage equivalent to the one-year  storm
volume.   It can be  seen that the maximum long-term demand of  25, 327
gallons/day (mean  runoff less 10  percent spill) can be sustained  at the
80 percent reliability level.  Similar relationships were found for each
of the other sub-watersheds indicating that the water quality requirements
on reservoir size result in a satisfactory reservoir from  the water supply
standpoint.  The  only other requirements found on reservoir size were
those related to available  land area and aesthetic considerations.  Since
these can only be determined by examination of a particular site with a
particular size and  construction type of proposed reservoir in mind, they
were not considered until  after the  systems analysis effort was complete
and conceptual designs were being produced from the results of the
analysis/  Sections  X and XII.
                                   93

-------
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 K
     3.0
2.0
     1.0
              One Year Storm Volume

                 = 782, 000 Gallons
                              _L
                                   _L
                                   50

                             Reliability (%)
                                                               28, 140 Gal/Day
                                                               25, 000 Gal/Day
                                                          20,000 Gal/Day
                                                                15,000 Gal/Day





                                                                10, 000 Gal/Day



                                                                 5, 000 Gal/Day
                                                        100
Figure 30.  Storage/Reliability Characteristics  vs.
             Yield,  Sub-Watershed No. 16
                          94

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As a result of .'a comparison of the various influences on reservoir and
pretreatment unit design, the following criteria have been selected as
adequate to protect all uses under consideration:
             i
1.    Net storage capacity of the  reservoir shall be equal to the
      maximum volume for the  sub-watershed or combination of
      sub-watersheds of a storm  just meeting the one-year
      return interval intensity.

2.    Release 'from the reservoir into the pretreatment unit will
      be controlled at a rate between 1. 2 and 2. 0 times the annual
      mean runoff rate.

3.    The pretreatment unit will be capable of operating at  2. 0
      times the annual mean runoff rate.

4.    No storage need be provided following pretreatment.

With respect to Criterion 2 above, it  is noted that no discussion has been
devoted to the effect of base flow  on  these criteria.  Due to the use of
the natural floodplains  as collecting storm drains, it is likely that a
significant amount of relatively constant flow will occur as  a result of
springs and seepage from the ground.  This quantity  is in excess  of the
volumes of runoff described in the analysis, although there is no ready
way of predicting its  quantity.  Due to the steady nature of the flow, it
places no  particular requirement on storage, but will increase the
required release rate and pretreatment  rate by  an amount equal to its
flow rate.  It is considered that in an area such as  Columbia, the  base
flow would probably not be more than 30 percent of the  mean rundff rate
from  storm water.  Hence the requirement of 2. 0 times the mean runoff
rate for pretreatment design.


CONSTRUCTION, OPERATION, AND MAINTENANCE COSTS

In addition to the design  criteriafor  storm water storage and pretreatment
facilities discussed above,  it was also necessary to develop information on
the cost of constructing,  operating, and maintaining these facilities. These
data were developed parametrically  in order to permit them to be used in the
computerized system model.  Estimates were made of  the costs of storage
and pretreatment facilities  and  of various capacities.  These data were
then plotted as  smooth curves.  The curves were then replaced by a series
of linear approximations  between the major infliction points. Tables were
then prepared as inputs to the computer program so that cost data for any
capacity system could be selected by linear interpolation between points
from  the tables.  A further discussion of this technique and the development
of the cost data used  in the  study  are included in Appendix C. It is noted
that these estimates are based on equipment and construction prices
existing in the  1967-1968 time frame.
                                 95

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SEDIMENT REMOVAL

This study was based on a system of reservoirs operating in an estab-
lished development which has restabilized.  Accordingly, the sediment
yields would not be excessive.  For this reason,  it was assumed that
a majority of the solids would be removed from the pretreatment units
and could be accomplished by pumping to tank trucks for transport and
disposal.  Periodically,  sediment removal from the storage ponds would
be required; however,  the cost on a per  gallon of runoff basis would be
approximately the same as the pretreatment unit cleaning.  The costs
for storage basin and pretreatment unit cleaning would be considerably
higher if the area was still under development or was undergoing con-
tinuing erosion due to the increased flows resulting from urbanization.
The methods for maintaining storage ponds  under these conditions  are
being considered as part of the  demonstration program discussed in
Section XIX.
                               96

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                            SECTION VIII

                      TREATMENT METHODS
Section VI described the wide range of pollutants and pollutant concen-
trations found in storm water by other investigators.   The  literature
searches reported in Sections V and VI failed to locate reports of success-
ful treatment of storm water immediately after collection from small
watersheds.  In the absence of a comprehensive storm water sampling
and analysis program in the Columbia area, it must be assumed that
storm  water pollutants  will be similar in number and concentration to
those found in runoff from comparable areas.   Table 10 in Section VI
listed the pollutants whose presence is assumed and indicated the expected
range of concentration of each.   Specification of unit processes intended
to achieve a given level of treatment must necessarily be conservative,
due to  the lack of reported field experience with similar problems.  The
use of  systems normally used for treating water from conventional sur-
face water impoundments was not considered directly applicable because
of the random nature of certain pollutants and the small capacity of the
individual treatment unit.

Section V described the four levels  of treated water quality tobe considered
in the systems analysis.  Various unit processes have been examined for
each level, with attention to the maximum pollutant concentrations expected
as well as the ability of the process to withstand severe shockloads. Table
20 lists the processes selected,  indicating the treatment levels for which
each is used.   Figure 31 is a flow sheet showing the processes associated
with each class of treatment.

Algae control is applicable only to those cases where storm water will be
stored in an open facility.  The term is  intended to include all treatment
steps necessary to prevent degradation of the stored water or the creation
of a nuisance condition. Under some  conditions,  this might include steps
to prevent mosquito or  other insect breeding as well as the control of
aquatic growths.   Further discussion  of these considerations can be found
in Appendix C. After thorough analysis of the actual water to be treated,
several of the processes listed might  become unnecessary.  Examples
are pH adjustment and  softening.  Limited sampling conducted  to date
indicates that total hardness is low  under base flow conditions and lower
yet during storm flows, while pH varies between 6. 3 and 8. 3, depending
on flow.  Further sampling might indicate a need for some chemical
adjustment of these parameters, however.

Descriptions of the systems that were assumed for treating the collected
storm  water as a function  of quality and reuse classification are described
in the following paragraphs.
                                  97

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                                          pH Adjustment
                                                          Chlorine
                                                                                 Coagulant
               Algae Control
          Effective Runoff
                                       Coagulant
Yield
Spills
CD
CO
          STORM WATER STORAGE
          •Algae Control* (all classes)
                                                   x
                                                 Sediment
                                                 Removal
                                                                           Air
                                Net Yield
Class "C" Water
to Surface Drainage
       PRETREATMENT
       *Flocculation (all classes)
       * Sedimentation (all classes)
       *pH Adjustment (all classes)
       •Chlorination (C)
                                                   Chlorine
                               Product
                                Water
                                                                                     Precoat
                                                       Filter Wash
                                                       or Strainer
                                                       Backwash
                                          FINAL TREATMENT
                                           •Straining (B)
                                           • Softening* (AA, A)
                                           •Flocculation*  (AA, A, B)
                                           •Filtration (AA, A)
                                           •Carbon Adsorption (AA)
                                           •Chlorination (AA, A, B)
                                           •Aeration (AA, A)
          *If required
                                          Figure SI.  Treatment Systems

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                             TABLE 20.  PROPOSED TREATMENT PROCESSES


                     Unit Process Type                                 Water Use Category
             Raw Water Storage with Algae Control

             Aeration

             Sedimentation

             Flocculation

             Straining (with pre-coat)
CD
<£>             Sand Filtration
              pH Adjustment

              Softening

              Chlorination

              Carbon Adsorption


                     *IP required
A-A
X
X
X
X
^
X
X
X
X
X
A
X
X
X
X
fr
X
X
X
X

B
X

X
X*
X

X

X

c
X

X
X*


X

X


-------
 TREATMENT TO CLASS "C" QUALITY

 Class "C" treatment consists of mechanical trash screening, raw water
 storage with algae control, sedimentation, pH adjustment, andchlorination.
 Trash is  excluded from the storm water collection system to a degree by
•the inlet design, which incorporates gratings  and restricted openings.
 Smaller objects can enter the system, however, and parts of the subsequent
 collection system are open channels and natural watercourses, permitting
 further ingress of trash.  Due to the difficulty of preventing a stoppage at
 the entrance to a  storage facility,  it is anticipated that no screening be
 provided  at that point.  This  choice would depend on the difficulty of re-
 moving large objects from the storage basin itself.  The point of with-
 drawal from the storage facility would then be screened to exclude trash
 from subsequent treatment processes.  Since this screen would not be re-
 quired to operate at storm flows,  routine maintenance,  as discussed in
 Appendix C, should permit satisfactory operation without the installation
 of mechanical cleaning devices.

 Raw water storage might consist of any type of structure or basin, the only
 requirement being that its maximum elevation be at or below inlet eleva-
 tion.   This will permit storm flows to enter by gravity without  adversely
 affecting  the hydraulics of the storm water  collection  system.  The possi-
 bility of pumping  storm water at storm flow rates was excluded from the
 analysis for reasons of reliability. All available equipment designed for
 such  intermittent, high rate service is electric motor driven.  The corre-
 lation between electric power outages and severe thunderstorms is con-
 sidered relatively high in an  area  of this type and such a joint occurrence
 would result in spills of large quantities of  untreated  storm water.  Even
 though the facility could be designated to avoid flood damage  from such an
 occurrence, the overall reliability was considered inconsistent with the
 water quality objectives of the study.

 The decision to employ a specialized  sedimentation device,  or  pretreat-
 ment unit, effectively eliminated sedimentation considerations  from the
 design of the storm water storage facility.  The criteria which were
 employed in sizing this facility are described in detail in Section VII.
 The storm water  storage facility precedes the pretreatment unit and
 coagulants are introduced as the water is withdrawn from storage.  The
 pretreatment unit is used as  a point of application for pH adjustment
 chemicals, if required, and chlorine.   Effluent from this combined oper-
 ation is directed to  the Class "C"  water uses or allowed to overflow to
 the natural watercourse.


 TREATMENT TO CLASS "B" QUALITY

 Class "B" treatment consists of all the unit operations of Class "C, "
 namely storm water storage  with algae control (if necessary) and pretreat-
 ment, followed by a straining operation. This operation is the Microstrain-
 mg process of the Glenville  Kennedy Division of Crane Company, or equiv-
 alent.  It consists of a  fine mesh screen which is coated with an expendable
                                  100

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filter media, or precoat, so that effective removal of all particles  10
microns and larger can be achieved.  Additional chlorine is added after
this process in order to maintain an adequate residual throughout .the
distribution system.  Following straining,  the effluent is' available for
Class "B" or "c" water uses.  Excess water  will be permitted to over-
flow after the pretreatment process before entering the straining equip-
ment.  In this manner,  distributed water will be at least Class   B,  '
while excess water will be at least Class "C. "
TREATMENT TO CLASS "A  QUALITY

Class "A" treatment consists of the unit  operations of Class "C, " storm
water storage with algae control (if necessary) and pretreatment, fol-
lowed by aeration,  additional chemical coagulation,  and mixed media
filtration.  Chemical additions  and filter designs will be selected to en-
sure clarification of the effluent to 1. 0 Jackson Turbidity Unit or better.
This effluent, after rechlorination,  will be distributed to Class "A, "
"B, " or "C" uses.   Excess water will be permitted to overflow after the
pretreatment unit.

TREATMENT TO CLASS "AA" QUALITY

The  treatment processes for  Class  "A" and Class "AA" are identical
with the single addition of activated carbon adsorption in Class  "AA"
applications.  This process removes tastes and odors as well as pro-
viding  a buffer against occasional excessive concentrations of adsorbable
organics and other dissolved  materials.  An activated carbon column
utilizing a replaceable charge would be employed.  The  carbon  charge
would be periodically removed  and disposed of or regenerated at a cen-
tral  facility.  The capacity of the carbon column would be set at a value
substantially in excess of anticipated requirements,  in the interest of
long life and security.  Rechlorination would be practiced following the
carbon treatment.  As before,  excess water will overflow after the pre-
treatment step.


TREATMENT SYSTEM COSTS

For  each type of treatment described above, estimates were made of
the equipment, facility,  operating,  and maintenance costs.  These data
were prepared parametrically using the same techniques used for the
storm water storage facility and operating costs.  The basis for the
estimates of the treatment system costs  and the input data used in the
system analysis program are contained in Appendix D.


SUMMARY

The  foregoing paragraphs do  not represent suggested design for every
circumstance.   Actual configurations should be determined after suit-
able investigation of the characteristics and variations in the  quality of
                                 101

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the storm water actually available.  The processes described are only
intended to be representative of adequate treatment under most local
conditions and may well constitute over-design in many applications.
Due to the supplemental nature of the water supply being evaluated, fail-
safe controls can be employed to shut down the treatment facility in the
event of malfunction without loss of supply to the connected demand.  In
this manner, considerable redundancy commonly a part of municipal
water plant design can be eliminated and small package-type treatment
units of low cost might be profitably employed. For purposes of the
system analysis,  however, no innovations have been considered.   Every
process discussed above has known performance characteristics consis-
tent with the most difficult expected requirements.
                                102

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                             SECTION IX

                   REUSE DISTRIBUTION  SYSTEMS
The'distribution system for''storm water reuse is comprised of all the
pipes, valves,  meters,  and appurtenances required to conduct the water
from tHe point  of treated water storage to the point of ultimate use.  It
includes' connections to the existing public  water system for'makeup
water with anti-b'ackflow provisions  at the 'interface between the''two
systems.

Pipe  sizes throughout the distribution system have been selected for the
estimated peak flows as well as reasonable ease of maintenance.  Fire
flows have not  been assumed, since the  public system will retain that
function,  consistent with the discussion in  Section V.  No pipes smaller
than  two inches have been assumed  and the largest pipe diameters  are
six inches.  Where  a sub-potable distribution system serves a property,
double meter vaults have been assumed with meters  on both potable and
sub-potable systems. Costs for sub-potable distribution systems within
buildings include the additional costs of dual risers,  extra fittings,  etc.,
but do not include fixture costs.  Sub-potable distribution  systems have
been  designed for each of the distribution service areas described in
Section V and laid out in such a  way  that any combination of continuous
systems can be interconnected by simply operating valves (see  Figure 32).
This permits the evaluation of systems for various combinations of sub-
watersheds without  changing distribution costs,  as well as providing for
continued operation in the event of temporary failure of one  system.

The transmission main from the treatment  plant to the distribution  piping
has been calculated as a function of plant location only. The cost includes
the public water system connection,  which includes provisions for providing
makeup water to sub-potable systems without the possibility of backflow
into the public  system.  This might be accomplished by introducing public
water into  an open tank through  a float-controlled valve located above the
overflow, or,  local regulations  permitting,  by one of several types  of
backflow preventer valves. In the case of potable reuse systems, the public
connection is the point of injection into  the public potable water distribution
system. Some  type of backflow preventing  device might be employed here
to isolate sections of the distribution  system, depending on local conditions.


CLASS  "C" AND "B&C" USES

When treated storm water is to be used to flush toilets only or to sprinkle
lawns and flush toilets,  a relatively  simple  dual  distribution system is
required.  In addition to  a sub-potable distribution piping in the streets,
dual service connections and meters are required at  each home, along
with dual headers on the  individual plumbing. Connections from the sub-
potable  system  are made to the  outside  hose bibs for sprinkling use and
to toilet fixtures throughout the building.
                                 103

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\
                           RECYCLE  DISTRIBUTION   SYSTEM
                                                                   WILDE LAKE
                                                                 . WATERSHED
                                                                 '/ DISTRIBUTION
                                                                   SYSTEM
                                                                   POTENTIAL
                                                                   TREATMENT SITE
               /^^\  '-	

           /^  \  '
           MIDDLE PATUXENT •*• \—^-LITTLE PATUXENT
     Figure 32.  Distribution System Map -  Wilde Lake Watershed

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CLASS "B" USES

Reuse of treated storm water exclusively for lawn sprinkling requires
a sub-potable distribution system and dual service connections, but
minimizes the cost of plumbing alterations in each building.  The sub-
potable system is  confined to the basement or ground level and is
connected to  outside hose bibs only.


CLASS "A",  "A&B",  "A&C", AND "A, B, &C" USES

These use combinations also require a sub-potable distribution system
with dual service connections to each building.   The sub-potable plumbing
within the building, however, must be provided to each plumbing fixture
except kitchen and bathroom sinks. In many homes,  and particularly in
apartment buildings,  this will require virtual duplication of the entire
cold water system.  It is assumed that the hot  water system could be
split in multifamily units and perhaps in single family residences.


CLASS "AA,  A, B, & C" USES

When storm water is treated to potable water quality,  the distribution
system is greatly  simplified.  The transmission line is provided from
the treatment plant to the existing public water supply main where a
metered connection is provided.  The existing  public system is then
permitted to  distribute the potable water to all water uses within the
service area.  It was  anticipated that the service areas might be divided
by check valves or division valves, but in practice this would probably
not be desirable and the output of the treatment plant would supplement
the supply throughout the system.
CONSTRUCTION COSTS

All costs for the distribution systems were estimated on the assumption
that the necessary piping and plumbing would  be installed following
construction of the streets and buildings,  and that no particular economies
would be realized from concurrent construction with conventional facil-
ities.  Underground pipelines have been assumed to be cast iron and
buried with a minimum of four feet of cover, with conventional valves
and fittings.  Individual building connections and plumbing alterations
have been priced on a per unit basis.  The in-place  cost of cast iron
pipe was taken at $7. 50 per foot of six-inch pipe and $4. 75 per foot  of
two-inch pipe.  Table  21 lists the estimating figures used for building
service connections and for interior plumbing.  All  figures include
materials, labor,  overhead,  engineering,and construction contingencies
and are 1967-68 prices.   These prices are applicable to sub-potable
distribution systems only and include  provision for identification of
pipes and valves by  color coding, tagging,  etc.
                                  105

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                                 TABLE 21.  CONSTRUCTION COSTS FOR SERVICE
                       CONNECTIONS AND INTERNAL PLUMBING FOR SUB-POTABLE REUSE
o
en
         Type of Occupancy

         Single family residential,
           medium density

         Single family residential,
           low density

         Town houses

         Garden apartments
         Mid-rise apartments

         Schools,  500 pupils

         Commercial uses
  "C",  "B&C"


   $300/unit


   $300/unit

   $300/unit

$1000/20 units
or fraction plus
$65/unit

    $80/unit

$1000/building
   $200/unit


   $200/unit

   $200/unit

$1000/20 units
or fraction
$1000/building
 "A", "A&B",
   "A&C",
 "A, B, & C"


   $3 40/unit


   $3 40/unit

   $340/unit

$1000/20  units
or fraction plus
$100/unit

   $100/unit

$1000/building
         individually estimated

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QPERATION AND MAINTENANCE COSTS

Operation and maintenance of sub-potable distribution systems is pri-
marily composed of occasional repair of distribution  mains,  the portion
of the service connections in the public right-of-way,  and routine inspec-
tion and reading of the individual meters. Only the incremental cost of
reading the,  additional meter was computed,  since it would be read  simul-
taneously with the existing potable water meter. These costs were  esti-
mated on  a yearly basis as 0. 006 times  the construction cost of the sys-
tem.  The formula employed to convert  these costs to daily costs is:

     DAGOS     =     ATOT (0.006/365)                         (25)

where;

     ATOT      -     annual total construction cost of distribution
                       system

     DACOS     =     daily total operation and maintenance cost of
                       system

The portion of the service connection which is located on private  property
and the  internal plumbing would be maintained by the  individual property
owner in the same manner as the existing conventional plumbing which it
supplements.


INPUT TO SYSTEM MODEL

The construction cost for each service area,  or sub-watershed, was
computed for each group of reuse classes as  described in the preceding
paragraphs. These values were used as input to the computer program,
permitting the selection of the proper costs for any sub-water shed  or,
by adding costs for component areas, the proper value for any combina-
tion of sub-watersheds. The costs of transmission lines from treatment
plants were computed separately for each treatment plant location.
These values are shown as Tables 22 and 23, respectively.
                                 107

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                             TABLE 22. CONSTRUCTION COST VS.  SERVICE
                                     AREA - DISTRIBUTION SYSTEM
o
oo
   Sub-
Watershed

     1
     2
     3
     4
     5
     6
     7
     8
     9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
    22
Construction Cost for Reuse Level (Dollars)
"A"
17, 540
20, 990
10, 330
39, 060
45, 800
269, 920
141, 760
54, 500
151, 300
135, 650
80, 890
44, 180
54, 450
110, 820
22,460
82, 760
108, 720
31, 320
56, 360
101, 240
83, 330
33, 860
"B"
14, 600
18, 050
9, 210
27, 300
30, 120
163,400
85, 900
31, 900
136, 600
92, 250
63, 950
36, 200
41, 850
82, 000
18, 120
70, 300
78, 660
24, 840
50, 200
78, 840
50, 910
26, 020
"C"
16, 700
20, 150
10, 010
35, 700
41, 320
238, 930
125, 520
47, 720
147, 100
122, 575
76, 050
41, 900
50, 850
102, 300
21, 220
79, 200
104, 680
29,440
54, 600
93,440
72, 415
31, 620
"A", "B"
17, 540
20, 990
10, 330
39, 060
45, 800
269, 920
141, 760
54, 500
151, 300
135, 650
80, 890
44, 180
54, 450
110, 820
22,460
82, 760
108, 720
31, 320
56, 360
101, 240
83, 330
33, 860
"A" tl/-ill
17, 540
20, 990
10, 330
39, 060
45, 800
269, 920
141, 760
54, 500
151, 300
135, 650
80, 890
44, 180
54, 450
110, 820
22,460
82, 760
108, 720
31, 320
56, 360
101, 240
83, 330
33, 860
II A 11 ll-p II II fill
17, 540
20, 990
10, 330
39, 060
45, 800
269, 920
141, 760
54, 500
151, 300
135, 650
80, 890
44, 180
54, 450
110, 820
22, 460
82, 760
108, 720
31, 320
56, 360
101, 240
83, 330
33, 860
"B", "C"
16, 700
20, 150
10, 010
35, 700
41, 320
238, 930
125, 520
47, 720
147, 100
122, 575
76, 050
41, 900
50, 850
102, 300
21, 220
79, 200
104, 680
29, 440
54, 600
93, 440
72, 415
3, 162

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TABLE 23.  CONSTRUCTION COSTS VS. SERVICE
         ARE A-TRANSMISSION LINES
Treatment
Plant Location
(Sub- watershed)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Construction
Cost
(Dollars)
3000
3000
4500
2250
5550
2630
750
1800
2250
1950
3900
1500
750
1500
2400
3750
4280
2850
1730
1580
4280
1500
                        109

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                             SECTION X

                          SYSTEM MODEL


The system study of the local storage, treatment,and reuse of storm
water concept has been outlined in Section III.  The system was  defined
in Figure 1.  The objective function was stated as:

1.    Water released to surface  drainage from the Local Storage,
      Treatment,  and Reuse of Storm Water  system shall meet or
      exceed stated effluent standards.

2.    This condition will be achieved at the lowest net system
      cost, or maximum net system benefit.

Maximum net system benefit was,  in turn,  defined as:

      max/SB  - EC  - a EC.)
          \   a      a       i/
where:

      B    =     marginal annual benefits
       cL

      C    =     marginal annual operating and maintenance costs
       3.

      Op   =     marginal fixed construction and project costs

      a    =     capital recovery factor (Equation 3)

The effluent standards required by the first part of the objective function
were  developed in Section VI and shown as Table 10.  The constraints
on the objective function were identified and investigated and the results
reported in preceding sections.  All information obtained concerning these
constraints was prepared in a suitable form for input to a digital computer
code for maximization of the objective function subject to the constraints.

A review of the prior sections  indicates a large number of possible
physical systems, all of which would satisfy the stated physical,  tech-
nological, and institutional constraints.  Twenty-two sub-water sheds
were  considered,  and a local system could be placed in each of them.
In this manner,  the total watershed could be  served by twenty-two local
reuse systems,  making up the  overall  system for the watershed.  This
is only one of many ways to meet the requirements of the watershed,
however.  There are  many points in the watershed where two, three,
or more sub-watersheds can be collected at one point.  Figure 33 shows
the  flow pattern of the various  sub-water sheds  and can be used to deter-
mine feasible combinations of multiple sub-watersheds.  In these cases,
the  combined sub-watersheds are treated as a single area  and have a
single local reuse facility.  As many as eighteen sub-watersheds can be
combined into a single collection area, and four which discharge directly
                                 111

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2 	•*  3
        12 	*• 11
                                                                        19       22
                             13
                             14
16
                                           15
17
18 	».  9
                                 WILDE
                                 LAKE
                                                                      20
         6 -
                                                                         21       10
               Figure 33.  Wilde Lake Drainage Area Sub-Watershed Flow Pattern

-------
into Wilde Lake must remain independent.  An exhaustive analysis of the
flow diagram would reveal that more than 10, 000 combinations of various
sized collection areas are possible.  Fortunately, many of these are
trivial,  and others present varying degrees of  difficulty in terms  of
physically intercepting the storm flows at the required points. Close
examination of the watershed resulted in 173 workable combinations  of
service areas, each comprised of some number of sub-watersheds,
ranging from one to six.  In view of the study objective of evaluating
local storage, treatment,  and reuse of storm water,  an upper limit of
six sub-watersheds, or about 350 acres, was set for the initial attempt
at system optimization. It was planned to reconsider this decision after
the first trial,  but the results, reported below, indicated that the optimum
had been located within the range selected.

Each of the  173 overall systems  is made up of  a number of sub-systems,
namely,  the various storage units, pretreatment units, final treatment
units, treated water storage units, distribution systems,  etc., that
comprise the facilities in each collection area.  The  storm water might
be treated to any of four qualities and the distribution system might be
constructed to connect  to any of  eight  different combinations  of water
uses.  Within a given overall system,  the individual facilities might vary
from each other.  Each of these  possible sub-systems and overall systems
must have construction, operating, and maintenance  costs calculated,
adjusted to annual costs,  and subtracted from the net benefit that  would
be derived from the overall  system.   When the remainder from this
calculation is available from each of the possible systems, the optimum
system can be identified and described.  Due to the great complexity and
magnitude of the calculations required, the system optimization was
performed by a digital  computer.  The following sections describe the
preparation of inputs to the computer  program, the operation of the
program, and the  type  of outputs obtained.  The system optimization
results will be described,  and final investigation of alternatives reported.
DESIGN INPUTS
Storage Facilities

In order to insure that the systems under analysis all correspond to the
range of technologic and physical possibilities, the essential design
criteria have been determined and must be included as inputs to the
system model, prior to optimization wherever possible.  In the case of
storm  water storage, various types of storage were considered  which
might have varying applicability in different locations.  Steel and concrete
tanks,  both buried and at grade, were considered,  along with open ponds.
The system model was arranged for a  sub-optimization of storage facili-
ties, based on economic factors,  which is described later.  In the event
that local conditions prohibit  a free choice among the alternatives, the
program can be instructed to choose either open  ponds, buried tanks, or
nonburied tanks as the only possible construction method.   It can also
                                 113

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be instructed to choose only steel tanks or only concrete tanks, when
tanks are being considered.
                                I
Section VII described the anlysis performed to develop sizing criteria
for reservoirs. It was determined that the various reservoir purposes
could be  served adequately by sizing the storm water  storage facility at
the maximum expected volume of a storm just meeting the one-year
return interval criteria. The one-year storm volume  has been  calculated
for each  sub-water shed, using the results  of the hydrological analysis
reported in Section IV,  and these values are listed as  Table 24.


            TABLE  24.  EXPECTED MAXIMUM VOLUME
            	OF  ONE-YEAR STORMS	


                    One-year                             One-year
                  Storm Volume                        Storm Volume
Sub-water shed         (gal)	    Sub-water shed          (gal)      ;,

       1                460,800            12                594,200

       2                586,500            13                696,800

       3                530,000            14              1,030,000

       4                341,600            15                236,400

       5                530,500            16                782,000

       6              1,104,000            17              1,130,000

       7                803,200            18                290,000

       8                625,900            19                923,500

       9              1,460,000            20              1,203,000

      10              1,258,000            21                690,000

      11                854,000            22                358,400


Since it was originally anticipated that storage volumes would be a function
of demand, the  systems analysis computer program was arranged to test
the service area demand against the available supply before computing
storage volume.  The total runoff expected from each  sub-watershed was'
calculated by methods  described in Section IV.  Further analyses described
later disclosed that,  given  the design criteria selected for the  Wilde Lake
watershed, 90 percent of the total runoff will be  available for reuse at
                                114

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release rates of at least 1.13 q.  Accordingly, the total demand of any
service area under consideration can be compared to 90 percent of the
total runoff of that same area to determine the availability of the required
volume of treated water.  When the  demand exceeds  the available
supply, it ,is reduced to equal that supply.  This  insures that later cal-    >
culations of system costs,  benefits, etc.,  refer  only to the portion of
the demand that will be satisfied by treated storm water.  The balance
of the demand will be satisfied by the public water supply  system and
will not figure in the calculation of costs or benefits.  When the  demand
does not exceed the available supply, subsequent calculations will be
based on the actual demand.   Table  25 lists the available supply for each
of the sub-water sheds,  equal to 90 percent of total runoff.
   TABLE 25.  EXPECTED AVAILABLE SUPPLY FROM STORAGE


                 Available Supply                   Available Supply
Sub-water shed       (gal/day)       Sub-watershed       (gal/day)


       1               8,946             12              18,090

       2             11,565             13              24,989

    ,.   3             10,064             14              38,340

       4             11,807             15               9,129

       5             19,080             16              25,327

       6             43,513             17              50,305

       7             33,915             18    ,           9,630

       8             26,468             19              38,520

       9             43, 994             20              50, 193

      10             61, 997             21              28, 734

      11             30,552             22              13,410
When the service area under consideration consists of more than one
sub'•water shed,  storage volume and maximum demand can be found by
adding the values associated with each of the component sub-watersheds
on the tables above.
                                 115

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Pretreatment

Operating criteria developed in Section VIII for the pretreatment unit
stipulated that it must be capable of operating at twice the mean rate of
runoff.  This can be accomplished within the system model by inputing
a table of total annual runoffs from each sub-water shed (Table 26) and
using these figures to determine costs for the pretreatment unit.  Further-
more, when the total system of sub-watersheds is analyzed, each down-
stream pretreatment unit must process twice the mean runoff from its
own watershed as well as the total of the treatment rates of all the
upstream units.  The cost figures used for determining construction
and operating cost of pretreatment units (Tables D-l and D-7) are based
on total runoff and treated water demand,  respectively, and take into
account the operating rule suggested for the unit. Construction  costs  -"--'
are calculated to provide the necessary capacity, using the total annual .,--
runoff from Table  26.
    TABLE 26.  TOTAL ANNUAL RUNOFF VS.  SUB-WATERSHED


Sub - wate r she d
1
2
3
4
5
6
7
8
9
10
11
Total
Annual Runoff
(gallons)
3, 626, 640
4, 693, 608
4,073,400
4, 790, 547
7, 732, 769
17, 653, 330
14, 006,578
10, 740, 789
17, 817, 840
25, 123, 680
12, 377, 880


Sub -water shed
12
13
14
15
16
17
18
19
20
21
22
Total
Annual Runoff
(gallons)
7, 332, 120
10, 133, 568
15, 528, 105
3, 700, 224
10, 259, 712
20, 388,024
3, 905S 208
15, 636, 600
20, 351, 232
11, 652,552
5, 439, 960
                                116

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Final Treatment

No physical or technological constraints are placed on final treatment
facilities, other than their categorization into four classes of treatment,
as discussed in Chapter VIII.  Class "C" consists of pretreatment only
and only a portion of its operating costs are ascribed to final treatment.
Classes "B, " "A, " and "AA" are composed of pretreatment and various
levels of additional treatment.  In all cases,  demand is selected as the
parameter for determining costs, and the demand is tested prior to
calculation of treatment costs by the method described above in the
paragraph headed  "Storage Facilities. "


Pumping Facilities

Pumping facilities are sized by adjusted treated water demand and are
constrained only by  cost.


Treated Water Storage

As in the  case of stormwater storage,  a number of storage configurations
are analyzed.  Steel and concrete tanks,  above or below grade, as well
as elevated tanks, standpipes, and hydropneumatic  tanks are all estimated
for each application, unless  instructions are  input to do otherwise.  The
program can be instructed to select any of the storage configurations
without  reference  to the others.  Treated water storage tanks are sized
as a function of demand by the relationships shown as Equations D-l,
D-2,  and D-3.
Distribution System

The various physical constraints on distribution systems were discussed
in Section IX and were taken into account in developing distribution system
costs.  Distribution costs are  a function of the sub-watershed under study
and the level of reuse being considered.  Sub-water sheds can be combined
by simply adding distribution co'sts.  The transmission line to the treat-
ment  plant itself is listed separately (Tables D-10 and D-ll) and is a
function of treatment plant location only.  Where one treatment plant
serves two combined sub-watersheds,  the two distribution costs are
summed,  but only the transmission line costs  for the actual location of
the plant apply.
SYSTEM COSTS
Storage Facilities

Construction, operating,  and maintenance costs have been developed for
five different types of storm water storage facilities and presented as
                                 117

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tables of cost/capacity relationships.   Capital costs are composed of  .
land cost, site preparation costs, burial costs where applicable,  and
erection costs.  Appendix  C lists these costs.  Average cost of land in-'-
the Columbia area was taken as $12, 000 per acre.  Later discussions.
with the developer of Columbia led to a decision to confine facilities to
land already dedicated to public use, land not usable for other purposes ,
due to its function as natural floodplain.   Since the cost of this land
was not chargeable to the local reuse system,  land costs were set at
$0.00 per acre for purposes of systems analysis.  An auxiliary com- :
putation indicated that total system costs were reduced approximately -
seven percent by this assumption.  Land area,  for purposes of computing
land costs and site preparation costs,  is found from a land area table •.:":
(Table C-2)  in the case of  open ponds,  and computed from capacity and.-/)
H/D ratio (Table C-3) in the case of tanks.  Operation and maintenance1^ i
costs are made up of sediment removal costs and metal tank maintenaneei
Methods for computing these costs are given in Appendix G.   After  'i-'-'>~t<
evaluation of all component costs, the total system cost of a storm waters.'
storage facility of any desired configuration can be expressed as:     ••'-- -M
                                                                    , 'i:' ','<••
      C.    =     a(L. +  P. + B. + E.)/365 + (R. + M.)            (26)  .:,
       J            J    J   J    J         J     J                  ,-';,".
where:
                                                                    3'.''"'
      C.    =     total system cost of storage facility of
       ^         configuration j (dollars/day)                      •' :

      a      =     capital recovery factor (Equation 3)                 '•. r

      L.    =     land cost for storage facility of configuration       .  >
       ^         j (dollars)                                          ,  -

      P.    -     site  preparation cost for storage facility of
       ^         configuration j (dollars)                           < < • i

     B.    =     burial  cost, where applicable (dollars)            ." ' ;i:
                                                                    - t
     E.    =     erection cost (dollars)
       J                                                           t  "
      R-    =     silt removal cost (dollars/day)                      -,:i-
       J
     M.    =     tank maintenance cost, where applicable              -:
       J         (dollars/day)

All system costs were calculated as dollars/day to simplify the output
format.  The annual rate of interest was taken at the  1967 level recom-
mended by the Water Resources  Council for evaluation of water resources
projects - 0. 032 or 3. 2 percent annually.  It was recognized that  various
persons and agencies interested  in the  storm water reuse concept will
have a range of interest figures which they consider appropriate to the
analysis.  A common approach is to select a rate based on the current
                                 118

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cost of new capital to the agency considering construction of such a
facility.  This might range from 4. 5 percent for the Federal Treasury
(1967) to approximately 5. 0 percent for most local governments in late
1967 or early 1968,  to perhaps as much as 7. 0 percent for a private
developer..  Since the local reuse system is being  compared to a conven-
tional approach which is characterized by relatively high capital costs
and low operating costs as  compared to the  study concept,  the  selection
Of a high interest rate would tend to penalize the conventional central
system.  Accordingly, the  3. 2 percent figure was selected as the -lowest
interest rate that might be  considered for the analysis, a conservative
assumption from the standpoint of evaluating the local reuse concept.
The amortization period is likewise a subject of some difference of
opinion.  When such considerations are influenced by financing details,
the life of the bonds issued to fund the project is a common criterion -
frequently  about 30 years.  From an economic  sense,  the estimated
useful life  of the  facilities might be used,  preferably each individual
unit but possibly  the average useful life of all facilities. Fortunately,
in this case no  substantial  disagreement existed between the  two
approaches.  The estimated useful life of all facilities under consider-
ation is considered to average approximately 30 years.  For this  reason,
30 years was selected as the period of amortization.

The methods employed to calculate the total system cost on a dollar/day
basis of each of five possible configurations of  storage have now been
outlined.  Following these calculations, a sub-optimization is performed
for storm water storage configuration.  Unless constrained to  fewer
choices by the options described above, the five system costs are com-
pared and the lowest total system cost is selected.  Results of the other
four computations are destroyed and the selected system costs are
retained as the final costs of storm water storage.
Pretreatment

Appendix C described the development of capital costs for the pretreatment
unit.  Total annual runoff is obtained for a given watershed from Table 26,
and the pretreatment cost for this capacity is found by linear interpolation
of Table D-l.  Sediment removal costs are computed as part of the stor-
age facility costs,and other operating and maintenance costs are combined
with final treatment costs.  Total system cost of the pretreatment unit
is defined as:
      C     -     a(S )/365                                     (27)
where:
      C    =     total system cost of pretreatment unit (dollars/day)

      S    -     construction cost of pretreatment unit (dollars)
                                 119

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Final Treatment

Final treatment costs are composed of construction and operating costs,
each computed vs. daily treated water demand for four different levels
of treatment.  Costs for given demand and level of treatment can be
obtained by linear interpolation of Tables D-3 and D-7 with respect to
demand, using the sections pertaining to the treatment level selected.
In this manner a construction cost and an operating cost are selected,
and they are combined in the following manner:

      C,   =     a(S.)/ 365 + 0                                  (28)
       T            T          I-                    • ' -

where:

      C    =     total system cost of final treatment (dollars/day)

      S    =     construction cost of treatment unit (dollars)

      O,   -     operating and maintenance cost of treatment unit
                 (dollars/day)


Pumping Facilities

Construction costs of pumping facilities are obtained by linear inter-
polation of Table D-5.  Operating and maintenance costs have been
combined with final treatment costs.   Total  system costs  for pumping
are found by the following expression:

      Ch         a(Sh)/365                                     (29)

where:

      C,   =     total system cost of pumping (dollars/day)

      S,    =     construction cost of pumping facility (dollars)


Treated Water Storage                                                l

Seven different configurations of treated water storage facilities were  '
analyzed and costs developed for each of them.   The types of facilities
examined include standpipes,  elevated tanks, hydropnuematic tanks,
ground  level  steel and concrete tanks  both above and below grade. Con-
struction  costs for each of these are made up of land cost,  site prep-
aration costs, burial costs (where applicable),  and erection costs. Land
areas for land costs and site preparation costs  are computed from the
tank capacity  and the H/D factor. Costs are summarized in Tables C-6,
C-7,  and  C-9. H/D factors appear  in Tables C-3,  C-4,   and C-5. Tank
                                 120

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maintenance costs consist of periodic painting and maintenance of metal
tanks and are found  by the methods described in Appendix C.  As in the
case of storm water storage, a sub-optimization was performed for  each
case by computing the total system cost for each tank (unless constrained
by the instructions described above) as follows:



      Ck    =     a(Lk + Pk + Bk+Ek)/365+0k                 (30)
where:

      C,    =     total system cost of treated water storage
                  facility of configuration k (dollars/day)

      L^    =     land cost for storage facility of configuration k
                  (dollars)

      Pi    -     site  preparation cost for storage facility
                  of configuration k (dollars)

      B,    =     burial cost, where applicable (dollars)

      E,    =     erection cost (dollars)

      O,    =     operation and maintenance cost
                  (dollars/day)

The total  system costs for the five possible configurations are compared
and the least cost alternative is selected and its costs retained.  Costs
for the other approaches  are  not retained.

Distribution System

Costs for distribution systems for each sub-watershed and each level of
reuse are input directly to the computer  program.   These costs are  tabu-
lated  in Table 21. Service areas made up of several watersheds are
calculated by adding the  appropriate entries from the component sub-water-
shed costs.   The transmission line to the treatment plant is listed sepa-
rately on  Table 22 and is added to distribution cost.  Operation and main-
tenance cost is a function of total distribution capital cost and is calculated
by Equation 25.  Total system cost for distribution is calculated as follows:
      C ,    =     a(S, + S )/365 + O,                           (31)
       d            d    c         u
where:
      C ,    =     total system cost of distribution system (dollars/day)

      S,    =     construction cost of distribution system (dollars)
                                 121

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      S    =     construction cost of transmission line (dollars)
       c
      O    =     operation and maintenance cost of distribution
       d         system (dollars/day)


FEASIBLE SYSTEMS

Figure 33 illustrates the flow pattern of the 22 sub-watersheds in the
Wilde Lake watershed.  As discussed  earlier, preliminary investigation
revealed that a very large  number of combinations of sub-watersheds
might be considered as possible collection areas.  It was reported that,
in order to limit the number of cases to be calculated, no more than
six sub-watersheds would be considered a single collection area.   Also
many trivial and doubtful cases were neglected and it was found that . r
110 different collection areas could be defined which would permit 173
combinations for the entire watershed.  The collection areas, whichVare
virtually identical with  the corresponding service areas, were determined
by examination of topographic maps of the watershed and include eve'ry
case where runoff from one or more sub-watersheds is apparently avail-
able at a single place.   In each case, that point of collection was identified
by the sub-watershed within which it was located and the collection area
thus defined was assigned an index number.  Tables 27,  28, and 29 list
the collection areas  identified, showing the sub-watersheds which make
up each area,  the treatment plant location,  and the index number.  Each
separate table represents a single computer run and is assigned its own
set of index numbers.   The watershed was divided into three separate.
areas for analysis designated by  Computer Runs A, B, and C,  to simplify
the computer runs and to make the results of the first analysis available
at the earliest possible time,  in the event that modifications to the method
would be required.   The limitation of six sub-watersheds in a single .col-
lection area permitted the  total watershed to be so divided without any
significant penalty in terms of total number of combinations presented for
analysis.


COMBINATIONS OF COLLECTION AREAS

Having defined all the individual storm water storage,  treatment,  and
reuse facilities possible within the Wilde Lake watershed,  subject to the
stated constraints,  the  combinations of these systems which would serve
the entire watershed remain  to be defined.  Again, this may  be done by
inspection,and Tables 30,  31, and 32 list the combinations so  identified,
defined  in terms of index number.  Each index number,  in turn, refers
to the corresponding collection area for the same computer run.  In other
words,  Combination Number 11 in Run B (Table  31) is made up of Index
Numbers  2, 6,  and 24,  which are sub-watershed numbers  2, 6,  and the
combination of  1, 3, 11, and 12 (from Table 28).  Each combination
represents a portion of a complete system with storage,  treatment, and
reuse facilities for every  area in that  section of the watershed. The
various methods of assembling the 173 combinations result in 186, 300
ways of serving the entire  watershed.
                                 122

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TABLE 27.  COLLECTION AREAS - COMPUTER RUN A
Index
Number
1
2
3
4
5
6
7
8
9
10
ll
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
2§
29
30
31
32
33
34
35
36
37
38
39
40
41
Collection Area (Sub-watersheds)
4
5
6
7
8
14
4
4
5
6
6
7
7
4
4
5
6
7
6
4
5
5
4
4
4
4
5
4
5
6
4
4
4
5
4
4
4
4
5
4
4


5
14
14
8
7
8
14
5
7
7
7
8
7
5
6
7
6
7
5
6
6
7
7
7
5
5
6
6
5
5
5
6
6
5
5









14
14
14
14
14
8
7
7
8
7
8
7
7
7
8
8
8
6
7
7
7
6
6
7
7
7
6
6




















14
14
14
14
14
14
7
8
8
8
8
7 14
8 14
8 14
8 14
7 8
7 8 14
Treatment
Location
4
5
6
7
8
14
4
14
14
6
7
7
14
14
14
14
14
7
7
7
7
7
7
7
14
14
14
14
14
14
7
7
7
7
6
14
14
14
14
7
14
                         123

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TABLE 28.  COLLECTION AREAS - COMPUTER RUN B
Index
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Collection Area (Sub-Watersheds)
1
2
3
11
12
13
1
1
2
3
3
11
11
12
1
1
1
2
2
3
3
11
1
1
1
2
2
3
1
1
1
2
1






2
3
3
11
12
12
13
13
2
3
3
3
3
11
11
12
2
3
3
3
3
11
2
2
3
3
2














3
11
12
11
12
12
13
13
3 11
11 12
11 13
11 12
11 13
12 13
3 11 12
3 11 13
11 12 13
11 12 13
3 11 12 13
Treatment
Lbcatidh
1
2
3
11
12
13
2
3
3
11'
12 !
11
13
13-'
3
11
12
11
12
11
13
13-
11
11
13
11
13
13
11
13
13
13
13
                        124

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TABLE 29.  COLLECTION AREAS - COMPUTER RUN C
Index
Nurnber
1
2
3
4,
5
6
7
8
9
10
11.
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
Collection
15
16
17
18
9
20
10
19
21
22
15
15
15
16
17
18
9
15
15
15
15
16
17
18
15
15
15
15
16
16
17
15
15
15
16
15


16
17
18
18
18
9
20
16
16
17
18
18
18
9
16
17
16
18
17
18
18
16
17
16
17
16
Area









17
18
18
9
9
9
20
17
18
18
9
18
9
9
17
18
18
18
17
(Sub -water sheds)
















18
9
9
20
9
20
20
18 9
9 20
9 20
9 20
18 9 20
Treatment
Location
15
16
17
18
9
20
10
19
21
22
16
17
18
18
18
9
20
17
18
18
9
9
9
20
18
9
9
20
9
20
20
9
20
20
20
20
                           125

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                                  TABLE 30.  COMBINATION OF AREAS - COMPUTER RUN A
05
Combination
 Number

    1
    2
    3
    4
    5
    6
    7
    8
    9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
Index Numbers of
Collection Areas
41
40
39
38
37
36
35
35
34
34
33
33
32
31
30
30
29
28
27
26
25
25
24
24
23
23
22
22
21
21
20
20
19
19


6
1
2
3
5
13
4
8
1
9
2
3
5
7
1
1
2
1
2
10
3
9
2
9
2
8
1
8
1
10
3
14
7








6

6

6
6
6

2
3
3
5
5

5
3
3 6
5
5 6
3
3 6
5
5 6
6
5 6

6

Combination
Number
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
. 61
62
63
64
65
66
67
68
69
Index Numbers of
Collection Areas
19
19
19
18
18
17
17
16
16
15
15
14
14
14
14
13
13
13
13
12
12
12
12
11
11
11
11
10
10
10
10
9
, &
- 7-
i
8
9
1
7
1
7
1
10
1
10
2
11
12
10
3
7
7
10
1
7
8
9
1
7
8
9
1
7
8
9
1
1
2
3
2
2
1
2
3
2
5
2
1
3
2
3
5
3
4
4
10
3
1
2
3
2
1
2
5
2
1
2
4
2
1
2
3
3
4
3


6

3

5

5

5



5

5
2
3
6
3
3
3
6
5
5
5
6
4
4
4
4
4
5
4

-------
                          TABLE 31.  COMBINATION OF AREAS - COMPUTER RUN B
CO
Combination
  Number


     1
     2
     3
     4
     5
     6
     7
     8
     9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
    22
    23
    24
    25
    26
    27
                              Index Numbers of
                              Collection Areas
33
32
31
30
29
28
28
27
26
25
24
23
23
22
22
22
22
22
21
21
20
20
19
19
18
18
17

1
2
5
6
7
1
1
1
2
2
14
5
15
7
8
9
1
7
1
7
1
13
1
14
1
13






2
5
6
5
6

6

3
2
1
2
5
2
6
2
1
4
1
5
2

















3

5

6

6

6

Combination
  Number


    28
    29
    30
    31
    32
    33
    34
    35
    36
    37
    38
    39
    40
    41
    42
    43
    44
    45
    46
    47
    48
    49
    50
    51
    52
    53
    54
Index Numbers of
Collection Areas
17
16
16
15
15
15
15
14
14
14
14
14
13
13
13
13
13
12
12
11
11
10
10
9
8
7
6
2
14
2
12
13
14
4
10
9
8
7
1
11
9
8
7
1
7
1
7
1
7
1
1
2
3
5
4
2
5
6
5
4
5
7
4
4
4
2
7
1
2
3
2
4
2
4
2
5
2
4
4
4
4
6

6



6

1
2
3
3

5
5
5
3
6
4
6
4
6
5
5
5
5
3











4




5

6

6

6
6
6
6
2

-------
TABLE 32.  COMBINATION OF AREAS - COMPUTER RUN C
Combination
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
36
35
34
33
32
31
31
30
30
29
28
27
26
25
25
24
24
24
24
23
23
22
22
21
20
20
19
19
18
18
18
17
17
17
17
17
17
17
17
16
16
16
15
15
14
14
13
12
11
1
Index Numbers of Collection Areas
7
1
3
2
6
11
1
12
1
1
2
3
2
17
5
18
11
12
1
11
1
12
1
2
17
2
17
3
16
17
4
11
12
13
11
12
14
15
1
11
12
1
11
1
12
1
2
2
3
2
8
7
7
7
7
7
2
7
3
6
3
6
6
7
6
7
3
2
2
6
2
6
3
3
2
5
3
5
6
4
5
15
14
2
3
2
1
1
2
3
2
2
5
2
5
3
3
4
4
3
9
8
8
8
8
8
7
8
7
7
7
7
7
8
7
8
7
7
3
7
6
7
6
6
7
6
7
6
7
7
6
7
7
3
4
4
3
2
3
6
6
3
6
5
6
5
5
5
5
4
10
9
9
9
9
9
8
9
8
8
8
8
8
9
8
9
8
8
7
8
7
8
7
7
8
7
8
7
8
8
7
8
8
7
7
7
7
7
4
7
7
6
7
6
7
6
6
6
6
5
10
10
10
10
10
9
10
9
9
9
9
9
10
9
10
9
9
8
9
8
9
8
8
9
8
9
8
9
9
8
9
9
8
8
8
8
8
7
8
8
7
8
7
8
7
7
7
7
6


10

10
10
10
10
10

10

10
10
9
10
9
10
9
9
10
9
10
9
10
10
9
10
10
9
9
9
9
9
8
9
9
8
9
8
9
8
8
8
8
7














10

10

10
10

10

10


10


10
10
10
10
10
9
10
10
9
10
9
10
9
9
9
9
8


































10


10
10
10
10
10
10
9
                                                          10
                          128

-------
Since each section of the complete watershed that was isolated for a com-
puter run is,  by the terms of the assumptions, independent of the others,
each can be optimized  separately and the optimum system for the water-
shed will be the summation of the individual  optimum systems.  This
approach reduces by several orders of magnitude the number of cases
which must be examined.
                                 129

-------
                            SECTION XI

          SYSTEM MODEL OUTPUTS AND OPTIMIZATION
Section V discussed the water demands which are under consideration as
possible  areas of storm water reuse.  It was determined that the four
classes of demands could be served in eight different ways:  the storm
water system could be connected to the "AA, A, B, and C" demands,  the
"A, B, and C" demands,  the "A and B, " "A and C, " or "B and C" de-
mands, or simply be  connected  to the "A, " "B, " or "C" demands indepen-
dently of the others.  In each case,  the distribution system and treatment
system required are different from any of the other cases.   Tables 27,  28,
and 29 presented various collection areas that couldbe  considered, each of
them made up of one or more sub-watersheds,  but permitting storm water
to be collected,  stored, and treated at a single central location.  The
first step in the optimization was, therefore, to compute total system
costs for each feasible arrangement of facilities within each  possible
collection area.
TABLE OF NET BENEFITS

These results are displayed as a Table of Net Benefits, a sample of which
is reproduced as Figure 34.  The case numbers in the left-hand column
can be observed to correspond to the index numbers of Table 27.  Each
line represents a particular collection area,  with the sub-watersheds and
treatment plant location listed in successive columns. The entries under
the eight water service level columns correspond to the net system bene-
fit for the facilities which would serve the demands indicated in the col-
lection area listed.  The final column reflects the maximum net benefit
appearing on that line and identifies the optimum configuration for that
collection area alone.  Negative net benefits are identical with net system
costs.  All values are in dollars/day and are computed as follows:

      B    =     B   — (_*.  — C,  — C,,   C_>,  — C^T   — \~s ,            /oo\
       n           gjopthkod            (32)

where:

      B    =     net system benefits  (dollars/day)

      B    =     gross  system benefit,  computed as discussed
       ^         (see Section.XI) (dollars/day)

      C.    =     sub-optimized system cost  of storm water
       3°        storage from Equation 33 (dollars/day)

      C    -     system cost of pretreatment from  Equation 34
       p         (dollars/day)
                                 131

-------
                                                      ****   TABLE  OF  NET   BENEFITS  ****
CO
to
        CASE

        NUMBER


          1
  b
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
33
 34
35
36
37
38
39
40
41
WATERSHED
NUMBER
PLANT
LOCATION
4
5
6
7
8
14
4
4
5
6
6
8
7
4
4
5
t>
8
6
4
6
8
6
8
4
4
5
4
5
6
4
4
4
5
4
4
4
4
5
4
4
0
0
0
0
0
0
5
14
14
8
7
7
14
5
7
7
7
7
7
5
7
7
7
7
5
6
6
8
8
7
5
5
6
6
5
5
5
6
6
5
5
0
0
0
0
0
0
0
0
0
0
0
0
0
14
14
14
14
14
8
7
5
5
4
4
7
7
7
7
7
8
6
8
7
7
6
6
a
7
7
6
6
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
14
14
14
14
14
14
7
7
8
8
8
7
7
B
e
7
7
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
14
14
14
14
8
a
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
14
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
4
5
6
7
8
14
4
14
14
6
7
7
14
14
14
14
14
7
7
7
7
7
7
7
14
14
14
14
14
14
7
7
7
7
6
14
14
14
14
7
14

A
-9.18
-10.74
-41.24
-21.72
-10.76
-19.77
-15.58
-24.93
-25.95
-45.92
-58.38
-26.75
-35.28
-31.15
-40.25
-41.19
-69.22
-41.47
-62.49
-31.02
-62.58
-32.32
-62.71
-31.38
-46.15
-73.07
-72.63
-46. 54
-47.48
-72.39
-66.58
-37.28
-66.34
-65.90
-54.44
-76.47
-52.18
-76.20
-75.70
-69.75
-79.40

8
-7.54
-10.09
-27.41
-16.96
-9.07
-15.59
-12.84
-18.65
-20.64
-31.93
-39.64
-21.58
-28.06
-23.69
-31.16
-33.13
-50.75
-32.52
-44.21
-25. 16
-44.71
-26.62
-42.75
-24.63
-36.24
-53.86
-55.82
-35.74
-37.70
-55.32
-47.82
-29.69
-47.32
-49.28
-40.11
-58.93
-40.81
-58.77
-60.44
-52.39
-64.12

C
-5.78
-7. 12
-27.72
-12.08
-6.03
-13.47
-10.71
-17.36
-18.14
-27.75
-37.85
-16.35
-23.79
-22.09
-27.75
-28.55
-43.51
-27.93
-37.99
-20.85
-39.16
-21.07
-40.31
-20.29
-32.55
-46.11
-46.90
-32.03
-32.83
-46.35
-41.57
-25.05
-40.38
-39.44
-33.20
-50.85
-36.83
-50.30
-51.06
-43.39
-54.88
WATER
A,B
-8.60
-9.80
-41.24
-21.72
-8.91
-16.43
-13.43
-21.06
-21.47
-45.92
-58.38
-26.75
-33.97
-25.52
-38.31
-38.17
-69.22
-38.13
-62.49
-31.02
-62.58
-30.95
-62. 71
-31.09
-42.39
-73.07
-72.63
-42.15
-41.71
-72.39
-66.58
-35.28
-66.34
-65.90
-54.44
-76.47
-45.56
-76.20
-75.70
-69.75
-79.40
QUALITY
A,C
-8.60
-9.17
-41.24
-21.72
-8.88
-16.43
-13.43
-21.06
-21.11
-45.92
-58.38
-26.75
-33.97
-25.52
-38.31
-38. 17
-69.22
-38.13
-62.49
-31.02
-62.58
-30.95
-62.71
-31.09
-42.39
-73.07
-72.63
-42.15
-41.71
-72.39
-66.58
-35.28
-66.34
-65.90
-54.44
-76.47
-45.56
-76.20
-75.70
-69,75
-79.40
-
A,B,C
-8.60
-9.17
-41.24
-21.72
-8.88
-16.43
-13.43
-21.06
-21.11
-45.92
-58.38
-26.75
-33,97
-25.52
-38.31
-38.17
-69.22
-38.13
-62.49
-31.02
-62.58
-30.95
-62.71
-31.09
-42.39
-73.07
-72.63
-42.15
-41.71
-72.39
-66.58
-35.28
-66.34
-65.90
-54.44
-76.47
-45.56
-76.20
-75.70
-69.75
-79.40

B,C
-7.20
-8.67
-31.94
-15.83
-6.46
-11.50
-10,-21
-14.10
-15.22
-33.86
-44.91
-16.90
-24.02
-17.70
-28.00
-27.79
-52.99
-27.49
-47. S8
-21.07
-48.68
-20.67
-48.89
-20.87
-31. 3G
-54.98
-53.54
-29.85
-28.41
-52.10
-51.31
-24.64
-49.87
-48.43
-41.52
-55.52
=30.40
-54.04
-52.54
-50.42
-54.38

AA,A,B,C
-6.61
-6.52
-4. 16
-4.57
-5.26
-4.48
-5.20
-3.55
-2,93
-1.39
-0.14
-2.40
-1.00
-1.54
0.53
1.51
5.09
2.71
3.52
-1.95
2.37
0.11
1.39
-0. 87
3.09
6.80
7.89
4.29
5.37
9.09
4.02
1.65
5.22
6.31
2.66
9.61
7.08
10.84
11.99
8.02
13.85

MAX
-5.78
-6.5?
-4.16
-4.57
-5.26
-4.48
-5.20
-3.55
-2.93
-1.39
-0.14
-2.40
-1.00
-1.54
0.53
1.51
5.09
2.71
3.52
-1.95
2.37
0.11
1.39
-0,87
3.09
6.80
7.89
4.29
5.37
9.09
4.02
1.65
5.22
6.31
2.66
9.61
7.08
10.84
11.99
8.02
13.89
                                       Figure 34.  Table of Net Benefits - Computer Run A

-------
      C^   -     system cost of final treatment from Equation 35
                 (dollars/day)

      Ch   =     system cost of pumping from Equation 36
                 (dollars/day)

      C,   =     sub-optimized system cost of treated
                 water storage from Equation 37
                 (dollars/day)

      C,   =     system cost of distribution from Equation 38
                 (dollars/day)


TABLES OF CAPITAL COSTS AND DAILY COSTS

Figures 35 and 36 show computer listings of capital costs and daily
operating and  maintenance costs for each of the collection area/reuse
level alternatives considered in one of the computer runs.   The Table of
Capital Cost indicates the total construction cost,  in dollars,  for each
alternative.  Case Number 11, for example, is a collection area composed
of sub-watersheds Numbers  6 and 7 and for the reuse level  "C" (only
Class "C" uses considered) has a capital cost of 0.03958E06, read as
0. 03958 x 106, or $39, 580.  This includes  all costs associated with the
construction of a storm water storage facility, a pretreatment unit,
pumping facilities,  treated water storage,  and a ' C" level distribution
system. No final treatment  was provided,  since only Class "C" water
was  required. The next entry on the same line, for reuse level "A, B," in-
dicated a capital  cost of  0. 4658E 06 or $46, 580 and includes a Class "A"
treatment plant as well as the additional cost of the "A, B"  distribution
system. Pumping and treated water storage facilities maybe sized some-
what differently due to increased total demand.

The  Table of Daily  Cost,  Figure 36,follows the same format as Figure 35,
except that entries  are for total operating and maintenance cost, expressed
in dollars/day.  The alternative used in the example above, Case Number 11
at reuse level "C,"can be found  to have an operating and maintenance cost
of $19. 70  per  day.   The  "A,  B" reuse level for the same case hasanoper-
ating and maintenance cost of $30. 20 per day, largely due to the additional
cost  of operating the Class "A"  treatment plant.  These costs include silt
removal,  maintenance costs of storm water and treated water storage,
where applicable, operating  and maintenance costs of pretreatment,final
treatment, pumping, and distribution facilities. The total system cost
of each alternative  in dollars/day is the sum of the daily costs from
Figure 36 and the capital costs from Figure 35 multiplied by the capital
recovery factor and divided by 365.
                                 133

-------
                                               **  TABLE OF CAPITAL  COST  **
LASt

NUMBtk
  1
  2
  3
  4
  5
  Q
  7
  a
  9
 10
 ii
 12
 13
 1*
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 2d
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
WATERSHED
NUMBER
PLANT
LOCATION A
4
5
6
7
a
14
4
i.
>3
6
t>
d
7
^
4
5
o
8
o
4
6
8
6
8
4
4
5
4
5
6
4
4
4
5
4
4
4
4
5
4
4
0
0
0
0
0
0
5
14
14
8
7
j
14
5
7
7
7
7
7
5
7
7
7
7
5
6
6
a
8
7
5
5
6
6
5
5
5
6
6
5
5
0 0
0 J
0 0
0 0
0 u
0 0
0 0
0 0
0 0
0 0
0 0
0 u
0 0
14 0
14 C
14 0
14 0
14 0
8 0
7 0
5 0
5 0
4 0
4 0
7 14
7 14
7 14
7 14
7 14
8 14
6 7
8 7
7 8
7 8
6 8
6 7
8 7
7 8
7 8
6 7
6 7
0
0
0
0
0
u
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
C
0
0
0
0
0
0
0
0
0
0
14
14
14
14
8
8
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
14
0
u
0
0
u
0
0
0
0
0
0
u
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
u
0
0
0
u
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
u
0
0
u
0
0
0
0
0
u
0
0
0
0
0
0
0
u
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
i,
5
6
7
8
14
4
14
14
6
7
7
14
14
14
14
14
7
7
7
7
7
7
7
14
14
14
14
14
14
7
7
7
7
6
14
14
14
14
7
14
0.7069E
0.8307E
0. 3145E
0. 180UE
0. 8976E
0. 1505E
0. 1235E
0. 1933E
0. 2019E
0.3779E
0.4658E
0. 2441E
0.3051E
0.2449E
0.3481E
0. 3567E
0.5925E
0. 3663E
0. 5294E
0.2769E
0. 5185E
0.29S9E
0.5092E
0. 2873E
0.3997E
0. 6370E
0. 6470t
0.4101E
0. 4186E
0.6583E
0. 5626E
0.3389E
0. 5740E
0. 5840E
0.4741E
0.6914E
0.4622E
0.7025E
0. 7121E
0.6285E
0.7556E
050.
050.
060.
060.
050.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
060.
B
6113E
6915E
2060E
1233E
6836E
1227E
9704E
1527E
1567E
2427E
2964E
1607E
2148E
1867E
2451E
2489E
3880E
2510E
3335E
1881E
3306E
1947E
3268E
1907E
2793E
4163E
4222E
2822E
2860E
4250E
3610E
2248F
3639E
3677E
3073E
4525E
3164E
4554E
4590E
3981E
4887E
050
050
060
060
050
060
050
060
060
060
060
060
060
060
060
060
060
060
060
060
060
060
060
060
060
060
060
C60
060
060
060
060
060
060
060
060
060
060
060
060
060
WATER QUALITY -
C A, 8 A,C A,B,C B,C AA,A,
.5139E
.6231E
-2642E
. 1454E
.66C9E
. 1246E
.9845E
.1629E
.1700E
.3181E
.3958E
.1992E
.2578E
.2086E
.2964E
. 3035E
.5086E
.3102E
.4497E
.2304E
.4421E
. 2449E
.4347E
.2378E
.3421E
.5474E
.5545E
.3496E
.3566E
.5619E
.4810E
.2835E
.4885E
.4959E
.4030E
.5930E
.3952E
.6004E
.6073E
. 5345E
.6449E
050.7100E 050.7100E 050.7100E 050.6982F 050.5752E 05
050.8357E 050.8391E 050.8391E 050.8081E 050.6405E 05
060.3145E 060.3145E 060.3145E 060.2835E 060.7175E 05
060.1800E 060.1800E 060.I800E 060.1644E 060.6493F 05
050.9073E 050.9075E 050.9075F 050.8495E 050.6257E 05
060.1528E 060.1528E 060.1528E 060.1446E 060.6894E 05
050.1248E 060.1248E 060.1248E 060.1175E 060,6644-E 05
060.1963E 060.1963E 060.1963E 060.1839E 060.7394F 05
060.2053E 060.2056E 060.2056E 060.1910E 060.7686E 05
060.3779E 060.3779E 06C.3779E 060.3382E 060.8194E 05
060.4658E 060.4658E 060.4658E 060.4161E 060.8293E 05
060.2441E 060.2441E 060.2441E 060.2199F 060.7586E 05
060.3060E 060.3060E 060.3060E 060.2792E 06C.8203E 05
060.2490E 060.2490E 060.2490E 060.2305E 060.8181E 05
060.3494E 060.3494E 060.3494E 060.318'4E 060.8698E 05
060.3587E 060.3587E 060.3587E 060.3261E 060.8989E 05
060.5925E 060.5925E 060.5925E 060.5302E 060.1031E 06
060.3686E 060.3686E 060.3686E 060.3332E 060.9143E 05
060.5294E 060.5294E 060.5294E 060.4708E 060.9397E 05
060.2769E 060.2769E 060.2769E 060.2513E 060.7852E 05
060.5185E 060.5185E 060.5185E 060.4630E 060.9080E 05
060.2968E 060.2968E 060.2968E 060.266BE 060.8372E 05
060.5092E 060.5092E 060.5092E 060.4554E 060.8788E 05
060.2875E 060.2875E 060.2875E 060.2591E 060.8081E 05
060.4024E 060.4024E 060.4024E 060.3654E 060.9551F 05
060.6370E 060.6370E 060.6370E 060.5695E 060.1109E 06
060.6470E 060.6470E 060.6470E 060.5772E 060.1156E 06
060.4137E 060.4137E 060.4137E 060.3732E 060.9962E 05
060.4237E 060.4237E 060.4237E 060.3809E 060.1043E 06
060.6583E 060.6583E 060.6583E 060.5851E 060.1197E 06
060.5626E 060.5626E 060.5626E 060.5023E 060.9769E 05
060.3403E 060.3403E 060.3403E 060.3060E 060.8867E 05
060.5740E 060.5740E 060.5740E 060.5102E 060.1018E 06
060.5840E 060.5840E 060.5840E 060.5178E 060.1065E 06
060.4741E 060.4741E 060.4741E 060.4244E 060.9487E 05
060.6914E 060.6914E 060.6914E 060.6164E 060.1233E 06
060.4682E 060.4-682E 060.4682E 060.4202E 060.1121E 06
060.7025E 060.7025E 060.7025E 060.6241E 060.1272E 06
060.7121E 060.7121E 060.7121E 060.6314E 060.1315E 06
060.6285E 060.6285E 060.6285E 060.5572E 060»1143E 06
060.7556E 060.7556E 060'.7556E 060.6696E 060. 1382E 06
                                  Figure  35.  Tatsle of Capital Cost - Computer Run A

-------
                                                   **  TABLE OF DAILY COST  **
00
Ol
    CASE

    NUMBER
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
WATERSHED
NUMBER
PLANT
LOCATION
4
5
6
7
8
14
4
4
5
6
6
8
7
4
4
5
6
a
6
4
6
8
6
8
4
4
5
4
5
6
4
4
4
5
4
4
4
4
5
4
4
0
0
0
0
0
0
5
14
14
8
7
7
14
5
7
7
7
7
7
5
7
7
7
7
5
6
6
8
8
7
5
5
6
6
5
5
5
6
6
5
5
0
0
0
0
0
0
0
0
0
0
0
0
0
14
14
14
14
14
8
7
5
5
4
4
7
7
7
7
7
8
6
8
7
7
6
6
8
7
7
6
6
0
0
0
0
0
0
0
0
0
0
0
0
c
0
0
0
0
0
0
0
0
0
0
0
14
14
14
14
14
14
7
7
8
8
8
7
7
8
8
7
7
0
0
0
0
0
0
0
c
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
14
14
14
14
8
8
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
14
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
4
5
6
7
8
14
4
14
14
6
7
7
14
14
14
14
14
7
7
7
7
7
7
7
14
14
14
14
14
14
7
7
7
7
6
14
14
14
14
7
14
                                                                       -  WATER  QUALITY  -

                                                                     C        A.B      A,C
                                                                                                     A,B,C
                                                                                                                B,C
AA.A.B.C
3.63
4.91
17.84
12.81
7.00
9.93
8.53
13.55
14.82
26.62
30.20
21.83
24.93
18.44
28.32
29.52
41.99
31.46
38.36
23.56
36.32
26.72
34.16
25.53
32.91
45.30
47.07
34.85
36.04
48.90
39.85
30.11
41.68
43.44
36.68
50.39
39.08
52.21
53.98
46.76
57.29
2.16
2.21
8.36
5.19
3.26
5.96
4.37
8.11
8.16
11.61
13.54
8.43
11.13
10.31
13.28
13.33
19.48
14.38
16.78
9.54
15.74
10.64
15.69
10.59
15.48
21.63
21.68
16.53
16.58
22.72
17.89
12.79
18.93
18.98
15.96
23.83
18.73
25.22
25.00
21.13
27.83
2.15
2.89
11.54
8.00
4.09
6.44
5.03
8.58
9.32
17.02
19.70
12.07
14.42
11 .46
16.59
17.34
28.30
18.58
25.29
13.02
23.85
14.95
22.43
14.21
19.54
30.90
31.65
20.78
21.53
32.86
26.55
17.13
27.97
29.27
23.33
33.81
23.73
35.02
35.76
31.44
37.93
4.27
5.93
17.84
12.81
9.01
13.63
10.88
17.88
19.83
26.62
30.20
21.83
26.11
24.26
30.07
32.24
41.99
34.48
38.36
23.56
36.32
27.96
34.16
25.79
36.05
45.30
47.07
37.88
39.65
48.90
39.85
31.92
41.68
43.44
36.68
50.39
42.96
52.21
53.98
46.76
57.29
4.27
6.62
17.84
12.81
9.05
13.63
10.88
17.88
20.23
26.62
30.20
21.83
26.11
24.26
30.07
32.24
41.99
34.48
38.36
23.56
36.32
27.96
34.16
25.79
36.05
45.30
47.07
37.88
39.65
48.90
39.85
31.92
41.68
43.44
36.68
50.39
42.96
52.21
53.98
46.76
57.29
4.27
6.62
17.84
12.81
9.05
13.63
10.88
17.88
20.23
26.62
30.20
21.83
26.11
24.26
30.07
32.24
41.99
34.48
38.36
23.56
36.32
27.96
34.16
25.79
36.05
45.30
47.07
37.88
39.65
48.90
39.85
31.92
41.68
43.44
36.68
50.39
4?.Qfe
52.21
53.98
46.76
57.29
3.04
3.82
12.99
9.16
5.79
9.57
7.24
12.69
13.37
20.24
23.85
15.46
20.01
17.32
24.21
26.54
34.68
28.92
32.15
17.27
30.38
21.99
28.05
19.66
30.27
36.89
37.98
31.39
32.49
39.11
33.23
26.19
34.36
35.45
30.89
40.19
34.69
41.31
42.40
37.66
44.61
4.21
6.82
15.57
12.17
9.47
13.72
11.02
17.91
20.52
24.53
26.86
21.61
25.26
24.27
28.87
31.11
37.86
33.39
34.81
22.94
32.71
27.46
30.47
25.22
34.59
40.89
42.76
36.49
38.37
44.67
35.92
31.07
37.83
39.70
33.97
45.79
41.39
47.69
49.57
42.73
52.59
                                       Figure  36.   Table of Daily Cost - Computer Run A

-------
TABLE OF BENEFITS

The gross system benefits for the alternatives discussed in the preceding
sections were calculated and displayed on a Table of Benefits,  shown as
Figure 37.  Benefits were taken as the marginal cost from the alternate
source of the water used.  In this case, benefits were the marginal cost,
to the consumer,  of an  equal volume of water purchased from the Howard
County Metropolitan Commission.  Under the rate  structure in effect in
July 1968, that cost is $0.45 per 1000 gallons.  The use of this very ele-
mentary measure of benefits overlooks the effect of such use on the public
water supply system.   Many of the costs associated with providing the
public water  supply to the demand area under study would not be reduced
by the introduction of the  supplementary source. The distribution system,
the  cost of billing  and  collection, the overhead structure of the Metropolitan
Commission  - all of these would be essentially unchanged. Since all of the
water distributed by Howard County is purchased from Baltimore City and
the  Washington Suburban Sanitary Commission, the most clear-cut reduc-
tion in true costs would be the reduction in the quantity of water purchased,
which accounts for less than half of the total selling price of water. Other
costs would be reduced in a less easily determined manner, such as booster
pumping costs, storage  costs, transmission main costs, etc. To properly
evaluate the total impact of the study  system on the public supply system,
a detailed study of the financial structure of  the Metropolitan Commission
would be required, a task outside the scope of this work. Since the Wilde
Lake area constitutes a small portion of the county water distribution area,
it was considered that the elimination of a portion of the demand in this
watershed would not have a significant overall effect on the cost of supplying
water to the county. For this reason, the  full price of water was taken as
a benefit, although in  a proposed  large-scale application of the local reuse
concept, this assumption would require careful review in light  of local
circumstances. Ideally, the economic benefit due to water supply shouldbe
taken as the marginal reduction in the total long-term costs of the public
water system,  due to the  reduction in demand on that system.

At the time the computer runs were performed, the marginal cost of water
in Howard County had recently been revised to $0. 50 per 1000  gallons.
Shortly after the runs were completed, however, the  rate was reducedto
$0.45 per 1000 gallons. Accordingly, Figure 37 shows benefits calculated
on the basis of the higher figure,  and subsequent discussion of net benefits
in this chapter will be in terms of $0.50 per 1000 gallons marginal cost of
water. Prior to the defintion of the conceptual optimum systems described
in Sections XII-XV, however, and prior to the system evaluation reported
in Section XVII,the benefit rate was revisedto $0.45 per 1000 gallons and
economic comparisons made on that basis. Since the benefit is, in this
case, completely linear and independent of other assumptions, manipu-
lating the rate has no effect on system optima.  The individual benefits
listed on Figure 37 are calculated as the  product of the  treated water
demand in gallons per day and marginal cost of water to consumer, from
public  system in dollars per gallon.  The net system benefits  can also
be calculated as the difference between the gross system benefits  on
Figure 37 and the total  system costs (Capital Cost from Figure 35 -r 365
x Capital Recovery factor + Daily Cost from Figure  36).
                                 136

-------
                                                 **   TABLE OF  BENEFITS   **
CASE

NUMBER
             WATERSHED  MUMBbR
PLANT

LOCATION
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Jl
32
33
34
35
36
37
38
39
40
41
4
5
6
7
8
14
4
4
5
6
6
b
7
4
4
5
fa
8
6
4
6
8
6
8
4
4
i>
4
5
6
4
4
4
5
4
4

-------
TABLE OF NET BENEFITS FOR COMBINATIONS OF WATERSHEDS

Tables 30, 31, and 32,  described earlier,  defined the various combina-
tions of collection areas which would satisfy the entire section of the
watershed under consideration.  The entire watershed was analyzed in
three sections, each the subject of a single computer run.  In order to
compare and rank the various alternative systems which would  serve the
section under study, it  is necessary, for each combination of collection
areas, to add the net benefits associated with the most attractive reuse
levels  for each of  the component collection areas, obtaining the total net
benefit for the combination.  This is done by adding the net benefits
appearing in  the final column of the  Table of Net Benefits (Figure 34) for
the collection areas which make up a given combination.  When this is
done for  each possible combination, the results can be ranked and the
optimum system for that section identified.

In order  to obtain  as much1 information about alternative strategies as
possible, a five-level output was obtained.   This  output defined optimum
systems  under each of the following assumptions:

1.    All levels of reuse possible

2.    Only reuse up to water quality "A" possible

3.    Only reuse up to water quality "B" possible

4.    Only reuse up to water quality "C" possible

5.    No reuse possible

This output for computer Run A is displayed as Figures 38 and  39.
Figure 38 lists total net benefits for all possible combinations under the
first four assumptions noted above.   Column "AA"  reflects combinations
of optimum  subsystems when all levels of reuse are possible.   It should
be noted  that the optimum  subsystems   might be composed of any assort-
ment of reuses. The only requirement is that each collection area be
served by the system having the maximum  net benefit for that area. These
subsystems  are those  identified by the MAX column  of Figure 34.
Column "A" follows the same pattern,  except that all subsystems involv-
ing the use of "AA" water are excluded from the analysis.  Column "B"
excludes all  "AA" and "A" uses and Column "C" excludes  all but "C. "
The assumption of no reuse required a separate computer run,  due to the
limitation of the system to storm water storage andpretreatmentfacilities,
Since no  benefits,  as defined in the economic analysis, derive from this
application, the net benefits reported are identical with system cost.
Figure 39 lists the totals for the various combinations.  This assumption
describes a system which retains only water pollution control as its
purpose  and permits direct comparison with the alternative method of
water pollution control  described in later chapters.
                               138

-------
                  «***   TABLE  OF  NET  BENEFITS  FOR  COMBINATIONS  OF   WATERSHEDS  ****
COMBINATION

  NUMBER
PLANT COMBINATIONSr   PERMISSIBLE  MAXIMUM  QUALITY

                                        AA
4
2
3
t,
5
6
J
8
9
10
11
12
13
14
15
16
17
IB
L9
20
21
22
23
24
^5
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
41
40
39
38
37
36
35
35
34
34
33
33
32
31
30
30
29
28
27
26
25
25
24
24
23
23
22
22
21
21
20
20
19
19
19
19
19
18
18
17
17
16
16
15
15
14
14
14
14
13
13
13
0
6
1
2
3
5
13
4
8
1
9
2
3
5
7
1
1
2
1
2
10
3
9
2
9
2
8
1
8
1
10
3
14
7
a
9
1
7
1
7
1
10
1
10
2
11
12
10
3
7
7
10
0
0
0
0
0
0
0'
6
0
6
0
6
6
6
0
2
3
3
5
5
0
5
3
3
5
5
3
3
5
5
6
5
0
6
2
1
2
3
2
5
2
1
3
2
3
5
3
4
4
10
3
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
6
0
6
0
6
0
6
0
6
0
0
0
0
6
0
3
0
5
0
5
0
5
0
0
0
5
0
5
2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
a
0
0
0
0
0
0
0
0
0
a
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
o
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
13.85
3.54
6.20
4.33
2.93
4.35
1.66
-6.40
2.77
-3.96
2.29
-5.78
-6.99
-5.72
3.88
-3.21
-4.57
-6.39
-3.15
-4.97
1.69
-6.33
-7.95
-16.02
-6.80
-14.86
-7.59
-14.31
-6.43
-13.15
-7.83
-15.85
1.98
-6.17
-6.55
-5.20
•13.27
-6.65
•13.75
-5.37
-12.46
-5.66
-13.68
-7.37
•15.40
-6.94
-8.09
-7.51
-15.53
-7.60
-15.62
-14.69
-54.38
-54.90
-56.84
-57.42
-57.82
-56.88
-57.00
-56.79
-53.54
-56.72
-55.60
-59.00
-63.55
-59.11
-56.56
-59.25
-61.61
-64.39
-58.71
-59.26
-59.05
-64.74
-62.92
-66.32
-61.56
-64.96
-62.18
-65.36
-59.29
-62.48
-60.11
-65.80
-55.69
-59.70
-59.21
-58.99
-62.40
-65.11
-67.80
-59.75
-62.45
-61.33
-67.02
-62.63
-68.32
-61.58
-61.46
-57.54
-63.23
-61.76
-67.45
-64.45
                                                                                   -54.90
                                                                                   -56.84
                                                                                   -57.42
                                                                                   -57.82
                                                                                   -56.88
                                                                                   -57.00
                                                                                   -56.79
                                                                                   -53.54
                                                                                   -56.72
                                                                                   -55.60
                                                                                   -59.00
                                                                                   -63.55
                                                                                   -59.11
                                                                                   -56.56
                                                                                   -59.25
                                                                                   -61.61
                                                                                   -64.39
                                                                                   -58.71
                                                                                   -59.26
                                                                                   -59.05
                                                                                   -64.74
                                                                                   -62.92
                                                                                   -66.32
                                                                                   -61.56
                                                                                   -64.96
                                                                                   -62.18
                                                                                   -65.36
                                                                                   -59.29
                                                                                   -62.48
                                                                                   -60.11
                                                                                   -65.80
                                                                                   -55.69
                                                                                   -59.70
                                                                                   -59.21
                                                                                   -58.99
                                                                                   -62.40
                                                                                   -65.11
                                                                                   -67.80
                                                                                   -59.75
                                                                                   -62.45
                                                                                   -61.33
                                                                                   -67.02
                                                                                   -62.63
                                                                                   -68.32
                                                                                   -61.58
                                                                                   -61.46
                                                                                   -57.54
                                                                                   -63.23
                                                                                   -61.76
                                                                                   -67.45
                                                                                   -64.45
                                                                              „g/j „ 86
                                                                              -56.86
                                                                              -54.84
                                                                              -57.42
                                                                              -6*,55

                                                                              -57,QQ
                                                                              -58.75
                                                                              -56.80
                                                                              -58.69
                                                                              -58.53
                                                                              -60.97
                                                                              -6^^2-4
                                                                              -61.08
                                                                              -57.06
                                                                              -59.25
                                                                              -66.34
                                                                              -66.88
                                                                              -59.26
                                                                              -60.30
                                                                              -66.30
                                                                              -66.15
                                                                              -68.60
                                                                              -64.48
                                                                              -66.93
                                                                              -66.15
                                                                              -68.05
                                                                              -62.55
                                                                              -6*.45
                                                                              -62-07
                                                                              -68.07
                                                                              -60.08
                                                                              -62.17
                                                                              -62.47
                                                                              -61.92
                                                                              -66.36
                                                                              -68.55
                                                                              -60.25
                                                                              -62.45
                                                                              -62.09
                                                                              -62.63
                                                                              -68.63
                                                                              -65.97
                                                                              -66.16
                                                                              -61.92
                                                                              -61.42
                                                                              -62.26
                                                                              -68.26
                                                                              -64.45
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
13
12
12
12
12
11
11
11
11
10
10
10
10
9
8
7
1
1
7
8
9
1
7
8
9
1
7
8
9
1
1
2
3
2
2
3
2
1
2
5
2
1
2
4
2
1
2
3
3
4
3
3
6
3
3
3
6
5
5
5
6
4
4
4
4
4
5
/t
5
0
0
0
6
0
0
0
6
0
0
0
6
5
5
6
5
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
6
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
                                                        -22.71
                                                        -16.24
                                                        -16.61
                                                        -15.27
                                                        -23.34
                                                        -15.09
                                                        -15.46
                                                        -14.11
                                                        -22.18
                                                        -15.66
                                                        -16.03
                                                        -14.68
                                                        -22.75
                                                        -22.70
                                                        -24.05
                                                        -23.68
                                                        -30.77
                                                   -70.14
                                                   -65.47
                                                   -64.98
                                                   -64.76
                                                   -68.17
                                                   -65.59
                                                   -65.10
                                                   -64.88
                                                   -68.29
                                                   -61.55
                                                   -61.06
                                                   -60.84
                                                   -64.24
                                                   -66.53
                                                   -66.75
                                                   -67.24
                                                   -69.93
-70.14
-65.47
-64.98
-64.76
-68.17
-65.59
-65.10
-64.88
-68.29
-61.55
-61.06
-60.84
-64.24
-66.53
-66.75
-67.24
-69.93
-70.45
-63.25
-68.55
-68.00
-70.44
-68.06
-68.36
-67.81
-70.25
-64.OZ
-64.32
-63.76
-66.21
-69.76
-70.32
-70.02
-72.21
         Figure  38.   Table  of Net  Benefits  of Combinations  of Watersheds,
                                     Reuse    Computer  Run  A
                                                    139

-------
           **** TABLE  OF  NET  BENEFITS  FOR  COMBINATIONS  OF  WATERSHEDS
XUMb 1 NA 1 1OTM
NUMBER
1
2-
3
4
5
6
7
—8—
9
l'\
1 1
1 2
13
-t-* —
1 5
16
17
18
1 9
-2f— •
21
22
23
24
25
- 26- -
27
28
29
30
31
-32-
3 3
34
35
36
37
38
3°
4-™-
41
42
43
44
45
46
47
48
49
5-i
51
52
53
54
•35
56
57
55
59
6'.,
61
-6-2-
63
64
65
66
67
6-fl
69

41
-4-9-
39
33
37
36
35



-6 	 d--
1 <"
2 •;
3 ,)
s a
13 '<
-^5 — *- — 6—
34
34
33
33
32
~tt—
3C-
3^
29
28
27
gO -
25
25
24
24
23
-23-
22
22
21
21
2i.':
8 T
1 6
9 C
2 6
3 6
— 5- — 6 —
7 2
1 2
1 3
2 3
1 5
-2 	 5 —
It  ^
-A 	 r3 	 *• 	 a 	 »"
'! '1 " V
,-, '1 - (V '.
3 (".' ', f  ^ A A
J 0 V '/ -J
_3| 	 £ 	 £ 	 f 	 fj.
.) '.'' •" 0 )
-5 "-' ^ -3 '''
C i: -" C' v
JJ -f ~ T.1 ~ 'I
"^ ^ v J ^
~a — * — r. — o — *•
o •: c c -5
->t t - -> o -t>
> 0 i" u .J
-6 c •:> <> -->
-J f, '! 1? ')

C 0
	 ^ 	 0-
0 0
" O
i> '.1
C fl
-; o
— t— -if-
:'. ">
•} lJ
0 3
r- e^
V 0
— $ 	 9 —
•1 fi
it- -0
f. 0
-- "5 -*
<^ 0
— f> 	 1»-
,•> ,)
-e- -6-
(. 0
- --(- -7
v 0
--2- 	 g 	 e. 	 a- — •" 	 T- 	 f 	 f- — -ft
8 3
1 - 3
8 5
1 5
If 6
•> 0 0 f ij
-6 &-:— 7-~ ,• o ; 3
•Sit 	 3- 	 5— -6 	 -n 	 %'— •* 	 i
19
19
19
19
--48-
18
17
17
16
16
-IS
15
14
14
14
14
-13
13
13
13
- 12
12
1 2
12
11
1 1
1 1
1 1
- K- -
1,.
1 ',
1 •
9
fl
--7 -
1
i •+ '.>
7 «
8 2
9 - 1
1 2
-.7. - 3_.
1 2
7 5
1 2
1C1 1
1 3
-1 ^ - - 2
2 3
11 5
12 3
!/>. 4
3 4
-7 -1--J.
7 3
U- 1
1 2
- 7 - -3— -
8 2
9 1
1 2
7 5
8 2
9 1
1 2
7 	 A- —
8 2
9 1
1 2
1 3
2 3
- 3- -4 -
2 3
-> K i; fr --fl
j i' " C' />
C/ 1,- -r - 0 i5
6 0 C "' >
-,: ._»•; 	 M---4 	 <3-
3 >•• C r j
,j ' ,', 41 -',
s <: i" " •!
11 -£- .'. ',
5 r
^ ^ ^
5 •• -: c j
c- o ;'• •'> i
; o ^ .\
"- '-- '- i'' U
5 •- ' o •;
.? . %i. _. / — -u _ .>
5 f " r '}
2 i. ., >;,
3 5 • r* 1
-6 — <- — ^- •-• , ,
3 t i V ''
3 .j <• 1 *
3 6 <• t 0
-6- -ft- , 	 C- - A
5 • ^ j
5 -, ,;- .7
So,. - ••
- 6-- -} — •"" - --"- - -
4 '.' • i
4 • rt i"
46- •• j
45-- >;- -i
4 5 1 v ';
-S- -6-- ... -.,v -.6
456--'
fi r.
-<* — -0-
''"• 0
- -•> -J
r J
— 1 	 9-
- 0---5-
i) 0
- fl- -&
' 9
	 fi — -0-
r-' c
o u
'' n
t ^
' 'i
|(. _^
" e
-*> j*
•• ?
*" o
•) o
.-4. 	 ;>
r .^
<, -U
,; •)
--J 	 <5-
«
- C <>
o o
- •- - '>
,-\ y
•J :>
f C1
- ->.-„ t.
\ -j
C rT
"• HIJ
,,
P -i
- ~ -* cf .
-
                                        NO REUSE
Figure 39.  Table of Net Benefits of Combinations of Watersheds,
                 No Reuse - Computer Run A
                             140

-------
OPTIMIZATION OF SYTEM

The discussion of sizing criteria for multiple purpose reservoirs which
appear sin Section VII included reference to various physical and aesthetic
constraints which exist at reservoir sites. Since the application of these
criteria is a function of the size of reservoir required at a given site as
well as the type of reservoir  selected, application of these constraints
was not attempted within the systems analysis.  In order to define the
final optimum system, however, tentative optima must be tested for the
physical and aesthetic constraints not included in the  computer analysis.
Many of these factors are determined by the exercise of judgement on the
part of the engineer, the owner, and the owner's representatives,  includ-
ing architects  and land planners.  For these reasons and others,  they
are not  considered susceptible to  quantitative analysis. The methodused
to test for  these constraints was as follows:

1.    The total net benefits for  a particular section of the watershed
      and particular level of output were placed in order  of decreasing
      net benefit.

2.    The highest-ranking system was defined in terms of reservoir
      types, sizes,  and locations.

3.    Each location was examined physically and via topographic and
      land use maps for feasibility of installation of the required facility.

4.    If any of the reservoirs in a given combination appeared not
      feasible due to insufficient usable space,  appearance, impact
      on the neighborhood,  etc., that combination was discarded and
      the next-highest ranking one selected.

5.    The process was repeated until the optimum feasible system
      was located for the  section and output level.

6.    The same method was applied to each output level and to each
      watershed section until all final optimum systems were defined.

These final systems are described and discussed in Sections XII,  XIII,
XIV,  and XV.  Information and guidance were obtained from the planning
and engineering staff of the Howard Research and Development Corporation,
developers of Columbia, with respect to land uses, aesthetic considerations,
and acceptability.   The responsibility for the exercise of judgement in
qualitative matters rests,  however,   solely with the  staff of Hittman
Associates, who performed the  analysis and made the final decisions.

It is interesting to note that the system actually selected from computer
Run A, all-reuse-level option,  was the thirty-first ranking system. Its
total net benefit was $20.  79 per day lower than the highest-ranking sys-
tem.  Had the local reuse system been afactorinthe original planning
of this area, it is reasonable  to assume that land  planning would have
provided for a system of  significantly higher net benefit,  thus improving
the economics of the concept over those detailed in this report.
                                 141

-------
SYSTEMS ANALYSIS COMPUTER PROGRAM

The method employed to analyze and optimize the local reuse system has
been described in detail in this and the  previous chapter.  The  actual
computations and organization of data referred to in the report were per-
formed on an IBM 360-65 digital computer system, utilizing a computer
code developed as part of this study.
                                142

-------
                            SECTION XII

            DEVELOPMENT OF CONCEPTUAL DESIGNS


The conceptual design and cost estimates of the  Local Storage, Treatment,
and Reuse system were prepared for three cases.  These are:

1.    Local Collection, Storage, and Treatment of Storm Water
      for Potable Reuse

2.    Local Collection, Storage, and Treatment of Storm Water
      for Sub-Potable Reuse

3.    Local Collection, Storage, and Treatment of Storm Water
      for Pollution Control

The system analysis  and optimization studies discussed in the two pre-
vious chapters had provided a complete  analysis of the various combina-
tions  of components  and locations based on least overall cost.  The sys-
tem analysis program had not been programmed to evaluate actual site
constraints and other design conditions.  Accordingly, the development
of conceptual designs and cost data involved (1) the selection of the sys-
tem configuration and locations  which could be constructed and operated
in the Wilde Lake Watershed at  the least overall cost,  (2) the preparation
of typical designs and drawings,  (3) modification of costs based on actual
site conditions, and (4) compilation of performance characteristics and
cost data.
SELECTION OF PLANT LOCATIONS AND SYSTEM  CONFIGURATIONS

A typical output of the system optimization program  was previously shown
as Figure 38,  "Table of Net Benefits for Combinations of Watersheds, "
and was discussed in Section XI.  Similar output sheets were produced
for each of the three sectors of the Wilde Lake Watershed for which con-
ceptual designs were desired.   These tables provide a listing of the
various combinations of plants and the net benefit (or cost) expressed  in
terms  of do liars/day.

As a first step it was necessary to examine the topography, boundaries,
and other site conditions to determine the maximum  size reservoir that
could be constructed at each possible location.  This involved plotting
the contours of the maximum water levels associatedwith various heights
of dams, planimetering  storage areas, estimating additional storage
quantities that could be obtained by excavation, etc.   In this examination,
the existing land use plans and lot boundaries were considered  invariant
to assure a practical design based on actual site conditions.
                                 143

-------
The next step was to determine the available storage capacities of vari-
ous combinations of reservoirs and to compare the  available storage
with the calculated volume for storms of one-year return interval.  For
each type of local storage system, the plant combination showing the
maximum benefit or least cost was found from among the first feasible
plant combination in the case of systems for potable reuse for the south-
west section  of the Wilde Lake watershed (CombinationNo.46, Figure 38).

Having selected the least cost and first feasible plant combination,  the
system configuration was also identified. The computerized system anal-
ysis program automatically calculates the capital and operating costs  of
alternative systems and selects the least cost configuration.  Accordingly,
it was only necessary to examine the printout of the program to deter-
mine the components that had been selected by the computer program
for the various  plants.  In  all cases,  the least  cost plant was based on
the use of open storage reservoirs.   The system analysis program also
calculates and prints the amount of water supplied for reuse.


PREPARATION OF PLANT LOCATION  AND TYPICAL DESIGN
DRAWINGS

The conceptual design drawings  showing the plant locations were pre-
pared based on the selected least cost plant combinations.  In the case
of the "Local Collection, Storage, and Treatment of Storm Water for
Sub-Potable Reuse, " it was also necessary to lay out a distribution sys-
tem.  These  drawings  are  contained in Sections XIII, XIV, and XV, with
discussions of the conceptual designs of the three systems.

Since this system study also involved the preparation of conceptual de-
sign drawings of the facilities for  a demonstration program,  the loca-
tions for the  demonstration facilities were used as the  basis for the
preparation of typical design drawings for storage reservoirs,  pretreat-
rnent systems,  and treatment plants.


MODIFICATION OF COSTS BASED ON ACTUAL SITE CONDITIONS

The typical design drawings of the facilities for the  demonstration pro-
gram were also used for another purpose.  Detailed unit and material
takeoffs were made and cost estimates based on the actual designs were
prepared.  These cost estimates were compared to  the capital costs
generated by the system analysis program.  The capital  cost inputs for
the system analysis program had been based on parametric cost data as
a function of  reservoir capacity  and  treatment  rates.  Although all the
major components were considered,  it was not possible to consider  all
of the possible  site conditions in this type of analysis.  Based on the
comparison of the computer-generated costs and the estimates based on
the typical designs prepared for the  demonstration program, the cost
data used for the  storage reservoirs  and pretreatment  units were found
to be low.  This was due to the following local  conditions.
                                 144

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1.    The storage reservoirs would be "Class 3 Impoundments" in
     accordance with recent regulations of the State of Maryland.
     "Class 3 Impoundments" are required to have spillways de-
     signed on the basis of a 100-year storm interval intensity.
     This regulation requires a dam of greater height and longer
     wing walls to retain the water.  Approximately two feet were
     added to typical embankment height,and embankment lengths
     were generally doubled.

2.    The reservoirs for the demonstration programs were
     designed to have a minimum pool depth of two feet to pre-
     clude weed growth.  This, plus the "Class  3 Impoundment"
     requirement, increased the  amount of excavation required.

3.    The demonstration plant estimate includes  fencing around
     the reservoirs.

4.    The allowances for contingencies and engineering the dem-
     onstration plant are based on "first of a kind" facilities and
     the construction of a limited number of facilities.

The treatment plant designed for the demonstration program would prob-
ably not  be  typical of those  used  for the treatment of storm  water in
future installations, particularly  where the quantity of water is relatively
small.   This plant is designed as  a general purpose test plant in which it
would be possible to evaluate various treatment processes.  Once treat-
ment processes  are established for storm water,  it is most likely that
packaged treatment plants would be designed  for  this purpose.  These
would be automated plants designed to shutdown automatically uponfail-
ure and could be installed in either underground  chambers or  small
surface structures.

For purposes of estimating the capital costs of constructing local storage,
treatment,and reuse systems in the Wilde Lake Watershed, the estimated
costs for the demonstration program storage reservoirs and treatment
units were used  in order to be conservative.   This was done by plotting
the estimates for the three demonstration reservoirs and  pretreatment
systems on the parametric cost curves used in the system analysis.  New
curves of costs vs. capacity were generated,and  the  appropriate costs
were determined for each of the reservoirs required.  Treatment plant
costs were not modified.  The treatment cost data used in the  system
analysis program are considered conservative, particularly since packaged
treatment plants would be used.


COMPULATION OF PERFORMANCE CHARACTERISTICS AND COST
DATA

Each of the three local collection,  storage, and treatment systems
consists of a number of reservoirs, pretreatment, treatment,  and dis-
tribution facilities.  Accordingly,  the  conceptual design of the system
                                145

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involved the compilation of the performance data for each of the indi-
vidual installations and the evaluation of the overall effectiveness as a
means of pollution control and water supply augmentation for the entire
watershed.  Similarly,  the capital and operating costs of the individual
installations were compiled to evaluate the overall cost of the system,
the economic benefits of reuse, and the net costs of pollution control.
These costs were then broken down to establish the costs per acre, per
dwelling unit,  and per thousand gallons of runoff.  The performance and
cost data for each of the three local collection, storage, and treatment
systems is presented in the next three sections.
                                146

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                           SECTION XIII

        LOCAL COLLECTION,  STORAGE,  AND TREATMENT
             OF STORMWATER FOR POTABLE REUSE

         I
The "Local Collection,  Storage, and Treatment of Storm Water for Potable
Reuse" system,  hereafter referred to as the "Potable Reuse System," con-
sists of a series/parallel arrangement of storage reservoirs which collect
flows from the associated sub-watersheds and treated water and overflows
from the upstream storage reservoirs.  Table 33 lists the locations of the
10 reservoirs and the sub-watersheds and upstream reservoirs from which
flow is collected.  The locations are shown on Figure 40.


               TABLE 33.  POTABLE REUSE SYSTEM
            STORAGE RESERVOIR COLLECTION AREAS

                                     Source  of Flow
Location           Sub-Watershed                 Upstream Reservoir
   A         1     2     3
   B        11    12    13                                 A
   C         4     5    14                                 D
   D         6     7                                      E
   E         8
   F         9    15    16    17    18     20                B, C
   G        19
   H        22
    I        21                                            J
   J        10*

*The only feasible location for a storage reservoir  in sub-watershed 10
  is Location J.  At this location only 40 percent of  the flow from the sub-
  watershed is intercepted.

A pretreatment unit is installed at each  of the storage reservoirs. These
pretreatment units treat the storm water to Class  ' C" quality for dis-
charge to Wilde  Lake or for further treatment and reuse.  Treatment
plants are located at nine of the storage reservoirs. The treatment plants
take Class  "C" water from the pretreatment units and treat the water to
potable quality,  Class "AA. "  Table 34 lists the  type of storage,  storage
capacity, pretreatment capacity,  quality of water produced, and the  final
treatment plant capacity. No treatment plant is  provided at Location H
because incremental costs of treatment  exceeded possible benefits from
reuse.   Pretreatment units are sized for maximum  flow independent of
water diverted for treatment upstream.

Each of the nine treatment plants includes pumping facilities and connections
to the public water systems.   The treated storm water is supplied as a sup-
plementary source of water and is distributed through the public water dis-
tribution systems to meet all types of demands,  Classes "AA" "A" "B]1 and ' C.
                                 147

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oo
                                                LOCAL COLLECTION, STORAGE, AND
                                                TREATMENT OF STORM WATER FOR
                                                         POTABLE RE-USE
                                                                                             FWPCA Contract No 14-12-20

                                                                                              WILDE LAKE WATERSHED
                                                                                                 Columbia, Md.
                                      Figure 40.   Potable  Reuse System  Location Plan

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CO
                         TABLE 3-4.  LOCAL, COLLECTION,  STORAGE, AND TREATMENT
                        OF STORM WATER FOR POTABLE REUSE - CONCEPTUAL DESIGN

Location
A
B
C
D
E
F
G
H
I
J

Storage
POND
POND
POND
POND
POND
POND
POND
POND
POND
POND

Capacity
(Gal)
1, 577, 300
2, 145, 000
1, 902, 100
1, 907, 200
625, 900
5, 101,400
923, 500
358, 400
690,000
503, 200
Pretreatrnent
Capacity
(gpd)
67, 900
231, 400
386, 100
232, 400
58, 900
1, 036, 300
85, 700
29, 800
63, 800
55, 100
Water
Quality
Produced
AA
AA
AA
AA
AA
AA
AA
C
AA
AA
Final
Treatment Capacity
(gpd)
30, 400
81, 800
76, 900
86, 800
29, 500
209, 400
38, 400

31, 900
24, 780*

Connected
Demands
AA, A, B, C
AA, A, B, C
AA, A, B, C
AA, A, B, C
AA, A, B, C
AA, A, B, C
AA, A, B, C

AA, A, B, C
AA, A, B, C
                        percent of watershed intercepted by storage facility.

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COMPONENT DESCRIPTIONS

Figure 41 is a flow diagram  of a typical  "Potable Reuse System"
installation.  Each of the installations (except at Location H) consist of
the following:

Storage Reservoir

These reservoirs are open storage reservoirs, or ponds, formed by
the construction of concrete dams.

Pretreatment  Units

The pretreatment units are installed downstream and receive flow by
gravity from the storm retention reservoirs.  The pretreatment units
consist of a float-operated valve,  chlorination equipment chamber, and
a tube settler.  The pretreatment units have a sump for the collection
of sediment and use float valves to control flow.

Treatment Plant

The treatment plant takes flow from the pretreatment unit.  The plant
consists of a mixed media filtration unit followed by an activated carbon
column for carbon absorption. Provision  is made for chemical feed
prior to filtration and for chlorination prior to discharge to the  treated
water storage tank.  The piping is arranged for backwashing the mixed
media filter with a connection to  the sanitary sewer.

Treated Water Storage

The treated water storage consists of  steel tanks at grade.  The treated
water storage tank also serves as the  filter backwash storage tank,  the
distribution pump clearwell,  and the chlorine contact tank.

Pumping System

The pumping distribution system consists  of a pump with associated con-
trol and a connection for supplying treated water to the public water sys-
tem.

Sewer Connection

A connection is provided to public sewer systems to receive filter back-
wash.  Appropriate measures are taken to prevent any possibility of back-
flow from the  sewer.
                                 150

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Distribution System
Storage Reservoir
                                                                                      Chlorine
                                           Pressure
                                          High Service
                                            Pump
                               Chemical
                                Feed
                                     Overflow to Chemical
                                       Stream
                                                  Feed
                                 L...
Sediment
Removal
                              Pretreatment Unit
                 Treated Water
                    Storage
                               To Sanitary
                                   Sewer
                                                                           .
                                                                     Media)
                       ravel
                                        Acti-
                                        vated
                                       Carbon
                                                                                        -H-f
                                                                   Mixed Media
                                                                     Filtration
                                       Carbon
                                      Adsorption
                         Figure 41.  Potable Reuse System Flow Diagram

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PERFORMANCE CHARACTERISTICS

The demands for potable water in the Wilde Lake Watershed will exceed
the amount of storm water runoff available even with the higher runoff
quantities that will result when the area is further developed.   In addition,
since the treated storm water would be supplied to and distributed by the
public water system, the  demands of any part of the watershed can be
supplied.  This is contrasted to systems using a separate distribution
system  in which the supply and demand  of the individual sub-watershed
must  be considered.  Table 35 contains  a listing of the annual potable
water requirements,  the total amount of storm water runoff, and the
amount of treated water supplied to the service areas from  the treatment
plants.

Since the demands of the watershed exceed the available supply, the
"Potable Reuse System" was designed to produce the maximum treated
water in order to maximize the reuse benefit. An upper limit of 90 per-
cent of the available storm runoff was used in the design of  the individual
reservoirs and treatment plants, in order to  assure that a portion of the
storm runoff would still go to  Wilde Lake, in addition to the base flow.
As finally designed,the "Potable Reuse System" will provide 202,942,000
gallons per year of calculated annual runoff of 246, 967, 000  gallons. This
represents 82 percent of the available supply. About 29, 000, 000 gallons
of treated water would be  released to Wilde  Lake  and  an additional
15, 000, 000 gallons of storm water runoff would go directly  to the lake
since the only possible location for a  reservoir in sub-watershed 10 is
at Location J which can only intercept some 40 percent of the runoff from
the sub-watershed.

The pretreatment units are designe_d to treat  storm water at twice the
mean annual daily runoff rate,  2  x q.  In order to maximize the treated
water supply, the pretreatment units would be  operated  at 1.  1 to 1. 4 x q,
plus the base flow.   At this rate, there is an  increased probability  of not
having the reservoir emptied sufficiently to receive the runoff from a
subsequent storm.  In terms of_the design criteria of storms of one-year
recurrence  intervals, the 2 x _q  discharge rate would retain 98. 5 percent
of the runoff, whereas a 1. 13 x q discharge rate would retain 97. 3 percent
of the flow.   Expressed in terms of all storms including those greater than
one-year recurrence interval, the following relationships were calculated.

                                                  Percent of Total
Condition                                         Runoff  Retained

One-year storm design    no residual assumed            92. 6
One-year storm design    2 x q_discharge rate            91. 2
One-year storm design    1. 13 q discharge rate           90. 0

Accordingly, with the "Potable Reuse System" not more than 10 percent
of the runoff would normally overflow the reservoir and not  receive the
full Class  C  treatment.   However,  even the overflows will be retained
in the storage reservoirs  for a time period adequate to allow settlement
                                152

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                     TABLE 35.  POTABLE WATER REQUIREMENTS, TOTAL STORM WATER
                                        RUNOFF,  AND AMOUNT SUPPLIED
                                             (Amounts in Gallons/Year)
Ul
GO

Potable Water Requirement
Treatment Plant Pretreatment
Location Sub-watersheds By Sub-watershed Plant
A 1
2
3
B 11
12
13
C 4
5
14
D 6
7
E 8
F 9
15
16
17
18
20
G 19
H 22
I 21
J 10
4, 519,000
4, 551,000
1, 858, 000
15,283,000
7,234,000
11,852, 550
9,278,000
10,289,000
24,229,000
67,435,000
35,679,000
16, 542,000
22,907,000
3,927,000
15, 830,000
24, 794, 000
6,216, 000
20, 122,000
8, 399,000
7,296,000
22,601, 000
45,045,000


10,928,000


34,369,000


43,796,000

103, 114,000
16,542,000





93,796,000
8, 399,000
7,296,000
22,601,000
45,045,000
Total Storm Water Runoff
By Watersheds
3,627,000
4,694,000
4,073,000
12,378,000
7, 332,000
10, 134,000
4, 791,000
7,733,000
15, 528,000
17,653,000
14,007,000
10, 741,000
17,818,000
3,700,000
10,260,000
20, 388,000
3, 905,000
20, 351, 000
15,637,000
5,440,000
11,653,000
25, 124,000
Per
Treatment Plant


12,394,000


29, 844,000


28,052,000

31, 660,000
10,741,000





76,422,000
15,637,000
5,440,000
11, 653,000
10, 049, 000*
                                                                                                          Amount
                                                                                                          Supplied
                                                                 11, 104, 500


                                                                 26,754, 500


                                                                 25,155, 800

                                                                 28, 185, 300
                                                                  9,621,400
                                                                                                        68,612, 700
                                                                                                        14,009, 900

                                                                                                        10,453,600
                                                                                                         9,044, 500
          Totals
385,886,000      385,886,000    246,967,000     231,892,000     202,942,200
          ^Intercepts 40 percent of the sub-watershed.

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of the heavier participate matter.   Added to the runoff that cannot be
practically intercepted, this would represent  22, 000, 000 to 40, 000, 000
gallons per year compared to the 247, 000, 000 gallons or greater amount
of runoff that would otherwise be discharged directly to the lake.  Neither
estimate includes the base flow from the watershed which is not affected
by individual storms.

Most of the water reused by the "Potable Reuse System"  would eventually
return to the river basin as effluent from the  wastewater treatment plant.
Since this is  downstream from Wilde Lake, the remaining flow of the lake
must also be considered.  Water must be supplied to Wilde Lake to provide
for the evaporative losses,  seepage from the  lake, andthe release require-
ments placed on the  Wilde Lake dam by the State of Maryland.  The evapora-
tive losses of the lake were calculated to be about  22, 000, 000  gallons per
year.  However, the  rainfall directly into the  lake  represents an equal or
slightly greater amount of water.  The state requirement on release is a
general requirement that precludes  diversion of the water from the lake
itself.

The 29,000, 000 gallons of treated water and the 22, 000, 000 to 40, 000,000
gallons of untreated  water that would be  discharged to the lake  did not
include the base flow from the stream.  As discussed in Section II, a tem-
porary gaging station was installed and operated on al30-acre  sub-water-
shed in Wilde Lake as part of this study.   The  measured base flow of
0.05 cfs,  extrapolated to the entire  1140-acre watershed, would indicate
an annual base  flow to the lake in excess of 104, 000, 000 gallons per year.
The total flow of 150 to 170 million gallons of water per year to Wilde Lake
would correspond quite closely to the natural  condition of the area with a
runoff calculated at 43, 000, 000 gallons per year plus the base flow.


DESIGN AND CONSTRUCTION COSTS

The "Potable Reuse  System" will consist of 10 storage reservoirs and
pretreatment units and nine storm water treatment plants, pumping sys-
tems, and connections to the public  water  and sewer system.  The major
design and construction items are summarized in Table  36.

As discussed previously,  land costs were  not included on the basis that
all of the  storage reservoirs and treatment plants  could be locatedwithin
the floodplain which  is dedicated to open space in the case of Columbia.

In order to provide conservative estimates of the  design and construction
costs for the "Potable Reuse System" for comparison with other systems,
the cost estimates in Table  36 are based upon the assumptions and criteria
used in the system analysis.  As noted previously  in Section XII, the esti-
mated costs of  the storage reservoirs and pretreatment units have been
scaled up to take full account of local conditions.   It is considered that
these costs could be  reduced substantially by  further design work.  Like-
wise,  estimates for  the treatment plants are based on small size conven-
tional treatment plants.  It is  envisioned that  packaged treatment plants
                                 154

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would be developed for future "Potable Reuse Systems, "  and these costs
would also be substaintailly reduced.


OPERATION AND MAINTENANCE COSTS

The operation and maintenance costs for the "Potable Reuse System"
were estimated using the assumptions and criteria used in the system
analysis as discussed in Appendices C and D.  Since a number of nearly
identical installations are involved which would be located in a relatively
small area,  the parametric cost estimates were modified based on the
actual designs that had been developed.  For example, checks and oper-
ations can be perfomed by personnel moving from one location to another,
Likewise, maintenance items such as the cleaning of sediment from res-
ervoirs can  be accomplished by a crew handling a number of facilities at
one time. Certain of the costs (i.e.,  chemicals, pumping power,  etc.)
can be directly related to the  quantities of water processed.  As dis-
cussed in Appendix D, the costs for operation and maintenance,as based
on this work being performed by extension and expansion of an existing
organization and a supporting organizational and overhead structure,has
not been included.

Table 37 contains  a summary of the operation and maintenance for the
"Potable Reuse System. "
                                155

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                 TABLE 36.  LOCAL COLLECTION, STORAGE, AND TREATMENT OF STORM
                   WATER FOR POTABLE REUSE - DESIGN AND CONSTRUCTION COSTS
                                               (Amounts in Dollars)
A
B
C
I>
E
Location
       F
::-
                                                                                       I.
                                                                                               .
                         ____
Construction
   Storage Reservoirs   61,000   71,500   67,500  68,000   40,500  109,000  47,000   32,500   42,000  33,500
   Pretreatment Units    8,200    9,600   10,200   9,600    8,000   11,400   8,600    7,300    8,200   7,600
   Treatment Plant      35,600   41,800   41,100  42,400   35,400   78,400  36,600            35,800  35,000
   Pumping and Distri-
     bution
   Subtotal
                                                                                                               Total
                        12,400   12,320   12,600  12,800   10,200   19,400  10,800            10,600  12,100
                      117,200  135,200  131,400 132,800   94,100  218,200 103,000   39,800   96,600  87,600  1,155,900
Design, Inspection and
   Field Engineering    17,500   20,300   19,700  20,000   14,100   32,700  15,600    6,000   14,600   13,200   173,700
Contingencies and
   Escalation
   Total
                       11,700   13,500   13,100  13,300    9,400   21,800  10,300    4,000    9,700    8,800   115,600
                      146,400  169,000  164,200 166,100  117,600  272,700 128,900   49,800  120,900  109,600 1,445,200

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              TABLE 37.  LOCAL COLLECTION, STORAGE, AND TREATMENT OF STORM:
          WATER FOR POTABLE REUSE - ANNUAL OPERATING AND MAINTENANCE COSTS-


Storage Reservoirs
(1) Routine Checks
(2) Trash Removal and
Nuisance Control
(3) Sediment Removal
Pretreatment Units
(1) Routine Checks
(2) Sediment Removal
(3) Chemicals
(4) Preventative Mainten-
ance and Repair
Treatment Plants
(1) Routine Inspections
(2) Water Tests
(3) Routine Operation
(4) Chemicals
(5) Preventative Mainten-
ance
(6) Electrical Energy
(7) Sewer Change
Pumping Facility
(1) Routine Checks
(2) Preventative Mainten-
ance and Repairs
(3) Electrical Energy
(4) Distribution
Miscellaneous
Totals
Labor
(man hours)

260

240


260



610

2, 920
940
1, 880


2, 350



240

700



10,436
Labor
($)

750

690


750



1, 760

8,400
3,060
5,400


7, 640



715

2, 260

120

31, 545
Material Equip. Rental*
($) ($)



250
2,400


3,250
4, 500

880


400

2,500

3, 820





1, 130


14,090
26,840 5,650
Miscellaneous
($> Totals
4,090






10, 110



35,030






3,000
810

6, 390


3, 000

14,090
6., 810 70, 845
^Include Operators

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                            SECTION XIV

      LOCAL COLLECTION, STORAGE,AND TREATMENT OF
            STORM WATER FOR SUB-POTABLE REUSE
The "Local Collection, Storage, and Treatment of Storm Water for Sub-
Potable Reuse" system, hereafter referred to as the "Sub-Potable Reuse
System, " consists of a series/parallel arrangement of storage reservoirs
which collect flows from the associated sub-watersheds and treated water
from the upstream storage reservoirs.  Table 38 lists the locations of the
10 storage reservoirs and the  sub-watersheds and upstream reservoirs
from which flow is collected.  The locations are shown on Figure 42.


            TABLE 38.   SUB-POTABLE REUSE SYSTEM
            STORAGE RESERVOIR COLLECTION AREAS
                                   Source of Flows
Location
A
B
C
D
E
F
G
H
I
J
*Reservoir
Sub -water sheds
1
11
4
6
7
9
19
22
21
10
J only
2
12
5
8

15


*
3
13
14


16 17 18



intercepts 40 percent of
Upstream
Reservoirs
-
A
D
E
-
20 B, C



sub -water shed 10.
The "Sub-Potable Reuse System, " like the "Potable Reuse System, " has
pretreatment units which treat the storm water to Class "C" quality for
discharge to Wilde Lake or for further treatment. In the case of the
"Sub-Potable Reuse System" the water from the pretreatment units is
either distributed as Class "B" or Class "C" water.   In the case of Class
"B" reuse, a treatment plant is  installed with a pumping station which
takes the water from Class "C" to Class "B" quality.  In the case of
                                159

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      LOCAL  COLLECTION, STORAGE, AND
      TREATMENT  OF STORM WATER FOR
            SUB-POTABLE RE-USE
                                                     FWPCA Controct No.14-12-20

                                                      WILDE LAKE WATERSHED
                                                         Columbia. Md.
Figure 42.  Sub-Potable Reuse System - Location flan

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Class "C" reuse, the water is taken from the pretreatment units through
a pumping station.  As shown on Figure 42,  a distribution system is
provided for the sub-potable water in each sub-watershed.  Connections
are provided from the pumping stations to the distribution system in the
sub-watershed or combination of sub-watersheds from which runoff is
collected.

Table 39 lists the type of storage/ storage capacity,  pretreatment
capacity, water quality produced, final treatment quality, and the con-
nected demands for each of the reservoirs and treatment plants used
with the "Sub-Potable Reuse System."

Comparing Table 33 and Table 38 it is notedthat the "Potable Reuse System"
and the "Sub-Potable Reuse System"  differ with respect to the collection
areas of reservoirs D and E. As shown on Figure 38,the optimal feasible
case for the "Potable Reuse System" is the Combination  Number  46
(Cases 14,  11, and 5),whereas the optimal sub-potable combination is
number 48  (Case 14,  10,  and 4) for Class "C" water.
COMPONENT DESCRIPTIONS

The components comprising the "Sub-Potable Reuse System" installations
are similar to those of the "Potable Reuse System"  described in
Section XIII. The two types of systems differ only with respect to the
treatment plants and the sub-potable distribution system.

The "Sub-Potable  Reuse System" has two types of treatment facilities.
Figure 43 shows a flow diagram for a  Class "B" treatment plant of the
type used at Locations A, B,  C, and F.  For this type  plant,  water from
the pretreatment unit goes through a microstrainer and is pumped to
a treated water storage tank which also serves  as a chlorine  contact tank.
A high pressure service pump supplies the sub-potable distribution
system.  A connection from the public water supply system provides
water when the local treatment plant is not operating.

Figure 44 is a flow diagram for a Class "C" treatment plant of the type
used at Locations  D,  E,  G, H, I,  and  J.  With this type plant, flow from
the pretreatment unit goes directly to  a treated water storage tank which
is also a chlorine  contact tank and is then  pumped to the sub-potable
distribution system.  A connection from the public water supply is also
provided to provide water when the plant is not  operating.

The sub-potable distribution system consists of underground pipe lines as
shown on Figure 42 and the separate piping systems withinthe houses, town
houses, apartments,  schools,  and commercial  buildings.   The design
is based on the construction of the sub-potable distribution system follow-
ing installation of  other utilities.  In actual practice, such a system might
be placed at the  same time  as the  public water supply and sewer system.
This would appreciably reduce the cost of  the sub-potable system.
                                 161

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 TABLE 39.  LOCAL COLLECTION, STORAGE, AND TREATMENT OF
 STORM WATER FOR SUB-POTABLE REUSE - CONCEPTUAL DESIGN


Type of
Location Storage
A
B
C
D
E
F
G
H
I
J
POND
POND
POND
POND
POND
POND
POND
POND
POND
POND
Stora
ge
Capacity
(Gal)
1, 577,
2, 145,
1,902,
803,
1, 729,
5, 101,
923,
358,
690,
503,
300
000
100
000
900
400
500
400
000
000*
Pretreatment
Capacity
(gpd)
67,
231,
386,
232,
155,
1, 036,
85,
29,
63,
55,
900
400
100
400
600
300
700
800
800
100
Water
Quality
Produced
B
B
B
C
C
B
C
C
C
C
Final
Treatment Capacity
(gpd)
23,
54,
65,
33,
77,
160,
4,
5,
20,
20,
500
000
400
600
800
200
300
400
100
700
Connected
Demands
B,
B,
B,
C
C
B,
C
C
C
C
C
C
C


C




#40 percent of watershed intercepted by storage facility.

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O5
CO
                               Auxilllary Source

                                 (Public Supply)
              Backflow
              Preventer
              Valve
           Distribution
           System          "*"
                                                        Pressure
                                                      High Service
                                                         Pump
                                              Chemical
                                              Feed
                                                        Overflow
                                                        System
Treated Water
   Storage
Chemical
Feed
                                                                                                     Chlorine
             Storage Reservoir
                                                             "[Sediment
                                                           	I Removal
                                               Pretreatment Unit
                                                                                         rf—M-
                                                                          Microstrainer>
                               Figure 43.  Sub-Potable Reuse System Flow Diagram -
                                                 Class "B" Treatment

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        Backflow
        Preventer
        Valve
   Distribution System
05
                        Auxiliary Source

                        (Public Supply)
                                                  Pressure
                                                High Service
                                                   Pump
                                                Chemical
                                                Feed
   Treated Water
      Storage
Overflow to
  Stream
                             Chlorine
               Storage Reservoir
                                                                  Sediment Removal
                                                Pretreatment Unit
                          Figure 44.  Sub-Potable Reuse System Flow Diagram -
                                           Class "C" Treatment

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PERFORMANCE  CHARACTERISTICS

In the case of the "Sub-Potable Reuse System, " the water is distributed
for use to the sub-watersheds from which it is collected.  Unlike the
"Potable Reuse System, " the "Sub-Potable Reuse System" must consider
the available supply of water and the demands for sub-potable water on
a sub-water shed by sub-watershed basis.  Table 40 contains a listing
of the sub-potable water requirements by class of water to be distributed
for each sub-water shed and treatment plant,the total storm water runoff
available from each sub-watershed at each treatment plant, and the amount
of water supplied.

The amount of water supplied for reuse in the Wilde Lake watershed
would be 167, 849, 000 gallons per year.  This represents 46. 5 percent
of the total water requirements of the area.

The pretreatment units would be  operated in the same manner as
previously described for the "Potable Reuse System. "  The probability
of spills and quantities of water overflowing the reservoirs or going
directly to Wilde  Lake without the full Class "C" treatment would be
essentially the same for the "Sub-Potable Reuse System. "

With respect to maintaining adequate flow to Wilde Lake, the  "Sub-
Potable Reuse System" would normally discharge about  70, 000, 000 gal-
lons  of treated water to the lake.  This would be in addition to the base
flow,  possible overflows, and the 15, 000, 000 gallons from sub-watershed
10 that cannot be  intercepted in a practical manner.  Accordingly, more
than  adequate flow will be maintained to the lake.

The 167, 849, 000  gallons of water supplied to the area represents an
annual benefit of $75, 532 at the current distribution price of 45 cents
per thousand gallons.


DESIGN AND CONSTRUCTION COSTS

The major construction items for the "Sub-Potable Reuse System" will
be the same as those for the "Potable Reuse System" in Section XIII
with the following exceptions:

1.    As discussed above,  the treatment plants will have fewer
      components

2.    The sub-potable distribution system, composed of:

      a.    Underground piping

      b.    Dual systems within buildings

Table 41 contains a summary of the  estimated design and construction
costs for the "Sub-Potable Reuse System. "  As shown, the cost of the
                               165

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             TABLE 40.  SUB-POTABLE WATER REQUIREMENTS, TOTAL
                   STORM WATER RUNOFF, AND AMOUNT SUPPLIED
                                (Amounts in Gallons/Year)
Sub-Potable Water Requirement
Treatment
Plant Location
A
B
C
E
D
F
G
H
I
J
Totals
Sub-
Watersheds
1
2
3
11
12
13
4
5
14
6
8
7
9
15
16
17
18
20
19
22
21
10

Class
B, C
B, C
B,C
C
C
B, C
C
C
C
C

by Sub-watersheds
Quantities
3, 369,000
3,401,000
1,420,000
8,658,000
4,278,000
6, 924,000
5,212,000
4,923,000
13, 724,000
23, 327,000
5,497,000
12, 238, 000
17, 166,000
2,230,000
10,957,000
12,038,000
3,697,000
12,363,000
1, 540,000
1, 964,000
7,315,000
12, 687,000
174, 928, 000
Per
Treatment
Plant
8, 190,000
19, 860,000
23, 859,000
28, 824,000
12, 238,000
58,451,000
1, 540,000
1,964,000
7, 315,000
12, 687, 000
174, 928,000
Total Storm
by
Watershed
3,627,000
4,694,000
4,073,000
12, 378,000
7, 332,000
10, 134,000
4, 791,000
7, 733,000
15, 528,000
17, 653,000
10, 741, 000
14.007, 000
17, 818,000
3,700,000
10,260,000
20, 388,000
3, 905,000
20, 351,000
15, 637, 000
5,440,000
11, 653,000
25, 124,000
246, 967,000
Water Runoff
per
Treatment
Plant
12, 394,000
29, 844,000
28,052,000
28, 394, 000
14, 007,000
76, 422,000
15,637,000
5,440,000
11, 653, 000
10, 049, 000*
231, 892, 000
Amount
Supplied
8, 190,000
19, 695, 000
23,856, 000
25, 555,000
12, 238, 000
58,451,000
1, 540,000
1, 964,000
7, 315,000
9, 045,000
167, 849. 000
*Based on intercepting 40 percent of sub-watershed

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03
                         TABLE 41.  LOCAL  COLLECTION,  STORAGE,  AND TREATMENT
                                 OF STORM WATER FOR SUB-POTABLE  REUSE
                                      DESIGN  AND CONSTRUCTION COSTS
                                              (Amounts in Dollars)            	
Construction

Storage Reservoirs
Pr e - Tr eatment
Treatment Plants
Pumping System and
  Connection
Subtotal
Distribution
Subtotal
                                    Location
  ABCDEFGHIJ
 61,000  71,500   67,500  45,000  65,000  109,000  47,000   32,500  42,000  33,500
  8,200   9,600   10,200   9,600   9,200   11,400   8,600    7,300   8,200   7,600
 15,000  15,900   16,200                   18,700

 12,700  11,200   13,300   5,700   5,800   27,700   5,500    5,400   5,900   7,800
 96,900 106,200  107,200  60,300  80,000  166,800  61,100   45,200  56,100  48,900    828,700
 37,400 134,800  143,400 230,000 100,400  380,000  43,600   25,200  57,900  97,100
134,300 241,000  250,600 290,300 180,400  546,800 104,700   71,400 114,000 146,000 2,074,200
      Design,  Inspection and
        Field Engineering     21,100   36,200  37,700  43,500  27,600   81,100  15,800   10,800  17,100  21,900
      Contingencies and
        Escalation            13,400   24,100  25,100  29,000  18,400   54,700  10,500   7,200  11,400  14,600
      Total
                       168,800 301,300 312,800  362,800 225,400 682,600 136,000   87,900 142,500  182,500 2,598,600

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sub-potable distribution system represents a major portion of the cost
of the overall system.  The design of the sub-potable system is based
on a system of comparable design to public water systems  and assumes
that it is installed as a separate entity.  As previously noted, in the case
of new developments, this system would probably be installed concurrently
with the public water and sewer system. In other cases where there is
a large irrigation or industrial demand  for sub-potable water,a simpler
or less expensive distribution  system could be used. Table 42 illus-
trates the limits  and effect of the cost of the distribution  system.
OPERATION AND MAINTENANCE COSTS

Table 43 contains a summary of the operation and maintenance costs
for the "Sub-Potable Reuse System. "

The operation and maintenance  costs for the  "Sub-Potable System" were
estimated on the  same basis as the  "Potable  Reuse System" with treat-
ment plant operating costs being lower and an allowance made for the
maintenance  of the distribution  system.
TABLE 42.  EFFECT OF DISTRIBUTION SYSTEM ON CAPITAL COSTS


System without Distribution Costs

      Construction Costs without Distribution          $   828, 700.00
      Design,  Contingencies, and Escalation (25%)           207,200.00
      Subtotal without Distribution                       1, 035, 900. 00
      Equivalent Cost per Year                             54, 220.00
      Equivalent Cost per Day                                 148. 54

System with Distribution Costs

      Construction Cost with Distribution                 2, 074, 200. 00
      Design,  Contingencies,  and Escalation               524,400.00
      Total with Distribution                             2, 598, 600. 00
      Equivalent Cost per Year                            136,013.00
      Equivalent Cost per Day                                ' 372. 64

      Value  of Sub-Potable Water per Year                  75, 532. 00
      Value  of Sub-Potable Water per Day                      206. 94
                                 168

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en
CD
                TABLE 43.   LOCAL COLLECTION,  STORAGE, AND TREATMENT OF STORM WATER
                  FOR SUB-POTABLE REUSE - ANNUAL OPERATION AND MAINTENANCE COSTS


Storage Reservoirs
(1) Routine Checks
(2) Trash Removal and
Nuisance Control
(3) Sediment Removal
Pretreatment Units
(1) Routine Checks
(2) Sediment Removal
(3) Chemicals
(4) Preventative Mainten-
ance and Repair
Treatment Plants
(1) Routine Inspection
(2) Water Testing
(3) Routine Operations
(4) Chemicals
(5) Preventative Mainten-
ance and Repair
(6) Electrical Energy
(7) Sewer Charge
Pumping Facilities
(1) Routine Checks
(2) Preventative Mainten-
ance and Repair
(3) Electrical Energy
(4) Connections
Distribution System
(1) Maintenance and
Repair
Miscellaneous
Total
Labor
(man hour)

260
240



260



520

1,460
1,040
1,454


406



312

394

36


1,054

69, 361
Labor
($)

750
690



750



1,730

4,200
3,060
4,200


1,320



900

1,280

120


3, 750

22,750
Materials Equipment Utilities
($) Rental ($) ($)


250

2, 400
1

3,250
4,500

850
1



3,000

660
1, 680
500



640
2, 400



3, 750
8,670
22, 320 5, 650 4, 580
                                                                                                       Totals
                                                                                                       10,050
                                                                                                       18, 520
                                                                                                        5,340
                                                                                                        7, 500



                                                                                                        8, 670
                                                                                                              55, 300

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                            SECTION XV

        LOCAL COLLECTION, STORAGE, AND TREATMENT
          OF STORM WATER FOR POLLUTION CONTROL
The "Local Collection, Storage, and Treatment of Storm Water for
Pollution Control" system, hereafter referred to as the "Local Pollution
Control System," consists of a series/parallel arrangement of storage
reservoirs which collect flows from the associated watershed and treated
water and overflows from upstream reservoirs.   Each storage reservoir
is connected to a pretreatment unit and the water collected by the reser-
voir is treated to Class "C" quality and discharged into the stream beds
and ultimately to Wilde Lake.   Figure 45 shows the locations of the
reservoirs and the pretreatment units.  Table  44 lists  the annual run-
off from each  sub-watershed  and  the  amount annually  collected by each
reservoir. Table 44 has been arranged to illustrate the interaction of
the  individual  installations and the  amount of flow coming from upstream
reservoirs,  the  total flow treated  annually and average per day,  and
the  sizing of the pretreatment units and the reservoirs.

Unlike the "Potable Reuse System" and the "Sub-Potable Reuse System"
described previously,  the "Local Pollution Control System" makes no
provision for the treatment of water beyond Class "C"  quality or for
distributing the water.  The conceptual design for the "Local Pollution
Control System" is  intended to provide a basis for comparison with
other  pollution control systems and a reference for evaluating the
benefits of reuse.  The "Local Pollution Control System" has been opti-
mized and conceptually designed as a system that could be applied for
pollution control independent of reuse  consideration.
COMPONENT DESCRIPTIONS

The "Local Pollution Control System" installations consist of two com-
ponents, a storage reservoir and a pretreatment unit.  These com-
ponents are essentially identical in design to the storage  reservoirs and
pretreatment units previously described for the "Potable Reuse System"
and the "Sub-Potable Reuse System. " The criteria used  in sizing the
reservoirs and pretreatment units for the "Local Pollution Control Sys-
tem" are slightly different since none of the water  is diverted for reuse.
With the "Local Pollution Control System," flow leaving the pretreatment
unit after receiving treatment to Class "C" quality is discharged directly
to the stream beds.
PERFORMANCE CHARACTERISTICS

Since the sole purpose of the system  is pollution control, the pretreat-
ment units would be operated at a higher rate than the two reuse sys-
tems previously discussed.  In the  case of reuse systems, pretreatment
                                 171

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CO
                                       LOCAL COLLECTION, STORAGE, AND
                                       TREATMENT OF STORM WATER FOR
                                          WATER  POLLUTION  CONTROL
                                                                                    FWPCA Contract No.M-12-20
                                                                                     WILDE LAKE WATERSHED
                                                                                        Columbia, Md.
                          3?-igUr-e 45.  Loca-l Pollution Control System - Location Flan

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       TABLE 44.  LOCAL COLLECTION,  STORAGE, AND TREATMENT OF STORM WATER
      FOR POLLUTION CONTROL RUNOFF BY SUB-WATERSHED AND PRETREATMENT UNIT
                        WITH PRETREATMENT AND RESERVOIR CAPACITIES
Reservoir/
Pretreatrm
Location
A


B


E
D

c


F





G
H
I
J
Sub -Water shed
2nt R unof ±
No. (gpy)
1
2
3
11
12
13
8
6
7
4
5
14
9
15
16
17
18
20
19
22
21
10
3,627,000
4,694,000
4,073,000
12,378,000
7,332,000
10, 134,000
10, 741,000
17,653,000
14,007,000
4, 791,000
7,733,000
15, 528,000
17, 818,000
3,700,000
10,260,000
20,388,000
3, 905,000
20, 351,000
15, 637,000
5,440,000
11,653,000
25, 124,000
Total Runoff Flow from
Per Reservoir Upstream Reservoir Total Flow Treated
(gpy) No. (gpy) (gpy) (gpd)


12, 394,


29,844,
10,741,

31,660,


28,052,





76,422,
15,637,
5, 440,
11,653,
10,049,


000


000 A
000

000 E


000 D




B
000 C
000
000
000
000*


12,


12,394,000 42,
10,

10,741,000 42,


42,401,000 70,




42, 238,000
70,454,000 189,
15,
5,
11,
10,


394,000


238,000
741,000

401,000


454,000





113,000
637, 000
440, 000
653,000
049, 000*


34, 000


116, 000
28, 500

116, 200


193, 000





518, 000
43,000
14, 900
32,000
26,000
Pretreatment Reservoir
Capacity Size
(gpd) (gals)


68,


232,
59,

232,


386,





1,036,
86,
29,
64,
53,


000


000
000

400


000





000
000
800
000
200


1,577,


2,145,
1, 729,

803,


1,902,





5,101,
923,
358,
690,
375,


30fr


000
000

000


000





000
500
400
000
000=1
             246, 967,000
''Based on intercepting 40 percent of the watershed

-------
flow rates would be regulated to maximize the water available for reuse.
The  "Local  Pollution Control System" would be operated at a rate of
twice the  mean annual daily flow rate to increase the probability that
the reservoirs will be able to collect the majority,  if not all, of sub-
sequent storms.  As  discussed in Section XIII,  with the pretreatment
unit  operating at twice the mean annual runoff plus  base flow,  98. 5 per-
cent of all one-year storms  will be stored. At this rate 91. 2 percent
of all storms, including those with return intervals greater than one
year, will be retained. '

With the "Local Pollution Control System" only that water from sub-
watershed number 10 will enter Wilde Lake untreated.  This amounts
to 15, 075, 000 per year and of the remaining 231, 892, 000 gallons of
annual runoff, only 3, 478, 000 gallons will not receive  the full Class "C"
treatment for any normal year and only 20, 407, 000 gallons for storms
of greater return intervals.  All water except that from sub-watershed
10 will be retained in the storage  reservoirs for a sufficient interval to
permit the heavy particles to settle out.  Expressed differently,  if the
water not receiving full treatment were to have a suspended solids con-
centration of 200 ppm, the resultant overall suspended solids in the lake
would be 43  ppm when diluted with the treated effluent  having 30 ppm
suspended solids,  assuming no  sedimentation in Wilde Lake  itself.
DESIGN AND CONSTRUCTION COSTS

The construction items for the "Local Pollution Control System" would
be the  same as the two reuse systems previously discussed with respect
to the storage reservoirs and pretreatment units.  Table 45 contains a
summary of the estimated design and construction costs for the "Local
Pollution Control System. "


OPERATION AND MAINTENANCE COSTS

The operation and maintenance for the "Local Pollution Control System"
would involve the same items of  work as the storage reservoirs and
pretreatment units for the two reuse systems previously discussed.
Table 46 contains  a summary of  the estimated costs for the "Local
Pollution Control System. "
                                  174

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       TABLE 45.  LOCAL COLLECTION, STORAGE, AND TREATMENT OF STORM WATER
             FOR WATER POLLUTION CONTROL  - DESIGN AND CONSTRUCTION COSTS



                                                           Location
                           A_       B_      _?_     IL     JL     JL     _G_     JL     !      I         Total
Construction

   Storage Reservoirs    61,000   71,500 67,500  45,000 65,000 109,000  47,000 32,500  42,000 33,500

   Pretreatment Units      8,200    9,600 10,200   9,600  9,200  11,400   8,600  7,300   8,200  7,600

   Subtotal               69,200   81,100 77,700  54,600 74,200 120,400  55,600 39,800  50,200 41,100    663,900


Design, Inspection and
   Field Engineering     10,400   12,100 11,700   8,200 11,100  18,000   8,400  6,000   7,500  6,100     99,500


Contingencies and
   Escalation              6,900    8,100  7,800   5,500  7,400  12,000   5,600  4,000   5,000  4,100     66,400


Total                    86,500  101,300 97,200  68,300 92,700 150,400  69,600 49,800  62,700 57,300    829,800

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         TABLE 46.   LOCAL COLLECTION,  STORAGE, AND TREATMENT OF STORM WATER FOR
             WATER POLLUTION CONTROL - ANNUAL OPERATION AND MAINTENANCE COSTS
Storage Reservoirs

   (1)  Routine Checks
   (2)  Trash Removal and
       Nuisance Control
   (3)  Sediment Removal
                                Labor
                              (man hrs. )
  260
  240
               Labor
                 ($)
  750
  690
              Material
                 ($)
           Equipment
           Rental ($)
            Utilities
               ($)
                Totals
                                          2,400
Pretreatment Units

   (1)  Routine Checks
   (2)  Sediment Removal
   (3)  Chemicals
   (4)  Preventative  Mainten-
       ance and Repair
   (5)  Electrical Energy
  260
  520
  750
1,730
4,500
1,730
                                          3,250
                                                        200
Miscellaneous
                             3,600
Subtotals
1,280
4, 320
9,830
5,650
200
$20,000

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                            SECTION XVI

       CONVENTIONAL STORM WATER TREATMENT SYSTEM


In order to evaluate the systems for "Local Storage,  Treatment, and
Reuse of Storm Water" it was necessary to develop a base for compar-
ison.  As a parallel effort, a conceptual design was prepared for a
system to control the pollution of Wilde Lake using conventional design
methods.  This work was performed by Whitman, Requardt and Asso-
ciates of Baltimore,  Maryland. A summary description of the Con-
ventional Storm Water Treatment System,  hereafter referred to as the
"Conventional Treatment System, " is contained in this chapter.


DESIGN REQUIREMENTS

The design of the Conventional Treatment System was based on the same
area,  runoff quantities, flow hydrographs, and same  quality of water
requirements as the Local Storage,  Treatment, and Reuse System.
Table 47 contains a summary of the design requirements.
             TABLE 47.  DESIGN REQUIREMENTS FOR
                CONVENTIONAL TREATMENT PLANT
      Area Considered:            Wilde Lake Watershed

      Treated Water Quality:       State of Maryland Water Quality
                                  Standards for "Water Contact
                                  Recreation" modified as discussed
                                  in Section V under Class  "C" water
                                  quality

      Water Quantity:              Runoff quantities as calculated
                                  using the synthesized hydrograph
                                  method with storms of one-year
                                  return interval as the basis for
                                  design
SYSTEM DESCRIPTION

The Conventional Treatment System consists, in part, of a central
treatment basin located at the head of Wilde Lake and the necessary
facilities to collect and pump the runoff water to the treatment basin.
As shown on Figure 46, the Conventional Treatment System is divided
by natural boundaries into two parts.  "Area A" consists of 954 acres
of the watershed from which water flows by gravity to the treatment basin.
                                177

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co
                                                                                                                        FWPCA Contract No.U-12-20
                                                                                                                         WILDE LAKE WATERSHED
                                                                                                                             Columbia, Mi
                        WHITMAN. REOUARDT-a ASSOCIATES
                                                                                                                                       ' PLAN  OF
                                                                                                                                   CONVENTIONAL  SYSTEM
                                                                                                                                         SCALE. l'."400'
                                                     Figure 46.   Plan  of Conventional Treatment System

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"Area B" consists of an area of 165 acres from which runoff must be
collected and pumped to the treatment basin.  The components comprising
the Conventional .Treatment System, are as follows:

1.    Holding Pond.  This pond is located at the east side of
      AreaB  and has a capacity of 1, 840, 000 gallons.  The pond
     receives the runoff from the major portions of sub-water-
     sheds 10, 20,  and 21 from a gravity interceptor on the west
     side of the pond.  The holding pond provides storage capacity
     in order to avoid pumping runoff water at storm rates.

2.    Pumping Station No.  1.   This station is located on the south
     side of Wilde Lake and pumps the water from the holding
     pond to Pumping Station No. 2  for transfer to the treatment
     basin.  This station also receives flow from gravity inter-
     ceptors which  collect runoff from the watershed adjacent to
     the south side  of Wilde Lake.  This station has a pumping
     capacity of 2.5 MGD.

3.    Gravity Interceptors. The northern-most gravity interceptor
     collects the runoff from the majority of sub-watersheds 9,
     16, and 19, and is located to permit this water to flow by
     gravity directly to the treatment basin.   The gravity interceptor
     located adjacent to the north side of Wilde Lake collects the
     runoff from the lower portions of the sub-watersheds,  which
     flows by gravity to the wet well of Pumping Station No.  2.

     A gravity interceptor located at the west of the head of
     Wilde Lake intercepts the majority of the flow from sub-water^
     shed 17 in order for the water to flow by gravity to the treatn-
     ment basin.  A second gravity interceptor located adjacent to,
     the southwest side of Wilde Lake collects the  runoff from the
     lower portion of the watershed which flows by gravity to
     Pumping Station No.  2.

4.    Pumping Station No.  2.   This  station receives runoff from
     the two gravity interceptors located adjacent to the north and
     southwest side of Wilde  Lake.  This station also transfers
     the waste  from the force main from Pumping Station No. 1
     to the treatment basin.  Pumping Station No.  2 uses dual
     5 MGD pumps  for a maximum capacity of 10  MGD.

5.    Treatment Basin.  The treatment basin is located at the head
     of Wilde Lake  as shown on Figure 46.  Figure 47 is a more
     detailed drawing of the treatment basin.  The treatment basin
     consists of an  earth and concrete dam and an  excavated
     basin sized to  retain a one-year  storm.   The treatment basin
     provides retention of the storm water runoff to allow sedi-
     mentation of suspended solids and incorporates a rock dam
     and gravel filter for filtration of water.  Chlorination
     equipment is provided to disinfect the effluent and is designed
                                179

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CO
o
                                                      PROFILE
                                                                                                                TREATMENT  BASIN
                                             Figure 47.  Conventional System  Treatment Basin

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      to provide variable dosages to meet the range of overflow
      rates.   The normal pool elevation is maintained by stop
      logs in the outlet structure and the pool may be drained for
      silt removal and other purposes by removal of the logs.
      The principal features of the treatment basin are as follows:
      Dam height


      Spillway length

      Spillway overflow
      elevation

      One-year storm maximum
      water level

      Normal pool storage

      Maximum storm storage


      High water level

      High water volume


      Area at high water level

      Maximum water level for
      dam design
15 feet from existing stream
bed to top of dam elevation 349. 0

60 feet
344. 5 feet


344.0 feet

2. 6 MG

12.4 MG from normal pool
to spillway overflow

346.0 (10-year storm)

16.6 MG from normal pool
to high water level

424, 000 square feet (9. 75 acres)


346. 8 (100-year storm)
      The outlet from the treatment basin is a 24-inch conduit
      which will drain the basin in 19 hours at an average flow
      of 20 MGD varying from 27. 5 MGD at the high water level
      elevation to 0. 5 MGD at the low pool elevation.
PERFORMANCE CHARACTERISTICS

The Conventional Treatment System is designed to collect and transfer
storm water runoff to the treatment basin at the runoff rates and quan-
tities of a one-year storm.  The system is designed to drain the holding
pond and the treatment basin to the minimum levels within a 24-hour
period in order to minimize the probability that these storage basins
will not be sufficiently empty to receive subsequent storms.  The treat-
ment basin is designed to meet the State of Maryland requirements for
a Class 3  impoundment and the dam and spillway design is based on a
100-year storm.  However, at  storms of greater than one-year return
interval, the capacity of gravity interceptors and the pumping stations
may be exceeded and a portion of the runoff will overflow directly to
                                181

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Wilde Lake.  All of the runoff flowing directly to the treatment basin
would be retained for some period.

The treatment provided the storm water with the Conventional Treat-
ment System consists of sedimentation,  gravel filtration,  and chlori-
natioru  The  removal of suspended solids and resulting reduction of
turbidity in storm water by natural sedimentation is a function of the
water surface area and overflow rate of the reservoir.  Table 48
contains a listing of the size particles that would be removed with the
treatment basin used for the Conventional Treatment System.
              TABLE 48.   PARTICLE REMOVAL WITH
                CONVENTIONAL TREATMENT BASIN
                        Water                        Size of Particles
  Water    Effluent   Surface Area    Overflow Rate       Removed
Elevation  Q(MGD)   (square ft)      (gal/day/sf)        (Microns)

  337  0       10.0       181, 000           55                 7. 5
  33G.O       14.0       186,000           75                 8.8
  340.0       19.5       196,000          100                10.1
  342.0       24.0       219,000          110                10.6
  344.5       28.0       320,000           89                 9.5
  346.0      278.0       424,000          660                26.0


Table 48 shows that the treatment basin will remove silt particles
(approximately 10 microns) for overflow rates up to the spillway (ele-
vation 344. 5 feet) which includes the one-year storm (elevation 344. 0
feet).  However,  it is considered that  Class "C" water will require a
greater reduction of turbidity and settlement of particles smaller than
10 microns.

In order to provide for treatment to a  quality comparable to Class "C, "
the treatment basin incorporates a rock dam backed by a gravel filter-
through which storms of less than 5, 000, 000 gallons of runoff would
pass,  as would at least this amount of runoff from storms greater than
5, 000, 000 gallons.  Storms of 5, 000, 000 gallons magnitude  are exceeded
six percent of the time.  In terms of quantity of runoff,  the 5, 000, 000
gallon filtration capability  would represent about 60 percent of the total.

A storm of 18, 600, 000 gallons per day on the entire drainage  will utilize
12, 400,  000 of the storage capacity of the basin without overtopping the
spillway.  For the five years of record, storms of 18, 600, 000 gallons
per day were exceeded 0. 25 percent of the time, which represents two
to three percent of the total flow.
                                182

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DESIGN AND CONSTRUCTION COSTS

As part of the conceptual design of the Conventional Treatment System,
an estimate of the design and construction costs Was prepared.  Table 49
contains a summary of this estimate.
          TABLE 49.  DESIGN AND CONSTRUCTION COSTS -
               CONVENTIONAL  TREATMENT SYSTEM

      Construction Costs

           Holding Pond                        $  24, 000
           Pumping Station No.  1                i 17, 000
           Force Main                           30, 000
           Interceptor System                   205, 000
           Pumping Station No.  2                300, 000
           Treatment Basin                     263,000
           Subtotal                                     $  939,000
      Design,  Field Engineering,& Inspection               187,800

      Contingencies and Escalation                         187, 800

      TOTAL                                           $1,314,600
The $1, 314, 600 construction cost for the Conventional Treatment System
translates to a daily cost of $198.50 for the system using the same
amortization rate previously used with the Local Storage, Treatment, and
Reuse System.
OPERATION AND MAINTENANCE COSTS

The operating and maintenance costs for the Conventional.Treatment
System were estimated at $25, 000 per year which translates to $68. 49
per day.
                                183

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                           SECTION XVII

                       ECONOMIC COMPARISON
Table 50 is an economic comparison of the four systems presented in
Sections XIII, XIV, XV, and XVI.  To more thoroughly analyze these
results, a benefit/coat evaluation was made of the various  system alter-
natives.
POTABLE REUSE

Capital costs associated with the optimum potable reuse system presented
in Section XIII were $1,445,200.  Whenthese costs are amortized over the
life of the facilities,  capital costs are found to be equivalent to uniform
costs equaling $207.21 per day.  Operating and maintenance costs are
estimated at $194. 10 per day.  The sum of capital,  operating, and main-
tenance costs is the total system cost and can be found to equal $401. 31
per  day over the estimated life of the facilities.  Offsetting these costs
are tangible benefits from two sources.  The treated water which is pro-
duced for reuse has been evaluated at $0. 45 per thousand gallons and
totals $278. 00 per day in the  case of potable reuse.   The total system
cost of the conventional storm water treatment system  was computed as
$256. 99 per day (based on capital costs of $1, 314, 500 and annual operating
and maintenance costs of $25, 000).  Taking the imputed value of water
pollution control as  the total system cost of the best available alternative,
total benefits can be computed as the  sum of the value of reused water
and the cost of conventional treatment,  or $534. 99 per  day.   These com-
putations are summarized as Case 1 on Table 51.

This computation of benefits and costs can be used to evaluate a benefit/
cost ratio of 1. 26 or a daily net benefit of $105. 88 depending  on the pur-
pose of the analysis.  Several other factors bearing on  this analysis
should be considered in the interest of a comprehensive evaluation.  The
benefit/cost summary just  outlined is appropriate to a water  resource
project having a variety of  purposes and potential benefits.   Two of the
principal benefits,  water supply and water pollution control,  have been
quantified and compared to total system costs.  Other intangible benefits
are discussed in later sections  of this chapter and must be considered  as
part of the evaluation.  The costs and benefits presented above can be
organized somewhat differently in the case of projects intended principally
as water supply facilities  or as water pollution controlfacilities.  Table 51
includes analyses of this  type and lists the cost of potable water after full
credit is taken for the water pollution control aspect of the system, as
well as the cost of water  pollution control after full  credit is  taken for
the value of the potable water.  Both of these costs are shown in units
which permit ready  comparison to other cost indices.

Critical to the calculation of benefit/cost  ratios is the method used to
evaluate benefits.  The benefits noted above and on Table 51 are computed
consistent with the assumptions described in other sections of this report.
The sensitivity of the results to these assumptions can  be investigated
                                  185

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CO
en
                   TABLE 50.  ECONOMIC COMPARISON OF POLLUTION CONTROL SYSTEMS


                                        Amortized   Average  Value of
                              Capital    Capital     O&M   Reuse        Net Cost of System _
                               Costs      Costs      Costs   Water  - ^ -
                                ($)       ($/day)    ($/day)  ($/day)  ($/day)  ($/acre-year)  ($/DU-year)
Local Pollution
Control System        829,800   118.99      54.79           173.78       55.25        16.88


Local Potable
Reuse System       1,445,200   207.21     194.10   250.20  151.11       48.05        14.68


Local Sub -Potable
Reuse System       2,598,000   151.51     372.64   206.94  317.21       100.85        30.82


Conventional
Treatment System   1,314,600   188.50      68.49           256.99       81.71        24.96

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                                          TABLE 51.   BENEFIT/COST ANALYSIS OF  WATER SUPPLY
                                         	AND PQ-LLUTIQN CONTROL ALTERNATIVES	




                                                                          Case 1                     Case 2                    Case 3                     Case 4

      Costs

            Capital Cost of System                                      $  1,445,200.00            $   1,445,200.00           $  2,598,600.00           $  2,598,600.00
            Amortized Capital Cost ($/Day)                                       207.21                     207.21                     372.64                    372.64
            Operating and Maintenance Cost ($/Year)                           70,845.00                  70,845.00                  55,300.00                 55,300.00
            Operating and Maintenance Cost ($/Day)                               194.10                     194.10                     151.51                    151.51
            Total System Cost ($/Day)                                           401.31                     401.31                     524.15                    524.15

      Benefits

            Water Reuse

            Quantity of Reused Water (Gallons/Year)                      202,942,000.00            202,942,000.00            167,849,000.00            167,849,000.00
            Value of Reused Water ($/Year@$0. 45/1000 Gallons)                91,324.00                  91,324.00                  75,532.00                 75,532.00
            Value of Reused Water ($/Day)                                       250.20                     250.20                     206.94                    206.94

            Water Pollution Control

(-JQ          Capital  Cost of Conventional System                            1,314,600.00                 829,800.00              1,314,600.00                829,800.00
-j          Amortized Capital Cost ($/Day)                                      188.50                     118.99                     188.50                    118.99
            Operating and Maintenance Cost ($/Year)                           25,000.00                  20,000.00                  25,000.00                 20,000.00
            Operating and Maintenance Cost ($/Day)                                 68.49                      54.79                      68.49                     54.79
            Total System Cost ($/Day)                                           256.99                     173.78                    256.99                    173.78
            Total Benefits ($/Day)                                               507.19                     423.98                    463.93                    380.72

       Multipurpose  Water Resource  Project

            Net Benefits ($/Day)                                                 105.88                      22.67                    -60.22                   -143.43
            Benefit/Cost Ratio                                                     1.26                       1.06                      0.89                      0.73

       Water Supply Project

            Total Cost Less Water Pollution Benefit ($/Year)                   52,680.00                  83,050.00                 97,510.00                127  890.00
            Net Cost of Treated Water ($/1000 Gallons)                              0.26                       0.41                      0.58                   '   0^76

       Water Pollution Control Project

            Total Cost Less Water Supply Benefit ($/Year)                     55,160.00                  55,160.00               -115,780.00                115  780.00
            Net Cost of Pollution Control ($/Acre-Year)                             48.05                      48.05                    100.85                   ' lOo! 85
                                        ($/DU*-Year)                             14.68                      14.68                      30.82                     3o! 82
                                                 *DU = Dwelling Unit


                                                Case 1.  Potable Reuse System vs. Conventional Storm Water Treatment
                                                Case 2.  Potable-Reuse System vs. Local Storage Without Reuse

                                                Case 3.  S-ub-Potable Reuse System vs. Conventional Storm Water Treatment
                                                Case 4.  Sub-Potable Reuse System vs. Local Storage Without Reuse

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rather easily.  The value of reused water, for example, has been taken at
$0. 45 per thousand gallons.  Should this water be purchased by the local
water utility and distributed and  sold by them, the value of the treated
water should conform to the cost of the water utility of an alternative
supply.   In the case of the Howard County Metropolitan Commission, this
would be the incremental cost of water purchased from Baltimore City as
well as  other incremental costs associated with  pumping, storing,  and
conveying that water to the  Wilde Lake watershed. An exact determination-
of this cost  would require a thorough study of the financial structure of the
Metropolitan Commission.  Another consideration might be the effect of
higher water values, such as those existing in other areas of the country,
on the economic evaluation.  A comparison of this type is of limited  value,
since the system cost figures refer to a specific installation at Columbia,
Maryland,and costs might vary widely in  different locations.   Case 1 on
Figure 48 shows the relationship of the Net Benefit  measure developed in
Table 51 to  the value of the reused water.  It can be seen that the riet bene-
fits are zero, that is,  the system can be  considered break-even in ,;an eco-
nomic sense when the value of water is approximately $0. 26 per thousand
gallons.  When the  value  is set higher than this level,  positive net benefits
result,  and  when it is lower, a net cost develops which must be compared
to the nonquantified secondary benefits described in later sections.-:

Although the conventional storm  water treatment system developed;by
Whitmah, Requardt and Associates can be said to be fairly representative
of the best available method of achieving  the water quality objective using
current technology,  the sensitivity of the conclusions to pollution control
costs associated with advanced technology should be investigated. 'The
local storage concept itself offers an advanced method of water pollution
control when optimized for  that purpose alone, without reuse.  This  type
of system is described in Section XVI and will be compared to the conven-
tional approach later in this chapter.  Using the  costs of the  local storage
system  without reuse as the imputed value of water pollution control also
permits  convenient examination of the economics of reuse separately from
the storm water control and treatment aspects of the system.  Case  2 on
Table 51 summarizes economic analyses of the potable reuse system as a
multipurpose project,  in each case using the costs of the local storage
system  without reuse as the imputed value of water pollution control. The
lower value  assigned to the water pollution control function results in lower
net benefits  in the  multipurpose analysis  and a higher  incremental cost of
treated  water.  The analysis of the system as a water pollution control
project  is,  of course,  unchanged.  Case 2 on Figure 48 shows the effect
of the value  of treated  water on the net benefit function when the local
storage system is  used as the source of water pollution control costs.


SUB-POTABLE REUSE

The optimum system for  sub-potable reuse is described in Section XIV.
The cost of  this system totals $2, 598, 600, of which  $1, 562, 700 represents
distribution  system costs.  These costs are amortized over the life of the
facilities and added to  the operating and maintenance costs, resulting in
                                 188

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     CASE 3
    (w/o Distribution
     System)
CASE 4
(w/o Dist.
 System)
                                             CASE 3
                                             (w/Distribution
                                                   System)
                                                       1.00
                                      CASE  4
                                      (w/Distribution System)
                  Value of Treated Water ($/1000 Gal.)
Figure 48.  Net Benefits vs. Value of Treated Water
                        189

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a total system cost of $524. 15 per day.  Further details appear as Case 3
on Table 51.  Total benefits are calculated at $463. 93 per day,  producing
a negative net benefit or net cost of $60. 22 per day.   The sub-potable reuse
system then, when considered as  a multipurpose project, fails to generate
tangible benefits equal to the costs.

Other comparisons were carried out as described in the previous section
to investigate the effect of water supply and water pollution control consid-
erations.  The results of the  analysis as a water supply project are
further illustrated by Case 3 on Figure 48, where the effect of various
values of treated water is  plotted.  Figure 48 also illustrates the influence
of the cost of the distribution  system on the overall results. It can be seen
that treated water  could be priced at $0. 10 per thousand gallons at the
treatment plant (the  zero cost intercept of plot  "without distribution sys-
tem") but that the cost of providing the distribution system  increases  the
break-even price to  $0. 58 per thousand gallons.  Recomputation of bene-
fits based on the use of the local storage  system to establish the value of
water pollution control leads to Case 4.  It can now be seen that the portion
of the total system cost allocable  to water supply is substantially higher,
but that the apparent cost of water pollution control remains at $30. 82 per
dwelling unit.


NO REUSE

Costs for the local storage system without reuse have been presented in
previous sections as an alternative measure of the value of water pollution
control.  Total system cost has been given as $173. 78 per day,  compared
to $256. 99 per day quoted  for the  conventional system.  In addition,  the
local storage system offers the secondary, unquantified benefits described
later in Section XVIII.
SUMMARY

The economic comparison of the three local storage systems and the
conventional storm water treatment system has been conducted in several
different ways.  When the local storage  systems are treated as multi-
purpose water resource projects, only the  potable reuse system yields
a benefit/cost ratio greater than unity, regardless of the base  employed
for evaluation of water pollution control benefits.  The ratio was as high
as 1.26 when the conventional system was used as the base and fell to
1.06 with the local pollution control system as the base.   Investigation
of the value placed on treated water revealed that all values greater
than $0. 26 per thousand gallons resulted in positive net benefits when
the conventional system was employed as a base.  Use of the local pol-
lution control system as a base increased the break-even point to $0. 41
per thousand gallons.  When the system was analyzed as a water pollution
control project,  the net cost of pollution control amounted to $55,  160 per
year, or $14. 68 per dwelling unit-year.  This can be compared to the
cost of pollution control by conventional means of $24. 97 per dwelling
                                 190

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 unit-year and $16. 88 per dwelling unit-year by the local storage  system
 without reuse.  Analyzed on another basis, it can be found that if the
 system is installed as a pollution control system and the necessary facil-
 ities for potable water reuse are added, the additional cost involved in
 treating and distributing the potable water will total $0.41  per thousand
 gallons of water distributed.

 The sub-potable reuse system exhibits benefit/cost ratios  as low as
 0. 73 and is characterized by a moderately high net cost even after full
 credit is taken for all quantified benefits.  The cost of treated water is
 higher than the  cost of water from the present alternative source when
 the system is analyzed as a water supply project.  Furthermore, when
 analysis is based on water pollution control considerations, the cost of
 pollution control is higher than any of the  alternatives.  The excessive
 cost of the  sub-potable system can be seen to be wholly caused by the
 cost of the  sub-potable distribution system.  The construction, operation,
 and maintenance of this facility alone accounts for an additional cost of
 approximately $0. 48 per thousand gallons of treated water which is more
i than the total incremental cost of the alternative supply of  water.

 Operation  of the local storage system without reuse as  a water pollution
 control method was compared to the conventional system and found to
 result in a  net benefit of $83. 21 per day, somewhat less than the  benefit
 associated with the operation of a potable  reuse system which yields
 $105. 88 per day.
                                  191

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                           SECTION XVIII

                       SECONDARY BENEFITS


The primary objectives and benefits  of the local storage,  treatment,  and
reuse concept have already been discussed.  Although the system was de-
signed for optimum realization of these primary benefits, other benefits,
both tangible and intangible,  do result from the installation of such a system
in an urban watershed. Although these benefits may be considered secon-
dary,  they are nevertheless important and might be as economically signif-
icant in many watersheds as pollution abatement and reuse.

STORM WATER MANAGEMENT AND FLOOD CONTROL

As any area begins to urbanize,  the hydrology of the watershed alters
drastically.  With an increase in imperviousness and improved channels,
the runoff from a given storm increases both in volume and peak flow.
The previously derived regression model  and hydrograph analysis clearly
indicate these effects.  Such increases generally result in greatly raising
the potential for flooding the low areas adjoining the waterways.  Flood-
plains which,  in a natural  state,  were subjected to inundation once every
few years might become flooded  several times each year.

To indicate the seriousness of this problem, reference can be  made to
Figure 5 which shows that a natural area which is developed  to an imper-
viousness of 0. 35 will yield over 400 percent more runoff from an inch of
rainfall.  The effects on the peak flow may be just as serious,  with 100
percent to 300 percent increases, depending upon the configuration of the
drainage basin.

In areas where the floodplain is developed, flooding resulting  from urban-
ization can cause severe economic losses.   Even in those areas where the
floodplain is  left as dedicated open space, the use potential decreases as
the probability of flooding  increases.

A system of small reservoirs located along the stream reaches within
the watershed, as previously described, has the ability to significantly
reduce the frequency of flooding. This has been demonstrated in the past
with large reservoir  systems, and the principles underlying  these flood
control projects hold true  for the local systems discussed in this report.

As a means of graphically portraying the flood control potential of these
reservoirs,  an analysis was made of the operation of two  small storage
reservoirs'in series  during a large storm.  For simplicity,  the water-
sheds supplying these reservoirs are hypothetical, with approximately
rectangular shapes.  It was assumed that  initially the watersheds had an
imperviousness of 0.  1 and, using the hydrograph analysis and  stream
routing equations, the runoff hydrographs  at the outflow points in each
basin were calculated for a five-year storm.
                                 193

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A development of the basins was then assumed to take place with the
imperviousness of the upper basin increasing to  0. 5 and that of the lower
basin to 0. 3.  This development also altered the  lag time in each basin,
reducing it from 12 minutes to four minutes in the  upper basin and from
24 minutes to  12 minutes in the lower basin.  Two  more calculations of
the runoff hydrographs were performed assuming first that no reservoirs;
existed, and then that reservoirs were installed  immediately above the
outflow point in each watershed.  The three basin configurations used
for analysis are shown in Figure 49 with the size of the areas and reser-
voirs indicated.

It was necessary to select an initial water level in  the reservoirs since
their ability to dampen flood peaks is dependent upon the available storage.
To accomplish this, a frequency distribution of water levels in one  of the
proposed Wilde Lake reservoirs was prepared.  A probability level of
0. 85 was chosen as a reasonable (and conservative) criterion for selection
of  a  storage level.  The frequency distribution indicated that for 85 per-
cent of the time, during the wettest year, the reservoir was'at one-third
capacity or less.

Using this value for both reservoirs,  hydrographs  were obtained for the
developed area without reservoirs, and were then routed through the
reservoir storage.  This yielded three different hydrographs at the two
outflow points: one from the natural area, one from the developed area
with no reservoirs, and one from a reservoir system.

The  results  of this analysis are shown in Figures 50 and 51 which are
plots of the runoff hydrographs at points A and B, the  outflows of the two
basins. It can be seen that at point A the development  increased the peak
flow by 112 percent with no reservoirs and actually reduced it to a level
below the natural peak with a reservoir.  At point B the increase was
110 percent  with no reservoir and only nine percent with the reservoir.

This analysis  clearly indicates the ability of the local storage reservoirs
to  dampen the  runoff peak for even very large storms.  The savings in
economic losses due to flooding in urban areas can be an important
consideration  in any analysis of the desirability of  such a reservoir
system.


EROSION CONTROL

Any  area, whether in a natural condition or undergoing urbanization,  is
subject to erosion.  This process is entirely a natural one, resulting
from the action of both rainfall and runoff on the  ground surface  and stream
channels.  It may, however, be tremendously accelerated by man-induced
changes in the hydrology of an area.   Such accelerations are well docu-
mented, with typical sediment yields from areas under construction or
already developed  10 to 1000 times those from the  natural area.
                                194

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    Natural A re
2.   Developed Area without Reservoirs
3.    Developed Area with Reservoirs
                                      Area 2  100 ac.
                                      I   . 3
Area 1  50 ac
                                      t,   12 mm.
Reservoir Capacity =
     1.2 mg
                                              Reservoir Capacity
                                                  1.7m
   Figure 49.  Basins Used for Hydrograph Damping Investigation
                                 195

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C/2
fe
u
o
G
d
     375




     350




     325




     300   -




     275   •




     250   -




     225   •
     200  -
175



150





125



100




 75





 50




 25



  0
Developed

Without
Reservoirs
                                      Developed with Reservoirs
                10    20   30    40    50    60    70    80


                          Time from Start of Storm (Min)
                                                       90    100   HO   120
                           Figure 50.  Runoff at Point A
                                        196

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                                    Developed without
                                        Reservoirs
                                         Developed vlth
                                           Reservoirs
K
    25 '
       0     10    20
30   40    50    60    70    80   90
     Time from Start of Storm (Min. )
                                                             100   110  120
                      Figure 51.  Runoff at Point B
                                  197

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Although much of this increase in sediment and erosion can be attrib-
uted to the stripping of vegetation from the land during development,  a
still significant portion results'from the increased runoff discussed pre->
viously.  The  erosion of either land surface or stream channels is a
function of both the kinetic energy per unit volume and the total volume  '-•
of the runoff.  Since kinetic energy is  proportional to the velocity squared,
a. large change in velocity or flow rate will have an even greater effect
on the kinetic  energy and erosion potential of the water.  Velocity, flow,
and volume increases are all significant during urbanization,  and  even
after construction in a watershed has been terminated, the increased
erosion of the stream valley continues.

There are many case histories of once natural streams becoming severely
eroded when their watersheds are developed. The stream bottoms are cut
deeper and the banks begin to become  undercut and collapse. Deep gullies
are formed in areas of the floodplain  where there previously  were small
rivulets.  Once a stream approaches this condition, there is generally
public pressure to have the banks and  bottom paved, completely destroying
its original character.  Improved channels further accelerate peak flows
and create hydraulic and erosion problems  downstream.

For the reasons discussed with respect to flood control,  this condition
does not  have to occur in an area with reservoir-controlled runoff. The
reduction of flows and high volumes of water by reservoir storage  can
help to retain  the natural stream channels and floodplains.  Although
dampening hydrographs do not  always  lead to a proportionate decrease
in downstream erosion (due to  changes in flow regimen), the ability to
control release rate and the diversion of a substantial quantity of water
to reuse  should result in significant reduction in channel erosion.
NUTRIENT REDUCTION

An increasing awareness of the problems of nutrient enrichment of lakes
and estuaries is developing throughout the country.  Although  many
causes of such  enrichment are offered, there is general agreement that '
urban runoff  can add a significant amount of nitrates and phosphates to
a receiving body.

The operation of the treatment plants associated with the storage reser-
voirs cannot  be expected to remove more than a token quantity of the
nutrients present.  By returning  a sizable portion of the  runoff to  the
watershed through the  reuse system, the nutrients will eventually be
transported out of the area through the sanitary sewers.

While this does not remove the nutrients from the water, it does have
two beneficial effects:  it prevents a large portion of the  nutrients from
entering the small urban lakes which are prone to eutrophication,  and
it transfers them to a large treatment plant where they may be even-
tually removed economically.
                                198

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ECOLOGICAL PRESERVATION

As,a watershed  changes from rural to urban,  there is generally a drastic
alteration of the ecological characteristics of the streams and their flood -'
plains due to the increased storm flows, high silt loads, erosion of natural
banks, and pollution.

Atypical history of a small stream situated, in a watershed undergoing,
urbanization might be as follows:

      During the stripping and excavating of the land, which takes
      place  in the construction phases of development,  the stream
      begins to become clogged with sediment.  Bottom organisms
      found  in the natural stream cannot live once the thick layer
      of  silt has settled over the previously rocky bottom.  Larger
      organisms;  including the original fish population which were
      •dependent upon these organisms, begin to  disappear.   As con-
      struction  proceeds, larger areas of the  watershed become im-
      pervious and the  storm flows greatly increase.  The former
      banks of the stream fail to hold the increased flow, and mud
      flats are deposited along the stream valley.  Erosion increases
      greatly and the combination of erosion and mud deposition
      begins to  destroy the natural vegetation  along the stream
      banks and in the  floodplain.   Eventually this entire area
      changes in appearance with little of the natural flora or fauna
      remaining.  Trash, debris,  and pollutants carried by the
      stream help to spawn a new ecology, usually including rats,
      leeches,  scavenger fish, and mosquitoes.  The stream valley
      in  this condition is shunned by the residents of the watershed.

Such a history,  although typical, is not necessary.  As was previously
discussed, a series of  reservoirs within the floodplains of the streams
can abate many  causes of the destruction of a  natural ecology.  The elim-
ination of most  sediment, the dampening of floods,  and the reduction of
erosion can assist in the maintenance of the original ecological conditions
not only  in the stream but in the  surrounding floodplain as well. The
effects of preserving this original appearance on the recreational potential
of the area are  discussed in the following section.


RECREATIONAL AND AESTHETIC CONSIDERATIONS

Water is an important part of our natural landscape and environment.  Its
value has been recognized and employed by planners and administrators
in projects such as the Baltimore City Inner Harbor Development and the
Columbia City Project  in Maryland.  The aesthetic and recreational value
of water, whether in a natural or urban setting, cannot be overemphasized.

In the case of the local storage ponds,  the setting would be primarily a
natural one  with as little excavation as possible and immediate  replanting
of natural vegetation.  The choice and treatment of construction materials
would become a part of, and possibly enhance, the local natural environment.
                                 199

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The ponds present the opportunity for development of both active and
passive recreation areas adjacent to the water.  Aside from creating a
body of water,  the development of the ponds produces  clear flowing
streams  of good quality water, thus improving the entire floodplain.
With the  now decreased flood activity,  the  floodplain can be developed
and treated as useful productive land.

Three  possibilities of handling the pond and its floodplain are a com-
pletely natural setting,  development of a  passive  recreational area, and
development  of an active recreational area.

In the completely natural setting,  care is taken during construction to
preserve the character of the area, leaving  as  much natural vegetation
and rock formations as possible.  After construction,  the area is land-
scaped to resemble the surrounding environment.  The spillway is masked
with rock or  vegetation and the entire area is  allowed to be overtaken by
the wild vegetation present.  Figure 52 shows  the appearance of a typical
pond in a natural setting.

The development of the floodplain as a scenic walk and picnic area with
seating facilities and lighting is another possibility.  Incorporating the
pond,  spillway,  and  natural surroundings into  a creative, stimulating
design could  prove quite valuable to the local community.  Such a,design
concept is illustrated by Figure 53.

Simple structures could be developed in more  populated areas to turn the
pond and  spillway area into a recreational playground facility.  In the event
that local conditions dictate fencing of the ponds,  the development of these
recreational  facilities will produce a positive  result by having the fencing
contain a usable function rather than merely guarding the pond. One
recreational  design that might be considered for such an application is
shown  in  Figure 54.
                                 200

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CO
o
                                  Figure 52.  Local Storage Pond in Natural Setting

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DO
O
IND
                                  Figure 53.   Local Storage Pond in Wooded Park Setting

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DO
O
CO
                               Figure 54.   Local Storage Pond in Recreation  Area Setting

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                            SECTION XIX

                    DEMONSTRATION PROGRAM
Upon completion of this study in 1968, the results were reviewed with
the State of Maryland, the Environmental Protection Agency, Howard
County officials,  and the  developers of Columbia,  Maryland.  It was
generally agreed that the  concept of providing retention of storm water
for pollution control and as an alternative water supply had merit.
However, it was the concensus that the control of sediment generated by
construction and urban development was a greater pollution problem
than post-development pollution control and that these aspects of the
study should be given priority in any subsequent demonstration programs.
During this period, the State of Maryland enacted House Bill No.  1151
for the control of grading, erosion, and sediment during construction
and development throughout the state.  In the interest of developing
additional guidelines for the implementation of this  law, the Department
of Water Resources of the State of  Maryland agreed to serve as the
sponsor of the demonstration project,  and Howard Research and
Development Corporation and the Columbia Parks and Recreation
Association agreed to contribute to the project.  An application was
made to the Environmental Protection Agency and the demonstration
project was initiated in July 1970.  The scope of this  demonstration
project,  which is now in progress and scheduled for completion in late
calendar year 1972, is described in this section.
OBJECTIVES

The objectives of the Environmental Protection Agency demonstration
grant project 15030 FMZ as specified in the grant application and offer
are as follows:

1.    Evaluate the effectiveness and costs of advanced methods
      of erosion control in urban areas

2.    Evaluate the effectiveness and costs of various methods
      for the transport,  drying, conditioning,  and disposal
      of sediment

3.    Demonstrate urban storm water pollution control during
      construction and following development by the use of a
      local storage and treatment system

4.    Collect and analyze data on the effects of urbanization
      and various control measures on hydrology, water quality,
      stream ecology, and channel hydraulics

In addition to the regular reports,  an "Erosion and Sediment Control
Manual for Urban Development" is to be prepared covering the erosion
                                 205

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and sediment control practices demonstrated under this project and
other practices that can be used in urban development.


DEMONSTRATION SITE AND FACILITIES

The demonstration project is being conducted on a 200-acre watershed
in the Village of Long Reach in the new city of Columbia, Maryland.  At
the beginning of the project in 1970,  only the rough grading of access
roads within the watershed had been completed.  This rural agricultural
area was selected for the  demonstration project because it was scheduled
for complete urbanization over the period of the demonstration project.

Upon the initiation of this  project, an earth-filled dam was constructed
at the lower end of the demonstration watershed to form a three-and-
one-half acre lake to serve as a sediment retention pond during the course
of the construction and the project.  As discussed later,  this pond is
also being used to demonstrate storm water management techniques
and sediment handling and removal methods.

Two  sub-water sheds at the upper end of the demonstration area have
been respectively designated as reference and experimental sub-water-
sheds. Gaging and sampling stations have been installed to monitor the
flows and to collect samples of the storm water draining from each of
the two  sub-water sheds.   Within the reference sub-water shed, the
erosion and sediment controls are those applied by the developers in
accordance with applicable  county and state regulations. Within the
experimental sub-watershed,special methods of erosion and sediment
control  are being applied and evaluated.

Two  other gaging and sampling stations have been installed.  One is
located  immediately above the storm retention pond to monitor flows
and collect samples of storm water runoff from the entire demonstration
watershed.  The other station is located downstream of the storm retention
pond. This station records the overflow from  the pond and the flow over
the emergency spillway during  major storm events.

Three recording rain gages are installed on the watershed and the clocks
are synchronized with those used in the gaging and sampling stations.


EROSION CONTROL

In the demonstration project, primary emphasis is being placed on
erosion control practices  on the basis that the  most effective method
of control is the retention of the soil and the  elimination of sediment as
a pollutant.  For purposes of demonstration, evaluation, and definition
of future applications,  erosion  control practices have been categorized
on the following pages.
                                 206

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Long-Term Stabilization Using  Vegetative Cover

      Limitation of grading, excavation,  and fill to retain
      maximum natural cover

      Limitation of period of  exposure or denudation, especially
      with regard to frequency of high intensity rainfall events

      Scheduling of earth-moving operations to utilize germina-
      tion and growing  seasons,  whenever possible

      Design for and use of proper equipment in the preparation
      of soils and the planting of vegetative cover

      Use of natural material, matting, and/or artificial
      methods to:

            Stabilize areas during' the planting and development
            of vegetative cover

            Provide long-term root reinforcement for vegetative
            cover on critical  slopes and drainage ways

      Use of special ground cover, shrubs, or trees to  supplement
      permanent grasses on critical areas

      Use of turf to provide expeditious development of  permanent
      ground cover

      Use of vegetative cover to stabilize engineered and'temporary
      erosion and drainage control structures

      Establishment of vegetation with higher velocity tolerance in
      areas of concentrated overland flow

Long-Term Engineered Erosion and Drainage Controls

      Chutes, flumes,   and energy dissipators to convey runoff in
      critical areas where volume and/or velocity is beyond
      vegetative tolerances

      Erosion checks and level  spreaders for reduction  of flow
      velocity

      Structural stabilization  using rubble,  stone,  or grouted
      riprap

      Sediment traps that may be converted to beneficial use
      (recreation, wildlife habitat, etc.)  after development and
      construction operations have been completed
                                 207

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      Trickle channel and outfall protection using prefabricated
      or field-fabricated devices

Interim Erosion and Drainage Controls

      Temporary diversion and interceptor dikes

      Level spreaders

      Existing naturally vegetated waterways

      Temporary chutes, flumes,  and downdrains

           Bituminous concrete

           Reinforced synthetic fabric

           Chftmical stabilizers

      Temporary sedimentation basins

      Temporary seeding of denuded areas

      Temporary mulching of denuded areas

           Straw and hay

           Chemical soil stabilizers

           Chemical soil flocculants

           Wood fiber

           Fiber glass

      Temporary stabilization of denuded areas

           Mats

            Natural material
            Synthetic material

           Nets

            Plastic
            Fiber glass
            Natural material

      Turf
                                208

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      Temporary erosion checks

            Weirs (log, stone, chemically stabilized aggregate)

            Natural fibers

            Plastic materials

            Fiber  glass products

            Chemical products

Emergency Erosion and Drainage Controls

      Diversion ditches and berms

      Diversion with nylon bags filled with soil or sand

      Interceptors built of nylon bags filled with soil or sand

      Chutes and flumes of rigid or semirigid plastic material

      Chutes and flumes of chemical sprays

      Chutes and flumes of synthetic fiber

      Level spreaders of  synthetic material

      Chemical soil stabilizers, blankets, and flocculants

      Interceptors built of rock and gravel

As a part of this project,  a large number of manufacturers and vendors
of erosion control and landscaping materials and equipment are providing
products for demonstration and evaluation purposes.  These include:
chemical soil stabilizers  and mulches, blanketing products, fabric form
for bank and stream stabilization, hydroseeders,plus other materials.


SEDIMENT HANDLING AND DISPOSAL

A survey was made of methods for the removal of deposited sediment
from  storm retention ponds early in the project.  The removal methods
considered included the use of conventional construction equipment, use
of underwater roads with  conventional equipment,  draglines,  underwater
scoops, barge-mounted back hoes,  and small dredges.  Based on the
equipment available at the time, the use of an underwater scoop operated
off deadmen and the use of conventional front loaders were selected for
demonstration.
                                209

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An "engineered forebay" has been constructed at the upper end of the
storm retention pond.  This consists of an underwater dam and a flow
spreader which form a widened section in the channel entering the pond.
The forebay serves two purposes.  First, it provides an area in which
the heavier sediment can be trapped before entering the pond and an
area in which this material can be removed by front loaders with minimal
disruption of the area around the pond.  Secondly,  the forebay provides
an area to which the deposited  sediment from the pond proper can be
transported by the underwater  scoop for dewatering and subsequent
removal.

Laboratory tests  have been conducted on the dewatering characteristics
of various types of sediment with and without chemical additives.  Test
beds are to be constructed to demonstrate selected techniques in the field.

For the demonstration,  conventional dump trucks will be usedto transport
the sediment to the dewatering and disposal site.  As necessary,  plastic
liners will be used to stop  leakage from the trucks.
STORM WATER MANAGEMENT

The key features of the local storage and treatment concept of pollution
control considered in the original system study are being demonstrated.
Using the gaging and sampling  stations located upstream and  downstream
of the storm retention pond,  data are being developed on the effectiveness
of this method of storm water management.  Special tests are being
conducted in which the level of the retention pond is lowered between
storm events.  The effects of the additional available storage capacity
on the downstream hydrographs are being determined.  This  will also
provide information on the need to provide bank stabilization  on ponds
operated with variable water levels.

The size of the storm  retention pond makes it a relatively effective
settling basin for most suspended solids. Accordingly,  it is  being
operated without supplemental  treatment to determine the  extent to
which pretreatment and treatment would be required to use water from
storm retention basins as a supplemental water supply.


EFFECTS OF URBANIZATION

The data from the rain gages and the gaging stations are being  analyzed
to determine the extent to which storm water runoff is being changed by
the installation of storm sewers and the urbanization of the area.  Actual
site and rainfall data  are being used as input to the Environmental
Protection Agency, Storm  Water Management Model (49),  and the cal-
culated runoff will be compared to actual field data.

Aerial photographs of  the demonstration watershed area are being
acquired quarterly to document the status of construction and development
                                 210

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and other site data.  This information is being retained to allow gener-
ation of input data for future runoff models for comparison with actual
runoff.  These aerial photographs are also being used to monitor changes
in stream and other drainage channels in the area.

In addition to the aerial photographs, ground surveys are being made
quarterly of the retention pond and the major stream flowing to the pond.
Profiles are being prepared from previously established bench-marks
to determine the extent of stream erosion and the deposition of the
sediment in the stream and pond.

An inventory of the aquatic  life existing in the area was established early
in the project and periodic ecological surveys are  being made to monitor
the changes that have occurred in the stream and pond during development.

Extensive photographic coverage of the  erosion controls,  sediment
removal operations, facility construction,  etc., is being maintained,
and slides are being accumulated to  show sequential effects.
                                 211

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                            SECTION XX

                       ACKNOWLEDGEMENTS
Hittman Associates wishes to acknowledge the assistance of the various
individuals and organizations who made important contributions to the
study, .design,  and evaluation of the storage,  collection,  and use of
storm water.  Hittman Associates wishes to especially acknowledge the
efforts of the organizations which participated directly in this effort:

     Whitman,  Requardt and Associates, Baltimore, Maryland,
     who participated  as a subcontractor in the review of water
     usage,  public codes and regulations,  and performed the
     conceptual design work on the "conventional system" and
     the facilities for  the demonstration program.

     The Land  Planning and  Management and the Construction
     Management staffs of The Rouse Company,  The Howard
     Research  and Development Corporation, and the Columbia
     Association, who provided detailed data on the projected
     development of the Wilde  Lake watershed and assistance
     in the planning  of the demonstration program.

     Department of Health,  State of Maryland, who provided
     guidance on the general health aspects of storm water use
      and reviewed the plans  for the demonstration program.

     Howard County Metropolitan Commission, who reviewed
     the concept for application to the County.

     Department of Water Resources, State of Maryland, who
     provided assistance on the pollution control aspect  of the
     program and sponsored the  demonstration project based
     on this study.

Hittman Associates also wishes to thank George Kirkpatrick and William
Rosenkranz of the Environmental  Protection Agency for their comments
during the course of the program  which provided valuable guidance in
the evaluation of the system; Marshall T. Augustine of the Department
of Water Resources,  State of Maryland, who assisted in the formulation
of the demonstration  project;  and  Ernst P. Hall and John J.  Mulhern of
the Environmental Protection Agency  for their guidance and support  in
the conduct of the demonstration program.   The  assistance of Sidney
Beeman of EPA in the editing of this revised report is also gratefully
acknowledged.
                                 213

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                            SECTION XXI

                           REFERENCES
 1.    Linsley, R. K. ,  M. A. Kohler,  and J. L. H. Paulhns, Hydrology
      for Engineers.  McGraw-Hill, 1958,  pp.  193-209.

 2.    Holtan, H. N., andD.E.  Overton, Storage-Flow Hysteresis in
      Hydrograph Synthesis. Journal of Hydrology #2, 1964.

 3.    Espey,  W. H. , and others, A Study of Some Effects of Urbanization
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 4.    Horton, R. E. ,  An Approach Toward a Physical Interpretation of
      Infiltration Capacity, Soil Science Society, American Proc. 5,  1939.
                                                           «
 5.    Horn,  D. R. , and N. Dee, Synthesis of the Inlet Hydrograph from
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 6.    Ongerth, Henry J., and Judson A.  Harmon,  "Sanitary Engineering
      Appraisal of Waste Water Reuse," Journal AWWA, Vol. 51,
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 7.    Haney,  Paul D., and  Carl L.  Hamann, "Dual Water Systems, "
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10.    Merz, Robert C. , "Direct Utilization of Waste Waters,  "Water and
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11.    McGauhey,  P. H. , "The  Why and How of Sewage Effluent Reclama-
      tion, " Walej^nd_Sejvagj_Works, June 1957, pp. 265-270.

12    Marks  R. H. , "Waste Water Reclamation:  A Practical Approach
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13    Viessman, Warren,  Jr., "Developments in Waste Water Reuse, "
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14    Spiewar I. , and W. F.  Schaffer, Jr., "Survey of the Potential Use
      of Nuclear'oerived Energy Sources in Waste Water Treatment, "
      Atomic Energy Commission, Unpublished Report,  Date Unknown.
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15.   Brandel, A. J. ,  "Recirculation of Cooling Water in Petroleum
     Refining. " Industrial and Engineering Chemistry,  Vol. 48, No.  12,
     December  1956,  pp.  2156-2158.

16.   Biladeau, Archie L. ,  "Reuse of Cooling Water in an Atomic Energy
     Commission Installation, " Industrial and Engineering Chemistry.
     Vol. 48, No. 12, December 1956, pp. 2159-2161.

17.   Maguire,  John J. ,  "Biological Fouling in Recirculating Cooling
     Water Systems, " Industrial and Engineering Chemistry,  Vol.  48,
     No.  12, December 1956,  pp.  2162-2167.

18.   Brown, Howard B. , "Conservation of Water in the Pulp and Paper
     Industry Through Recycle, Reuse,  and Reclamation,  "industrial
     and Engineering  Chemistry,  Vol.  48,  No.  12,  December 1956,
     pp. 2151-2155.

19.   Noll, D.E.  and H. M.  Rivers, "Reuse of Steam Condensate as
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     No.  12, December 1956,  pp.  2146-2150.

20.   Powell, Sheppard T. , "Adaption of Treated Sewage for Industrial
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21.   "industry Utilizes Sewage and Wastes Effluents for Processing
     Operations, " Wastes Engineering, September  1957, pp. 444-467.

22.   Connell, C. H., and E. J. M. Berg, "industrial  Utilization of Munic-
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     February 1959,  pp.  212-220.

23.   Derby,  Ray L. ,  "Water Use in Industry, " Journal  of the  Irrigation
     and Drainage Division, ASCE, Vol.  83, September 1957, pp.  1364-1
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24.   Dykes,  D. R. , T. S.  Bry, and C. H. Kline, "Water  Management: A
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25.   Reid, G. W. , "Projection of Future Municipal  Water  Requirements, "
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26.   Linaweaver, F. P. ,  Jr.,  and  Jerome B. Wolff, Residential Water
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     Johns Hopkins University, Baltimore, Maryland,  May 1964.
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27.   Linaweaver, F. P. , Jr., James C. Beebe, and Frank A. Skrivan,
     Residential Water Use.  Report IV on Phase Two, Data Report on
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28.   Wolff,  Jerome B. , F. P. Linaweaver,  Jr.,  and J. C. Geyer,
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29.   Public  Health Service Drinking Water Standards - 1962,  U.S.
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30.   Pollutional Effects of Storm Water and Overflows from Combined
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31.   Weibel, S. R. , R. J.  Anderson,  and R. L.  Woodward, "Urban Land
     Runoff  as a Factor in Stream Pollution, " ^Journal Water Pollution
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32.   Weibel, S. R. , R.B.  Weidner,  J. M. Cohen, and A. G. Christiansen,
     "Pesticides and Other Contaminants in Rainfall and Runoff,"  Journal
     AWWA, Vol.  58,  August 1966,  pp. 1075-1084.

33.   Weibel, S. R. , R.B.  Weidner,  A. G. Christiansen, -and R. J.
     Anderson, "Characterization, Treatment, and Disposal of Urban
     Storm Water, " Paper Presented at Third International Conference
     on Water Pollution Research,  Munich, Germany, Section 1,
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34.   Riis-Carstensen, E. , "improving the Efficiency of Existing Inter-
     ceptors, "  Se_wa^e_j.ndJndjis_trJ^JJA[ajtes, 27, 10, 1115, October 1955.

35.   Sylvester, R. O. , "An Engineering and Ecological Study for the
     Rehabilitation  of Green Lake," University of Washington, Seattle,
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36.   Wilkinson, R. , "The Quality of Rainfall Runoff Water from a
     Housing Estate, " Journal Institute Public Health Engineers,
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37.   Shigorin, G. G. ,  "The Problem of City Surface Runoff Water, "
     Voodsnabzhenie i Sanitarnayo Tekhnika,  2, 19, 1956.

38.   Akerlinch, G. , "The Quality of Storm Water Flow, " Nordisk
     Hygienisk'Tidskrift (Stockholm),  31, 1, 1950.
                                217

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39.   Stander, G. J. ,  "Topographical Pollution - The Problems of the
      Water and Sanitary Engineer, "  40th Annual Conference,  Institute
      Municipal Engineers,  National Institute Water Research, 1961.

40.   "Water Resources Regulation 4. 8: General Water Quality Criteria
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      and Department of Water Resources, Annapolis, Maryland, May 1967.

41.   "Criteria for the Classification of Maryland Streams," Department
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      February, 1949.

42.   Fair,  G. M. , and J. C. Geyer,  Water  Supply and Waste  Water
      Disposal, Wiley, New York,  1954.

43.   "Runoff, " Hydrology Handbook,  Chapters, Am. Soc. Civil. Eng. ,
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44.   Private Communication, Vaden Haddaway,  Whitman,Requardt and
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45.   Private Communication, Donald E. Strickhouser, Assistant Director
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46.   Hansen, S. P.  and G. L.  Gulp,   "Applying Shallow Depth  Sedimenta-
      tion Theory, Journal AWWA. Vol. 59,  p. 1134 (1967).
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48.   Hazen, Allen,  "Water Supply, " American CivilEngineer's Handbook,
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49.   Storm Water Management Model,  Vols.  1, 2, 3, and 4,  Metcalf
      and Eddy Engineers,  Palo Alto, California,  1971.
                                218

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                           SECTION XXII

                           APPENDICES
                                                             •rage

A.     Derivation of Hydrology Equations	     221

B.     Field Gaging and Sampling	     225

       Figure B-l:  Temporary Stream Gaging Station
                   Drainage Area	     226
       Figure B-2:  Temporary Stream Gaging Station Site
                   Plans	     227
       Figure B-3:  Observed Hydrograph - Storm 1	     229
       Figure B-4:  Observed Hydrograph - Storm 2	     230
       Figure B-5:  Observed Hydrograph   Storm 3	     231

       Table B-l:   Comparison of Gaged and Calculated
                   Runoff	     228
       Table B-2:   Water  Quality Versus Runoff Rate,
                   June 26 to  27, 1968  (Storm 1)	     232
       Table B-3:   Water  Quality Versus Runoff Rate,
                   July 12,  1968 (Base Flow)	     233
       Table B-4:   Water  Quality Versus Runoff Rate,
                   July 15,  1968 (Storm 3)	     234

C.     Storm Water Storage and Pretreatment Costs	     237

       Figure C-l:  Land Area  Versus Capacity  - Open
                   Ponds	     239
       Figure C-2:  H/D Versus Capacity - Ground Level
                   and Elevated  Tanks	     241
       Figure C-3:  H/D Versus Capacity - Standpipes   . . .     241
       Figure C-4:  Site Preparation Costs Versus Capacity -
                   Storage Tanks	     244
       Figure C-5:  Burial Costs Versus Capacity  - Storage
                   Tanks	     244
       Figure C-6:  Erection Costs Versus Capacity  -
                   Concrete and Steel Above Ground Tanks,
                   Elevated Tanks, and Standpipes	     247
       Figure C-7:  Construction Costs Versus Capacity -
                   Open Ponds	     247

       Table C-l:   Reservoir Construction Types	     237
       Table C-2:   Land Area  Versus Capacity - Open
                   Ponds	     242
       Table C-3:   H/D Versus Capacity - Ground Level
                   Tanks	     242
       Table C-4:   H/D Versus Capacity - Elevated Tanks.  .     242
                               219

-------
                     APPENDICES (Continued)
                                                              Page
       Table C-5:   H/D Versus Capacity - Standpipes	   242
       Table C-6:   Site Preparation Costs Versus Capacity .  .   243
       Table C-7:   Burial Costs Versus Capacity  .......   245
       Table C-8:   Summary of Tank Erection Cost
                   Estimates	   246
       Table C-9:   Erection Costs Versus Capacity - Storage
                   Tanks	   248
       Table C-10:  Summary of Construction Cost Estimates -
                   Open Ponds	   250
       Table C-ll:  Construction Cost  Versus Capacity -
                   Open Ponds	   251
       Table C-12:  Summary of Sediment  Removal Costs  .  .  .   251

D.     Treatment System Costs	   254

       Figure D-l:  Pretreatment Capacity Versus Capital
                   Costs	   255
       Figure D-2:  Final Treatment Capacity Versus Capital
                   Costs	   255
       Figure D-3:  Daily Demand Versus  Capital Cost of
                   Pumping Facilities	   259
       Figure D-4:  Operation and Maintenance Cost Versus
                   Capacity - Final Treatment	   265

       Table D-l:   Summary of Construction Cost Estimates -
                   Pretreatment	   254
       Table D-2:   Construction Cost  Versus Capacity -
                   Pretreatment	   254
       Table D-3:   Summary of Construction Cost Estimates -
                   Final Treatment	   256
       Table D-4:   Construction Cost  Versus Capacity -
                   Final Treatment	   257
       Table D-5:   Summary of Construction Cost Estimates -
                   Pumping Facilities	   258
       Table D-6:   Construction Cost Versus Capacity  -
                   Pumping Facilities	   260
       Table D-7:   Summary of Operating Cost Estimates -
                   Treatment	   263
       Table D-8:   Operation and Maintenance Cost Versus
                   Capacity - Treatment	   264
                                220

-------
                            APPENDIX A

             DERIVATION OF HYDROLOGY EQUATIONS
Section IV of this report  "Storm Water Hydrology," contains a discussion
of the methods Used td describe the storm flow characteristics of the
Wil'de Lake drainage area.  This appendix contains the derivation of the
equations used to modify the regression model for calculating the runoff
for individual storms which are contained in Section IV.  These deri-
vations are as follows.
Alteration of the Regression Equation

Let   Qrp  ~     runoff /unit area from Herring Run

      Qp   =     runoff /unit area from the pervious portion of
                 Herring Run or Wilde Lake

      Q    =     runoff/unit area from the impervious portion
                 of Herring Run


      Q p  =     BR. + CR.2 + DR.          (neglecting base flow)

      Q    =     Qp(l-I) + QTI             (I = Fractibn Impervious)
      Qp(l-I)  + Qjl  = BRt + CRt2 + DR.3
                               2      3    KXR1
                               2      3
      %   =     TT (BRi+ CRi  + DRi> - —

      Q    =     J_ [(B-KXI)R. + CR,2 + DR.3]
       P         1 -I L         l      l      L s
       P

Let   Q' ,   =     runoff/unit area from the impervious portion of
       11         Wilde Lake

      Q .   =     runoff/unit area from Wilde Lake
      ^••T I LJ


      Qr
     QIlp =     KXR.I' + (^) [(B-KXI)Ri
                                  221

-------
Adding the base flow term:
                 A + KXI'R. + Y-J  (B-KXDR + CR.2 + DR.3
Derivation of the Expression Defining X
    QT-Q
                 (I+1)0.339(R)1.75(ApI)0.0741


                                 0.0973 -            (Ref' 3)
                               D




where:




      I     =     percent imperviousness



      R    =     precipitation in inches



      API  =     antecedent precipitation index



      D    =     duration of storm, minutes



      Qj    =     runoff volume in inches from an area

                 with I percent imperviousness
Let  Q0   =     runoff for 1 = 0, and let X = fraction of rainfall on

                 impervious areas that actually runs off.  Then:



     Q    =     XRI + ^  /100-I
       •I          100   ^o \ 100



                 XRI
     I ^o        100    TM
     X    -     10° ^
     x    -     -RT Q-
"RT^i  \L '  07  I1   Too
                     ). 339
     x     _    j~L |1QO  + /   i-ioo

                      [      Ui+i)°-339
                                222

-------
Derivation of the Equation Defining P


Let   P     =     fractional increase in unit yield of the developed

                 area over the natural area
                     Qp
whe re:
      Qrp  =     A + KXI'R. + (jZf)(B -KXI)R. + CR.2 + DR.3


      Q     =     A
Let  [(B-KXI)Ri + CR.2 + DR.3] = Y
                    KXI'Ri +      Y - A +
                 I-JKXR.-Y
Simplifying:


                                       2
                 I'  KX - B - CRt - DRt
                  -=,—  -KXI+B+CR.+DR.2
                   rl.               11
                                  223

-------
                             APPENDIX B

                   FIELD GAGING AND SAMPLING
GAGING STATION RESULTS

A temporary stream gaging station was installed in one of the sub-water-
sheds on which little development had taken place.  This gaging station
had two primary objectives:

      To provide streamflow data to verify the regression model
      which was used to calculate runoff

      To provide water quality data to compare with the data
      provided by the literature search

The watershed that was  selected for gaging  was a 130-acre  area in the
upper end of the Wilde Lake drainage  basin scheduled for devel-
opment during the end of 1968.  At the time of installation,  several
roads had been completed,  giving the area an imperviousness of six
percent.  The undeveloped portion of the area consists of woods and
a meadow with two main stream channels joining several hundred feet
above the gage site (Figure B-l).

The instrumentation (Figure B-2) consisted of a compound weir located
at the end of a long reach of a straight channel approximately six feet
wide and two and one-half feet deep.  When the weir plate was put  into
place,  the water formed a distinct pond for a distance of 40  feet upstream.

Stage measurements of discharge over the weir were made using a
stilling well, float,  and  Stevens A35 water level recorder. This recorder
was located in an instrument box and was powered by a storage battery
and power inverter.   It provided a continuous record of water level with
both good time and stage resolution.

The stage measurements were related to discharge over the weir by the
use of an equation derived by model studies  conducted by the Bureau of
Reclamation.  Field measurements were made of the flow by timing the
rate  of fill of known-volume containers, and these measurements closely
agreed with the values calculated by the equation.

Approximately 40  feet upstream from the end of the weir pond, an auto-
matic water sampler was installed. This took water samples at preset
time intervals and was usually hand-started whenever rain was forecast.
These samples were collected and returned to the laboratory for analysis.

A University of Maryland weather station located a short distance from
the watershed provided total rainfall information to be used in the regres-
sion model.
                                 225

-------
IN3
CO
              UNIVERSITY OF MARYLAND
              WEATHER STATION -
                                                                                          -TEMPORARY GAGING STATION
                                                                                                           LIMIT OF DRAINAGE AREA
                                   ROADWAY —-
                                     Figure B-l.   Temporary Stream Gaging  Station Drainage Area

-------
CO
CO
                                                             STEVfMS  Type A3S
                                                                                                                             •LEVEL FLOAT
                                                                                                  SECTION A-A
       Hittman Associate*, Inc.
                                                 SfCTION C-C
                                                                                                   SECTION
                               Figure B-2.   Temporary  Stream Gaging Station Site  Plans

-------
During the time of operation of the gaging station, three storms occurred
from which runoff hydrographs were obtained.  These three hydrographs
are  shown in Figures B-3 through B-5.  From the hydrographs, the
volume of runoff was determined and compared to the  runoff volume
calculated by regression model for the same amount of rainfall.  Table
B-l  gives the results of this comparison.


 TABLE B-l.   COMPARISON OF GAGED AND CALCULATED RUNOFF


                     Rainfall    Measured Runoff    Calculated Runoff
Storm      Date      (inches)       (cfs-days)           (cfs-days)


   1     6/26-6/27     0.79           0.242              0.352

   2     6/27-6/28     0.66           0.236              0.254

   3     7/19           1.16           0.70               0.60


          Correlation between measured and calculated = 0. 92
For the first and last storms, water samples were also collected.  The
results of the analysis of these samples,  ag well as the analysis of base
flow,  will be presented in a subsequent section.
FIELD SAMPLING RESULTS

In order to permit early verification of the expected pollutant concen-
trations listed in Table 10, a  sampling point was established in the
Wilde Lake Watershed in conjunction with the gaging station described
above.  An automatic sampler  was used to collect runoff samples at
one-hour intervals from a point immediately upstream from the weir
pond.  These samples were correlated with measured stream flow at
the time of sampling and analyzed for various pollutants by Hittman
Associates.   The results  of this analysis are presented as Tables B-2,
B-3, and B-4.  Tables B-2 and B-4 reflect water quality during two of
the storms whose hydrographs  were analyzed above and  identified as
Storms  1 and 3.   Table B-3 lists data on water quality during a typical
period of minimum flow,  when  no storm runoff was present.

All samples were excessively high in suspended and total solids,  due
to a high level of construction activity in the watershed during the period
under study.  A large portion of the floodplain itself had been denuded
as a  result of the construction  of a sanitary sewer, and erosion was
severe.  For this reason,  the results obtained cannot be treated as
typical of this area.  Furthermore,  little urbanization has occurred
on the gaged watershed at the present time.  At the time of sampling
                                 228

-------
            2. 0
to
CO
             0. 2 _
                2000
                                                                                Storm 1

                                                                           6/26/68 - 6/27/68

                                                                            Rainfall = 0.79"
2200
 2400       0200
^-f-^- 6/27/68
0400      0600
    Time
                                                                              0800
1000
1200
                                                                                     1400
                                      Figure B-3.  Observed Hydrograph - Storm 1

-------
             1. 2
to
CO
o
             1.0 \-
         •Z  0.6  (—
             0.2 |—
               0
                1800
2000
                                                                              Storm 2

                                                                          6/27/68 - 6/28/68

                                                                           Rainfall = 0. 66"
2200      2400       0200       0400
  6/27/68  ^ |  »- 6/28/68  Time
                                                                               0600
                                                                                         0800
1000
1200
                                           Figure B-4.  Observed Hydrograph - Storm 2

-------
CO
<«-<
o
o
s
      0
                                                      Storm 3

                                                      7/15/68

                                                  Rainfall = 1.16"
      1400
1430
 1500

7/15/68
1530

   Time
                                                1600
                                           1630
1700
       Figure B-5.  Observed Hydrograph - Storm 3
                                 231

-------
1X3
oo
to
                                 TABLE B-2.  WATER QUALITY VERSUS RUNOFF RATE
                                             JUNE  26 TO  JUNE  27,  1968 (STORM 1)
Sampling
Time

16:30
17:30
18-30
19:30
20 30
21-30
22-30
23:30
24-30
01 30
02-30
03:30
04-30
05:30
06:30
07:30
08:30
09:30
10-30
11:30
12-30
13:30
14:30
Runoff
Rate
cfs

0.04
0. 04
0.04
0. 04
0.04
0.04
0. 04
1. 00
1.65
0.60
0.44
0.33
0.23
0. 20
0. 17
0. 16
0. 15
0. 14
0. 15
0. 13
0. 10
0. 15
0. 14
Turbidity
JTU

190
125
78
130
82
103
85
4, 500
3,500
1, 500
1,050
820
325
270
	
151
	
235
103
1, 050
310
105
1, 300

Suspended
Solids
mg/1

140
	
50
	
75
	
80
11, 450
5, 780
1,950
1, 105
823
	
290
	
150
	
238
	
925
310
	
1, 500
Settable
Solids
mg/1


	
	
	
	
	
	
10, 830
5, 250
1, 550
920
	
	
	
	
	
	
	
	
	
	
	
1, 220
Total
Solids
mg/1

252
	
	
	
185
	
	
11,650
	
2, 100
	
970
	
	
	
255
	
	
	
1, 110
	
	
1,680
Chemical
Oxygen
Demand
mg/1
20
__
__
20
__
-_
30
40
--
30
20
30
--
--
--
_-
_-
30
--
-_
_-
-_
30
PH


8. 3
	
8. 3
8. 3
	
	
7.9
7. 1
7.2
7. 3
	
7.6
	
	
	
8.0
	
8.2
	
	
	
	
7.2
Alkalinity
(CaCO3 )

55
__
„_
55
__
__
55
20
20
25
-_
25
--
--
__
30
-_
35
_-
-_
__
__
10
Hardness
(CaCO3)

50
_-
__
50
__
__
45
30
25
25
--
30
__
--
__
35
__
40
--
__

__
30
Chloride
(CD
mg/1

8
	
	
7. 5
	
	
7. 5
24
12
11.5
	
12
	
	
	
10
	
9.5
	
	
	
	
10
Nitrate
(Nitrite)
mg/1

0. 7
	
	
0.5
	
	
0.6
0. 1
0.0
0. 2
	
0.3
	
	
	
	
	
0.6
	
	
	
	
0.5
                                                                                                                        Phosphate
                                                                                                                          (PO4-)
                                                                                                                          mg/1
                                                                                                                          3.4
                                                                                                                          0.3
                                                                                                                          1.1
                                                                                                                          1.7

-------
TABLE B-3.
WATER QUALITY VERSUS RUNOFF RATE
JULY 12,  1968 (BASE FLOW)









to
to
CO


Sampling
Time
02:00
04:00
06:00
08:00
10:00
12:00
14:00
16:00
18:00
20:00
22:00
24:00
Runoff
Rate
cfs
0.04
0.04
0.04
0.04
0.04
0. 04
0.04
0.04
0.04
0.04
0. 04
0.04
Turbidity
JTU
32
35
35
32
38
45
38
40
35
38
30
35
Suspended
Solids
mg/1
15
12
10
10
14
21
16
18
11
8
12
16
Settable Total
Solids Solids
mg/1 mg/1

	 130
	 	
	 129
	 	
	 140
	 	
	 138
	 	
	 122
	 	
	 130
Chemical pH
Oxygen
Demand
mg/1

15
--
20
--
15
--
10
--
15
--
10
7.55
7.55
7.55
7. 55
7.60
7.55
7. 55
7. 55
7.60
7.55
7.60
7. 60
Alkalinity
(CaCO,)
mg/11*

45
--
40
--
40
--
40
-_
43
--
40
Hardness
(CaCO,)
mg/ld

30
--
30
--
33
--
30
__
35
--
30
Chloride Nitrate
(Cl~) (Nitrite)
mg/1 mg/1

7.5
.__
7.5
	
7.5
	
7. 5
	
7.5
	
7.5

0.32
	
0. 30
	
0.29
	
0. 27
	
0. 25
	
0. 27
                                                                                      Phosphate
                                                                                        (P04=)
                                                                                        mg/1
                                                                                        0.10


                                                                                        0.10


                                                                                        0.08


                                                                                        0. 12


                                                                                        0. 10


                                                                                        0.09

-------
TABLE B-4.
WATER QUALITY VERSUS RUNOFF RATE
    JULY 15, 1968 (STORM 3)
Sampling
Time
13:00
14:30
15:10
15:20
15:30
15:45
16:00
16:15
16:30
CO 17-30
CO
^ 18:30
19:30
20:30
i i.^n
Runoff
Rate
Q
cfs
0.05
0.05
19. 50
12:50
8.20
4. 70
2. 70
2.20
1.00
0. 30
0. 30
0. 20
0. 20
n ns
Turbidity
JTU
30
35
5, 200
4, 600
4, 300
4,000
3, 600
2,600
2, 300
1, 100
1, 150
750
1, 900
Rft
Suspended
Solids
mg/1
23,
14,
10,
7,
6,
3,
3,
1,
1,
10
20
800
600
500
750
000
900
040
955
030
725
510
sn
Settable Total Chemical pH
Solids Solids Oxygen
mg/1 nag/1 Demand
mg/1


23, 300 23, 950 10
1 3 Rfto ?n
9, 800 10, 680 30
5,380 6,200 40
3,500 	 20
3 170 30
- - 40
- - 20
1 n
	 I 680 10
s
7.50
6.95
6. 55
6.35
6. 25
6.50
6.80
7.00
7. 10
7.00
7. 05
7. 15
7. 25
7 A*.
Alkalinity
(CaCCU
mg/1*
40
43
15
15
10
8
10
11
10
10
18
20
25
•}«;
Hardness Chloride Nitrate Phosphate
(CaCO3) (Cl~) (Nitrite) (PO4=)
mg/1 mg/1 mg/1 mg/1
30
30
30
25
20
25
25
20
25
23
25
28
35
qn
7.5
7/5
15.0
12.5
22.5
10
22. 5
12.5
10
9
9
9
14
7 ^
0.28
0. 3-1 -,
0. 15
0. 34
0.60
0. 20
0.60
0. 35
0. 34
0.45
0. 27
0. 28
0.32
ft O«
0. 10
0.30
0.07
1.90
4.60
0.50
5.30
2. 20
0. 15
0.18
0.27
0. 20
0. 15
ft 9£

-------
facilities were not available for determining BOD, and a GOD test was
employed instead.  Due to the atypical conditions existing,  however, the
results of the tests during storm flows are judged to have little value
with respect to estimating future pollution loads.  The data presented
on Table B-3 is of some interest in that the base flow water quality
might be expected to be relatively independent of watershed conditions.
As the data indicate,  this flow was found to be of excellent quality,
well within the expected limits. The continuation of this sampling
activity throughout the period of urbanization of this watershed would
be of considerable value in assessing the effect of construction and
subsequent population on runoff quality.
                                  235

-------
                             APPENDIX C

        STORM WATER STORAGE AND PRETREATMENT COSTS


RESERVOIR CONSTRUCTION COSTS

Construction costs were calculated for the five types of storm water
Storage reservoirs listed in Table 12.  All types except the open ponds
have an alternate application as treated water storage facilities and the
same construction costs were employed for both applications.  In addition,
other types of storage were considered for treated water  only, namely,
standpipes, elevated tanks, and hydropneumatic tanks. Table C-l lists
all types of storage considered for either application. This section will
describe the methods employed to compute parametric costs for each
of these storage types.  The following section will outline operation and
maintenance costs for the  storm water application only.   Similar costs
for treated water storage applications can be found in Appendix  D.


           TABLE C-l.   RESERVOIR CONSTRUCTION TYPES

                                                Application

Construction Type                     Storm Water     Treated Water

Natural Storage
      Open Pond                           X

Ground Level Storage
      Steel Tank - Above Grade             X               X
      Steel Tank - Below Grade             X               X
      Concrete Tank  - Above Grade         X               X
      Concrete Tank  - Below Grade         X               X

Elevated Storage
      Standpipe                                              x
      Elevated Tank                                         x

Pressure Storage
      Hydropneumatic Tank                                  x
                                237

-------
Construction costs for storage facilities were considered to be made up
of the following:

1.    Land costs, applicable wherever the purchase of the  land is a
      necessary cost of the  system.

2.    Site preparation  costs, including clearing and grubbing, rough
      grading,  finish grading,  and  seeding or sodding after
      construction.

3.    Burial costs,  including excavation and backfill for tanks which
      are installed below grade.

4.    Erection costs, which include foundations, tank erection,
      painting of metal parts,  and in the case of ponds, necessary
      excavation, fill,  embankment, spillway construction, ;'and
      bottom and slope preparation.                      -,'•'

In each case,  actual estimates were made of construction costs for a
number of hypothetical installations of various types and- sizes  in the
Columbia area.  Prices  of 1967 to  1968 were used and,allowances made
for  engineering, inspection, and construction contingencies.  The
estimates were then plotted against the appropriate size parameter and
a smooth curve extended between the points.  This curve was then
replaced by a series of linear approximations which closely followed
it and the inflection points reduced to a table of sizes  and costs.  This
table was input to the computer in the  systems analysis,  so that the
cost of any size facility could be estimated by a linear interpolation
between two points on the table.  In general, the original estimates
were made at sizes which permitted the curve to be well defined in the
range of possible application in the systems analysis.


LAND COSTS

In most applications, land can  be purchased for a per-acre price which
is relatively uniform throughout the project  area.  Methods for computing
the  required land area for each type and size of tank or pond were
developed,and costs  were determined by simply permitting the  computer
program to multiply the  land area in acres by the cost in dollars per acre,
which was input separately.  Computation of required land area for  open
ponds required the conceptual siting of a variety of pond  sizes in the
Wilde Lake Watershed and the computation of the  land area.  In every
case,  a 30-foot border was  provided beyond the high water line to protect
slopes and permit decorative fringing  with trees and shrubbery.  No
attempt was made to force areas into regular shapes except for ease of
computation.  Figure C-l shows the resulting land area/capacity curve,
with the  linear approximation overlaid.  Table C-2 lists the inflection
points of the linear approximation which were input to the computer for
pond land area computations.   All other types of storage were treated
as cylindrical tanks  and  their land  requirements were computed on the
                                 238

-------
DO
CO
CD
     tn
     0)
     tn
     O
     OS

     o!
     CD
     -a
     c
     cd
15  -
          10 -
           5  -
              Estimates

          A   Linear Approximation
                                     40
                                                       50      60       70
                                                   Capacity (million gallons)
80
90
100
                                   Figure C-l.   Land Area vs.  Capacity - Open Ponds

-------
       TABLE C-2.  LAND AREA VS. CAPACITY - OPEN PONDS
              Capacity                         Land Area
              (gallons)                          (acres)

                       0.0                      0.0714
                  10,000                        0.0714
                 100,000                        0.340
               1, 000, 000                        1. 690
               4, 000, 000                        4. 110
              10,000,000                        7.645
              20,000,000                       12.250
              40, 000, 000                       19. 550
             100, 000, 000                       36. 370
basis of height/diameter (H/D) ratios.  These ratios,  found by dividing
tank height by tank,diameter, were determined by plotting H/D for
standard designs of a variety of tanks.  Figure C-2 shows such a plot
for ground level tanks and elevated tanks.  Figure C-3 shows H/Ds for
standpipes.  The corresponding linear approximations can also be  seen
on these figures,  and Tables C-3, C-4, and C-5 list the ratios used in
the computer program.

Required land area is found by  adding 30 feet to the diameter, thus
providing for a minimum 15-foot  border around the tank.  This calcu-
lation is performed as follows:

      BAR =     0.000018 (DIAM + 30. O)2                       (C-l)

where:

      BAR =     required land area, acres

Since the land to be used in  the Wilde Lake Watershed was entirely
public open space, the initial systems analysis computer runs were
made with land cost set  at zero.  Should the value of land to be used
for system construction become a significant consideration, insertion
of the appropriate  per-acre cost  into  the computer input will result
in revised estimates.
                                240

-------
          Elevated
                                                                Ground Level
   0    1    23   4   5
                           67    8   9   10  11
                              Capacity (million gallons)
                                                    12  13   14   15
Figure C-2.  H/D vs.  Capacity - Ground Level and Elevated Tanks
                                           i.o
                        0.5
                            Capacity (million gallons)
             Figure 03.  H/D vs.  Capacity -  Standpipes
                                  241

-------
     TABLE C-3.  H/D VS. CAPACITY - GROUND LEVEL TANKS
          Storage Capacity
              (gallons)                          H/D

                      0.0                      1.0.00
                 50,000                        0.900
                200,000                        0.759
                500,000                        0.640
              1,000,000                        0.512
              2,000,000                        0.366
              3,000,000                        0.285
              5,000,000                        0.210
              7,000,000                        0.180
             10,000,000                        0.165
           100,000,000                        0.0348
       TABLE C-4.  H/D VS.  CAPACITY - ELEVATED TANKS
          Storage Capacity
              (gallons)                          H/D

                     0.0                       0.995
               250,000                         0.995
               300,000                         0.900
               500,000                         0.710
               700,000                         0.588
             1,000,000                         0.490
             1, 250, 000                         0. 442
             1,500,000                         0.410
          TABLE C-5.  H/D VS. CAPACITY - STANDPIPES
              Capacity
              (gallons)                         H/D

                     0.0                       17.25
               180,000                          3.00
             1,500,000                          2.20


SITE PREPARATION COSTS

Since the costs treated under this heading are primarily related to land
area and not to type of construction, they were evaluated on a per-acre
basis and applied to all tanks.  The single exception to this is the case
                                242

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of open ponds,  where site preparation costs were considered as part of
erection costs  and included in that tabulation.  Figure C-4 shows the
curve plotted from  estimates and the linear approximation.  The table
of values used  in the computer program is  shown as Table C-6.  Land
area is computed as described in the previous paragraph on land costs.
Per-acre site preparation costs corresponding to various capacities
are obtained by linear interpolation of the table.  The interpolated value
is then multiplied by the land area to yield  total site preparation cost.
      TABLE C-6.  SITE PREPARATION COSTS VS. CAPACITY
              Capacity                  Site Preparation Costs
              (gallons)                  	($/acre)	
                       0.0                      34,500

                100,000                        27,750

                300, 000                        20, 300

                700,000                        14,200

              1,150,000                        11,000

              1,500,000                          9,500

              2, 000, 000                          8, 200

              2,500,000                          7,400

             10,000,000                          3,400

            100,000,000                          3,400


BURIAL COSTS

Burial costs are computed  only for the ground level storage tanks installed
below grade  In these cases,  the total cost of excavation and backfill
associated with the  construction of various underground tanks was esti-
mated and the results plotted as Figure C-5.  This figure also shows
the linear approximation of the curve which is represented by Table C-7.
The tank capacity is used to interpolate between points on the table,
yielding burial costs in dollars per gallon.  When this figure is multiplied
by the capacity,  the total burial costs are obtained.
                                 243

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                                                        Estimates
                                                        Linear Approximation
Figure C-4.   Site  Preparation Costs vs.  Capacity - Storage Tanks
      0.06
                                                     Estimates
                                                     Linear Approximation
      0.02
      0.01
1 1 1 1
1 I 1 1 1 1 1 1 1 1
                                     7    8   9  10   11   12   13   14  15
                                   Capacity (million gallons)
     Figure C-5.  Burial Costs vs. Capacity - Storage Tanks
                                   244

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              TABLE C-7.  BURIAL COSTS VS. CAPACITY


                 Capacity                    Burial Costs
                 (gallons)                      ($/gallon)


                          0.0                   0.0510
                   100,000                     0.0480

                   500,000                     0.0390
                 1,000,000                     0.0310

                 1,500,000                     0.0269

                 2,000,000                     0.0230
                 2,500,000                     0.0206

                 3,000,000                     0.0188
                ° 3, 500, 000                     0.0176

                 4,500,000.                     0.0162

                10,000,000                     0.0134
               100,000,000                     0.0134
 ERECTION COSTS

 Estimates were obtained from tank fabricators and erectors for in-place
 costs of a variety of tank types and sizes.  Table C-8 is a summary of
 that information.  Figure  C-6 shows curves for various types of above
 grade and elevated tanks.   Tanks designed for burial must be constructed
 somewhat differently to account for the additional stresses,  and infor-
 mation  from fabricators indicated an approximate 15 percent increase in
 the tank cost.  When the burial option is selected in the program,  then
 15 percent is added to the tank erection cost in addition to the computation
 of the burial cost.   Table  C-9 lists the program inputs used to describe
 the erection cost capacity relationships for various tank types.

 In the case  of open ponds,  the erection cost is highly site-dependent.
 Furthermore,  a tradeoff exists between excavation of the site to increase
 storage and providing additional spillway elevation.  In addition to being
 dependent upon the relative costs of excavation and spillway and embank-
 ment construction, the optimum combination is a function of the site
 topography and the spillway-embankment width.  In order to arrive at
 an approximate parametric relationship between pond capacity and cost,
 a site was selected from the Wilde Lake watershed  (sub-watersheds
 number 4 and 5) and a dam location determined.  Using a large-scale
 topographic map with one-foot contours, pond capacity was determined
for each foot of elevation of the dam up to the maximum feasible elevation
 at the site.  These capacities were those of completely natural ponds with
                                 245

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    TABLE C-8.   SUMMARY OF TANK ERECTION COST ESTIMATES
Ground Level Tanks  Steel
Ground Level Tanks-Concrete
Elevated Tanks
Standpipes
(1)  Pittsburgh-DesMoines Steel Co.
(2)  Chicago Bridge and Iron
(3)  The Crom Co.
(4)  The Preload Co.
Capacity
(gallons)
50, 000

100, 000

200, 000
500, 000

1,000, 000

2, 000, 000

5, 000, 000
10, 000, 000
100, 000
250, 000

;. 500, 000

750, 000
1, 000, 000

2,000, 000

5, 000, 000

10,000, 000

50,000

100, 000

200, 000

500, 000

1, 000, 000

2,000, 000

100, 000
500, 000
1, 000,000
2,000, 000
Erection
($)
10,000(1)
8,400(2)
13, 000(1)
11, 000(2)
15, 500(2)
30, 000(1)
27, 000(2)
53, 000(1)
44, 000(2)
110, 000(1)
77, 000(2)
175, 000(2)
340,000(2)
18, 500(3)
28,000(3)
45, 000(4)
45,000(3)
68, 000(4)
80,000(4-)
69,000(3)
100, 000(4)
125, 000(3)
150,000(4)
250, 000(3)
325, 000(4)
500, 000(3)
500, 000(4)
38,000(1)
30, 000 < 	 >
45, 000(1)
38, 500 < 	 >
60,000(1)
42, 500 < 	 >
110,000(1)
85,000 < — >
220, 000(1)
170,000 < 	 >
375,000(1)
290, 000 <— ->
19,000(1)
45, 000(1)
80, 000(1)
130, 000(1)
Costs




























33,000(2)

44, 000(2)

52, 500(2)

95,000(2)

186,000(2)

330, 000(2)




                                 246

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   1000
   800
»  600
   400
    200
                                                                   Concrete
                                                                   Steel
                                                                   Estimates
                                                                   Linear
                                                                   Approximation
                                                     12   13
                                                                15
       012   345    67    89   10   11
                                Capacity (million gallons)
   Figure C-6.  Erection Costs  vs. Capacity -  Concrete and  Steel
         Above Ground Tanks,  Elevated Tanks,  and Standpipes
   300
   250 -
~  200 -
-  150 -
 a
 O
    50 -
                               Estimates
                               Linear Approximation
           10
                 20
                        30
40     50     60     70     80
   Capacity (million gallons)
                                                                  100
     Figure C-7.   Construction Costs vs.  Capacity - Open Ponds
                                     247

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TABLE C-9.  ERECTION COSTS VS.  CAPACITY - STORAGE TANKS
  Ground Level Storage
        Steel
   Ground Level Storage
        Concrete
   Elevated Tanks
   Standpipes
Capacity
(gallons)

10,
50,
200,
400,
700,
1, 000,
2, 000,
5, 000,
100, 000,

10,
50,
100,
300,
900,
1, 500,
2, 500,
3, 500,
5,000,
10,000,
100,000,

10,
50,
100,
200,
350,
500,
1, 000,
1, 500,

10,
50,
200,
400,
700,
1,500,
0. 0
000
000
000
000
000
000
000
000
000
0. 0
000
000
000
000
000
000
000
000
000
000
000
0. 0
000
000
000
000
000
000
000
000
0. 0
000
000
000
000
000
000
Erection Cost
($)
5,
5,
11,
21,
32,
48,
65,
122,
263,
5, 260,
15,
15,
20,
25,
51,
100,
139,
197,
259,
355,
625,
6, 250,
26,
26,
45,
55,
72,
102,
132,
258,
367,
15,
15,
20,
32,
51,
82,
137,
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
000
                                 248

-------
no excavation.  Next,  capacities were recalculated for each elevation
with excavation of the basin until the incremental cost of excavation
(in dollars per gallon) equaled the incremental cost of the next change
in dam elevation. These final capacities were used to develop the cost
versus capacity curve which appears  in Figure C-7.  In general, exca-
vation accounted for about one-third of the final pond volume.  A sum-
mary of the cost estimates appears in Table C-10.  Table C-ll has the
final values used in the computer input.
OPERATION AND MAINTENANCE

In the preparation of the preliminary parametric cost data for use in
the computer program, the operation and maintenance costs for the
storm water storage facilities were  considered to be under three
headings.  These were:

1.    Routine checks of storage and  pretreatment facilities

2.    Trash removal from storage facilities

3.    Sediment removal from storage and pretreatment facilities

In this initial analysis, it  was assumed that the routine  checks of the
facilities would be conducted approximately once per week and would
require one-half man-hour per reservoir.  It was assumed that trash
removal would be required on half of the inspections and an additional
two-tenths of a man-hour  were allotted for these inspections.

In the generation of the parametric cost data, it was assumed that sedi-
ment would be removed by pumping from the  tanks and pretreatment
facilities using tank trucks.  One hour was allotted for this operation
requiring a semiskilled laborer  and an equipment operator. It was
assumed that this operation would be required 25 times per year and
that the tank truck rental would be $100 per day or $8. 33 per hour or
per operation.

For the disposal of the sediment, it  was assumed that a satisfactory
dumping site would be available within two miles of the reservoir.  No
allowance was made for the operation and maintenance of a sediment
disposal facility in this study.

The labor rates used in this  initial analysis were based on  the use of
semiskilled laborers at the rate of  $2.50 per hour,  plus 15 percent
for fringe benefits,  or $2. 88 per  hour, for the routine checks, trash
removal,  and as  a helper  on the  sediment removal operations.  The
labor rate for the equipment operator was estimated at $3. 50 per hour,
plus 15 percent,  or  $4.03  per hour.

Table C-12  summarizes the  estimated cost of the routine checks and
trash and sediment removal used in the development of the parametric
                                249

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                TABLE C-10.  SUMMARY OF CONSTRUCTION COST ESTIMATES - OPEN PONDS
CO
01
o
Capacity
(gal)
52,
91,
159,
238,
339,
465,
630,
858,
1,015,
1,105,
1,780,
950
950
450
800
300
000
000
000
000
000
000
Concrete
x-unu
Excavation Area
Yards
16.
20.
23.
39.
42.
52.
70.
87.
102,
110.
151.
02
11
89
22
77
03
37
00
00
00
00






1,
1,
1,
1,
2,
Yards
87.9
161.9
263.8
393.4
560. 1
768.4
037. 0
416.7
660.0
800.0
850.0
(sq.ft.)
2, 500
4, 000
5, 500
7, 000
9, 000
11, 250
15, 000
20, 500
23,000
24,400
35,000
(Cost Items in Dollars)
Embank-
Concrete ment Excavation Clear
Cost
1, 153
1, 448
1, 720
2, 820
3, 078
3, 746
5, 063
6, 226
7, 344
7,920
10,872
Cost
30
30
30
54
60
71
101
497
520
529
840





1
1
1

1
2
3
Cost
160
360
535
810
, 050
, 320
, 300
608
,850
,,040
, 358
Rip
& Grub Rap
30
40
55
70
90
112
150
207
230
244
350
109
402
740
786
1, 142
1, 031
970
1, 878
1, 536
1, 187
3, 500
Net
Total
1,482
2, 280
3, 080
4, 540
5, 420
6, 280
7, 584
9,454
11, 480
11, 920
18, 920
Cont.
+25%
371
570
775
1, 135
1, 355
1, 570
1, 896
2, 364
2, 870
2, 980
4,730
Gross
Total
1, 853
2, 850
3, 855
5, 675
6, 775
7, 850
9, 480
11, 818
14, 305
14,900
23, 650

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         C-ll.  CONSTRUCTION COST VS. CAPACITY  OPEN PONDS


              Capacity                  Construction Costs
              (gallons)                  	($)	


                       0-0                     1,765
                 50,000                        1,765

                200,000                        5,000
              1,000,000                      13,290

              4,000,000                      33,800

             10,000,000                      62,600
             20,000,000                      99,800



      TABLE C-12.  SUMMARY OF SEDIMENT REMOVAL COSTS


          Number of                                          Total
(
Routine
Check
Trash
Removal
Sediment
Removal
Jccurrences
per Year
50
25
25
; Man-
hrs
0.
0.
1.
1.
5
2
0
0
Rate
2.
2.
2.
4.
88
88
88
03
Labor
Cost
1.
0.
2.
4.
44
58
88
03
Equip.
Cost
0.50
	
8. 33
Per
Occurrence
1
0
11
. 94
.58
.47
per
Year
$ 97.00
14.50
381.00
    Total trash and sediment removal, cost per year          $492. 50

    Trash and sediment removal,  cost per gallon runoff   $0. 00004925
cost data for the computer program.  These costs are based on a storage
facility receiving 10, 000, 000 gallons of runoff per year.

It is noted that this study was based on reservoirs operating in an estab-
lished and stabilized community.  As  such, the estimates were not based
on the quantities of sediment that would be generated during construction.
This is further discussed in Section VII.
                                 251

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The parametric cost data selected and used in the computer program were
$0.00005 per gallon for runoff for both the tank type storage and open ponds,
independent of size. As discussed in Section XII,  the operating and main-
tenance costs for the storage reservoirs and pretreatment unit were fur-
ther refined in making the cost estimates for the various local storage and
reuse systems. In these estimates,  the costs for sediment  removal from
the storage reservoirs  and pretreatment unit were separately estimated
and the frequency of the various operations and man-hour estimates were
revised based on the actual design. These later operation and maintenance
costs also include the cost of chemicals used in the pretreatment units and
the labor  and materials for preventive maintenance and repair.

In addition to the costs  of the routine checks and cleaning of the storage
reservoir and pretreatment unit, the parametric cost input included pro-
vision for painting and repair of metal surfaces, hatchways,  doors, etc,,
as well as repair to concrete structures. Ground maintenance was not
included since  the normal maintenance that would be given to the  open
space where the facilities are located is expected to be adequate.  Minor
repairs and painting can be accomplished as part of the routine inspec-
tions noted above.  Concrete structures  are not expected to  require sig-
nificant maintenance during the time  span of the economic analysis.      .,  t
Metal tanks,  however,  must be periodically painted and repaired. Buried
tanks require maintenance of their internal surface,  while tanks installed
above grade have two surfaces to be maintained. Repair and maintenance  ,
experiences with a  number of tanks in the Baltimore area were supplied, ,
by Whitman,  Requardt and Associates, along with the number of square
feet maintained in each case. The total  cost, taking into account painting
and repairing exposed metal surfaces, has been found to average $0. 05
per square foot per  year.

The inside surface  area of buried  tanks was  computed as follows:

      SURI =     3. 14159 DIAM (HIGH + 0. 5 DIAM)               (C-2)
where:

      HIGH =     tank height  tank diameter  times H/D ratio, feet

      SURI       total inside surface area, square feet

This area includes inside walls, floor, and ceiling.  The outside area of
above-grade tanks was computed to include outside walls and  roof  as
follows:

      SURO-     3.  14159 DIAM (HIGH + 0.25 DIAM)              (C-3)
where:

      SURO =     total outside surface area, square feet

Total surface area of tanks above  grade  was taken as inside  area plus
outside area, or SURI + SURO. Maintenance costs are then computed by
multiplying tank area by $0. 05 per square foot per year.
                                252

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                             APPENDIX D

                     TREATMENT SYSTEM COSTS


EQUIPMENT AND FACILITY COSTS

Construction costs for pretreatment, final treatment, pumping, and
treated water storage were  determined by computing estimated costs
for each of a series  of design capacities and assuming that a continuous
function exists between the calculated points.  In each case, a minimum
capacity was determined, below which it was assumed that costs would
not decrease with decreasing capacity.  Underground construction within
the floodplain area was  assumed for pretreatment and final treatment
units,  both to minimize pumping costs and overflow provisions and to
permit unobtrusive installations in residential neighborhoods.  Under-
ground,  ground level,  and elevated options were considered for treated
water  storage.
PRETREATMENT

Estimated construction costs for the pretreatment unit are listed in
Table D-l.  The pH adjustment process was not included in the para-
metric  costs,  due to its nominal  cost  and the high probability of a
satisfactory pH at the Columbia location.  Costs are based on a solution
feed of  both  coagulant and chlorine, obtained from hypochlorite.  Use
of chlorine gas was also investigated,  but not included in the parametric
cost analysis  due to the wide range of capacities being investigated
and the probable inapplicability of chlorine gas feed at the smaller size.

The complete pretreatment construction cost/capacity function was
approximated by fitting a curve to the points developed in Table D-l.
This curve was,  in turn, approximated by a series of  inflection points
and straight  lines, permitting the data to be  input to a computer
program as  a table of cost/capacity relationships.  This table is shown
as Table D-2 and the two curves  are illustrated on Figure D-l.
FINAL TREATMENT

Capital costs for the final treatment phase were developed in the same
manner as pretreatment costs.  Facilities for each treatment level
were estimated for  several capacities within the range of those being
investigated.  A capital cost/capacity curve was approximated and this
curve  in turn,  approximated by a series of straight lines.   The  inflec-
tion points of this last curve were reduced to a table for input to  the
computer program,  permitting calculation of a cost for any size  plant
by a simple linear interpolation between the appropriate points on the
table  The basic  cost data are summarized on Table D-3, and Figure D-2
shows the developed curves for each of treatment levels. Since no final
                                 253

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TABLE D-l.  SUMMARY OF CONSTRUCTION COST ESTIMATES - PRETREATMENT
(Costs in Dollars)
Engineering,
Excavation Structure, Contractor,
Capacity and Pipes, Tube Chemica] Construction Etc.
(gal/day) Backfill Etc. Settler Feeders Cost (@25%)
21, 600 150 315 125
130,000 280 650 750
650, 000 400 3, 350 3, 750
1,300,000 750 5,450 7,500
DO
01
TABLE D-2. CONSTRUCTION COST
Pretreatment
Capacity
(overflow rate -gallons /day)
15, 000
60, 000
150, 000
600, 000
1, 500, 000
5,500,000
250 840 210
400 2, 000 520
500 8,000 2,000
500 14, 200 3, 550
VERSUS CAPACITY - PRETREATMENT
Capital Cost
(dollars)
1, 050 -
1, 680
2, 800
9, 400
22, 200
42, 400
Total
Cost
1, 050
2, 600
10, 000
17, 750

-------
6
O
KstimatcH

Linear
Approximation
    10 L
       0      100    200    300     400     500     600    700    800    900    1000
                               Annual Runoff (million gallons /year)
    500.000
    400.000  I—
„   300, 000 -I—
    200,000 I—
    100,000 I—
         Figure D-l.   Pretreatment Capacity vs.  Capital Costs
                                                                             Class AA
                                                                            Class A
          6   100  a 00  300  400  SCO  600  700 800  300  1000 1100 1200  1300  1400 IFi'&O

                           Finnl Treatment Plant Capacity (thousands gal/day)

       Figure D-2.   Final Treatment Capacity vs.  Capital Cost
                                        255

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            TABLE D-3.  SUMMARY OF CONSTRUCTION COST ESTIMATES - FINAL TREATMENT
DO
On
Capacity
gal /day
100, 000
500, 000
1, 000, 000
Capacity
gal /day
100, 000
500,000
1, 000,000
Capacity
gal /day
100, 000
500, 000
1, 000, 000
Excavation
and
Backfill
500
1, 000
1,400
Excavation
and
Backfill
5,000
14, 000
22, 000
Excavation
and
Backfill
8, 000
23, 000
35, 500

(Cost in Dollars)
TREATMENT
CLASS "B"
Structure,
Elec. , Chemical Const.
Piping, Etc. Feeders Strainer Cost
3,500
4, 800
6,000
Structure,
Elec.,
Piping,
Etc.
9, 800
38, 000
89, 350
Structure,
Elec.,
Piping,
Etc.
15, 500
61,000
125,000
400 12,400 16,800
500 22, 500 28, 800
650 31,950 40,000
CLASS "A"
Chemical
Feeders Filter Monitors
400 3, 800 1, 000
500 12,000 1,000
650 27,000 1,000
CLASS "AA"
Engr., Cont. ,
Etc. (@25%)
4,200
7, 200
10, 000
Engr. ,
Cont. ,
Const. Etc.
Cost (@25%)
20,000 5,000
66,000 16,500
140, 000 35, 000

Engr. ,
Activated Cont.,
Chemical Auto. Carbon Const. Etc.
Filter Feeders Monitors Unit Cost (@25%)
3,800 400 5,300 11,000
12,000 500 6,500 45,000
27,000 650 6,500 65,000
44,000 11,000
148,000 37,000
260,000 65,000
Total
Cost
21,000
36,000
50,000
Total
Cost
25,000
82,000
175,000
Total
Cost
55,000
185,000
325,000

-------
treatment plant is required for Class "C" water, costs are shown for
Classes "B," "A,"  and "AA" only.  Table D-4 shows the final costs
input to the computer program.

      TABLE D-4.  CONSTRUCTION COST VERSUS CAPACITY  -
                        FINAL TREATMENT
Final Treatment Capacity
(gal /day)
CLASS "B" 0.0
100,000
200,000
400,000
600, 000
800, 000
1, 000,000
1, 200, 000
1, 500, 000
CLASS "A" 0.0
100, 000
200, 000
400, 000
600, 000
800, 000
1, 000, 000
1, 200, 000
1, 500, 000
CLASS "AA" 0.0
100, 000
200, 000
400, 000
600, 000
800, 000
1, 000, 000
1, 200, 000
1, 500, 000
Capital Cost
(dollars)
18, 000
21, 000
25, 000
34, 000
37, 500
40, 000
50,000
60, 000
75, 000
15, 000
25, 000
45, 000
65, 000
100, 000
150, 000
175, 000
215, 000
265, 000
40, 000
55, 000
95, 000
155, 000
215, 000
285, 000
325, 000
385, 000
440, 000
                                257

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As in the case of the pretreatment unit,  underground construction and
solution feed of all chemicals are assumed.  Softening and secondary
coagulation are not included in these costs.  Chlorine costs are not
shown separately, based on the assumption that the facility installed
in the pretreatment unit would provide chlorine to both injection points.

Both Classes "A" and "AA" treatment facilities will include continuous
effluent turbidity monitors to  insure proper operation of the filters.
This monitor will operate recorders, producing a  permanent record of
plant  operation,as well  as alarm systems which will be arranged to  shut
down  the plant in the event of  malfunction.  It is anticipated that the
maximum effluent turbidity can be maintained under 1. 0 Jackson Turbidity
Unit by the use of this control system.

Costs for Class  "AA" treatment include  more generous allowances for
equipment and instrumentation.  It  is anticipated that product water  from
this type of installation  would be introduced into an  existing potable water
distribution system, thus imposing a higher standard of reliability and
fail-safe operation.


PUMPING

Costs were developed for the  high-lift pumping requirement only.  The
below-grade installation of the treatment units permits gravity feed
between processes and  the cost of backwash or flushing pumps has been
included in the cost of the related piece of equipment.   Pump costs include
control and switchgear  costs and are based on a single pump for each
application.  Redundant facilities were not considered due to the supple-
mental and decentralized nature of  the facilities under  study.  Similarly,
it was not considered appropriate to cost premium-quality,  continuous-
duty equipment.   Table  D-5 summarizes the pump cost estimates  and
Figure D-3 shows the development  of the final cost  table.   This final
table  is shown as Table D-6.

  TABLE D-5.  SUMMARY  OF CONSTRUCTION COST ESTIMATES
             PUMPING FACILITIES (Cost in Dollars)

Capacity
(gal/ day)
1, 000
28, 800
72, 000
144, 000
720, 000
1, 440, 000

Pump &
Motor
110
315
570
1, 220
4, 940
10, 000
Controls
Switchgear
& Wiring
30
50
300
400
700
1, 400

Valves &
Appurt.
20
35
250
300
600
1, 000

Const.
Cost
160
400
1, 120
1, 920
6, 240
12,400
Eng. ,
Cont. , Etc.
(@25%)
40
100
280
480
1, 560
3,100

Total
Cost
200
500
1, 400
2, 400
7, 800
15,500
                                258

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CO
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CD
         -69-

         TJ
          M

          O
          m
          o
          U
a,
a
U
                 2  -
O  Estimates

   Linear Approximation
                  0   100
                   200   300  400    500   600  700    800  900  1000  1100  1200  1300  1400  1500
                                             Daily Demand (thousand  gallons/day)
                       Figure D-3.  Daily Demand vs.  Capital Cost of Pumping Facilities

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      TABLE D-6.  CONSTRUCTION COST VERSUS CAPACITY -
                        PUMPING FACILITIES
Pumping Capacity
(gal /day)
0.0
1,000
10,000
30,000
50,000
100,000
200,000
400, 000
700,000
1, 000,000
1, 500, 000
Capital Cost
(dollars)
200
200
250
600
1, 000
1, 840
3,100
5, 300
8, 000
11, 000
16, 000
TREATED WATER STORAGE

Seven different configurations of treated water storage were considered
and costs developed for each of them. These alternatives can be divided
into three different modes of operation,  namely:

1.    Ground level storage with direct pumping into
      distribution system, using storage as suction well

2.    Elevated storage supplied by pumping, storage floating
      on the distribution system

3.    Hydropneumatic tank floating on system and supplied
      by pumping

The seven storage configurations related to these modes  are:

1.    Ground level - steel tank below grade

2.    ground level   concrete  tank below grade

3.    Ground level - steel tank above grade

4.    Ground level - concrete tank above grade

5.    Elevated - elevated tank on legs or pedestal
                                260

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6.    Elevated -  standpipe

7.    Hydropneumatic   steel tank partly below grade

The development of construction costs for all except the last configuration
was discussed in Appendix C.  Hydropnuematic tanks were treated as
steel  tanks constructed above grade and sized at four times the required
storage.  This approach simplified programming requirements and proved
to be  relatively accurate.

Treated water storage facilities were sized as a function of the total daily
treated water demand.  A mass diagram of hourly water demands was
analyzed to determine storage requirements.  In each case, the storage
requirement  was taken as 0. 35 times the total daily demand. This can
also be stated as an eight-hour storage requirement.  Due to the various
configurations considered, the actual tank size  should be larger than the
storage requirement.  The following sizing relationships were used to
obtain tank sizes:

      For ground level storage and elevated storage  by elevated
      tank

           CAPT = 0.35 (DEMC)                                (D-l)

      For elevated storage by standpipe

           CAPT = 1.05 (DEMC)                                (D-2)

      For hydropneumatic tanks

           CAPT = 1.40 (DEMC)                                (D-3)

where:

      CAPT  =   tank size in gallons

      DEMC  -   daily treated water demand in gallons


OPERATING AND MAINTENANCE COSTS

Operation and maintenance costs were computed for  each  element of the
system to include the time and material necessary to insure continued
reliable operation.   System operation at all levels of scale was treated
as an incremental addition to a larger system.  This assumes that the
necessary labor, equipment,  and materials would be provided or procured
by an existing organization  whose overall  size and organizational structure
would not be  significantly changed by the largest system under consider-
ation  in this  study.   Depending on the nature of the final system,  the oper-
ation  responsibility might devolve upon the  Columbia Park and Recreation
Association,   a quasi-governmental  body which holds title to the public
                                  261

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space in the Columbia area,  including Wilde Lake and its tributaries,  or
to the Howard County Metropolitan Commission, a public water and sewer
authority.  In either case,  the assumption of a small incremental addition
to an existing organization is valid.

Using this approach,  labor costs are taken as direct cost plus an allowance
for labor fringe benefits.  Materials and supplies are costed at procure-
ment cost and equipment at established local rental rates.  No provision
is made for general or administrative overhead, for billing and collection,
or other nondirect items, since it was considered that the addition of the
system under study would not appreciably change any of these costs.
Wage rates and material costs are estimated on the basis of 1967-1968
prices.

Parametric costs were developed in the same manner as the construction
costs,  extrapolating a curve  from several calculated points.  The curves
were reduced to tables of points for linear interpolation by the  computer
program.  All operating and  maintenance costs are expressed in dollars
per day, based on yearly averages of flows and demands.


PRE TREATMENT

The principal costs associated with the operation of the preatreatment
unit are the replenishment of the various chemicals employed and the
periodic removal of accumulated sediment from the sump.   Typical
chemical requirements for this process are aluminum  sulfate (alum)
and calcium hypochlorite.  Dosage rates have been estimated at 10 mg/4
Al2(SC>4)3 and 0. 35  mg/ &  available chlorine.  This requires feed rates
of 85 pounds  of alum and 4. 25 pounds of calcium hypochlorite per million
gallons of runoff.  Other chemicals,  such as lime, polyelectrolytes,
soda ash,  etc. ,  might be required to adequately treat waters in certain
locations,  but published storm water analyses  indicate that the chemicals
named will be satisfactory in most applications. All chemicals will be
batch-mixed  in solution tanks and fed by metering pumps.  The feeders
will be checked daily and chemicals replenished as required.  Compu-
tation of operating costs did  not include  removal of sediment from the
pretreatment unit sump, as this operation was combined with cleaning
and inspection of the storm water reservoir and described with para-
metric costs in Appendix C.   Chemical costs,  electric power costs, and
costs associated with regular attention to proper operation are calculated
for the pretreatment unit and shown in Tables D-7 and  D-8,  as well as  in
Figure D-4.  These  costs can be identified as operation and maintenance
costs for Class "C"  treatment and are included in the costs shown for
higher levels of treatment.
                                 262

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                     TABLE D-7.  SUMMARY OF OPERATING COST ESTIMATES - TREATMENT
CLASS
"C"
Capacity
Gal /Day
100, 000
500, 000
1, 000, 000
Operation
Man/Hrs Rate
0.65
2. 00
5. 00
3. 50
3. 50
3. 50
Chemical
Cost
2.25
7. 00
17. 50
$/Day
0.45
2. 25
4. 50
Electric
Power
$/Day
8. 50
40. 50
81. 00
Misc. Main,
Supplies
$/Day
0.
4.
35.
50
25
00
. Misc.Oper.
Supplies
$/Day
0.
2.
25.
20
00
00
Contingency Total O&M
$/Day $/Day
0.
2.
5.
50
50
00
12.
55.
168.
00
00
00
       CLASS
        "B"
  100,000     1.50     3.50    5.25   0.75    9.00      1.00
  500,000     3.50     3.50  12.25   3.75   42.50      1.50
1,000,000     3.50     3.50  12.25   4.25   84,00      1.50
                                                      1. 00
                                                      1. 50
                                                      1. 50
                                                        1. 00
                                                        1. 50
                                                        1. 50
                                                             18.00
                                                             63. 00
                                                            105. 00
DO
OJ
CO
       CLASS
         "A"
  100,000     3.00     3.50   10.50   0.85     9.00      1.15
  500,000    10.00     3.50   35.00   4.25   42.50      2.75
1,000,000    13.00     3.50   45.50   8.50   85.00      3.50
                                                      1. 50
                                                      3. 50
                                                      4. 50
                                                        1. 50
                                                        2.00
                                                        3. 00
                                                             25.00
                                                             90.00
                                                            150.00
       CLASS
        "AA"
  100, 000
  500, 000
1,000,000
 3. 50
11.00
14.00
3. 50
3.50
3. 50
12.25
38. 50
49.00
 1. 50
 7. 00
14.00
10. 00
43. 50
86. 00
 1. 50
 5. 00
20. 00
 1. 75
 6. 00
31. 00
3. 00
4. 00
5. 00
 30. 00
105.00
205.00

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FINAL TREATMENT

Operation of the final treatment facilities consists of routine inspection
of the various items of equipment, daily tests of water quality to verify
chemical feed rates and to check  automatic monitors, backwashing of
filters or strainers, replenishment of chemical feeders, etc.  Preventive
maintenance is carried out on the various pieces  of equipment and minor
replacement of components is performed as indicated.  Solution-type
chemical feeders are used to add a precoat material to the straining
operation for Class "B" treatment and to provide a chemical coagulant
where required to the Class "A" and Class "AA"  plants.   It was assumed
for  costing purposes that this  coagulant would be  aluminum sulfate
(alum),  although in practice  other materials might be employed and
the  addition of alkalinity and pH adjusting chemicals,  such as lime or
soda ash, might be required.  Rechlorination will be  practiced at all
treatment points, using calcium hypochlorite.  Feed rates are estimated
at 50  pounds AL^SO^s and 8.5 pounds Ca(OCl)2- 4H2O per million gallons
of treated water. Daily attention to all  treatment  equipment has been
assumed.

Estimates also include energy cost for electric power to mixers,  metering
pumps,  sump pumps, etc. , as well as power for  high service pumping.
Table D-7 lists the detailed costs used to develop  operating and mainte-
nance costs for various sizes  of treatment facilities, and Figure D-4
shows the extrapolated cost curve, as well as the  approximated curve.
The table of values input to the computer program is  shown as Table D-8.
             TABLE D-8.  OPERATION AND MAINTENANCE
                 COST VERSUS CAPACITY - TREATMENT
Treatment Capacity        Operating & Maintenance Cost ($/day)
      (gal/day)        Class "C"   Class "B"   Class "A"   Class "AA1
             0.0          0.00       0.00         0.00         0.00

        60,000            7.00       9.00        15.00        18.00
       100,000           12.00      19.00        24.00        28.00
       200,000           24.00      27.00        41.00        48.00
       400,000           46.00      52.00        74.00        86.00

       600,000           64.00      73.00       103.00       119.00
       800,000           80.00      92.00       126.00       146.00

     1,000,000           90.00     108.00       145.00       168.00

     1,200,000           97.00     119.00       159.00       186.00

     1,500,000          106.00     132.00       174.00       206.00
                                 264

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02
01
cti
-O
^
M
-t-J
O
u
o
ni
OJ
~H
'cti
         T5
         CtJ

         O
         O
             240
             220  -
             200  -
             180  -
             160  -
             140  —
120

100

 80
      60   —
              40  —
              20
                                                                                                          Class AA
                                                                                                          Class A
                                                                                                         Class B
                                                                                                         Class C
                      100   200
                                                                                  Estimates
                                                                                  Linear Approximation
                         300   400  500    600   700   800   900   1000  1100  1200  1300  1400  1500
                             Final Treatment Plant Capacity (thousands gal/day)

                                Figure D-4.  Operation and Maintenance Cost vs.
                                          Capacity - Final Treatment

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PUMPING

Operating and maintenance costs of the high service pumping facilities
have been included in the Final Treatment costs detailed in Table D-8.
TREATED WATER STORAGE

Operation and maintenance costs were computed separately for each of
the seven storage options described previously.  These costs consist of
periodic painting and repair of the tanks and are a function of the surface
area to be maintained.  Appendix C describes the methods employed to
calculate the surface area for various types of cylindrical tanks.  Ele-
vated tanks  may be cylindrical, but are more frequently ellipsoidal.  In
addition, they stand on a pedestal or on legs which have appreciable
surface area themselves.  A variety of tank shapes and sizes were
analyzed.                            '  '  • '•  '' "

In calculating total maintenance cost for an  elevated tank, a cost of
$0. 05 per square foot per year was assumed.
-HJ.S. GOVERNMENT PRINTING OFFICE: 1973 514-151/1501-3    266

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  SELECTED WATER
  RESOURCES ABSTRACTS
  INPUT TRANSACTION FORM
                                        7. Report Vv.
                                                                  A/. (?.•;:'ioa ?!<:••
                                                           w
Title •
                                                               $.  Rep&rttyate
  THE BENEFICIAL USE OF STORM WATER,
         Mallory,  C. W.
         Hittman Associates, Inc.
         9190 Red Branch Road
         Columbia, Maryland  21045
                                                               8.
                                                               , -  Report No.
                                                                  11030DNK
                                                            :  Cont'ract'/Granttfo.
                                                             68-01-0173
                                                           13.  Type f Repp;,t and
                                                              Period Covered
  12.
  IS.
                         ,               .    .
                  Environmental Protection Agency report
                  number, EPA-R2-73-139, January 1973.
            This report covers work originally performed by Hittman Associates in 1968
under Contract 14-12-20. Only a limited number of reports were prepared and the pur-
pose of this report makes this information available for general distribution.
      A system study was conducted to determine the technical and economic feasibility
of using small storage reservoirs throughout an urban community as a means of storm
water pollution control.  Facilities were provided to treat the water prior to release or
to provide sub-potable or potable water for use in the community.  A conventional
approach  to controlling storm water pollution was defined  for comparative purposes.
      Computerized system analysis was used to select the optimal combinations of
reservoir locations,  type of treatment,  and type  of reuse on a least cost per day basis.
Alternatives were ranked and the optimal practical solution determined considering the
constraints.   It was determined that the use of local storage and treatment does repre-
sent a feasible and economical method  for  storm water pollution control.  Further, the
use of the treated water  can supply a large portion of the fresh water demands of a
typical urban residential community.
      A demonstration program was planned and  subsequently implemented to evaluate
erosion and sediment control practices which includes a three-and-one-half-acre lake,
evaluation of cleaning and sediment  handling methods, and sampling and  gaging stations
to monitor changes in water quality  and hydrology during urban development.
  17 a Descriptors
  * Storm Runoff, "'Reservoir Storage, * Water Pollution Treatment, *W'ater Supply,
  *Water Conservation,  Synthetic Hydrology, Regression analysis,  Water Demand,
  Water Distribution,  System Analysis, Optimum Development Plans, Erosion Control,
  Sediment Control
  * Storm Water Management,  Columbia,  Maryland,  *Storm  Water Reuse
  17c. COWRRField& Group  05G
  IX  A •'3:l-j?iil:ty
                    28. Security C/asv.
                       (Repo.1 ••

                    ."9. SP -nty C  ;s.
                                         21,
No. of
Pages
                                                    Send To:
                                                    WATER RESOURCES SCIENTIFIC INFORMATION CENTER
                                                    US DEPARTMENT OF THE INTERIOR
                                                    WASHINGTON D C 2O24O
           Charles W.  Mallory
                                          Hittman Associates, Inc.

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