United Stales
Environmental Protoction
Agency
Water Planning Division
WH-554
Washington, DC 20460
December 1983
Water
Results of the Nationwide
Urban Runoff Program

Volume I  - Final Report

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              RESULTS

              OF  THE

  NATIONWIDE  URBAN RUNOFF PROGRAM
           December,  1983
       VOLUME  I  -  FINAL  REPORT
       Water Planning Division

U.S. Environmental  Protection Agency

       Washington,  D.C.   20460
      National  Technical  Information Service (NTIS
      Accession Number:   PB84-185552

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                         DISCLAIMER

This  report has  been  reviewed  by  the  U.S.  Environmental
Protection  Agency  and  approved  for  release.   Approval  to
publish  does  not  signify  that  the  contents  necessarily
reflect any  policies  or decisions .of  the  U.S.  Environmental
Protection  Agency  'or  any  of  its  offices,  grantees,  con-
tractors, or subcontractors.

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                                  FOREWORD

The U.S.  Environmental  Protection Agency was  created because  of  increasing
public and government concern about environmental quality.  The complexity of
our environment  and  the interplay among its components  require concentrated
and integrated approaches to pollution problems.

The possible  deleterious water quality  effects of nonpoint  sources  in gen-
eral, and urban  runoff  in particular,  were  recognized by the Water Pollution
Control  Act Amendments  of  1972.  Because  of  uncertainties  about the true
significance  of  urban  runoff  as  a  contributor  to  receiving  water  quality
problems, Congress made  treatment  of  separate  stormwater discharges ineligi-
ble  for Federal funding  when  it  enacted  the  Clean  Water Act  in  1977.   To
obtain  information  that would help  resolve these uncertainties,  the Agency
established the  Nationwide  Urban Runoff Program  (NURP)  in 1978.  This five-
year program was designed to examine such issues as:

        The quality  characteristics of urban runoff, and  similarities or
        differences  at different urban locations;

        The extent to which urban  runoff is a significant contributor to
        water quality problems across the nation;  and

        The  performance characteristics  and the  overall effectiveness
        and utility  of management  practices for the control of  pollutant
        loads from urban runoff.
                      .*'
                                                              it
The interim NURP report, published in March 1982,  presented preliminary find-
ings of the program. This  document is the final  report  covering the overall
NURP  program.   Several specialized  technical  reports   are  published under
separate  cover.

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                                   PREFACE

The Nationwide Urban Runoff Program  (NURP) was conducted by  the EPA and many
cooperating federal, state, regional,  and  local  agencies,  distributed widely
across the  United  States.   The individual  project studies,  which  were con-
ducted over the  past five years, were  designed  and overseen using a common
technical team from EPA headquarters.  This approach  was  taken  to assure a
desired  level  of commonality and consistency  in the  overall program,  while
allowing each  individual project  to  specially  tailor  its  effort  to focus on
local concerns.

The program has yielded a great deal  of  information which  will  be useful for
a broad  spectrum of planning  activities  for many years.  Furthermore, it has
fostered  valuable   cooperative  relationships among  planning and  regulatory
agencies.   The most tangible products of  the program are  this  report, the
reports  of  various  grantees  (available under separate cover),  and several
technical  reports  which  focus  on specialized  aspects  of the  program,  its
techniques, and  its findings.  In addition,  a considerable  number of  indi-
vidual articles  drawing on  information developed under the NURP program have
already  appeared in the technical literature and  address  specific  technical
or planning aspects of urban runoff.

At the time of publication of this Final Report, the main  technical effort of
the NURP program is complete; the field studies  and the analysis  of most of
the resultant  data  are  complete enough that the  findings  reported  herein  can
be taken with confidence.   However,   there  is still some work in progress to
make  certain  details of"'the program  available for future  use.   The  products
of this  on-going work include:

         A summary database which  is being  compiled to  make all  technical
         information  from  the 28  projects  available for  review and  use
         (DECEMBER 1985);

         A  technical report which focuses on the program's  studies  and
         findings relative to  detention and.recharge devices   (MAY 1984);

         A  technical report  on urban  runoff effects  on the water  quality
         of  rivers and streams  (MARCH  1984)-;  and

         A  technical report  on the effectiveness of  street sweeping as  a
         potential "best management practice" for water pollution control
         (MAY  1984),.

This  report  and  the  supplementary  technical  documents identified  above,
supersedes  the  earlier   NURP  publication,  "Preliminary   Results  of  the
Nationwide  Urban Runoff  Program,"  March  1982.   Information presented there
has been expanded,  updated,  and in some  cases  revised.

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                              ACKNOWLEDGEMENTS

The Nationwide Urban Runoff Program was .unusual in  its  large  scale,  covering
a broad  spectrum of technical and planning  issues at many geographic  loca-
tions.  Because the program placed such emphasis on  tailoring the  results  to
support the planning process, it involved many participants - some from EPA,
some  from  other  federal agencies,  and many  from  state, regional,  and  local
planning agencies and other consultants.

The  program was developed,  implemented,  and managed  by the  Water  Planning
Division,  Office of Water, at EPA Headquarters, Washington,  D.C.   Principal
contributors were:   Dennis N. Athayde,  Program Manager; and Patrice M. Bubar,
Norman A. Whalen, Stuart S. Tuller, and Phillip H.  Graham, all of whom served
as  Project  Officers.   Additional  contributions from EPA  personnel came from
Rod E. Frederick'and Richard P.  Healy (Monitoring and Data Support Division),
Richard Field  (Storm and  Combined  Sewer  Section,  EPA Office  of Research and
Development), and many project staff in the various EPA Regional Offices.

As  described  elsewhere, much of  the  field work, water  quality analysis, and
data  analysis was   performed  by  the U.S. Geological Survey  (USGS),  under a
Memorandum  of  Agreement with EPA.   Both District  Offices  and National Head-
quarters participated actively.   The contributions of Messrs. Ernest Cobb and
David Lystrom are especially acknowledged.

Members  of the project team which provided  essential  strategic,  technical,
and  management assistance  to the  EPA Water  Planning Division through a con-
tract  with Woodward-ClySe Consultants were:  Gail B.  Boyd, JDavid Gaboury,
Peter Mangarella, and. James D. Sartor (Woodward-Clyde Consultants); Eugene D.
Driscoll  (E.  D. Driscoll  and Associates);  Philip E. Shelley  (EG&G Washington
Analytical  Services Center,  Inc.); John L.  Mancini  (Mancini  and DiToro Con-
sultants) ;  Robert  E.  Pitt  (private  consultant);  Alan  Plummer  (Alan Pluiraner
and  Associates);  and   James P.  Heaney  and  Wayne C.  Huber  (University  of
Florida).

The   principal  writers   of  this  report   were   Dennis N. Athayde   (EPA),
Philip E.  Shelley   (EG&G   Washington  Analytical   Services  Center,   Inc.),
Eugene D.  Driscoll   (E. D. Driscoll  &  Associates) ,  and  David Gaboury  and
Gail  B. Boyd  (Woodward-Clyde Consultants) .
                                VII

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                              TABLE OF CONTENTS

Chapter                             •                                     Page
             Foreword	     iii
             Preface  	       v
             Acknowledgements 	     vii
             Executive Summary (Bound Separately)
   1         INTRODUCTION	     1-1
   2         BACKGROUND	     2-1
             Early Perceptions	     2-1
             Conclusions From Section 208 Efforts  .  ..	     2-2
             EPA's ORD Effort	     2-3
             Other Prior/Ongoing Efforts  	     2-4
             Discussion  .....  	     2-5
             The Nationwide Urban  Runoff Program  ...  	     2-6
                         ,9>
   3         URBAN RUNOFF PERSPECTIVES   	     3-1
             Runoff Quantity  	     3-1
             Water Quality Concerns  	     3-3
             Water Quantity and Quality  Control  	     3-3
             Problem Definition 	  	     3-5
   4         STORMWATER  MANAGEMENT  	     4-1
             Introduction  	     4-1
             Stormwater  Management Planning  	      4-1
             Financial and Institutional Considerations 	      4-6
                        i
             Relationship Between  NURP  and WQM Plans	     4-17
                                      IX

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                         TABLE OF CONTENTS (Coht'd)

Chapter                                                                  Page
   5         METHODS OF ANALYSIS	     .5-1
             Introduction 	     5-1
             Urban Runoff Pollutant Characteristics 	     5-2
             Receiving Water Quality Effects  	     5-7
             Evaluation of Controls 	    5-18
   6         CHARACTERISTICS OF URBAN RUNOFF	  .     6-1
             Introduction 	     6-1
             Lognormality	     6-2
             Standard Pollutants  	     6-9
             Priority Pollutants	    6-44
             Runoff-Rainfall Relationships   	    6-57
             Pollutant Loads   	    6-60
   7         RECEIVINGSWATER QUALITY EFFECTS OF URBAN  RUNOFF   ....     7-1
             Introduction 	     7-1
             Rivers  and Streams	     7-2
             Lakes	     7-21
             Estuaries and Embayments	     7-23
             Groundwater Aquifers  	     7-24
    8         URBAN  RUNOFF CONTROLS   	      8-1
             Introduction  	      8-1
             Detention Devices  	      8-2V
             Recharge Devices  	     8-14
             Street Sweeping   	     8-17
             Other  Control Approaches	     8-22
    9         CONCLUSIONS	      9-1
             Introduction  	      9-1
             Urban  Runoff  Characteristics 	      9-1
             Receiving Water  Effects  .  .	      9-6
             Control Effectiveness   	     9-12
             Issues	     9-15

             Date Appendix  (Bound Separately)

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                               LIST OF FIGURES
Figure                                         '                          Page
2-1          Locations of the 28 NURP Projects	     2-7
4-1          Typical Changes in Runoff Flows Resulting
             from Paved Surfaces	     4-2
4-2          Incomplete Water Quality Planning  	     4-6
4-3          Integrated Water Quality Planning  	     4-8
4-4          Preliminary Matrix for Section of a Control
             App'roach  (Combined Sewer Overflows)	     4-8
4-5          Major Components of a Financial Institutional Data . .  .     4-9
4-6          Institutional Assessment for Educational Program
             to Control Chemical Substances . 	    4-14
4-7          Cost Analysis for Educational Program to Control
             Chemical, Herbicide, Fertilizer and Pesticide
             Runoff	    4-15
4-8          Ability to Pay Analysis for Educational Program to
             Control Chemical, Herbicide, Fertilizer and
             Pesticide Runoff 	    4-16
                       .*'
5-1          Lognormal Distribution Relationships    	-.  .  .  .      5-5
5-2          Idealized Representation of Urban Runoff
             Discharges Entering a Stream  .  	    5-14
6-1          Cumulative Probability Pdf of Total Cu  at
             CO1 116 and Claude Site	      6-5
6-2          Cumulative Probability Pdf of Total Cu
             at TNI SC Site	      6-6
6-3          Cumulative Probability Pdf of Total Cu  at
             NH1 Pkg. Site	      6-8
6-4          Range of TSS EMC Medians (mg/1) by Project	     6-21
6-5          Range of BOD EMC Medians (mg/1) by Project	     6-21
6-6          Range of COD EMC Medians (mg/1) by Project	     6-22
6-7          Range of Total  P EMC Medians  (mg/1) by  Project	     6-22
6-8          Range of Soluble P EMC Medians  (mg/1) by  Project ....     6-23
6-9          Range of TKN EMC Medians (mg/1) by Project	     6-23
6-10         Range of NO   -N EMC Medians  (mg/1) by  Project	     6-24
                                     XI

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                          LIST OF  FIGURES  (Cont'd)
Figure                                                                   Page
6-11         Range of Total CU EMC Medians  (yg/1)  by Project  ....     6-24
6-12         Range of Total Pb EMC Medians  (yg/1)  by Project  ....     6-25
6-13         Range of Total Zn EMC Medians  (yg/1)  by Project  ....     6-25
6-14         Range of Normalized EMC Medians at Denver (C01)  ....     6-27
6-15         Range of Normalized. EMC Median at FL1 and DC1	     6-29
6-16         Range of Normalized EMC Medians at IL1	     6-30
6-17         Box Plots of Pollutant EMCs for Different
             Land Uses	     6-33
6-18         Site Median Total P EMC Probability Density
             Functions for Different Land Uses	     6-36
6-19         Relationship Between Percent Impervious Area
             and Median Runoff Coefficient  	     6-59
6-20         90 Percent Confidence Limits for Median
             Runoff Coefficients  	     6-61
7-1 (a)       Regional Value of Average Annual Streamflow
             (cfs/sq KB.)   . '	 .  . . .     7-4
7-1 (b)       Regional Value of Average Storm Event
             Intensity  (inch/hr)  . 	      7-4
7-2          Regional Values for Surface Water Hardness  	      7-6
7-3          Geographic Regions Selected for Screening
             Analysis	      7-8
7-4          Probability Distributions of Pollute"1
             Concentrations During Storm Runoff Periods  	     7-11
7-5          Recurrence Intervals for Pollutant Concentrations   .  .  .     7-11
7-6          Exceedance Frequency for Stream Target
             Concentration  (Copper) 	     7-14
7-7          Exceedance Frequency for Stream Target
             Concentration  (Lead)  	     7-15
7-8          Exceedance Frequency for Stream Target
             Concentration  (Zinc)  	  	     7-16
7-9          Effect of Urban Runoff on Lake Phosphorus
             Concentrations  	     7-22
8-1          Regional Differences in Detention Basin
             Performance	      8-6
8-2          Average Stormwater Management  (Dry)  Pones
             Construction Cost Estimates Vs. Volume of  Storage  .  .  .      8-12
8-2          Cost  of Urban  Runoff Control Using Wet
             Detention  Basins  	      6-12

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                          LIST OF FIGURES (Cont'd)
Figure                                                                   Page
8-4          Long Term Average Performance of Recharge Devices  .  .  .     8-16
8-5          Eivariate PlotE of Median EMCs for Swept and
             Unswept Conditions 	     8-20
8-6          Street Sweeping Performance  	     8-21
8-7          Effect of Street Sweeping on Site Median EMC
             Values	     8-23
                               LIST OF TABLES
Table                                                                    Page
 2-1         NURP Project Locations	     2-7
 5-1         Summary of Receiving Water Target Concentrations
             Used in Screening Analysis - Toxic Substances
              (All Concentrations in Micrograms/Liter, pg/£)  	    5-12
                      .#
 6-1         Site Mean TSS EMCs  (mg/£)  	' .  .  .  .    6-10
 6-2         Site Mean BOD EMCs  (mg/£)  	    6-11
 6-3         Site Mean COD EMCs  (mg/£)  	    6-12
 6-4         Site Mean Total P EMCs  (ug/£)   	    6-13
 6-5         Site Mean Soluble P EMCs  (yg/£)	    6-14
 6-6         Site Mean TKN EMCs  (pg/£)  	    6-15
 6-7         Site Mean Nitrite Plus Nitrate  EMCs  (ug/£)	    6-16
 6-8         Site Mean Total Copper EMCs  (yg/£)	    6-17
 6-9         Site Mean Total Lead  EMCs  (yg/£)	    6-18
 6-10        Site Mean Total Zinc  EMCs  (yg/£)	     6-19
 6-11       Project Category  Summarized  by  Constituent 	     6-26
 6-12       Median EMCs  for All Sites  by Land Use Category 	     6-31
 6-13       Number of  Significant Linear Correlations
              By Constiuent	     6-38
 6-14        Sign of Correlation Coefficients by Sites	     6-39
 6-15        Correlation  Coefficient  Values  by Site 	     6-40
 6-16        Sites  With Many  Significant  Correlations 	     6-42
 6-17        Water  Quality Characteristics of Urban Runoff  	     6-43
                                     XI Ii

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                           LIST OF TABLES (Cont'd)
Table                                                                    Page

 6-18        Fecal Coliform Concentrations in Urban Runoff  	     6-45

 6-19        Summary of Analytical Chemistry Findings From
             NURP Priority Pollutant Samples1 	     6-47

 6-20        Most Frequently Detected Priority Pollutants
             in NURP Urban Runoff Samples1	     6-51

 6-21        Summary of Water Quality Criteria Exceedances For
             Pollutants Detected in at Least 10 Percent of
             NURP Samples:  Percentage of Samples in Which
             Pollutant Concentrations Exceed Criteria1  	     6-53

 6-22        Infrequently Detected Organic Priority
             Pollutants in NURP Urban Runoff Samples1 	     6-55

 6-23        Runoff Coefficients for Land Use Sites	     6-58
 6-24        EMC Mean Values Used in Load Comparison  .........     6-60
 6-25        Annual Urban Runoff Loads KG/HA/Year  .  	     6-64
 7-1         Average Storm and Time Between Storms for
             Selected Locations in the United States  	      7-3

 7-2         Typical Regional Values	- ....      7-7
 7-3         Urban Runoff Quality Characteristics Used in
             Stream Impact Analysis  (Concentrations  in yg/1)   ....      7-9
 7-4         Regional Differences in Toxic Concentration
             Levels (Concentrations in pg/1)  .°	    7-13
 8-1         Detention Basins Monitored by NURP  Studies  	     8-3
 8-2         Observed Performance of Wet Detention Basins
             Reduction in Percent Overall Mass Load	     8-5
 8-3         Observed Performance of Wet Detention Basins
              (Percent Reduction in Pollutant Concentrations)   ....     8-8

 8-4         Performance Characteristics of  a Dual-Purpose
             Detention Device  	    8-10
                                     xiv

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                                 CHAPTER  1
                                INTRODUCTION
Rain falling  on  an urban area  results in both  benefits  and problems.   The
benefits  range  from watering  vegetation  to  area  cleansing.  Many  of  the
problems  are  associated  with urban  runoff,  that portion  of rainfall  which
drains  from  the  urban  surfaces and  flows via natural  or man-made  drainage
systems into receiving  waters.

The  historical  concern  with urban  runoff  has   been  focused  primarily  on
flooding.  Urban development has the  general  effect  of  reducing  pervious land
surface area and increasing the impervious area  (such as  roof tops,  streets,
and sidewalks) where water cannot•infiltrate.   In comparison with  an  undevel-
oped area  (for  a  given storm event) ,  an  urban area will yield more  runoff,
and it will occur more  quickly.  Such increases in the  rate of flow and total
volume often have a decided effect on  erosion rates and flooding.  It is not
surprising, therefore,  that at the local  level the  quantity aspect continues
to be a principal concern.
                       .*'
In recent  years,  however,  concern  with urban runoff as a  contributor to re-
ceiving water quality  problems  has been expressed.  Section  62 of the Water
Quality Act  of  1965 (P.L. 89-234)  authorized the Federal  government  to make
grants for the purpose of "assisting in the development  of any  project which
will demonstrate  a  new or improved method of controlling  the discharge into
any  water of untreated  or  inadequately treated   sewage  or other  waste from
sewerage  which  carry  storm  water  or  both storm water  and  sewage  or other
waste  ..."   The  Federal  Water Pollution Control  Act  Amendments   of 1972
(P.L. 92-500) signaled a  heightened  national  awareness  of the degraded state
of the nation's surface waters and a Congressional intent that national water
quality goals be pursued.  The scarcely two-year old Environmental Protection
Agency built upon its predecessors' activities by taking up the challenge  and
implementing this far reaching legislation.

As a result  of Section 208 of The  Act, State  and local water quality  manage-
ment  agencies were  designated to integrate water quality  activities.  As
point source discharges were increasingly brought under control and funds  for
the  construction and  upgrading of  municipal sewage  treatment  plants were
granted,  the  awareness   of  nonpoint  sources  (including  urban   runoff)  as
potential  contributors  to water quality  degradation was heightened.   Uncer-
tainties  associated with the local  nature and  extent of  urban runoff  water
quality  problems,  the  effectiveness  of  possible management  and   control
measures,  and their  affordability  in terms of benefits to be derived mounted
as water  quality management plans  were developed.   The unknowns were  so great
and  certain  control cost estimates were  so high  that  the Clean Water Act of
1S77  (F.L. S5-217)   deleted  Federal  funding  for  the  treatment  of  separate
Etormwcter discharges.   The  Congress stated that- there was  simply not enough

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Known .'iboui urban runoff loads, impacts, and controls to warrant making major
j iivi-iii,ments in physical control systems.

'! n 3976, EPA Headquarters reviewed the results of work on urban runoff by the
technical community and t  • various 208 Areawide Agencies and determined that
additional, consistent da\ d were needed.  The NURP program was implemented to
build upon pertinent prior work  and  to provide practical information and in-
sights to  guide  the planning process,  including policy  and program develop-
ment  and  implementation.   The  NURP  program  included  28 projects,  conducted
separately  at the  local  level,  but  centrally  reviewed,   coordinated,  and
guided.  While these projects  were separate and distinct, most share certain
commonalities.  All were involved with one or more of the following elements:
characterizing'pollutant types,  loads, and effects  on  receiving water qual-
ity;  determining  the  need for  control; and  evaluating  various alternatives
for the control of stormwater pollution.  Their emphasis was on answering the
basic questions underlying the NURP  program and providing practical informa-
tion needed for planning.

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                                  CHAPTER 2
                                 BACKGROUND
EARLY PERCEPTIONS

As noted earlier, drainage is perhaps the single most important factor of the
urban hydrologi-c  cycle.   Nuisance flooding, more  than anything  else,  gives.
Public  Works directors  concern,  as  complaints  are  received  from  unhappy
motorists, residents, and business.   Drainage has typically been considered a
local responsibility, usually that of the City or County Public Works Depart-
ment.  Rarely does this  responsibility go to  the State or Federal level, ex-
cept  in  cases  of catastrophic flooding involving  risk  to  human  life and
extensive property damage.

By  1964,  the U.S.  Public Health  Service had  begun  to  be  concerned  about
identified pollutants  in urban runoff and  concluded that there  may be sig-
nificant water  quality problems associated with stormwater  runoff.  In  1969,
the Urban Water Resources Research Committee of the American Society of Civil
Engineers  (directed  by*M.  B.  McPherson  and  sponsored by  the  U.S. Geological
Survey)  recognized  the potential  threat of  pollution from urban runoff and
described a  research program intended to obtain needed  information to  char-
acterize urban  stormwater quality.

In the late 1960's, the Federal Water Quality Administration  (FWQA) conducted
a  study  in an  area  of  Tulsa,  Oklahoma  which  was served by separate  storm
sewers.   This first  attempt at using  regression analysis  on urban runoff in-
dicated that there was only a very poor correlation between stormwater  runoff
quantity and water quality constituents  (except for suspended solids).  Com-
paring the concentrations of  various  pollutants examined  by this  study  (sep-
arate storm  sewers)  with previous data on  combined sewer overflows  indicated
that storm runoff from areas having separate sewers had much  lower values for
BOD, fecal coliform, and most other pollutant concentrations.  The study con-
cluded  that  the largest portion  of  pollutants  resulted  from (1) washoff  of
material  from  impervious surfaces and  (2)  the  erosion of  drainage  channels
 (caused by high Arolumes  of runoff  from  the  impervious surfaces).  Control  of
urban runoff was recommended to reduce both runoff  volume and rates.

Atlanta, Georgia is  an example of  a  city that has both a combined sewer sys-
tem and a separate system.  In 1971,  EPA conducted  a  study which  compared  the
contribution of various  sources of pollutants.   It was concluded that,  on  an
annual basis, 64 percent of the BOD load came from  separate storm sewers,  and
IS percent  came  from combined sewers,  the  balance coming  from  treatment
plants.

In  1971,  EPA also conducted  B study  in  Oakland and Berkeley, California,  to
assess the infiltration  cf storinwater into  sanitary  sewers.  While  only four

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percent of the study area had  combined  sewerage  and  the  remaining 96 percent
separate, the study made it clear that infiltration can cause a separate sys-
tem to function as though it were combined.

Studies in Sacramento, California, which has both combined and separate storm
sewers, indicated that the  stormwater was  comparable to  the average strength
of domestic wastewater.  However, the concentrations for BOD were found to be
so unrealistically  high, that  contamination of  the runoff by  raw sanitary
sewage was considered to be a distinct possibility.

In  1973,  the  Council  on  Environmental Quality  published  a  report titled,
"total Urban  Pollutant Loads:   Sources and  Abatement  Strategies."  The pri-
mary  conclusion  was that  much pollution  was coming  from  urban  runoff and
that, unless it was taken care of, the  goals of the  Act would not be met.

CONCLUSIONS FROM SECTION 208 EFFORTS

EPA  guidance  for  conducting  the  early   208 planning  efforts   designated
17 topic  areas  (including  urban runoff)   that  were to  be  addressed  by all
Water Quality  Management agencies in developing their 208-funded plans.  Al-
though all topic areas were to be covered, the degree of emphasis  to place on
each was  left  to the  individual agencies  to decide.  As a result,  the  amount
of the 208 efforts  spent in the area of urban runoff varied greatly  (but was
rarely a major portion,).
                     v^
Many of  the  208 agencies began their studies with the assumption  that  urban
runoff  was  an  important  cause  of  water  quality  problems.   Although the
studies developed much information on runoff and  receiving waters,  not  enough
basic information was  known to  assess urban  runoff's role as  a major  cause of
problems.  This  was partly  because of interferences  by other  sources  and com-
plex  relationships within  the  receiving  waters.   It was  also  due  to the
difficulties in  deciding what  constitutes  a  "problem."   In  some  cases,  "prob-
lems"  were synonymous with criteria violations;  in others, "problems"  were
synonymous with  an impairment or denial of  beneficial uses.  In  many  cases,
"problems"  were  concluded  to  exist,   simply  on  the  basis  of  the  possible
presence  of certain  contaminants in  urban  runoff., based  solely on  values
taken  from literature regarding  studies  conducted  elsewhere.   The practical.
implication of these differences  (which were differences in viewpoints rather
than differences in physical conditions,  in many  cases) was  that local agen-
cies were very ..reluctant to commit  to  implementing urban runoff  controls  in
the absence of a clear problem definition.

Furthermore,  in  the early years of the 208 program, EPA's  guidance on how .to
address  urban  runoff was vague.   As  a result,  local agencies took a wait-and-
see  attitude  on the stormwater portion of their plans.   They simply  did not
know what  EPA  would eventually do on the  issue  of stormwater control.

Another  major  obstacle to implementation resulted  from  the  uncertainties re-
garding  the effectiveness  of  controls.   Many  of  the  measures  proposed for
controlling  urban runoff  are  either new  or special applications  of conven-
tional  practices developed  for other  purposes.   Little was known about how

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well  they  would  work in  urban  runoff  applications.   Engineers, planners,
public works  personnel,  and .other decision  makers  have been  understandably
reluctant to invest large amounts of  time and money  in  controls which  may  not
perform as hoped.

Another obstacle  to implementation  of controls was  a  lack of  basic  data on
sources, transport  mechanisms,  and  receiving water characteristics  (hydro-
logic  and  water  quality  aspects).   Some of  the  more  important  topic  areas
where knowledge was lacking are summarized below:

        Sources - Not enough was known about where pollutants originate.
        Major  sources certainly  include vehicles,  vegetation, erosion,
        fertilizer  and  pesticide application, litter,  animals,  and  air
        pollution.  However,  a better  understanding of source contri-
        butions could enhance control opportunities.

        Washoff/transport  mechanisms  -  Not enough  was known  about  how
        pollutants  get from the sources to the receiving waters.  Models
        could be  better used for simulating runoff in problem definition
        and control evaluation,  if they more accurately reflected wash-
        off and transport mechanisms.

        Impacts - It  was difficult to go beyond speculation in  assigning
        urban runoff  its  proper  share of responsibility for problems in
        cases  where  several  pollutant  sources  contribute.    In. cases
        where other sousces create obvious problems, it was difficult to
        determine the appropriate degree to which urban runoff  should be
        controlled.

        Relative  benefits - Planners had difficulty  deciding whether  the
        various benefits of controlling urban runoff quality justify  the
        costs  involved.   There  was  considerable controversy  over   the
        present dry weather standards'  relationship to beneficial uses,
        given the time and  space scales of storm  events and their inter-
        mittent nature.   Many plans  failed to be implemented  because of
        uncertainties  regarding:   How  much  control   is   enough?   Who
        benefits?   Who should pay?  Who should decide?

        Controls  -  Both cost and effectiveness  data on full-scale con-
        trol  programs were lacking.   Some of the control  measures cited
        for   typical  208 plans  were  plausible  candidates,   but their
        application for the purpose  of urban  runoff  pollution  control
        had not been  studied quantitatively.

 EPA'S ORD  EFFORT

 During the past  15  years,  EPA's  Office of Research  and Development  (ORD) has
 conducted  over  250  studies on  the characterization  and control of stormwater
 discharges and  combined  sewer  overflows, with  particular  emphasis  on the
 latter due to  their  greater pollution potential.  Consistent  with  overall
 Agency policies,  ORD  has  deemphasized studies on receiving water impacts and
 effects  (although  it  has done  some such  work).   Rsther,  ORD  has  focussed
 principally  on  multi-purpose  analyses  and  controls,  because  it is  nearly

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impossible tc  segregate  benefits and  strategies  of urban  stormwater  runoff
pollution control from drainage,  flood,  and erosion control.   Many signifi-
cant results have been obtained  by ORD's effort, which  has dramatically in-
creased the technical literature  in the area.

Data from ORE:  studies  indicate the high variability of  pollutant concentra-
tions in urban runoff.  Based on  loading projections,  it is safe to conclude
that urban stormwater can contribute significant pollutant  loads tc receiving
waters,  in  many cases  having  pollutant  concentrations  on  the  order  of
secondary treatment  plant effluent  for  some constituents.   Nonetheless,  in
its  efforts  to  find  direct  urban  runoff  generated receiving  water impacts
(using the conventional dissolved oxygen parameter  as  the indicator) ORD has
been only partly successful.   However, this  was  only  one  study and was not
intended to  be the final word.   Nonetheless,  based on  the size of the load
coming from  urban  runoff,  a  significant pollution  potential  is there for at
least some types of  receiving  waters.   For example, a small urban  lake  could
receive nutrient loads  sufficient to increase  algal productivity and accel-
erate the eutrophication  process.   The existence  of heavy  metals and certain
organics  (mostly of  petroleum origin) in  urban runoff  have  also been  docu-
mented by the  ORD program.

In  addition  tc studying urban  runoff loads, the ORD program has investigated
a  number  of management  and  control  approaches.   This  effort  has  been very
successful,  and many  innovative techniques  have  been  proposed and tested.
The  results  of such  research,  development,  and demonstrations  have been pre-
sented  in  reports  which  document  many of  these  potential controls, thereby
allowing the technology  to be utilized in  other  programs  and  at other  loca-
tions.  Included have  been  such  control measures as on-site  (upstream)  stor-
age; porous  pavement; the swirl  concentrator, helical  bend, tube settler,  anc
fine mesh  screens  for grit  and  settleable  solids  removal; street  sweeping;
disinfection;  and  high rate filtration,  dissolved  air  flotation,  and  micro-
screening for  suspended  solids and  BOD removal.  Most of  these controls were
developed  principally to deal with combined  sewer overflow problems.   How-
ever,  some may also  have  application in urban  runoff  control,  once their  ef-
fectiveness  has  been  conclusively demonstrated  and  initial and  operating cost
data are available to  allow the  necessary  trade-off studies to  be made.

The ORD  program's  reports constitute an invaluable  source of  data  and infor-
mation that  was  used  tc design and  guide  the development of the emerging NURP
program.  Also,  three-of  the NURP projects  were joint  efforts with ORD  (i.e.,
West Rcxbury,  Massachusetts, Bellevue,  Washington,  and Lansing, Michigan).

 OTHER PRIOR/ONGOING  EFFORTS

 The Clean  Water Act  requires  EPA to provide  Congress  with a needs assessment
 every  two years in  the  six  categories of  the construction  grant  funds pro-
 gram.   In  1974, the Needs Survey  for Separate Storm  Sewer Discharges  (Cete-
 gorv VI)  was cone  by each state.   Using the  goals  of  the Act. as the criteria
 to be met,  they identified a cost  of  about $235  billion  (June  1973 cellars).
 One state clone identified  $80 billion  in needs  tc  control  separate  storm
 sewer discharges.   In 1976,  the  Needs Survey was  conducted by  the  J-.ge;',cy , and.
 it was  found. that  Cetecorv VI would  recuire  $66  billior: tc meet the ooals


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the Act.   This survey broke the goals into three categories or levels  of  pol-
lution abatement;  (1) aesthetics,  (2) fish and  wildlife,  and  (3)  recreation.
Costs to meet each category were determined.

As  noted  previously, the  ASCE  defined  a program  in 196S  to identify  the
causes and  effects of urban stormwater pollution.  The  recommendations  were
not followed, so in 1974 at the Rindge,  New Hampshire, Engineering Foundation
Conference  (jointly  sponsored  with  ASCE's  Urban  Water Resources  Research
Council), a  similar program was. again  recommended.   A  similar  scenario oc-
curred at  the  Easton,  Maryland, conference  of 1976  sponsored  by the  same
group.

DISCUSSION      -

In the past  (ca 1890) ,  dilution was considered to be  the  appropriate way to
control  combined  sewer  overflows,  since  the  primary concern  was odor and
related nuisances.  Between 1890 and 1960 little concern was shown for storm-
water  pollution.   Stormwater  concerns  were  primarily  related  to  drainage
problems.   As  time  progressed,  water  quality  began  to be  considered,  and
workers began to  characterize  problems  in terms of concentrations of certain
pollutants and  loads of these pollutants.  In the 1970's, problems were being
defined  in  terms  of  pounds  of pollutants needing  to be  removed from over-
flows, in the interest of preventing pollution.

Past work,  reported  by,EPA and published in  professional journals, tended to
focus  on  determining (a) the  type  and  amount  of  pollutants  involved and/or
(b) methods  to  reduce the  loads.   However, such reports and articles did not
consider either the level of  improvement attainable  or  the  need to improve
quality of  the  receiving  water body associated with the study.   A conclusion
common to all such reports was  that not enough was known about storrowater to
adequately  understand cause and effect relationships.   Also  common to  such
reports  were recommendations  for  further study  and  more  data.   A  tangible
result of the lack of belief and uncertain attitude in  this area is  the  fact
that  stormwater controls for water  quality  have been implemented  in so  few
places throughout the nation.  Thus, there  has been  a  critical need to  ob-
jectively examine  the situation.

Many  factors led  to the development of NURP, one  being a  legally-mandated
necessity.   As  implementation  of P.L.  92-500 moved into full swing,  the lack
of  progress in  the area of urban  runoff  was  becoming apparent.  In  1974 EPA
lost  a court case, which  led  to the decision  that  EPA should  issue permits
for  separate storm sewer discharges.  In  1976  EPA  requested that the Areawide
Waste  Management Planning Program  focus .on the three or  four most  important
of  the 17 items required by the regulations.   Many of the 208  Areawide  Agen-
cies  cited  urban  runoff  as an  important  item.

Two  years  later, EPA reviewed ninety-three 208 Areawide Agencies'  work  plans
to  assess their basis for having identified  urban runoff as an  element upon
which  they  would  focus.  Review of these projects' methods  and findings did
not  provide much  tc further our  understanding of the  pollution aspects  of
urban  runoff.   If  one  reason  can  be  identified,  it was  the lack  of  site-
specific data to  define  the  local  conditions.

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As mentioned earlier,  the  Rindge  Conference recommended a  candidate  program
for obtaining the  data necessary  to provide a  good understanding  of storm-
water pollution  (EFC/ASCE,  1974).   It is not coincidental  that the NURP pro-
gram is quite similar in design to those recommendations.

THE NATIONWIDE URBAN RUNOFF PROGRAM

Program Design

NURP was not intended  to be  a  research  program,  per se,  and was not designed
as such.   Rather,  the program  was  intended to  be  a support  function which
would  provide  information  and  methodologies   for  water  quality  planning
efforts.  Therefore, wherever possible,  the projects selected were ones where
the work undertaken would  complete the  urban runoff elements of formal water
quality management  plans and the  results were  likely to be  incorporated in
future plan updates and lead to implementation  of management, recommendations.
Conduct of the  program provided direction  and  assistance to  28 separate and
distinct  planning   projects,  whose  locations  are  shown  in  Figure  2-1  and
listed in Table  2-1, but the results will be of  value to many other planning
efforts.  NURP  also acted  as a  clearinghouse and,  in that capacity, provided
a common communication link to and among the 28 projects.

The NURP  effort began with  a  careful review of what was  known about urban
runoff mechanisms,  problems, and  controls,  and then built upon  this base.
The twin  objectives of .«the  program  were to provide  credible  information on
which Federal,  State,  and  local decision makers  could base fu€ure urban  run-
off  management   decisions  and   to  support  both  planning  and  implementation
efforts at the  28 project locations.

An early step in implementing the NURP program involved identifying a limited
number of  locations where  intensive data gathering  and  study  could  be done.
Candidate locations were assessed relative to three basic selection criteria:

        Meeting program objectives;

     -  Developing  implementation plans  for those areas; and

     -  Demonstrating  transferability,  so  that  solutions  and  knowledge
        gained  in  the  study  area  could  be  applied in other areas,  with-  .
        out need for intensive, duplicative data gathering  efforts.

The program design  used for NURP  included providing  a full  range of technical
and management  assistance  to each project as the needs arose.   Several forums
for the communication  of experience  and  sharing  of  data  were provided through
semi-annual meetings involving  participants from all  projects.  The roles and
responsibilities of the various State,  local,  and regional agencies  and  par-
ticipating  Federal agencies  were  clearly  defined  and  communicated at  the
outset.   These   were  reviewed   and  revised where  warranted as the  projects
progressed.
                                       2-e

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Figure 2-1.  Locations of the 28 NURP Projects
      TABLE 2-1.  NURP PROJECT LOCATIONS
EPA
Region
T



•11




III


IV




NURP
Code
MAI

MA2
NH1
NY]

NY2
NY3

DC!

MDJ
FL1
NCI
SCI
TN]

Project Name/Location
Lake Ouinsigamond
(Boston Area)
Upper Mystic (Boston Area)
Durham, New Hampshire
Long Island (Nassau and
Suffolk Counties)
'Lake George
Irondequoit Bay (Rochester
Area )
WASHCOG (Washington, D.C.
Metropolitan Area)
Baltimore, Maryland
lampe, Florida
Winston-Salem, North Carolina
Myrtle Beach, South Caroline
knoxville, Tennessee
	 _____^__
EPA
Region
V





VI

VII
VIII


IX


X

NURP
Code
iLl
IL2
Mil
MI2
MI3
WI1
AR1
TX1
KS1
C01
SD1
UT1
CA1

CA2
OR1
WAI
Project Name/Location
Champa i gn-Urbana , Illinois
Lake Ellyn (Chicago Area)
Lansing, Michigan
SEMC06 (Detroit ffrea)
Ann Arbor, Michigan
Milwaukee, Wisconsin
Little Rock, Arkansas
Austin, Texas
Kansas City-
Denver, Colorado
Rapid City. South Dakota
Salt Lake City, Utah
Coyote Creek
(San Francisco Area)
Fresno, California
Springfield-Eugene, Oregon
Bellevue (Seattle Area)

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The 28 NURP projects were managed by  designated  State,  county, city, or  re-
gional  governmental  associations.   The U.S. Geological  Survey  .(USGS)   was
involved with EPA as a  cooperator,  through an inter-agency agreement, on 11
of the  NURP  projects.   The Tennessee Valley  Authority  was also  involved in
one project.

A major objective of the program was  the acquisition  of  data.   Because  these
data will  be  used for several years  to characterize problems, evaluate  re-
ceiving water impacts  from urban runoff, and evaluate management practices,
consistent methods  of data  collection  had  to  be  developed  and rigorously
employed.

Project Selecti6n

Projects were  selected from  among  the  93 Areawide  Agencies  that  had  iden-
tified urban runoff as one of their  significant  problems.   The intention was
to build upon what  these agencies had  already accomplished  in their earlier
programs.  Also, projects that would be a  part of this  program were screened
to be  sure that  they  represented a  broad range of  certain  characteristics
 (e.g.,  hydrologic  regimes,  land uses,  populations,  drainage  system types).
Actual  selection of  projects was  a joint  effort among  the  States,  local
governments,  and Regional  EPA  offices.   The  five  major  criteria  used to
screen candidate projects were as follows:

     1.  Problem Identified.   Had  a  problem relative  to urban  runoff
         actually  been  identified?  Could   that  problem  be directly
         related to separate  storm  sewer discharges?   What pollutant or
         pollutants were  thought to be causing  the problem?  Using the
         NURP problem  identification  categories,  what was the  "problem"
         (i.e.,  denying  a  beneficial   use,  violating   a  State  water
         quality standard, or public concern)?

     2.  Type of Receiving Water.   The  effects  of  stormwater runoff on
         receiving water  quality were  the NURP  program's ultimate- con-
         cern.    Because   flowing   streams,   tidal   rivers,   estuaries,
         oceans,  impoundments,  and  lakes  all have different  hydrologic
         and  water quality  responses,  the  types  of  receiving waters
         associated with each candidate 'project had to  be  examined to
         ensure  that an appropriately representative  mix was  included in
         the overall NURP program.

      3.  Hydrologic Characteristics.   The  pattern of  rainfall  in  the
         study  area  is perhaps  the single  most  important  factor in
         studying urban  runoff phenomena,  because  it provides the  means
         of  conveyance  of  pollutants from their  source to the receiving
         water.   For  this reason, projects  in  locations having  in dif-
         ferent  hydrologic regimes were chosen for  the program.

      4.  Urban Characteristics.   Characteristics  such  as   population
         density,  age  of  community, and  land  use  were  considered  as

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         possible  indicators  of  the waste  loads  and  ultimately  the
         rainfall-runoff water quality relationship.  The type  of sewer-
         age system was  another factor  considered  (e.g.,  whether  it  is
         combined, separate, or mixed;  how  severe  the infiltration  and
         inflow problems may  be) .   Such factors have different  effects
         on the quantity and quality of storm runoff, and were balanced
         as well as possible in selecting  projects.

     5.  Beneficial Use of Receiving Water.   Because  this  factor greatly
         affects the type of control measure that would be  appropriate,
         attempts  were  made   to  include  a  wide  range  in  selecting
         projects.

Although these were the primary criteria used to identify potential projects,
other  factors  also  had  to be  considered  (e.g.,  the  applicant  agencies'
willingness to participate, the State's acceptance of the project, the expe-
rience  of  the proposed  project  teams).   Because  the  NURP program  used
planning grants  (not  research funds) a major  consideration was  the antici-
pated  working  relationships with  local public  agencies  and the applicants'
ability to raise local matching funds.

Program Assistance

Technical expertise and  resources available  for urban  runoff planning varied
among  the  various projects  participating in NURP.   Therefore,  the program
strategy  called for providing  a  broad spectrum of  technical- assistance to
each project as needed  and  for  intercommunication of  experiences and sharing
of data in a timely manner.

Assistance was also provided to the applicants in developing their final work
plans.   This  was done  to  ensure   that  there  would be   consistency  among
methods, especially in  the  collection  of  data.   If there were to be differ-
ences  in  data  from city to city,  they must  be  due  to the characteristics of
each city and not a result of how the data were obtained.

Assistance with  instrumentation was provided during the program in the  form
of  information  on available equipment,  installation,  calibration, etc.   Be-
cause  one of  the  more  important elements  of a data collection program is the
"goodness" or  quality  of the  data themselves,  questionable data would be of
little use.  Accordingly, a quality assurance and quality control  element was
required in the plans for each project.

Periodic  visits  were  made to each  project  site to  ensure  that the  partici-
pants  were  provided  opportunities to discuss any problems, technical or ad-
ministrative.   The  visiting team typically  included an  EPA  Regional Office
representative,  an EPA  Headquarters representative,  and  one or  two expe-
rienced  consultants.   All  interested parties,  including representatives  from
State  or local governments, were requested to attend those  visits.

As  the projects, moved  farther into  their  planned activities and  the  time for
data analysis approached, each project was required to describe  how  they  were
going  to analyze their data.  No single method  was recommended for each proj-
ect,  because  it  was  believed that  a  broad  diversitv  of  available  methods

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would be suitable, if used properly.  Guidance on proper  use was provided as
a part of  technical  assistance  through project visits and  special workshops
for this purpose.

Communication

It  was  intended  that  the entire group  of NURP  participants function  as a
single team.   Accordingly,  a communication program  was  developed.  National
meetings were  conducted semi-annually so  that- key personnel  from the indi-
vidual projects  would have  an  opportunity to discuss their experiences  and
findings.

Reports were required  of  each project quarterly.   EPA Headquarters also  pro-
vided composite  quarterly reports summarizing the status of each project and
discussing problems encountered and solutions found.

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                                  CHAPTER  3
                          URBAN  RUNOFF  PERSPECTIVES
In evaluating  the  impacts  of urban runoff,  one's  perspective may be  influ-
enced  by one's  concerns and  priorities -  and  what  one  defines  to  be  a
"problem".  Recognizing  this,  the following  discussion covers several  such
perspectives,   including  concerns over  runoff quantity,  water quality,  and
control possibilities.

RUNOFF QUANTITY,

The following discussion covers a major cause and two major effects of runoff
problems  related  to  "quantity"   (i.e.,  increased  urbanization  as a  cause;
flooding and erosion/sedimentation as  effects).

Flooding Problems

As noted earlier,  drainage has  historically been the  principal  local-level
concern  regarding urban  runoff.   Concerns over quantity  can  be  divided into
two  basic  categories:   nuisance flooding   and  major   flooding.   Nuisance
flooding  (e.g., temporary ponding of  water on streets,  road  closings, minor
basement  flooding),  although hardly tolerable to those immediately affected,
rarely  affects an  entire urban populance.  Nonetheless,  the-concerns of the
(often  vocal)  minority of affected citizens commonly reach  the .point where
local  action is taken  to minimize the  recurrence  of  such events.  Such miti-
gation  activities  are  usually locally  determined,  funded,  and implemented
because  both the affected public and  government  decision makers .perceive and
concur  that such flooding constitutes a "problem".

Catastrophic flood  events,  on  the other hand, have  to  be thought about  dif-
ferently for several reasons:

         They typically affect the majority of the urban  populace.

         Mitigation   measures   often   involve  engineering  improvements
         extending well beyond  local jurisdictions.

      -  Mitigation  measures often  cost  more than  the  local  community
         could  afford.   Historically,  the  Federal  government  has  become
         involved,  in  major  flood control  efforts  through a number  of
         related  programs.   In such  cases, water  quantity problems  are
         relatively  easy  to  define because   the  extent  of  flooding  is
         readily  observable,  the  degree  of damage is easily  determined,
         and  the  benefits of  proposed  flood control  projects  can  be
         estimated.   Thus, decision  makers  face  a  relatively  low  risk
         in  prescribing courses  of action and justifying the associated
                                      -3-J.

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        costs  in  light  of  benefits.   As  will  be  discussed  later,
        decision making  in  the  case of water quality  concerns  is  less
        straightforward.

Erosion and Sedimentation Problems

Erosion results  from rainfall  and  runoff  when  soil  and other  particles  are
removed from  the land surface  and transported  into conveyance  systems  and
water bodies.   Since  land  surface erosion is the principle  source  of stream
sediment,  the type  of  soil,  land  cover,  and hydrologic conditions  are major
factors in  determining  the  severity  and  extent  of  sedimentation  problems.
Although erosion  is a natural  process, it  is  frequently  exacerbated  by  the
activities of man,  in both urban and rural environments.
                                             V
When addressing  the broad  spectrum of receiving water  problems which result
from sedimentation, it  is  convenient  to divide  cases into  two categories;
(1) those that  respond to control  measures  directed at nuisance  flood  pre-
vention,  and  (2)   those   that  are  not controlled  by  such measures.   When
natural loads are discharged into receiving waters,  the effects are primarily
physical  and only  secondarily chemical   (because the mineral constituents
which make up the primary sediment load are relatively benign in most cases).
Among the physical problems imposed upon the receiving waters are:

        Excess turbidity reduces  light penetration,  thereby interfering
        with sight  feeding and  photosynthesis;

        Particulate  matter  clogs  gills  and filter  systems  in aquatic
        organisms,  resulting, for  example,  in  retarded growth,  systemic
        disfunction, or asphyxiation in extreme cases; and

        Benthal  deposition  can bury  bottom dwelling  organisms, reduce
        habitat  for juveniles, and interfere  with  egg  deposition  and
        hatching.

Although sedimentation is storm-event related,  its resultant problems  are not
exclusively  either  "quantity"  problems  or water "quality" ' problems.  Being
hybrid  problems,  sedimentation  control has  received a mixed approach.   The
organizations involved range widely,  from Federal  agencies  (e.g., the Army
Corps  of  Engineers,  the Soil  Conservation Service)  to  local drainage and
sedimentation control  officials,  frequently with involvement from State and
county governmental agencies.

Urbanization as a Cause of Problems

Urbanization  accelerates erosion  through  alteration   of  the  land  surface.
Disturbing the land cover, altering natural drainage patterns,  and  increasing
impervious  area  all increase the  quantity and  rate of  runoff, thereby in-
creasing both erosion  and flooding potential.   Also,  the sedimentation pro-
ducts which result  from  urban  activities are generally not as benign as the
natural mineral  sediments which result  from soil erosion.   Atmospheric  depo-
sition  (assccieted  with  industrial,  energy,   and  agricultural  production
activities) and  added surface  particuiates (resulting from tire  wear, auto

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exhaust, and road surface decomposition)  fall in this latter category.   Their
effects on receiving waters tend to be  more "chemical" 'than "physical".   They
may contain  toxic substances and/or other  compounds which can have  adverse
impacts  upon   receiving  water  quality   and   the   associated   ecological
communities.

WATER QUALITY CONCERNS

The notion that  urban  runoff can be  a  significant contributor to the impair-
ment or degradation of the quality  of  receiving waters has  formed  only re-
cently  and is not universally  shared.   It  is the totality of receiving water
characteristics  (e.g.,  flow  rate,  size or volume, and physical  and chemical
characteristics)  that  determines  its use, although  some  characteristics are
more important  than others (e.g.,  there must be  present  an appropriate rate
of flow and/or volume  in the receiving water to support the desired use) .

In addressing the water  quality needed  to  support a  designated use, one must
consider  specific requisite characteristics.   For  example,  in the  case of
swimming,  total  dissolved solids  and  dissolved  oxygen levels are  far less
important  than  pathogenic  organisms.   For irrigation, the biochemical oxygen
demand  of  the water is  of little concern  to the fanner,  whereas  the  total
dissolved  solids  level  is of  immense concern  (to  minimize  salt buildup).
Although high nutrient levels  may  be detrimental to  the quality of impounded
waters  (by hastening eutrophication processes),  a farmer may welcome nutri-
ents in irrigation water.
                       j»
                                                               it
It  is  also important,  to note  that it is  the  concentration,  rather than the
mere presence  of a water  quality  constituent,  that  affects  use.   The  rela-
tionship between pollutant concentration  and  resultant impacts on receiving
water  use  are  quite  non-linear,  with  plateau  effects  not  uncommon.  For
example, consider dissolved  oxygen and its  effect upon fin fish.  Down to a
certain level  below  saturation,   there  are  virtually no  important effects
 (upon  a given  species).   As dissolved oxygen  levels  fall below this  thres-
hold,  the  more  sensitive  members  of the  species begin  to be affected.  As
levels  continue to fall, the  affected  percentage of the population will in-
crease  until a  level is  reached at which the entire population can  no  longer
survive.   Obviously,  any  further  reduction of  dissolved oxygen level  would
have no further effect upon  the community, since it no longer exists.   It  is
important  to keep this plateau effect in mind  when  considering  the practical
impacts of increased pollution and  the  practical value of remedial  measures
to  restore beneficial uses, since limited  removal  of a polluting  substance
may do  nothing  to'alleviate  the problem.   In the example given  above,  if one
were  to somehow  reduce  the  input  of oxygen demanding substances to  the  re-
ceiving water,  the result  might be that  the dissolved oxygen level of the re-
ceiving water  would rise from  1.0 mg/1 to  3 mg/1.   If the species of concern
were  trout,  they still  could  not  survive.  Even though  polluting  substances
were removed and money was spent,  the  desired benefit would not be achieved.

WATER QUANTITY  AND QUALITY CONTROL

There  is no question  that excessive urban  runoff causes  problems.   Remedial
costs   may  be  high, but the  benefits  are  obvious.   Currently,  there  is  a
growing national awareness that, if  steps  are taken  during the planning phase

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of development,  excessive  stormwater discharges can  be prevented, at  least
from typical  events  (large infrequent storms will  always present a  greater
threat).

Past And Current Work

During  the  past two decades  attention has been  focused on  reducing runoff
rates  and  volumes and  reducing flood damage.   During  the  early 1970"s,  a
manual  of  practices  was  prepared  under  grants  from  the  Office of  Water
Research and  Technology sponsored by  the  American  Public Works Association
stressing detention (Poertner, 1974).  The University of Delaware also issued
a manual of practices on methods to control rates  and volumes of urban runoff
(Toubier and^Westmacott, 1974).

Work done by  the ASCE Urban Water Resources Research  Council during the six-
ties stressed the  concept  of  natural easements for drainage, observing that
there were two drainage ways; major  routes for  large  events  and minor routes
for  smaller more frequent events  (Jones,  1968).   It was  claimed that money
could  be  saved by using  natural channels, swales,  etc., thus  reducing  the
need for more expensive concrete conveyances.

The  idea of intentionally  using  natural  runoff  courses, green belts,' and the
like was new  to  engineers  who had long been  trying  to control runoff through
more artificial  conveyances.   In 1970, EPA's  Office  of Research and  Develop-
ment initiated work on  a development known as the Woodlands project  in Texas
near Houston.   Studies  were  conducted to determine how stprm flows could be
managed  and  water  quality could  b'e  protected or  improved  by  the  use of
natural  drainage ways,  detention  facilities,  porous  pavements, increased
infiltration  rates, and a decrease in runoff rates (Characklis,  1979).

Federal Involvement

As part of its  national effort to control erosion  from agricultural  lands,
the  Soil Conservation  Service  (SCS)  (Department  of  Agriculture)   provides
technical  assistance  in developing  erosion  control  plans.   During  the  past
decade  or  so, the methods  they have  developed have been  applied much  more
widely  than  just to  agricultural situations.   SCS  has become  increasingly
involved in erosion control in urban areas and  has produced  a useful  document
for  assessing urban hydrology in small watersheds 
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The methods used tend to be preventive,  wherein  erosion  is  controlled by  pre-
scribing  certain  proven  design  practices   and   conventions.    Many  local
agencies are developing control plans along these  lines, so  this  report  will
not cov.er this aspect of control.

PROBLEM DEFINITION

As  pointed  out  earlier,  water quantity  problems  are relatively  easy  to
identify and describe.  Water quality problems,  on the other hand, tend to be
more elusive because  their  definition often involves  some  subjective consid-
erations,  including  experiential aspects  and  expectations of  the populace.
They  are not  immediately  obvious  and  are usually  less  dramatic than,  for
example,  floods.   They  also  tend  to vary markedly  with  locality  and  geo-
graphic  regions within the country.  For example,  a northwestern resident may
want to  upgrade  stream  quality  to  support  some  highly-prized species of game
fish,  while  a northeastern resident  contemplating the river flowing by the
local  factory might  be  grateful  to  see  any  game  fish  at  all.   Thus,  a
methodological  approach to the  determination  of  water quality  problems is
essential  if  one  is  to consider the relative role  of urban  runoff as a con-
tributor.  An  important finding of the  work conducted  during  this NURP pro-
gram  has  been  to learn  to  avoid  the  following  simplistic  logic train:
 (a) water  quality  problems  are caused by pollutants,  (b) there  are pollutants
in  urban runoff, therefore, (c) urban runoff causes "problems".  The unspoken
implication  is  that  a "problem" by definition  requires action, and any type
of  "problem" warrants equally  vigorous  action.   It becomes clear  that a more
fundamental  and more precise  definition of  a  water quality  "problem"  from
urban  runoff is necessary.  For this purpose,  the NURP has adopted the  fol-
lowing three-level definition:

         Impairment or denial of beneficial uses;

      -  Water  quality criterion  violation; and

      -  Local  public  perception.

The first  of these levels  refers to  cases  of  impairment or denial of a desig-
nated use.  An example  would  be a case where  a  determination has  been made
that  some  specific beneficial  use  should be attained;  however, present  water
quality  characteristics are such  that  attainment of the use cannot be  fully
 realized.

The second level  of  problem definition refers  to  violations of  a designated
water quality criterion.   An  example would be a case where some measure or
measures of water quality  characteristics  have been found  to  violate recom-
 mended or mandatory  levels for  the  receiving water  classification.   Some of
 the subtle  distinctions between  this  and the preceding problem definition
 arise in the fact  that receiving water  classification may not be appropriate,
 the beneficial use may not be  impaired or denied,  and the water quality cri-
 teria associated with that classification may  or may  not be  overly conserv-
 ative or directly  related to  the desired use.

 The third level of  problem definition  involves  public perception.   This may
 be expressed in a  number of ways,  such  as  telephone cells to public officials

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complaining  about  receiving  water color, odor, or general  aesthetic appear-
ance.  Public perception of  receiving  water body  problems  is highly variable
also.  Some  people enjoy  fishing for carp or gar, children 'will  play in al-
most any creek, and so on.  This level of problem definition can also include
one concept  of  anti-degradation.   Here  the thought is  that no polluting sub-
stances of  any  kind in any quantity should be discharged  into the receiving
water regardless of its natural  assimilative  capacity.   This concern has its
ultimate expression in the  "zero discharge" concept.   EPA's concept of anti-
degradation, on the other hand,  refers  to  degradation of use;  a subtle but
essential difference.

The  foregoing   levels  of  problem  definition  provide an  essential  framework
within which to discuss water quality  problems associated with urban runoff.
However, it is important to  understand  that  when one  is  dealing at a  local
level all three elements are  typically present.   Thus,  it is up to  the  local
decision makers, influenced  by other levels  of support and concern,  to  care-
fully weigh each,  prior to  making a final decision about the existence and
extent of  a problem and how  it  is to be defined.   It  follows that, if  this
step of problem definition is done carelessly, it will be difficult, if not
impossible,  to  plan an effective  control strategy and establish a  means for
assessing its effectiveness.

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                                  CHAPTER 4
                            STORMWATER MANAGEMENT
INTRODUCTION

This chapter is  included  for those who wish  to  know more about  how to plan
and implement  stormwater  management programs.  Most of  the  information con-
tained herein  was  developed  through several related programs  that were pro-
ceeding in parallel with the NURP program.

     -  The Southeast  Michigan  Council of Governments  (SEMCOG),  a NURP
        grantee, was developing stormwater management procedures.

        The Midwest Research  Institute  (MRI)  was collecting  cost infor-
        mation on control practices from selected NURP projects.

     -  A  related  EPA  Water Planning  Division  program,  the  Financial
        Management  Assistance Program  (FMAP), was  developing financial
        and institutional planning  procedures  designed  to be helpful in
        the implementation of stormwater management plans.

STORMWATER MANAGEMENT PLANNING1

Stormwater  management  planning develops policies,  regulations,  and programs
for the  control of runoff from the  land.   Stormwater  management planning  is
normally directed  toward  either or both of two primary goals:  the reduction
of  local  flooding  and/or the protection of water  quality.   However,  storm-
water  management planning is also generally used  to  insure that stormwater
programs   and  regulations   provide   multiple  benefits  to   the  affected
communities and do  so  in  a way  that does not create additional problems.

Stormwater  management  planning  need not involve  expensive technical studies.
Available  data and  maps,  the  experience of other communities, and advice from
experts  can be used to  develop  an  effective planning program.  Detailed tech-
nical  studies  can  then be targeted toward specific issues and problems.  Ef-
fective  local  planning can  alleviate  the need  for costly  remedial  public
works  projects.
    The material in this  section  of  the  chapter  is  largely  from  Technical Bul-
    letin No. 1:   Stormwater Management  Planning:   Cost-Saving  Methods  for
    Program Development,  the  first  of a  seven-part  bulletin  series on water
    quality management prepared by  the  Southeast  Michigan  Council of  Govern-
    ments  and  available   from Information  Service,  SEMCOG,  8th Floor,  Book
    Building,  Detroit,  Michigan  48226.

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  The Need

  Stormwater runoff  cannot be ignored in developing communities.   As urban  de-
  velopment  occurs,  the  volume  of  stormwater  and  its  rate  of discharge  in-
  crease.   These increases are caused when  pavement and structures cover -soils
  and destroy vegetation  which otherwise would slow and absorb runoff.  Pollut-
  ants,  washed  from the  land surface  and  carried  by  runoff  into  lakes  and
  streams,  may add to  existing water quality problems.

  Figure  4-1  illustrates  the effects  of paved  surfaces  on  stormwater  runoff
  volumes.   When natural  ground cover is present over the  entire site,  normally
  less  than 10 percent of the stormwater runs off  the land  into nearby creeks,
  rivers,  and lakes.  When  paved  surfaces  cover  10 to  30 percent of  the  site
  area,  approximately  20 percent  of the  stormwater  can be expected to  run off.
  As paved  surfaces  increase, both the volume and  the rate  of runoff  increase.
  Furthermore, paved surfaces  prevent natural  infiltration of  stormwater  into
  the ground, and  increased  runoff volumes  and rates  increase soil erosion and
  pollutant runoff.  Stormwater management planning can be used to develop pro-
  grams  to  reduce  adverse affects  and even to provide community benefits.
                   EVAPO-
                   TRANSPIRATION
                        NATURAL
                        GROUND
                        COVER
                                                   38%
                                                     EVAPO
                                                     TRANSPIRATION
      10% RUNOFF
     25%
     SHALLOW
     INFILTRATION
                                     20% RUNOFF
                                                           10-20%
                                                           PAVED
                                                           SURFACES
            DBF
            INFILTRATION
21%
SHALLOW
INFILTRATION
DEEP
INFILTRATION
                                                          21%
                 25%
                 35%
                   EVAPO-
                   TRANSPIRATION
30% RUNOFF
                        35-50%
                        PAVED
                        SURFACES
                                                    30%
                                                      EVAPO
                                                      TRANSPIRATION
                                             RUNOFF
                                                           75-100%
                                                           PAVED
                                                           SURFACES
20%
SHALLOW
INFILTRATION
                   DEEP
                   INFILTRATION
                 15%
   10%    f^ 5%
   SHALLOW     DEEP
   INFILTRATION   INFILTRATION
    Source: J.T. lourbier and R. Westmacott, Water Resources Protection Technology: A Handbook ol Measures to Protect Water
         Resources in Land Development, p. 3.

    Figure 4-1.   Typical Changes  in Runoff Flows  Resulting  from Paved Surfaces
                                           4-2

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Stormwater management can and should be directed toward two goals:   the  con-
trol of runoff flows  (i.e., volumes and rates) and the control  of  pollutants
in stormwater.  Control measures which emphasize  the  storage of  runoff rather
than the  immediate  conveyance  from the  site  and  from the  community often
provide benefits  which, meet both  goals.   Stormwater storage and  conveyance
measures, however, affect the community in a variety  of ways. .  Through storm-
water management planning the effects of alternative  policies,  programs,  con-
trol measures, and financing schemes can be evaluated.

Stormwater  management planning  is directed toward  basic policy  questions,
such as:                 •

        What should be done with runoff from the  land?

        Is the temporary (detention) or permanent (retention)  storage of
        stormwater runoff desirable?

     -  Under  the  circumstances,   should  retention  basins,   detention
        basins, natural  infiltration areas,  or  dished  parking  lots be
        used to store runoff?

        What requirements should be placed on new developments?

        Do stormwater runoff problems in developed areas warrant special
        attention?
                       ..*»
        Should communal retention or detention facilities be provided by
        the local jurisdiction?  If so, how can such areas be financed?

        Who should pay for retention and detention facilities on private
        property?

        Are the local  jurisdictions already carrying out programs  (such
        as  parkland  acquisition programs  or  wetlands  regulation) which
        affect  stormwater  runoff?  Can  programs and/or  regulations be
        coordinated  to achieve multiple purposes?

        Should  enclosed  drains  or natural  channels be  used  to  convey
        Etormwater to and from storage areas?

        Can  routing  and  storage  be  provided for  major  storms  (e.g.,
        100-year  frequency)   as well  as  minor  storms  (e.g.,  10-year
        frequency)?

        Who should be responsible  for facility maintenance?

The  specific questions to be addressed in  a local government planning program
will vary among  local jurisdictions,  reflecting varying  problems  and commun-
ity  objectives.   The answers to these questions may take the  form  of policy
statements, chances  in regulations  or engineering design  standards,  technical
assistance  materials for  .landowners or  consulting engineers, revisions  to
existing  programs, or a written plan document.

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Because stormwater  management  planning  for quantity  and  quality control  is
relatively new, and because community stormwater  concerns differ, there are
no easy formulas for preparing  stormwater management plans.

Stormwater Runoff as a Community Resource

Although,   stormwater  management programs  are  typically  undertaken to  avoid
problems  (e.g.,  flooding, pollution,  lawsuits),  effective planning can  also
be used to pursue potential community  benefits.   When effectively managed,
stormwater can provide benefits such as:

        Recharge of groundwater supplies;
               »
        Water quality enhancement;

        Recreational opportunities  (e.g.,  use of  large retention areas
        for boating, fishing,  or nature  study);

        Replenishment  of  wetlands  which  serve as wildlife  habitats,
        absorb  peak   floods,   and  naturally  break  down  certain
        pollutants;

        Maintenance of summertime lake levels and stream flows; and

        Enhancement of community appearance  and  image when  facilities
        are attractively designed.

The Role of Local Governments

In some cases,  the institutional systems for  stormwater  management may need
to be  complex,  largely because State, county, and  local  agencies' policies,
regulations, and  procedures may all affect stormwater control within a par-
ticular development.  For example,  in Michigan, the following  roles apply:

        County  drain  commissioners construct  and manage  county drains
        and also review subdivision plans to assure adequate drainage.

        County  highway departments affect drainage  in new  developments
        by regulating  connections to roadside  drains  and  ditches.

        The  State Department  of Natural  Resources  regulates  wetlands,
        dam construction, and  floodplain alterations.

        The  State  Water Resource Commission  issues  permits for  certain
        stormwater  discharges  when known water  quality  problems can  be
        linked  with a  particular activity,  (e.g., certain storm  drains,
        animal  feeding operations,  industrial  parking lots).

        Both the State Department of Public Health and county  drain com-
        missioners regulate drainage in proposed  mobile home parks.

        County  agencies and certain  local  governments issue erosion  and
        sediment control permits for certain  development  sites.

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Furthermore, there  has been  increasing  emphasis upon  the  consideration  of
environmental factors  in  land  use  decisions.   Recent amendments to the  City
or Village  Zoning  Act  and the Township  Rural  Zoning Act have  clarified  the
legal authority  of  locel  governments to complete site  plan reviews for  en-
vironmental management purposes.   Standards for the  review  of  land  uses  must
be included  in  local  ordinances  and take natural resource  preservation  into
account.  The Michigan Environmental Protection Act  (MEPA)  (Act 127, P.A.  of
1970) places a  duty on all  government  agencies to prevent  or  minimize water
pollution and other environmental problems while  carrying on  regular  activi-
ties.  Section  5(2) of MEPA  addresses  the  actions of local officials  in the
following terms:

     In any  ... administrative, licensing or other proceedings, and in
    . any judicial review  thereof,  any  alleged  pollution impairment or
     destruction of the  air,  water or other natural  resources, or the
     public  trust  therein,  shall be determined,  and  no conduct shall
     be authorized  or  approved which does,  or is likely to have such
     effect  so  long as  there is a  feasible and prudent  alternative
     consistent with the reasonable requirements of the public health,
     safety  and welfare.

Environmental aspects  of  stormwater runoff  may  be addressed  by local offi-
cials in response to MEPA.

None of  the above  laws  specifically require local  governments to undertake
stormwater management prbgrams.  Instead, local governments have a wide range
of possible  roles available to them.  Stormwater management planning programs
can  be  directed toward the review of  existing  State and county programs  af-
fecting stormwater  runoff and toward the evaluation of alternative roles  for
the  local government.

Possible  roles  for local governments in  stormwater management include  the
following:

     -  Planning -  The term  "stormwater management planning" refers to
        the  process of developing policies, programs, regulations,  and
        other recommendations to chart the  future  course  of   the  com-
        munity  in  terms of  stormwater management.   Such planning  can
        address  existing problems or help to avoid  future problems  and
        community expenses.

     -  Regulations -  Stormwater runoff  control  for  each site  plan and
        subdivision plan can  be reviewed  and approved by the  local
        government.

     -  Design  and  Construction -  Storm drainage  facilities  (e.g.,
        pipes,  basins, areas for retention) can  be designed  and con-
        . structed by the  local government.   Purchase of  lands  to serve
        as  community stormwater  retention areas  may also be undertaken.

        Inspection   and  Maintenance   -   Reouirements  fcr   recular
         inspection  and maintenance  of  stormwater  facilities,  including
         drains  and  retention or detention  basins,  may be  enforced by

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        local  governments.    Requirements  for  easements  are  usually
        part of maintenance programs.  Local governments may choose to
        undertake  maintenance  as  a  community  service  (such   as  a
        utility)  or  may   require  maintenance  through  contractual
        agreements with property owners.

The types  of programs developed  and the role  assumed  by a local government
should,  of course/ reflect  available financing  options  as well as program
needs and management  gaps.

FINANCIAL AND  INSTITUTIONAL CONSIDERATIONS2

The traditional planning approach would ideally  culminate in the  successful
implementation of  a detailed  design.  In many  cases, however, this  objective
is not  accomplished due  to financial and institutional  constraints.  Often a
study team will fail  to  adequately consider such institutional  and  financial
issues  as  who  will manage the system  and  how  will  it be  financed,  thus cre-
ating a  gap between  technical planning and implementation.  This omission is
illustrated in Figure 4-2.
                               SELECT
 ANALYSIS
   OF
 TECHNICAL  /|   TECHNICAL
ALTERNATIVES/   ALTERNATIVES
                                          DETAILED
                                           DESIGN
 SUCCESSFUL
IMPLEMENTATION
                Figure 4-2.   Incomplete Water Quality Planning


 The  implementation gap  that results  from  the traditional  planning  approach
 has  occurred all too  often  in attempts to control urban runoff.

 As  an illustration of the need to integrate financial and technical  planning,
 consider the  traditional process  for developing  a  program  to control  con-
 struction runoff.  A typical  outcome  of the process  is  a new  ordinance.   To
 reach this outcome, some of  the  issues  that are normally considered from the
 technical perspective include:

         What are the  technical construction requirements  to be  set out
         in the ordinance?

         What control  measures will be required?

         How will compliance be monitored?
 2  This material  is largely  from the  draft document,  Planning  for Urban
    Runoff Control:  Financial and Institutional  Issues,  December 1981, pre-
    pared for FMAF by the Government  Finance Research Center  of the Munici-
    pal Finance Officers Association, Washington, D.C.
                                      4-6

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To balance the  planning  process,  this technical analysis should be  expanded
to include financial and institutional issues such  as:

        Does the  city have legal  authority to  implement  each  require-
        ment in an ordinance?

        How much  will  each  cost,  and who will  pay  for  implementation
        of the control measures?

        Who will  conduct  compliance  review,  and who will pay  for  the
        reviews?

Numerous additional factors increase the need for financial and institutional
analysis in all water quality management planning.   Examples might  include:

        Implementation of  control programs  occurs  at the  local  level,
        and local  budgets  are  being tightened  as water  quality expend-
        itures compete with other local demands.

        Benefits  from  water  quality projects are difficult to quantify
        and often  accrue to people living downstream.

        It is becoming more  difficult to obtain municipal  funds through
        the bond market because of high interest rates.

        The cost of pollution controls is often sizable and difficult to
        allocate to specific polluters or beneficiaries.         <•

These  problems  affect  most areas of  water  quality management, but  they  are
especially important in  identifying  and implementing solutions to urban run-
off pollution.

Integrated Approach

An  integrated  planning approach  helps  water quality planners make  the best
control decisions  in  light of many  complex  issues.  This  approach  takes  the
traditional  planning  process  and  adds  to  it  financial   and institutional
elements  at each  step along  the way.   This  integration  is  shown in Fig-
ure  4-3,  with the traditional  approach illustrated along the  upper  track  and
the  financial and  institutional elements  added  along  the lower track.
                 - .-<
During the  early  planning  stages, financial and institutional  issues  are  re-'
viewed on a preliminary basis.   This information  becomes  more detailed  and
refined  as  planning proceeds.  Ultimately,  the information  forms  the  basis
for  a  financial and institutional plan  that  supports  the detailed  design of a
control alternative.

When  very complex problems  are being evaluated, it may be  advisable to use a
preliminary  matrix early in  the  evaluation process  for screening-out  unac-
ceptable  alternatives.   This approach  permits  a more detailed evaluation of
issues surrounding the two or three  best alternatives  before  a final selec-
tion  is mace.  An  example of a preliminary matrix  is  given in Figure 4-4.

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                         \
   ANALYSIS
      OF     \|_
   TECHNICAL  fT
  ALTERNATIVES/
PRELIMINARY
FINANCIAL &
INSTITUTIONAL
  ANALYSIS
 FINANCIAL AND
 INSTITUTIONAL
  ASPECTS OF
EACH ALTERNATIVE
                                 SELECT
                                TECHNICAL
                               ALTERNATIVES
                                               DETAILED
                                                DESIGN
                                           SUCCESSFUL
                                         IMPLEMENTATION
 IN-DEPTH
ANALYSIS OF
 SELECTED
ALTERNATIVE
                Figure 4-3.   Integrated  Water Quality Planning



CONTROL
APPROACH

• SEPARATE
SEWERS



• SELECTIVE
EXPANSION
OF
UNDERSIZED
TRUNK SEWERS


• CONSTRUCTION
OF DETENTION
BASINS







TECHNICAL
DESCRIPTION

CONSTRUCT
NEW STORM
SEWERS IN
COMBINED
AREAS
REMOVE
BOTTLENECKS,
REDUCE
NUMBER
OF OVERFLOW
EVENTS

CONSTRUCT
10 DETENTION
BASINS SIZED
TO HOLD THE
FIRST FLUSH
FROM A
STORM


EFFECTIVENESS IN
CONTROLLING
POLLUTION

100%
EFFECTIVE
IN
ELIMINATING
CSOs
50%
EFFECTIVE-





30%
EFFECTIVE





FINANCIAL
ISSUES

NET
PRESENT
VALUE
$1 BILLION




$200
MILLION





$50
MILLION







ABILITY TO PAY

EXCEEDS
CITY'S BONDING
CAPACITY


IF STAGED
OVER 10
YEARS,
COULD BE
FINANCED BUT
WOULD RESTRICT
OTHER PROGRAMS
IF STAGED
OVER 5
YEARS,
COULD BE
FINANCED;
COULD RESTRICT
OTHER PROGRAMS



INSTITUTIONAL
ISSUES

EXISTING
INSTITUTIONS
COULD HANDLE
THE PROJECT

EXISTING
INSTITUTIONS
COULD HANDLE
THE PROJECT



NEW
ORGANIZATION
MIGHT BE
NEEDED TO
MAINTAIN AND
AND OPERATE
BASINS
    Figure 4-4.   Preliminary Matrix  for  Selection of  a  Control Approach
                             (Combined  Sewer  Overflows)
                                           t-f-

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Once a  control approach  is selected,  a detailed  design and  a financial  and
institutional  plan can be prepared.   Figure 4-5  illustrates  the major  fea-
tures of  a financial and  institutional plan.   Key features  of the  detailed
analysis  required  to  prepare  this  plan  are  discussed   in  the  following
section.
   INSTITUTIONAL SECTION

     • RESPONSIBLE AGENCY
       - OPERATING PLAN
       - STAFFING WEEDS
       - ORGANIZATIONAL STRUCTURE
     • LEGISLATIVE NEEDS
       - LEGAL ANALYSIS
       - DRAFT ORDINANCES
       - ASSISTANCE NEEDED
FINANCIAL SECTION

  • PROGRAM COST
    - OPERATING BUDGET
    - CAPITAL REQUIREMENTS
  • PROGRAM REVENUE
    - FUNDING SOURCES
    - FLOW OF FUNDS
    - PROGRAM CASH FLOW
    - COST ALLOCATION FORMULA
  • OTHER FACTORS
    - FINANCIAL BURDEN ON PARTIES PAYING
      FOR THE PROGRAM
    - SENSITIVITY OF COST AND REVENUE
      ESTIMATES TO CHANGES  IN
      FINANCIAL ASSUMPTIONS
    - INDIRECT IMPACTS
     Figure  4-5.   Major Components of  a  Financial and Institutional Plan



Key Financial  and Institutional Elements

There  are six  essential  elements3  of  financial and  institutional  analysis
which provide  a structure for the integrated planning process;

        institutional assessment,

        cost analysis,

        revenue analysis,

        ability-to-pay analysis,

        sensitivity analysis, and

        indirect  impact analysis.
2  These  elements were  first defined  in  Planning for  Clean Water Programs:
   The   Role   of   Financial  Analysis,   u.£. EPA's  Financial  Management
   Assistance  Program  by  the  Government  Finance  Research  Center  of  the
   Municipal Finance Officers Association,  September 1961.

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Each of these elements threads through the planning process  and becomes more
definitive as  the  process proceeds.  The  following discussion defines each
element and identifies its major  features.

Institutional Assessment

The  institutional  assessment  identifies the  organizations  or. participating
agencies that would be affected or involved in implementing a particular con-
trol program.  The role of each entity in a program is evaluated with respect
to  its  interest  in solving the  problem and its planning,  management,  oper-
ating,  and  regulatory capabilities.  If the  study team  identifies  an  urban
runoff problem, a preliminary institutional analysis can provide insight into
capabilities' of agencies that may be asked to play a  role in the implementa-
tion and can, in some cases, aid in determining the types of technical alter-
natives that are analyzed.

The  key factors  to consider  in  evaluating an agency's  capabilities are its
statutory  authority  and organizational ability.   In  order  to control  urban
runoff, an agency must have or be able to obtain the authority to implement a
control measure.   The authority  of an  agency can be  assessed by thoroughly
reviewing  applicable  federal,  state,  and local  legislation.   This review
helps  to  determine which  agency  can  best manage  a given  problem  and  high-
lights  areas where additional legislation or local ordinances  are needed.

Cost Analysis'4     .*

A cost  analysis is performed to identify the additional  capital,  operational,
maintenance, and administrative costs of each activity that is part  of  a  con-
trol program.  These costs are estimated  for each agency responsible  for  an
activity.   Cost  estimates are prepared in uninflated dollars  (using today's
cost  for  all projections into the  future)  and  brought back to their present
value  (or present worth)  for comparison  among alternatives.  The  interest
rate  to  be used  in  the present  value  analysis is   the  agency's current
interest  rate  for borrowing funds minus the exp<. .  ed  rate of inflation.

Cost  analysis  of  control alternatives is  included  ir.  increasing  detail  in
each  step of the planning process.   It begins  with "ball park"  estimates  in
early  stages which are refined as the process progresses and finalized  in the
detailed  financial plan.
    A  substantial  part of  this  material  is  from  a  report,  Collection  of
    Economic  Data from Nationwide Urban Runoff Program  Projects,  prepared for
    EPA    by    the    Midwest    Research    Institute,    425 Volker Boulevard,
    Kansas  City,  MO 64110.

    For  o  further  discussion  of present  value  analysis,  see  pp 36  to  42 of
    Facilities  Planning 1981,  U.S.  Environmental  Protection Agency, FRD-20,
    1S61.

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Cost estimates  cannot  be  static.   They are  prepared  on a preliminary  basis
when an alternative is first considered and detail is  added as an alternative
becomes more  feasible.  As  the  planning  process  progresses, estimates  are
updated on a regular basis to account for changing costs.

To update  and  improve available data  on  the costs of  specific  urban  runoff
BMPs, EPA conducted a program to guide, assist,  and coordinate the efforts of
selected NURP  projects in gathering  cost  data  on the  BMPs   and  BMP  systems
which they were evaluating as part  of the  NURP  national workplan.  A report
was prepared to summarize the preliminary economic data submitted by the NURP
projects.  Economic  data  were submitted  for street sweeping,  detention ba-
sins,  catch  basin cleaning,  ocean  discharge control  systems, and  a  public
education/information program by nine  projects.   The  data  must be considered
preliminary and subject to  change,  particularly annual operating cost  data.
Most of  the  capital  cost data are  well  documented and represent the  actual
cost of the BMP control and will not change.  The annual operating cost data,
however, range from detailed  analyses  to  estimates, and some of the data re-
ported are  incomplete.   Since most of the projects  were  still  in progress,
incomplete operating cost data were to be expected.

The capital costs of street sweepers varied from $21,988 (in  1975) to $40,000
in 1981.  The  annual  operating costs  of  street  sweeping programs varied from
$53,445 to $1,138,097.  The  unit  cost varied from $16.80  to $45.45 per hour
of operation,  and  from $5.95  to $23.36 per curb-mile  swept.   This wide range
indicates that  many  variables affect  the  actual  cost of  operating a  street
                       ,*
sweeper.

The installed  capital  costs  of recharge  basins  in Fresno,  California,  ranged
from $933,750  to  $5,587,000.  BMP modifications to three detention basins in
Oakland County, Michigan, cost $2,345  to  $8,442.  'The installed capital cost
of the  modifications  to the  wet  pond in  the Lansing, Michigan project was
$50,149.  Construction of the wet pond in  the Salt Lake County, Utah project
cost $41,138;  modifications  to the  dry pond included  placing  aluminum plates
in an  existing underdrain  and installing a redwood outlet skimmer at  a nom-
inal cost of $371.

The  annual operating  costs  of  the  Fresno, California,  basins  range  from
$1,625 to  $7,975.  The annual cost  for the basin in Lansing,  Michigan  is  in-
complete  and  includes only  the  interest  cost  on a  7 percent,  $38,500 bond
used to  help  finance  the  project.  The  annual  operating  costs for the  ponds
in the Salt Lake ..County,  Utah project were estimated at $560 for  the wet pond
and $200 for the dry pond.

The costs of the  structural  control  alternatives to control  discharge  to  the
ocean in Myrtle Beach, South Carolina, were presented  in detail  and are valid
estimates of the costs that will be incurred  if one of  them  is constructed.
   Collection of Economic Data  From  Nationwide Urban Runoff Program  Projects
   - Final Report, April 7,  1982, EPA Contract No. 68-01-5052.   Detailed cost
   date provided by  the  projects are included in  the  appendices of  this  Re-
   port to show how the various projects prepared  the data  for  submission.

-------
The 1980  construction cost estimates ranged from  $32,849,200  to  $50,973,500,
and the annual operating cost estimates ranged from $3,735,400 to $5,301,900.
The cost of the public education program at Salt Lake  County,  Utah,  was  esti-
mated at $1,550.  The project will  report the  actual cost  of the  program upon
its completion.

Revenue Analysis

The revenue analysis identifies the funding sources needed.to match the  esti-
mated cost  for control  activities  by participating agencies.  This analysis
is important  because  it ensures adequate funding  to  implement the  technical
solution to an urban runoff problem.

There are three categories of funding that are typically used to pay for run-
off control:  Federal and State funds,  local public funds, and private funds.
These sources  include a  variety  of  different  financing  mechanisms,  each with
advantages  and disadvantages.   The use  of  any  or  a  combination  of  these
sources requires consideration regarding:

     -  Revenue  adequacy -  will  funds  be  available  in  the  long- and
        short-term?

     -  Equity  -  Are the  beneficiaries of  the control  program paying
        their full share?
                   .-*'
     -  Economic efficiency  - Is the  charge  that  is assessed equal to
        the social cost of the program?

     -  Administrative  simplicity  -  Can  the  funds  be  managed and
        directed  to the  control program  without  significant  adminis-
        trative problems?

Ability-to-Pay Analysis

The ability-to-pay  analysis  evaluates  the  implementing  agencies' and the  in-
dividual  user's  ability to pay  for the proposed  program by  determining  how
reasonable  a  proposed  revenue program  is  in  terms of  its  overall  impact  on
the community as a whole as well as on  individual  residents.

For a given revenue source, the additional burden  of  the  program is expressed
as a percentage  of the  base costs.  For example,  if  the proposed  program is
to be financed by  property  taxes and it adds $.50 to a  $1,000  tax bill,  the
additional tax burden is .05 percent.   In this  instance,  it would appear that
the homeowner's ability to pay is quite  high.

An important  factor  to  remember is that programs  to  control  urban  runoff are
not the only programs that are placing  a burden on the  people or institutions
who must  support  them.   Hence, the cost of a control program may  not  be ex-
cessive but  cannot be  imposed because  ability to pay has already been ex-
ceeded due to other projects.

-------
Sensitivity Analysis

The sensitivity analysis identifies the extent to which local ability to pay
varies with changes  in  the  assumptions used to estimate costs and  revenues.
Major assumptions that influence costs and revenues are:  phasing of capital
improvement,  anticipated  local  funding  requirements,  rate of inflation,
growth rate, and local fee policies.

The first  step in this  analysis is  to determine a range  of values for key
cost and revenue  assumptions  that  could  occur during  the program.   (For ex-
ample, inflation  may vary between  5  percent  and 15 percent.)   The ability-
to-pay analysis  is then  repeated  using the  high  and  low  values  for  these
assumptions.   *?he final  step is  to  evaluate the  changes  in  burden with
"best-"  and "worst-" case  situations in  comparison  with  burden  under the
"most likely" assumption.

The purpose of  this  analysis  is  to identify control programs that  are  least
vulnerable  to  changing  conditions.   It also helps to make  the  planner  aware
of best- and worst-case  scenarios so  that  contingency  plans can be  developed
to cope with such events.

Indirect Impact Analysis

The indirect impact  analysis  is  an  assessment of  the  costs and benefits that
are not  directly  attributable to a proposed program.    These costs  and bene-
fits can be economic, social,  and/or environmental.   Quantifying the indirect
impacts  of a program is usually quite  difficult,  so  the  planner  generally
resorts to qualitative measurement.

An Example:  Planning an Educational Program

To illustrate  further the process  of  identifying  and  resolving  the financial
and  institutional issues connected  with  implementation  of  an  urban  runoff
control  program,  the following  spells out the steps  involved   in  evaluating
one  control approach  applicable in  already  developed areas.   The example
chosen is  an   educational program to   inform citizens, industry,  and  public
agencies of the problems caused by runoff-borne lawn  and  garden  chemicals,
oil and chemical  residuals from industrial yards, and pesticides, herbicides,
and fertilizer from parks and golf courses.

In  this  example-,  the activities would include:  development of an  informa-
tional brochure,  including  printing and distribution,  and maintenance of an
information center.   In  Figure  4-6,  the institutional  characteristics  needed
to accomplish these activities are compared with the  capabilities of existing
agencies.   The  matrix shows that .the  County  Department of  Pollution  Control
could provide  the technical  input  to  the  Public  Information Center  to write
the  brochure.   The  Council  of Governments  might coordinate the  effort  and
assume overall responsibilities for getting the job done.

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INSTITUTIONAL
CHARACTERISTICS
NEEDED
• COMMITMENT TO
PROGRAM GOALS
• WORKING KNOWLEDGE
OF EACH WASTE
CONTRIBUTION TO THE
RUNOFF PROBLEM
• ABILITY TO WRITE
CLEAR AND CONCISE
INFORMATION FOR THE
PUBLIC
• ABILITY TO PRINT AND
AND DISTRIBUTE
BROCHURE

• STAFF TO RECEIVE
FOLLOWUP CALLS
• ABILITY TO ACCEPT
FUNDS FROM SEVERAL
AGENCIES TO PAY
FOR THE PROGRAM
AGENCIES
STATE
*

*

















COUNCIL
OF
GOVERNMENTS
*

*











*

*



DEPARTMENT
OF
POLLUTION CONTROL
*

#

















DEPARTMENT
OF
PLANNING
*

*







#









PUBLIC
INFORMATION
CENTER
*


.


*













CHAMBER
OF
COMMERCE
*










*
DISTRIBUTE
TO INDUSTRY






                                                                   83-2061-44
        Figure 4-6.   Institutional Assessment for Educational Program
                       to Control Chemical Substances
Cost Analysis.    Cost  analysis  determines  the  additional  funds  needed  to
implement a control alternative,  including capital improvements and operation
and  maintenance.   Additional  administrative  costs  are  Less  significant
because most  of these projects  are undertaken  by a  public agency  that  is
already performing the function to some extent.

Capital cost estimates are  best prepared by  the water quality  planner with
the assistance  of  the municipal engineer  and in some  cases his/her outside
engineering advisor.  These estimates identify  all  costs  related to the pur-
chase of a new  facility  or  piece of equipment  for  a  project and may require
some research  into vendor  prices  and  bids on  similar projects  around the
country.  For  programs  which require  changes to existing practices  (street
sweeping, etc.), the  cost  attributable to  the  water quality  program is the
incremental cost of the program.

Ultimately, the  cost  analysis is used  to identify the least-cost method(s)
for reducing pollution problems.  It is  important to remember that all  costs
associated with a  given  program  must  be considered.   It  is incorrect to as-
sume that  educational efforts,  for  example,   are  provided  at  nc additional
cost.

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As an example of a cost analysis,  a  possible budget  sheet for the educational
program for the current year is  presented  in Figure  4-7.
ACTIVITIES
1. DEVELOP BROCHURE
2. PRINT BROCHURE
3. DISTRIBUTE BROCHURE
4. CONDUCT INFORMATIONAL
MEETINGS
5. STAFF FOUOWUP
FOR PROGRAM
TOTAL
AGENCIES
STATE



$2.000

S 2.000
COUNCIL
OF
GOVERNMENTS



S 5,500
S 24,000
$29.500
DEPARTMENT
OF
POLLUTION CONTROL



$2,000

S2.00D
DEPARTMENT
OF
PLANNING

S 1,500
$ 800


52,300
PUBLIC
INFORMATION
CENTER
« 13.000




$13.000
TOTAL
$13.000
$ 1.500
$ 800
$ 9.500
$24,000
$48.800
         Figure 4-7.  Cost Analysis for Educational Program to
               Control Chemical,  Herbicide, Fertilizer and
                            Pesticide Runoff
Revenue Analysis.  After the program cost estimate is prepared, the potential
sources  of   revenue  ,*re   analyzed.   There are several critical  factors in
analyzing revenue for urban runoff programs including:

     -  Cost/Revenue Balance -  Will the revenues be  sufficient  to cover
        the costs on an annual  basis?
        Equitable Allocation of Costs to  Different  Groups  - Do those who
        contribute  to  the problem  pay  their fair  share?   Do  those who
        benefit from the program pay their fair share?

        Revenue Agreement - Do groups understand their participation in a
        program and  its  revenue formula?  Have written  agreements which
        define the cost allocation procedure been prepared ?

Revenue analysis  will  vary with the type  of  control  approach selected.  The
critical factor in the revenue  analysis  is the  identification of each entity
that  will  provide revenues and the development of an understanding by that
entity of the problem, the control approach, and its share of the cost.

Ability-to-Pay Analysis.  Most  of the costs  to  control runoff from  developed
areas are imposed on the general public or the benefiting population as a new
and  additional  governmental  expense.  The  ability-to-pay  'analysis  evaluates
this  increased  burden on  the  local  community  as  a  percentage  of property
taxes, average income, property evaluation, or other appropriate measures.

Figure 4-6 illustrates an abiiity-to-pay analysis for the educational program
example.  The key parameters  to determine homeowners'  ability to pay in this
case  are the cost of the program per household,  cost as a percentage of aver-
aqe  annual household income,  and cost as a percentace of prooertv taxes.

-------
       A. TOTAL PROGRAM COST (ONE-YEAR PROGRAM)

       B. NUMBER OF HOUSEHOLDS AFFECTED

       C. COST PER HOUSEHOLD
           IA DIVIDED BY B)

       D. MEDIAN  HOUSEHOLD INCOME

       E. COST AS A % OF MEDIAN HOUSEHOLD INCOME
           1C DIVIDED BY D TIMES 100)

       F. AVERAGE ANNUAL PROPERTY TAXES

       G. COST AS A % OF PROPERTY TAXES
           1C DIVIDED BY F TIMES 100)
$48,000

 19,000



$14,700



$ 1,200
$2.57
.02%
           .21%
     CONCLUSION: PROGRAM APPEARS TO NOT PLACE EXCESSIVE BURDEN ON
               LOCAL HOMEOWNERS
      Figure 4-8.  .Ability to Pay Analysis  for Educational Program
             to Control Chemical, Herbicide,  Fertilizer and
                            Pesticide  Runoff
Sensitivity Analysis.   The  sensitivity analysis will  vary depending upon the
revenue mechanism  and program  selected  for implementing  a proposed program.
The  most   common  revenue  mechanisms  for  programs  controlling  runoff  from
developed  areas  are  general  funds  and  fees.   Analyzing  the  sensitivity  of
general  revenues  requires  a   review  of  past  collections  relative  to  key
parameters—inflation,  housing  starts,  collection  rates,  capital  improve-
ments,  and  so on.   Collections are then projected  for worst  and best  case
scenarios.

An additional  consideration in the  sensitivity analysis  is revenue  require-
ments.  This  relates to phasing  a  program, either  handling capital  improve-
ments  or  starting  a  program on  a   limited  basis with expansion  to  come  in
later  years.   For  any  one  program, numerous   options   exist for  staggering
cash  flows,   and  different  scenarios  should  be  developed tc  assess  their
impact on the program as part of  the sensitivity analysis.

Indirect  Impact.   The  indirect  impact  of  a  runoff  control  program  for
developed  areas  are  extremely  difficult  tc quantify.   Educational  programs
will  raise  community awareness regarding the  impacts  of local  activities on
water pollution.   Other indirect impacts  from  control programs  may relate to
recreational  benefits,  local  improvements  in quality  of  life,  and increased
tourism.

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RELATIONSHIP BETWEEN NURP AND WQM PLANS

Of the locations selectee for projects under the NURP effort,  some 80 percent
had state-approved  (i.e., certified by the Governor)  water quality management
(WQM)  plans with elements which addressed urban runoff.   For 5 of these loca-
tions, the  NURP project  constituted  the urban  runoff  element of the  plan.
For the other  locations,  however,  the original 208 effort was unable  to  de-
velop the necessary information  on either water quality  effects  or  perform-
ance  of  best  management  practices  (BMPs)  to  justify  structuring  formal
implementation plans for urban runoff control.   Consequently,  the typical  WQM
plan  elements  dealing  with  urban  runoff  identified  the  need   for  further
study, usually specifying problem  assessment and BMP performance evaluation.
These elements became the focal points of the activities funded by NURP.

The WQM plans  for  the  remaining  20 percent of the  locations which  partici-
pated in the  NURP program did not  contain a  specific  urban  runoff  element.
Presumably this was due to time and resource constraints in relation to other
issues which were  assigned  higher priorities  in planning efforts.  In these
cases, the NURP projects  provided  the opportunity  to address a water quality
issue not adequately addressed in the original 208 planning studies.

Over two-thirds of the NURP project locations reported that NURP  findings and
recommendations have  or will be  incorporated  in  the  next annual update of
their formal  WQM  plans.  The  remainder generally indicate  that they  expect
the planning issues to  be addressed at the local  level  or that NURP results
will support planning and implementation activities,  even though they  do not
anticipate formal incorporation in WQM plans at this time.

Over half  of  the  NURP project locations  report  either  active or planned im-
plementation efforts based on the  results of NURP..  Thirty percent  indicated
that no implementation  is being  planned because the need for  or  value  of ur-
ban runoff  control was  not demonstrated.   The balance  (20  percent)  of the
NURP locations suggest that while implementation activities are  not  currently
planned, they  expect  NURP results to  influence  future  deliberations on  this
issue.
                               4-17

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                                 CHAPTER  5
                             METHODS  OF ANALYSIS
INTRODUCTION

This chapter identifies and briefly  discusses the methods adopted to assemble
and  analyze  the large  data base developed  by the  NURP projects  and also
provides the methods employed to develop and interpret results.  The chapter
is  structured  according  to  the three  prime  areas  of program  emphasis;
(1) characteristics of pollutants in urban runoff, (2) water quality effects
of urban runoff discharges  including water quality criteria/standards  viola-
tions and impairment or denial of beneficial uses of receiving water bodies,
and  (3)  the effectiveness of control measures to reduce pollutant loads.

The  procedures  employed  in this assessment were  designed  to provide  gener-
alized  results and  findings  about  urban  runoff  issues  of  interest  for
nationwide use.   This national  perspective,  and  the  need  to  consider  the
fundamental variability of urban runoff processes, has prompted  some  signif-
icant advancements in tjhe application of  statistical methods  and  models.   The
basic methods  used  were,  however,  largely developed  under  different  EPA
efforts, many  under  the  sponsorship of the Office of Research  and  Develop-
ment, or  other programs.   In  some  cases, similar  or equivalent  procedures
were applied in individual NURP projects; in other cases, methods  adopted by
individual projects in response to  local needs and interests were  different.
Where possible, comparisons  have been made  between either detailed  results,
or  conclusions drawn  from  such  results, as  derived  from  both  local  and
national perspectives.

The  descriptions provided in this chapter are brief  and  intended to communi-
cate  the  technical  framework upon  which the. results  and   conclusions  are
based.  More detailed information on the methods and  techniques are contained
in other documents developed by NURP.  Pertinent NURP reports cover, in sepa-
rate  volumes,  probabilistic  methods  for  analyzing  water  quality  effects,
detention and  recharge basins for  control of  urban stormwater  quality, and
street sweeping'for control of urban stormwater quality.   The Data Management
Procedures Manual, another  of the project documents,  is  an additional  source
of information on details of the analysis methods utilized.

Because field measurements and sampling  formed one of  the  most important  in-
formation sources, it was essential  that the monitoring and  analysis programs
produce  consistent and  sound  data.   Accordingly,  NURP  required  that  all
projects adopt  Quality Assurance/Quality Control elements  as integral  parts
of their work plans.  Key components of these plans include  the  following:

     -  Program Coordination.   Projects  were  required  to  designate  a
        QA/QC coordinator, responsible for the entire QA/QC  effort.

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-  Field Quality Assurance.  Guidance was provided to  the  projects
   for all key aspects of the data collection process.

   Laboratory Quality Assurance.  A manual prepared by EPA's  Envi-
   ronmental Monitoring and  Support Laboratory was provided  to all
   projects and contained analytical quality  control  information.

-  Data Management.  A manual entitled "Data  Management Procedures"
   was provided  to all  projects  and covered  such  topics as  data
   formatting, data reduction, and some analysis.

-  Data Analysis.   To encourage innovative  approaches and respon-
   siveness to  local  conditions,  uniform methods of  data  analysis
   were not  stressed.   Technical  guidance and mandatory  review of
   analytical procedures were provided.

I RUNOFF POLLUTANT CHARACTERISTICS

•al

•stantial  component of the individual NURP projects  was the acquisition
 subsequent  analysis)  of & data base for  a number  of storm events,  con-
ng  of precipitation  and  the resulting quantity and  quality  of runoff
a number of local urban catchments.  One of the principal  EPA  objectives
 e  analysis  of tvhese data  has  been to develop a concise  summary of the
 rteristies of urban runoff.   There are a  number of questions  concerning
  runoff  characteristics  which  need to be  addressed  for  water quality
 Lng purposes, including what are the appropriate measures  of the statis-
 characteristics of urban  runoff  (e.g., population distribution, central
 icy,  variability,  etc.)?   Do distinct subpopulations  exist and what are
  characteristics?   Are  there  significant   differences   in  data  sets
 ;d  according to  locations around  the  county  (geographic zones),  land
 season, rainfall  amount,  etc.?  How may these variations  be  recognized?
 .s the most appropriate manner  in  which to extrapolate the existing data
 to locations for  which there  are no or  limited  measurements?  Though
 questions cannot  be  fully answered given the  current  state  of knowledge
 rning  urban  runoff,  these  are the  types   of  issues  addressed by  the
 Is described  in this  chapter and  the  results presented in  Chapter 6.

 rincipal  thrust of the individual  NURP projects,  and  thus  this  nation-
 assessment  report, was the characterization of  what has  been adopted as
 lard  Pollutants"  of  primary  concern in  urban runoff.   These  include
 ;,  oxygen consuming  constituents,  nutrients,  and a  number of  the more
 •ly  encountered heavy metals.   The methods  used  to  characterize  these
 rd pollutants  are described under a  separate  heading below.

  roximetely  two-thirds of the NURF projects the occurrence  of compounds
  s  list of  "Priority  Pollutants"  was  investigated.   This  program element
 so describee under a separate  heading below.  A  number of  additional
   have also  been  addressee  in  the program.   These  are briefly discussed

-------
bolow because they  relate  closely  to the general issue of pollutant charac-
teristics.  These include the following:

     -  Soluble  vs  Particulate Pollutant  Forms.   The  distribution of
        soluble  and  particulate  forms of  a pollutant  in urban  runoff
        (particularly metals  and  nutrients)  was examined  in both  the
        standard  conventional pollutant  and priority pollutant  aspects
        of  the  study  because  certain  beneficial  use  effects  depend
        strongly  on the  form in which the contaminant is present.   The
        priority  pollutant   program  additionally  determined   "Total
        Recoverable" fractions, corresponding to contaminant  forms  used
        in EPA's published toxic criteria guidelines.

     -  Coliform Bacteria.  Fecal  coliform bacteria counts  (and  in  some
        cases total  coliform and  fecal streptococcus as  well)  in urban
        runoff were monitored  during a significant number of storms by
        seven of  the NUKP projects.   Though the data base  for bacteria
        is restricted,  useful results are provided in Chapter €>.

     -  Wetfall/Dryfall.   As  part  of  program  elements  designed  to
        examine  sources  of  pollutants  in  urban  runoff,  a  number  of
        projects  operated  atmospheric  monitoring  stations  for  char-
        acterizing pollutant  contributions  from precipitation {wetfall)
        and from dry weather deposition  (dryfall) .  Results of this work
        are  reported In  individual  project  reports  and n9t  included
        herein.

Standard Pollutants

The following constituents were adopted as standard pollutants characterizing
urban runoff:

                        TSE - Total Suspended Solids
                        BOD - Biochemical Oxygen Demand
                        COD - Chemical Oxygen Demand
                        TP  - Total Phosphorus  (as P)
                        SF  - Soluble Phosphorus  (as P)
                        TKN - Total Kjeldahl Nitrogen  (as N)
                    NO  q-N - Nitrite + Nitrate  (as N)
                        Cu  - Total Copper
                        Pb  - Total  Lead
                        Zn  - Total  Zinc

The  list  includes pollutants of general  interest which are  usually examined
in  both point  and  nonpoint  source  studies and  includes representatives  of
important  categories of pollutants—namely  solids,  oxygen consuming constitu-
ents, nutrients,  and heavy metals.

The  pollutant concentrations  found  in urban  runoff  vary considerably,  both
during  &  storm  event, as well  as from  event to  event  at  a given site and from
site  to site  within a given  city and across the country.  This variability is
the  natural  result of  high  variations  in rainfall intensity and occurrence,

-------
m-oui aphic  features  that affect  runoff quantity  and  quality,  and  so on.
Considering this  situation,  a  measure of the magnitude of the urban runoff
pollution level and methods  for characterizing  its variability were  needed.
The event  mean concentration  (EMC),  defined  as the  total constituent mass
discharge divided  by the  total runoff  volume, was  chosen  as  the  primary
measure of the pollutant load.  The rationale for  adopting  the EMC  for  char-
acterizing urban runoff  is  discussed  in the receiving  water  effects  section
of this chapter as well  as  in subsequent chapters.   Event mean concentrations
were calculated for each event at each site in  the  accessible data  base.   If
a  flow-weighted  composite  sample was  taken,  its  concentration  was  used  to
represent the  event  mean concentration.  Where sequential discrete  samples'
were taken  over  the  hydrograph,  the event mean concentration was  determined
by  calculating the area  under the  loadograph  (the  curve of  concentration
times discharge rate over time) and dividing  it by the  area under  the hydro-
graph  (the  curve of runoff  volume  over time).  Details of  the  calculation
procedure have been described  in the Data Management  Procedures  Manual.  For
the purpose  of determining  event mean  concentrations,  rainfall events were
defined  to  be separate  precipitation  events  when  there was an  intervening
time period of at least  six  hours without rain.
                                            \
A  statistical  approach was  adopted  for  characterizing the properties of EMCs
for standard pollutants.  Standard statistical procedures were used to define
the probability distribution,  central tendency  (a  mean  or median)  and spread
 (standard deviation or  coefficient  of  variation)  of EMC  data.   EMC data for
each  pollutant  frqji  all storms  and  monitoring   sites were  complied  in  a
central data base management system at the National Computer Center.  The SAS
computer  statistical  routines  and  other standard statistical  methods were
used to explore and characterize the data.  The statistical methods used are,
for  the most  part,  not explained  in  this  report since these  are readily
available  in  the literature.  Nor  are the operations  of  the  SAS routines,
which are available at most computer centers.

The  underlying probability  distribution of  the  EMC data was  examined and
tested by both visual and statistical  methods.  With  relatively few  isolated
exceptions, the  probability distribution of EMCs  at  individual  sites can be
characterized  by  lognormal  distributions.   Given  this,  concise characteriza-
tion  of the variable urban  runoff characteristics at  each of  the sites is
defined by  only  two values,  the mean  or median and the coefficient  of  varia-
tion  (standard deviation.divided by mean).  Because the underlying  distribu-
tions  are  lognormal,  the   appropriate  statistic  to  employ  for comparisons
between  individual  sites or groups of sites  is the median value, because it
is less  influenced  by the small number  of  large  values typical of  lognormal
distributions  and,  hence,  is  a  more  robust  measure  of  central  tendency.
However,  for  comparisons  with  other  published   data  which  usually  report
average  values and  for  certain computations  and  analyses  (e.g., annual  mass
 loads), the mean value is more appropriate.

Relationships  among a number of statistical properties  of  interest  are  easily
determined  when  distributions are  lognormal.   Figure 5-1  illustrates  some
 relationships  for lognormal distributions.   In  (a)  the frequency  distribu-
 tions  of  two variable  data  sets  which are  loo-normal  and have  the  same
median  are   shown.  The loo transforms  of the  date  result  in   normal  bell

-------
     3.0
     2.5
o    2.0
sS
     1.5
     1.0
       (c)
MEAN AS
MULTIPLE OF MEDIAN
FDR LOG NORMAL
DISTRIBUTIONS
                        1.0

                       COEF  Of VARIATION
                                          2.0
                                2.6
                                     90TH PERCENTILE AS
                                     MULTIPLE OF MEDIAN
                                     FOR LOG NORMAL
                                     DISTRIBUTIONS
                   O.b      1.0       1.6       2.0

                           COEF OF VARIATION
                                   2.5
          (a;
      '. ifotier.  Reietionsnins

-------
shaped distributions; more  variable data  (higher  coefficient of  variation)
result in  a greater  spread.   Frequency histograms  prepared using  untrans-
formed  data values  produce  skewed  distributions,  as  shown  by  (b)  which
illustrates two data sets which have the same arithmetic  mean.  The effect  of
coefficient of  variation  is shown as well  as  the  relation between  mean and
median  for  lognormal  distributions.   An  established  relationship  exists
between median and mean, as shown by (c) and described  by:
                          Median
                                              var)
When a  distribution  is  known to be lognormal the best estimate  of  the popu-
lation  mean * is  that  derived  from the  lognormal  relationships.  For small
samples  it  can be  expected  to be different than  the  result of a  straight
arithmetic  averaging of sample data; the two estimates of  the mean  will give
similar values when the number of samples is very large.

In addition, the expected value at any probability or frequency of occurrence
(X ) can be determined by:


                          X -  exp  (u,   + Z  a.  )
                           a         Inx    a  Inx

where :
                   ••*
     Z    =  the standard normal probability              '

     p,   =  mean of log-transformed data
      Inx              r

     o.   =  standard deviation of  log-transformed data
      ^ J 1 *v

X  can  be expressed  as . a  ratio to the median value by the following  equation

which defines the ratio in terms of the  coefficient of variation

                   X
                        = exp  (Z V In  (1 +  (Coef Var) 2) ) .
                 Median         a

This  relationship  is  shown  by  (d) for  90th percentile  values  (10 percent
exceedance, Z  = 1.2817).

The  establishment  of  the  fundamental  distribution  as  lognormal,  and  the
availability  of  a  sufficiently  large  sample population of  EMCs to provide
reliable derived statistics,  has a  number  of  benefits:

     -  Concise summaries of  highly variable  data  can be  developed.

     -  Comparisons  of  results from  different  sites, events,  etc.,  are
        convenient  and are more easily understood.

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        Statements can be made concerning frequency of occurrence.  One
        can express how often values  will  exceed various magnitudes -of
        interest.

        A more useful method of  reporting data  than  the use  of  ranges  is
        provided; one which is less  subject  to  misinterpretation.

     -  A framework is provided for examining  "transferability" of  data
        in a quantitative manner.

Priority Pollutants

In  cooperation, with  EPA's  Monitoring and  Data  Support  Division  (MDSD),  a
special study element was built into  two-thirds  of  the NURP projects  (20  of
28)  to identify which of the compounds on EPA's list of "Priority  Pollutants"
are found in  urban  runoff,  and  the  concentrations at which they  occur.   The
base  effort  collected 121 samples of  urban runoff which were analyzed  for
priority  pollutants.    A   supplementary   special   metals  study   secured
147 samples.  Methods  utilized  in this  study  element  are  described  in  the
following report which covers this activity:

     "NURP Priority Pollutant Monitoring  Project:  Summary of Findings",
     December 1983; EPA Monitoring and Data Support Division,  Office  of
     Water Regulations and Standards,  Washington, D.C.
                      f-
In  addition  to  the above special study, as previously mentioned,  most  NURP
projects  monitored  selected  heavy  metals   (principally  total copper,  total
lead,  and  total zinc)  in  their  routine monitoring programs.  Summaries  of
these data are presented in Chapter 6.

Hydrometeorological Statistics

Consistent with the adoption of a  storm "event" as the fundamental time scale
used in the analysis of data and the interpretation of effects, rainfall clata
were analyzed to define "event" statistics  for a significant number of loca-
tions throughout the  country.  The SYNOP program was  employed for developing
the  statistical parameters  of  rainfall  intensity,   duration,   volume,   and
interval between  storm  events.   This  program  has  been detailed  in the NURP
"Data Management Procedures Manual."

In addition to rainfall, rainfall-runoff relationships were characterized  for
monitored  storm events.  The  runoff   coefficient,  defined  as the  ratio  of
runoff volume to rainfall volume,  was  computed, and effects of such catchment
characteristics as  land use  and  imperviousness were investigated.  Long-term
streamflow  records  for  numerous  stations across the  country  were  also
analyzed to characterize regional  trends.

RECEIVING WATER QUALITY EFFECTS

General

A number  of individual NURF  projects examined  the  site-specific  impacts, of
urban runoff  on water qualitv  for £ variety of beneficial  uses and receivinc

-------
water types.   These results provide  important  information on the  extent  to
which urban runoff constitutes a "problem" as well as "Qround truth" measure-
ments against  which more  generalized techniques  car:  be  compared.   Method-
ologies • employed  in  these  local  studies  vary  enc  ere  described  in  the
individual project reports.  Relevant site-specific proiect results are cite'd
in Chapter 8.

Receiving water  impact analyses cannot be readily  generalized  because there
is a  high degree of site-specificity to the  important  factors.   The  type of
beneficial use dictates the pollutants  which are of principal  concern;  the
type  of  water body  (e.g.,  stream,  lake,  estuary)  determines  how receiving
water quality  responds to  loads;  and physical characteristics  (e.g.,  size^
geometry,  flows)  have  a major  influence on  the  magnitude of  response  to a
particular load.

Despite  the  inherent limitations  of a set of generalized receiving water im-
pact  analyses, a' screening  level  analysis was considered a necessary element
for  a nationwide assessment of the general  significance  of  urban runoff in
terms  of water •quality problems,  especially adverse  effects  on beneficial
uses.  Accordingly,  a  set of analysis methodologies were  adopted and utilized
as  screening  techniques for  characterizing  water  qualitv effects  of urban
runoff  loads  on  receiving  water bodies.   A  key requirement was to delineate
the  severity  of  water quality problems by quantifying  the magnitude,  and in
the  case  of  intermittent  loads, the frequency of occurrence of water quality
impacts  of  significance.   These   procedures are  identified  and described
briefly  below.  Significant  technical aspects  are detailed  further  in the
supplementary  NURF  report which addresses  the receiving water  impact analysis
methodology.

It was  not possible  to perform  a  "National Assessment"  in  the usual sense of
the  term.  NURP  has determined that  it  is  not  realistic  (if  the basis is
effect  on beneficial  use  of  a  water  body)  to estimate  the  total number of
water quality  problem  situations  in the  nation which result from  urban storm-
water runoff  or  the  cost  of  control which would  ultimately  result.   The
available analysis  methods  do permit an  assessment  of a different  kind.   NURF
applied  the  analysis  procedures  as a screening  type  analysis to define  the
conditions under  which problems of different  types  are likely  or  unlikely to
occur.   From the results of these  screening analyses, NURP has drawn  infer-
ences and made general statements  (Chapters 7 and 9)  on  the  significance of
urban runoff.   Where   it  has   been possible  or  practical  to co so,  these
general   screening  analyses were   applied  to  local  situations  which  exist
within   certain  of  the individual  NURF  projects.    Comparisons  were  made
between  specific water quality effects  or  broader  conclusions   relative  tc
problems derived  from  both  local  analysis and general screeninq methods.

Time Scales  of Water Quality  Impacts

There are three  types  of water  quality  impacts  associated with urban  runoff.
The  first type is  characterized by rapid,  short-term changes in water duality
during  and shortly  after storm  events.   Examples cf this water quality "impact
 include  periodic dissolved oxygen depressions  cue tc  oxidation  cf  contami-
nants,  or short-term  increases ir.  the receiving water

-------
or more toxic  contaminants.   These  short-term, effects  are believed to be  an
important concern and were the prime focus  of,  the NURP  analysis.

Long-term water quality impacts,  on  the  other  hand,  may be  caused by contami-
nants associated with suspended solids that settle  in receiving waters  and  by
nutrients which enter receiving water systems with  long retention times.   In
both instances, long-term water quality  impacts  are  caused  by increased resi-
dence  times  of  pollutants  in   receiving waters.  Other  examples  of  the
long-term water quality impacts include depressed dissolved  oxygen caused  by
the  oxidation  of organics  in bottom sediments,  biological  accumulation  of
toxics as a result  of up-take by organisms in the  food chain, and increased
lake entrophication as a  result of  the  recycling of nutrients contributed  by
urban runoff discharges.   The long-term  water  quality impacts of  urban  runoff
are  manifested  during critical periods normally  considered  in  point  source
pollution studies,  such as summer,  low  stream flow  conditions, and/or  during
sensitive  life cycle  stages of  organisms.   Since long-term water  quality
impacts occur during  normal  critical periods, it is necessary to dirtinguish
between the relative  contribution of urban runoff  and the  contribution from
other sources, such as treatment plant discharges  and other nonpoint sources.
A site-specific analysis  is required to  determine  the  impact of various types
of  pollutants  during critical  periods,   and  this aspect  of  urban  runoff
effects was not addressed in detail  in NURP.

A third type of receiving water impact is  related  to the  quantity or physical
aspects of flow and includes short-term  water  quality  effects caused by scour
and  resuspension  of pollutants  previously  deposited in the  sediments.  This
category  of impact was   not addressed by NURP,   in  general,  although  one
project provides some information.

As indicated previously,  the first type  of change  in water quality associated
with discharges from  urban runoff is  characterized  by  short-term degradation
during and  shortly  after  storm events.  The rainfall process is highly vari-
able ,in  both  time  and space.   The  intensity of  rainfall at  a  location  can
vary from minute  to  minute  and  from location to  location.   Phenomena which
are  driven by rainfall such as urban runoff and associated pollutant loadings
are  at least  as variable.   Short   term  measurements,  on  a time  scale  of
minutes,  to define  rainfall, the runoff flow hydrograph,  and concentrations
of  contaminants  (pollutographs)  feasibly  can be  taken  at  only a   rather
limited number  of locations.  These measurements  have usually been employed
in  an  attempt to refine  or  calibrate calculation  procedures for estimating
runoff  flows 'and  loads.   Most  urban  areas"  contain   a  network  of  drainage
systems which  collect and discharge urban  runoff  into one or more receiving
water bodies.   Since  the  rainfall,  runoff, and pollutant  loads  vary  in both
time and  space,  it  is impossible to  determine  by  calculation or  measurement
the  very  short time  scale  (minute-to-minute)  changes  in  water  quality of a
receiving  water  and  assign the  changes  to  specific   sources  of   runoff.
Although  very short duration exposures  (on the order of minutes)  to very high
concentrations  of toxics  can produce environmental damage  (mortality  or sub-
lethal  effects)  to  aquatic  organisms,  it  is  likely  that  exposures  on  the
order of  hours  have the  highest  possibility cf causing adverse  environmental
impacts.   This  results,  in  part,   from   the  smoothing  obtained  by  mixing
numerous  sources which have high frequency  (short-term) variability.

-------
              In view of the above discussion, the time scale used by NURF  for  analysis  of
              short-term receiving water impacts is the rainfall event time  scale which  is
              on the order of hours.  To represent the average  concentration of pollutants
              in urban  runoff produced  during  such  an  event,  NURF  used  the  event  mean
              concentration.

              Criteria/Standards and Beneficial  Use Effects

              As discussed  in previous  chapters,  three  definitions have been  adopted  to
              assess receiving water problems associated with urban runoff;  (1) impairment
              or denial  of beneficial  use,  (2)  violation of numerical  criteria/standards,
              and  (3) local perception  of a  problem.   The procedures and methods  employed
 ;             in the NURP assessment focus on the  first two problem definitions.  A frame-
 ;             work  for  identifying target receiving  water  concentrations  associated  with
              the  criteria standards and beneficial  use  problems  are provided  below.   The
              third  problem  type,  local perception  of  a problem  and  degree  of  concern
              cannot be addressed by these quantitative procedures.

              The  analysis methods employed make  it  possible  to project  water  quality ef-
              fects  caused  by  intermittent,  short-term  urban runoff  discharges.   Where
              appropriate, these effects are  expressed in terms  of the frequency at which a
              pollutant concentration in the water body is equalled or  exceeded.  However,
              if the basis for  determining the  significance  of such water  quality impacts
              (and  hence  the  need for  control)  is taken to be the effect  such receiving
              water  concentrations  have on  the  impairment  or  denial  of a  specific bene-
              ficial use, then it"is necessary to go one  step further.  ^A basis is required
              for  judging the degree to which a  particular water quality  impact constitutes
;              an impairment of  a beneficial  use.  With  intermittent  pollutant discharges,
              effects are variable and are best  expressed in  terms of a probability distri-
              bution from which  estimates can be made of the frequency with which effects
              of various magnitude occur.

•;'              There  is  a  rather broad  consensus that  existing  water  quality criteria,  and
              water uses based on such criteria, are most relevant when considered  in  terms
              of  continuous  exposures  (ambient  conditions).   Even where  continuous  dis-
              charges are involved,  there has been  discussion  and debate  as to whether a
              particular criterion should be interpreted as some appropriate "average" con-
              dition or a "never-to-exceed"  limit.   The basic issue  is whether  the  more
'•...             liberal interpretation will provide acceptable protection  to the beneficial
;              use  for which the  criterion in  question has been  developed.   The  only  reason
:'             such distinctions  become  an issue is  because  the practical feasibility  or
|            . relative  economics,  or both,  are  sufficiently different  that one is  encour-
              aged to  question  whether  the more restrictive interpretation is overly  (or
•              even excessively)  conservative  in terms of providing protection for  the  as-
.':             sociated beneficial use.

'I             The  issue (i.e.,  whether  traditional  ambient  criteria  are excessively con-
.?             servative  measures  of  conditions  which  provide  reasonable  assurances  of
I             protection  for  a  beneficial use  when  exceeded • only  intermittently)  is par-
              ticularly  appropriate  in  the  case of urban storm runoff.  Analysis  of  rain-
              fall records  for   a  wide  distribution  of  locations  in  the nation  indicates
              that,  even in the wetter'parts of the country, urban  runoff events occur only
                                                   5-10

-------
   *ix,n!t  'JO percent -of  the time.   There .are regional  and seasonal difference
fv ;)iin  typical  values for annual  average  storm characteristics  in  the east*
   }j*> l: of the United States are:

Storm Duration
Interval Between
Storm Mid-Points
Average
(Hours)
6
80
Median
(Hours)
4.5
60
90th Percentile
(Hours)
15
200
          estimates are based on results  from an analysis of long-term rainfc
          t>  for  40 cities  throughout the  country.  Median  and  90th percenti
         i are  derived  from  data mean and variance  based  on a  gamma distributee
          has been shown to  characterize  the underlying  distribution  of  stc
      ptvl  parameters quite well.

           semi -arid regions  of  the western half  of the country,  average  stc
      rations  tend to be comparable  to  the above,  but average  intervals betwe
               storms increase substantially  (two  to  four  fold)   and  are high
      )IH>h*il.   With urban storm runoff,  therefore,  one is dealing with pollute
               which occur  over  a  period  of  a few  hours  every  several days
         OT  after  long dry  periods.   In advective  rivers and streams, the wa1
         influenced by urban  runoff  tends  to  move  downstream in  relatively di
          pulses.  Because 'of the  variability in the magnitude of the pollute
       8*  from different storm events,  only a small percentage  of these puls
              pollutant concentrations.

      |jr,f-  6»e currently no formal "wet weather" criteria and,  thus, no  genera]
        pt*<3  way  intermittent exposures  having time scale characteristics typic
              runoff can be  related to use  impairment.   In  the  belief that
       ||l"Jir  inappropriate to ignore such  considerations in  a general  evaluate
             runoff, NURP has developed estimates  for  concentration  levels  whi
           in  adverse  impacts on beneficial  use when exposures  occur  internu
           at intervals/durations   typical  of  urban   runoff.    These  "effec
          ** were  used to interpret  the significance of the variable,  intermitte
          quality  impacts of urban runoff.   It  should  be understood  that  th«
          t*  levels do  not  represent  any  formal position taken  by EPA, but £
           the most reasonable yardsticks available to  meet  the . immediate  nee
        |>t' ^valuation of urban runoff.  As used  in the  screening analysis  proc
        fc , alternative  values for  "effects levels"  may be  readily  substitul
         fcithcr more accurate estimates can be made, or more  (or less) consen
         approaches are indicated in view of the importance of  e  particular wa1
         OJ  beneficial use.

        * £••.-]  Kummarizes  information on water quality  criteria  for  a  number
                  routinely   found  in  urban  storm  runoff.   The  data  present
            Koior quality criteria  for  substances on EPA's  priority pollut-
            fl,,i.  list  (45 FR No. 79316,  11/28/80).   These   criteria  provide

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                                         TABLE  5-1.    SUMMARY  OF  RECEIVING  WATER  TARGET  CONCENTRATIONS USED  IN
                                                                  SCREENING  ANALYSIS  -  TOXIC SUBSTANCES
                                                           (ALL  CONCENTRATIONS  IN MICROGRAMS/LITER,
(n
 I
I-'
                                    NOTES:
Contaminant.
Connor



Zinc



Lead



Chrome (*3)

Chrome (+6)
Cadmium


Nickel


Water
Hardness
mg/1
(as Ca C0?)
50
100
200
3 00
50
100
200
300
50
100
200
300
50
100
300
-
50
100
300
50
100
300
Freshwater
Aquatic Life
24 Hour
5.6
5.6
5.6
5.6
47
47
47
47
0.75
3.8
12.5
50.0

(44)
(0
0.29
0.01
0.02
0.08
56
96
220
Max
12
22
42
62
ieo
321
520
ROO
74
172
400
660
2,200
4,700
15,000
21.0
1.5
3.0
9.6
1,090
1,800
*,250
Saltwater
Aquatic Life
24 Hour
4.0 -
4.0 *
4.0
4.0
58
58
58
58

(25)

(C)

N.P.
18

4.5


7.1

Kax
23
23
23
23
170
170
170
170

(670)

(A)

(10,300)
(A)
1260

59.0


140.0

Human
Inqestion
(1)
NP



NP




50.0



170.00
50.0

10


13.4

Estimated Effect Level
For Intermittent
Exposure
Thresh-
hold
20
35
80
115
380
680
1.200
1,700
150
360
850
1,400

8,650

3
6.6
20



Siqni f icant.
Mortality
50 - 90
90 - 150
!.?0 - 350
265 - SOO
870 - 3,200
1.550 - 4,500
2,750 - 8,000
3,850 - 11,000
350 - 3,200
820 - 7,500
1,950 - 17,850
3,100 - 29,000



7 - 160
15 - 350
45 - 1,070



                                      NF - No  criteria  proposed.
                                      Some toxic criteria are related  to Total  Hardness of  receiving water.  Where this applies,  several values  are shown.  Other
                                      values may he calculated from equations presented in  EPA's Criteria Document (Federal Register, 45,231,  November 28, 1980).
                                      Where a  single value is shown, water hardness does not influence  toxic criteria.
                                      Concentration values shown  within parentheses ( ) are not formal  criteria values.  They reflect either chronic (C) or acutf
                                      (A) tnxicity concentrations which the EPA toxic criteria document  Indicated have been observed.  Values  of  this type were
                                      reported where the data bast was insufficient (according to the formally adopted guidelines which were used  in developing  the
                                      criteria) for EPA to develop 24 hour and  Max values.
                                      Mote (1):  The "Human Ingestion" criteria developed by the EPA Toxic Criteria documents are indicated to relate to ambient.
                                      receiving water quality. The Drinking Water Criteria relate to finished water quality at the point of delivery for
                                      consumption.
                                      Estimated Effects levels reflect estimates of the concentration levels which, would impair beneficial uses under the kind of
                                      rxnnsiire conditions which would be produced by Urban  Runoff.   They are ar. estimate of the relationship between continuous
                                      exposure and intermittent,  short duration exposures (several  hours once every several days).  Threshold  concentrations  are
                                      these estimated to cause mortality of the most sensitive individual of the most sensitive specits.
                                       innificant Mortality concentrations are  shown as  a range which  reflects 50  percent of the most sensitive  species and
                                       nrtalMy of the most sensitive individual of the  25th^^enti 1* species sensit.iv. ty.

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        an  extensive  set  of  numerical values  -derived  from  bioassay
        studies.

        Estimates  of  "effects  levels" which  are  suggested by  NURP  an-
        alysis  to be  relevant  for the  intermittent exposures  charac-
        teristic of urban .runoff.

By  incorporating  the  numerical   values  for  EPA's  ambient  water  quality
criteria  and the  concentration  levels  suggested by  NURP for  intermittent
effects in the  same  table  (or on the  same graph  in  Chapter 7),  a convenient,
concise comparison is  provided of  the practical  implications  of applying one
or  the  other as  the  yardstick  for judging  the  protection or  impairment  of
water use.  The two sets of numerical values thus provide measures for two of
the  three  options for defining a  problem:   violation of  criteria  or actual
'impairment of a beneficial use.

Comparison of  the pollutant concentrations  in urban  runoff  showing the  fre-
quency  and  magnitude of  exceedance  of  ambient  criteria and  intermittent
effects levels  provides  a  qualitative sense  of the  control requirements (and
implications  regarding costs)  attendant  on the  adoption of  either problem
definition as the operative one.

Rivers and Streams

The  approach  adopted to quantify  the water  quality  effects  of urban runoff
for  rivers and  streams'^focuses  on  the inherent  variability ,of  the runoff
process.   What  occurs  during  an   individual  storm  event  is  considered
secondary  to  the  overall  effect of a continuous spectrum of storms  from very
small to  very large.  Of  basic concern is  the probability  of occurrence  of
water quality effects  of some relevant magnitude.

To  consider the  intermittent  and variable  nature  of  urban runoff,  a sto-
chastic approach  was  adopted.  The  method  involves  a  direct calculation  of
receiving  water quality statistics  using  the statistical  properties of  the
urban  runoff  quality and  other   relevant  variables.   The  approach  uses  a
relatively  simple  model  of the physical behavior of  the stream or  river  (as
compared  to many of  the  deterministic simulation  models).   The results  are
therefore  an  approximation, but appropriate  as a  screening tool.

The  theoretical basis of  the  technique is  quite powerful as it permits  the
stochastic nature  of  runoff process to  be explicitly  considered.  Application
is  relatively  straightforward,  and  the procedure  is  relevant  to  a  wide
variety of cases.  These  attributes  are particularly advantageous  given  the
national  scope  of the NURP assessment.  The details  of  the  stochastic method
are  summarized  and presented below.

Figure  5-2  contains  an  idealized  representation of  urban runoff  discharges
entering  a stream.   The  discharges usually  enter the stream  at  several  loca-
tions but are considered  here to  be  adequately represented by  an  equivalent
discharge  flow  which  enters the system at a  single  point.

Receiving  water concentration  (CO) is the resulting  concentration  after com-
plete   mixing  of   the runoff end stream flows  and  is interpreted as the mean

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                                                                 CM
                                                                 co
      URBAN RUNOFF
  QR =FLOW
  CR-CONCENTRATION
  STREAM FLOW
   '* UPSTREAM

OS = FLOW
CS = CONCENTRATION
                                           DOWNSTREAM
                                           (AFTER .MIXING)
                                       QO= FLOW
                                       CO = CONCENTRATION
     Figure 5-2.  Idealized  Representation of Urban Runoff Discharges
                           Entering a Stream
stream  concentration  just  downstream of  all of  the  discharges as  shown in
Figure  5-2.  The four input variables considered are:

       Urban runoff flow (QR)

       Urban runoff concentration  (CR)

     -  Stream flow (QS)

       Stream concentration (CS)

Each is considered to be a  stochastic random variable, which together combine
to determine downstream flow and concentration.   In  addition, all variables
are assumed to be independent,  except urban  runoff flow and streamflow where
correlation effects can be  incorporated as warranted.

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An essential condition of  the  current computational  structure  is  that  each  of
the four variables which contribute to downstream receiving water quality can
be  adequately  represented  by  a  lognormal  probability  distribution;  from
analysis of data  or  other estimating  procedures, the statistical  properties
of each of  the input  parameter  distributions  are defined.  Examination of  a
reasonably broad  cross-section  of data  indicates that  lognormal probability
distributions can  adequately  represent  discharges  from the  rainfall/runoff
process, the concentration  of contaminants  in the  discharge, and  the  daily-
flow record  of  many  rivers end streams,  particularly  for  a  national  scale
screening approach.   It.should  be noted,  however, that modifications of  the
computation techniques could be made to accommodate the use  of other  distri-
butions (e.g.,  gamma, exponential) for some or all of  the  parameters.

The analysis procedure is described  in more detail  in the supplementary NURP
report cited earlier.  It  essentially  operates as follows:

     -  Downstream Concentrations.   Stream concentrations  of a pollutant
        are considered  to result  from the combination  of upstream flow
        at  background concentration  and runoff  flow  at  its concentra-
        tion.   Variations  in  stream  concentrations  below   the  urban
        runoff discharge result from variations in each of these inputs;
        the most significant source  of variation being whether or not an
        event is  occurring (i.e., whether  runoff  flows  and  loads are
        present).  Stream flows must be considered  because of the major
        effect of dilution on  the  resulting  concentrations.   Upstream
        concentrations 'can,  however,  be  set at  zero  for  the  calcula-
        tions;  in  which  case,  the  result  obtained   is  the exclusive
        effect of  urban runoff  discharges, and not the overall  expected
        stream concentration.    Effects of urban  runoff  can be evaluated
        by  considering only the periods during which runoff occurs.

     -  Parameter  Estimates.  Estimates for  runoff  flows  and  concentra-
        tions  are  developed  from  information  derived  from  the NURP
        monitoring programs.  Information on  stream flow  can  be 'obtained
        from analysis of  local  stream gage records.  Upstream concentra-
        tions  tend  to be  very  site-specific;  for   this  reason,  the
        screening  analysis  calculated only  the  effect of urban  runoff
        discharges.

     -  Statistical   Calculations.    From  the   statistical   properties
         (specifically,  the  means  and standard  deviations)  of the  flows
        and concentrations,  properties  of  the  dilution ratio can be
        defined,  and the -statistical properties of  the resultinc  in-
        stream  concentrations  are  calculated directly.   The  frequency
        with  which  any  particular  target   concentration  is  exceeded
        during wet weather can be calculated from the statistical pro-
        perties   of   stream   concentration,   using  formulas  or  scaled
        directly  from a standard plot  of cumulative   (lognormal)  proba-
        bility distributions.

        The frequency with which  the target concentration  is  exceeded
        during all periods -- wet and  cry -- is simply  the  product  of

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       the  wet  weather  frequency and the probability  (frequency)  that
       it  is  raining.   The probability that it is  raining  at  any time
       is  defined  by the ratio  cf  mean  storm duration to  mean inter-
       storm period, derived from the rainfall statistics.

       D =  mean duration of storms        .     ....    ...
       	:	—	 = fraction of time it is wet
       A =  mean interval between
              storm midpoints

       Mean Recurrence  Interval.   In  the  presentation of  results in
       Chapter  7,  the probability  distribution of  event  mean stream
       concentrations  of  an  urban  runoff  pollutant  during  runoff
       periods  is  converted to  a  Mean Recurrence  Interval  (MRI)  as a
       device  to  assist in the  interpretation  of  results.   The recur-
       rence  interval  is  defined  as  the  reciprocal  of probability.
       Because  the basic  calculation  is based  on  storm events,  this
       definition  yields  the  overall average number of storms between
       specific  event occurrences.  Event  recurrence  is converted to
       what is believed  to be  a more  meaningful   time  recurrence by
       dividing  by  the  average number  of  storms  per year,  which is
       developed from analysis of rainfall  records  and  defined  as

            Hours/year = 8760                   ,  ,
            	{JL—.	I-TT	 = average * storms per  year
            Average  interval between
                  ^  storm  midpoints

       As  an  example of the MRI calculations consider  a  stream concen-
       tration  which  has  an  exceedance  probability  of   1.0 percent
        (Pr =  0.01)

            Recurrence  Interval  =  1/Pr =  1/0.01 =  100

       The analysis is in terms of storm events,  not  time.   Therefore
       this result is interpreted  as  one storm in  every 100  events on
       average,  will produce concentrations  greater than  the  selected
       value.   For an area where  rainfall  patterns  produce  an average
       of   100 storms  per year, the  average  recurrence interval  ex-
       pressed  in  time  units  rather than events,  is:

             Recurrence  _  event  recurrence _   100 events    _
            -.- Interval   ~   # events/year    ~ 100 events/year     y
             (time)
Currently,  the primary use of  the  above procedure is  as  a screening tool  in
which  approximate  results and relative  values  are  of  interest.   In  this
regard, NURP believes the  Mean Recurrence Interval  is a  very useful defini-
tion.  It  should be interpreted  as the  long-term  average  interval between
occurrences.

When results  of this nature are interpreted,  the following factors  should  be
noted.  The recurrence intervals  of most interest relate to very low  proba-
bilities of  occurrence.    The  tails  cf  distributions may  have  appreciable
uncertainty,  and in the  natural water systems, distributions may be  lognormal

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    iivt.-i the bulk  of  the range but may deviate from the assigned distribution at
    -tin   extremes.   Computed stream  concentrations  at  long  recurrence  intervals
    *!•   likely  to  be conservative, that  is,  overstated because there are likely
    4-(  be-  practical upper  limits  for  runoff concentrations and  lower  limits -to
U«J.v: *l ream flow.

      i  ijlso should  be noted that  serial correlations of streamflows or  the  tend-
    ency of wet and dry years to  occur in  clusters, though not a general behav-
          may  be  significant  in   some  cases.   This  situation would  cause  the
   !&$v«-rage one year  condition,  for example, not to repeat itself every year  but
           to occur several times  per year,  at intervals greater than  one year.
     HMier Receiving Waters
          receiving  waters of general interest in assessing urban  runoff  effects
            lakes, estuaries,  embayments,  and coastal  zones.   The methods  adopted
         lakes  are  briefly described below.  The other receiving  waters generally
     p-»quire site-specific and often complex analysis techniques  (numerical meth-
         multi-dimensional modeling,  etc.).  Given this,  a  generalized screening-
     l*>vel  assessment  was not  believed to  be appropriate  for  this  report.   A
     Dumber  of  the individual  NURP projects consider  these coastal  water bodies
         report on  the  specific methods  adopted  and results  obtained.

         lake eutrophication problems, the  time  scale  for  analysis is considerably
     longer .than  the  short  (event  scale)  periods  necessary  for  estuaries  and
     fivers.   For  this case",   annual  average loads  were  used  in.  a  steady-state
     Mita lysis performed using  the  type of empirical model  advanced by Vollenweider
     Mid  others.    The  EMC  data  developed  from  NURP monitoring  programs   can  be
     |'*odily converted  to  annual  loads  directly from  annual flows  or indirectly
          on annual  rainfall.
>i  total phosphorus,  typically the  limiting nutrient  of concern,
»ncentrations  are  calculated using  the  following  formula:
                                                                           average
  $?>•
  t
   !&.
                                  P  =
                                      H/T
                                           1000
         input values include pollutant  mass loading  (W1),  lake  physical charac-
     teristics of  depth  (H)  and residence time  (T)  and reaction rate coefficients
     4\< ) .   The relative contribution of all load  sources  to lake total P concen-

     trations  can  be  defined by  solving  this equation for each of the sources.  By
     •t'Omiparing results in terms of lake  concentrations for initial conditions  (no
     •ftcmtrol) , and then  modifying loads to  reflect  various levels of control,  al-
     iprnative control operations can be compared directly to effect -on lake water
     wome judgement  is  involved in  defining acceptable  lake water  quality  con-
     centrations,  which  depend  in part  on water  use and  on regional  norms  and
     expectations.

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EVALUATION OF CONTROLS

General

The  evaluation  of  controls  has two  elements:   (a)  characterizing the  con-
trols'  performance  capabilities and  (b)  defining  costs.   For this  report,
only  the  characterization of  performance  is emphasized;  cost relationships
are  addressed  to  a  more  limited  extent.   EPA's Economic Analyses  Staff,
Office  of  Analysis  and Evaluation, has prepared the following report  under
contract:

      "Collection of  Economic Data from Nationwide Urban Runoff Program
      Projects," EPA Office of  Water Regulations  and  Standards, April 7,
      1982.

This  report,  issued  at  an  early  stage  in the  NURP program,  assembled and
analyzed  cost  information  on  potential  control  measures.   Useful  cost
information for detention basins was  developed by the  Washington,  D.C. area
NURP  project and is discussed further in Chapter 8.

Detention Basins

There are  a  number  of procedures which can be adopted  for evaluation of de-
tention basin  control devices.  Procedures adopted  by  individual NURP  proj-
ects  are  describe^,  in project  reports.   The procedure adopted by  NURP to
generalize  the  analysis of  detention basins, and provide  a  planning  level
basis for  estimating capabilities and requirements,  is detailed  in a  deten-
tion  basin handbook being issued by NURP as a supplementary  report.

Results  presented  in Chapter 8 provide  a  summary  of  observed  performance
characteristics of the detention devices monitored under the NURP program and
a projection of long-term performance expected on the basis  of basin  size and
regional rainfall characteristics.  The  latter  result is based on the  proba-
balistic analysis methodology described in  the  supplementary  report.   Plan-
ning  level  cost estimates for  control  of urban runoff using  this  technique
are  also presented.

Street Sweeping

A number of the individual NURP projects adopted street sweeping  as  a princi-
pal  subject ...of  investigation.   Procedures and results  are  described  in indi-
vidual project  reports and are consolidated  and  summarized in Chapter 8.  The
adopted procedure  and  detailed results  are presented  in  the  supplementary
NURP report, which was cited earlier.

Recharge Devices

Recharge  devices  include impoundments  or  other  structures  such   as pits,
trenches,  retention  basins,  percolating  catch basins, in-line  percolation
chambers or perforated pipes,  which function by intercepting  some portion of
storm runoff and allowing it to percolate  into  the ground.

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One of the basic questions which  arises  when controls of this  type  are  con-
sidered is whether  the percolation  encouraged  will produce  undesirable  de-
gradation  of  groundwater  quality.   This  aspect was  examined  by  two  NURP
projects,  and is discussed in Chapter 7 of this  report.

Evaluation of percolating basins  of any  size is readily accomplished using
the standard storage/treatment routines of stormwater models such as STORM or
PWMM.  In  such  cases the local soil permeability  (the percolation  rate)  is
iupplied as the  treatment  rate.  In  addition,  statistical  analysis procedures
described  in  "A Statistical  Method  for  the Assessment of  Urban Stormwater"
(EPA 440/3-79-023,  May 1979)  have been developed.   A  probabalistic analysis
methodology adapted from the latter approach has been used by NURP to provide
estimates  of   performance   capabilities   of  recharge  devices,  which  are
presented in Chapter 8.  A detailed discussion of the methodology is provided
in the supplementary NURP report on detention/recharge devices  cited earlier.

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                                  CHAPTER 6
                       CHARACTERISTICS OF URBAN RUNOFF
3 INTRODUCTION

This chapter presents a condensed summary of data developed by the individual
NURP projects together with analysis results and interpretations based on the
aggregated data from all projects.

Both the format for the summaries and the evaluations performed were selected
1.0 best serve  the  NURP objective of developing a  national  perspective.   The
results presented  do not exhaust the  useful information and  insights  which
can be derived  from  the extensive  data base 'that has been  assembled.   Indi-
vidual project  reports and a  substantial  number of articles  published  in a
variety of technical journals independently examine specific aspects of urban
runoff, often from the perspective of local issues.

Comprehensive tabulations of NURP data  have been assembled and  will  be made
available to interested*parties  for use in  local  planning  or continuing re-
search or engineering activities.  As noted  below,  only  a  portion of the en-
t.ire  data  base  generated  by  the  28 NURP projects  has  been  made  generally
accessible at  this time.   Under an  ongoing effort, the entire  data  base is
being subjected to final quality assurance  checks-and placed  into a separate
file, copies of  which  will  be  made  available to interested parties upon re-
quest.   In  addition,  a summary of  the event  averaged data,  used  for the
analyses presented in  this  chapter,  is reproduced  in a  Data  Appendix issued
with this report.

Field monitoring was conducted to characterize urban runoff flows and pollut-
ant concentrations and mass loadings.  This was done fcr a variety.of pollut-
ants  at  s substantial  number  of sites  distributed throughout  the country.
The  resultant  data represent  a  cross-section of  regional  climatology,  land
use types, slopes, and  soil conditions  and  thereby provide a  basis for  iden-
tifying patterns  of  similarities or differences and testing  for their  sig-
nificance.  To meet the objective of maximizing the degree of transferability
of urban runoff  data,  the  NURP approach involved  covering  a  spectrum of  re-
gional and  land  use  characteristics, requiring  consistent  quality assurance
programs among  all projects,  and encouraging each  of  the  projects to obtain
'data for a statistically significant number of storm events at a  site.

The portion of the NURP data base used in  the characterization of urban  run-
off presented in this  section  excludes  monitoring  sites which are  downstream
of devices  which modify runoff  (e.g.,  detention basins).  The  data base of
acceptable "loading  sites"  consists  of 61  sites in 22  different cities,  and
includes more then  2300 separate  storm events.  The  actual number of events

-------
for specific pollutants  varies, .and  is  somewhat  smaller than the total  number
of storms monitored because all pollutants  were not measured for  all  -storms
at all sites.

Data summaries and analyses were performed  using  storm event average values;
within-event  fluctuations  are  not  considered.   An event mean  concentration
(EMC)  for  pollutants of  interest  has been  determined  for each  monitored
storm.  Preliminary results presented in an earlier NURP report were based on
analysis of  "pooled" EMCs  which  were  available  at  the  time  regardless  of
site.  This  provided a useful start, a reference  for individual NURP project
activities,  and  established  the  order of  magnitude  of  concentrations  of
various pollutants in urban runoff.  With  the  substantially larger data set
now  available,  a more  useful  approach  is  possible.   For   the  analyses and
comparisons  presented  in this  chapter,  the  storm  event average  data  were
aggregated by  site to describe  site characteristics.   Site mean values were
then aggregated or compared.

Summaries, comparisons,  and evaluations were restricted to concentrations and
runoff-rainfall ratios.   Although loading data  (Kg/Ha)  are also  available for
all monitored  storms, they  have not been  used  in comparisons for the  follow-
ing  reason.   Mass  load  is  very strongly  influenced by the size  (volume) of
the monitored  storm  event.   Monitored events usually  represent a very  small
sample of  all  storms for  an area,  are generally biased toward  larger  events,
and are different  from  site to  site.  Therefore comparisons between sites or
locations  using  loading  data derived  from  monitored  storms are quite likely
to present a distorted picture.

Event mean  concentrations,  on the  other hand,  have been  determined  to be  es-
sentially uncorrelated with runoff  volume,  as discussed further later  in this
chapter.   Site comparisons  can be  made with  high  confidence levels  using
concentration  data,  and the most meaningful load comparisons would be  those
developed by using concentrations,  area rainfall  volumes, and  runoff-rainfall
relationships.

Separate  summaries of  results  are  provided below  for  standard  pollutants,
coliform bacteria, pollutant loads,  and priority  pollutants.

LOGNORMALITY

As  was  pointed out in Chapter  5,  the key to the  mathematical  tractability of
the  NURP  methodologies  is  that  the date can be  well  represented  by  a  known
probability  density  function (pdf).  There are actually  two issues involved;
 (1)  the adequacy of the  assumed  pdf  in  terms  cf representing  the essential
characteristics  of the  data set  in question,  and (2) the  estimation of the
parameters  of the population pdf  that the  observed  data set  is  presumed to
represent.   These  will  be discussed in turn.

Adequacy of  Representation

One can fit a polynomial of order  (n-1) exactly  to  any data set of n numeri-
cal  items,  but its utility  in predicting the probability of realizing a given
velue on  e subsequent trial (either within or  outside the- original data 'set,

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i.e.,  the  interpolation  or  extrapolation  problem)  is  likely to  be  very
limited.  The number  of  parameters  involved and the need  to  investigate its
properties on an individual basis are further deterrents  to  such a practice.
There is no dearth of  pdf's that have been  the  subject  of intensive investi-
gation.  However, the  selection of a pdf is an  objective  choice that  is best
made based on professional knowledge of  the  processes deemed  important to the
desired probability model and the use to be made of  it.   For  example,  if the
data ere known  to  result  from the product of many  small  effects,  their logs
will be the sum of the logs of these effects.   By appeal to the central limit
theorem, it  is  known  that this sum  is  asymptotically normal  and,  therefore,
that the data will be lognormally distributed.   Based upon  such natural ex-
pectations and  prior  experience (of a  growing  body of  other  workers  in the
field as well), the lognormal pdf was chosen.   The fact  that the variables of
interest can assume only positive values with a finite mean and a finite non-
zero lower bound (even in a standardized form)  leads  to  the  rejection of any
pdf defined over the  entire real  domain,  such as the normal  distribution for
instance.

There are a number of  statistical procedures  for evaluating  the normality of
a  complete  sample;  at least  nine  can  be  found  in the  current literature.
Some are  origin and  scale invariant (e.g., the Shapiro-Wilk,  standard  third
moment,  standard  fourth  moment, and studentized range)  and  thus  are  appro-
priate  for testing the composite hypothesis of normality.  Others require the
complete specification of the null  distribution (e.g.,  Kolmogorov-Smirnoff,
Cramer-Von Mises, weighted  Cramer-Von Mises,  modified Kolmogorov-Smirnoff-D,
and chi-squared), and  typically, the mean and variance  of the'specified nor-
mal  hypothesis  are  taken to be  the known  mean  and  variance  of the complete
sample.  Some procedures  (e.g.,  chi-squared)  utilize the specified theoreti-
cal pdf, while others  (e.g., the modified Kolmogorov-Smirnoff  D-test) utilize
the cumulative frequency distribution.

In testing for  normality  (in  the logorithmic  domain in  our case) , one  speci-
fies the  level  of significance  (a), i.e.,  the  probability  of rejecting the
null hypothesis when  it  is in  fact true  (Type I  error) .  The  choice of a
requires tempered judgement, however.   The  power of a test (6)  is the  proba-
bility  of  rejecting  the  null  hypothesis when it is in  fact false.  The pro-
bability of  accepting the null hypothesis 'when  it  is in fact  false  (Type  II
error)  is  l-(5.   For  e given sample  size and  test,  fixing a value for  a also
determines a value for £•  (i.e., they are not  independent).  The smaller the a
level,  the  less powerful the  test.  Thus  one  is  forced to make  a  trade-off
between the consetjuences  cf a Type  I or II error when selecting an a  value.

The  median EMC  values  for each constituent  at  each site  were  calculated,  and
these   sample  sets  were  examined  for  lognormality using  the  Kolrriogorov-
Smirnoff D test.  The  a  levels for  TSS, Total P, TKN, Total  Fb, and  Total  Zn
were all greater than  0.15, indicating  a  high power level.    In other  words,
these  sample sets are  extremely well represented by a lognormal distribution.
For  COD and nitrate *  nitrite the a  levels were 0.059 and 0.057 respectively,
indicating a  lower power  level  but suggesting  that  even for  these  constit-
uents  the logncrmal  distribution  quite  well  describes  the  data.   Because
BOD, Soluble P,  end Total Cu  were measured  at  fewer than  half of  the  project

-------
sites,  the  D-test .could  not  meaningfully be  used  (i.e.,  n  is too  small).
Stated another way,  at  the a = 0.05 level, the  hypothesis that the  samples
were drawn from a population with  a  lognormal  distribution cannot be  rejected
for any of the constituents examined.

Turning to  the  individual sites,  there were  very  few instances where n  was
large enough to support the meaningful use of the D-test,  and  so a  different
approach for examining the  appropriateness of  the  lognormal distribution  was
used.  Essentially  it  consisted of examining  the  cumulative  frequency  dis-
tributions  (in  log  space) and  third  and  fourth moment based  statistics  for
adequacy of representation.  Taking into  account detection limit phenomenon,
uncertainties associated  with  sampling and  analytical determination errors
(especially, at  low concentration levels),. and  an  occasional  outlier,  well
over 90 percent of  the constituent distribution  at  all  NURP sites  were quite
well represented  by the  lognormal  distribution.  For the  few  remaining  data
sets, the lognormal distribution, although not  perfect, was adequate for our
purposes.

Estimation of Parameters

As noted in Chapter 5, the  lognormal  distribution  is  completely specified by
two  parameters,  the mean  and  the coefficient  of  variation.   The  values of
these two parameters as calculated from the sample  data set are the best .es-
timates of  the  parameters of the underlying  population in the maximum like-
lihood  sense.    For this  reason,  they  were  used  in   the  NURP  analysis.
However,  due  to  tne existence of detection limit  problems  and  sampling/
analytical  determination  errors,  the reasonableness of  this  decision  was
examined in  general for  all  constituents and in great detail for Total Cu,
the  results of which will be described below.

For  each  of the  49 NURP  sites where  at  least  five  Total Cu  determinations
were made,  data  were plotted (in logarithmic  form) on  probability paper.  \
line of best  fit was drawn in, using  professional judgement where detection
limit or outlier  problems existed, and the values  of  the  median and  standard
deviation were read from the plot and converted into  arithmetic space.  These
were  then  compared with  those  values calculated  from the data themselves.
One  example is  given  in  Figure  6-1   (the  116th and Claude  Street  site  in
Denver) .  Here the  median and coefficient of variation from the -plot  (20  pg/1
and  0.75)  compare  very  well with  those calculated  directly  from the  data
 (22  pg/1 and 0.74).

An  example  of  an outlier plot  is  given  in Figure 6-2  (the strip  commercial
site in Knoxville,  TN) .  The one very low value  (1  pg/1)  is one-twentieth the
typical  detection  limit  (20  pg/1)  and clearly  does  not   belong to  the' same
distribution that the other values  do.   Ignoring  it, a very good  fit  exists
and  the parameters of  the  plot are  30 pg/1  and 0.37  for  the  median  and
coefficient of variation  as  compared  with the 25 yg/1 and  1.35 values  calcu-
lated  from  the data.  The  difference in medians  is not  too  great, but  the
difference  in  coefficients  of  variation  is  quite  large  (over a  factor  of
3.5).  This means that  the upper end  of  the tail  of the pdf  is quite  over-
estimated  by the   parameters estimated from  the data and,  consequently,  that

-------
JE

n
O
    n.m    n.ns n.i  n.2
                                                                                                        an.n 99.9
99.99
                                                       PERCENT LESS THAN
                           Figure  6-1.   Cumulative Probability Distribution of  Total Cu
                                             at  C01 116 and  Claude Site

-------
-/I
n.ni
         I   I	L
            J	I	L
0.05 0.1  0.2   05  1
                                               I     III
                                                                   J	U
10      20    30   40   50  60   70    RO

              PERCENT LESS THAN
                                                                               90    95
                                                                                    98  99
—I	1—
 99.R 99.9
                                                                                                                     99.99
              Figure 6-2.   Cumulative  ^robability Distribution  of Total Cu at TNI  SC Site

-------
          subsequent  analyses will be  extremely  conservative,  i.e., higher values of
          copper concentrations  will  occur  less often  than  predicted.   In general, the
          effect of  an outlier is to increase or decrease  the  estimate of the median,
          depending  upon whether  the  outlier  is high  or  low,  and  to  increase the
          estimate of the coefficient of variation as compared  to  those obtained from
          the remainder  of the data.

          An  example  of a detection  limit problem is  given  in  Figure  6-3, the plot of
          copper data of the Durham, NH parking  lot  site.   Although only four points
          appear on  the plot, actually  n = 31, meaning  that  27 points  are  represented
          by  the first plotting  position (90.6 percent).  These values  (all  reported at
          100 ug/D  are presumably the  detection limit of  the analytical  laboratory.
          Of  course in  reality not all  27 values  are 100 yg/1 ; they are  simply  equal to
          or  less  than  this  value.   Fitting  a line to  the  remaining  four data points
          merely assigns appropriate plotting positions to these  "less than" values.
          The  estimates of the  median  and  coefficient of variation from the plot are
          63  ug/1  and 0.36 respectively, as  compared to  the estimates  from the data of
          103 pg/1 and 0.13.   In this case,  the latter significantly overestimates the
          .median  and  significantly  underestimates  the  coefficient of  variation, and
          this  is  the  general  effect when a  detection  limit  problem  is present.  In
if         terms  of  the effect on prediction of rare occurrences  of high copper levels
;'         . (the upper  tail of the pdf) these effects are somewhat counterbalancing.  To
          the  extent  that the increase  in the coefficient  of  variation  dominates, the
          results  of  subsequent  analyses will not be conservative,  since larger concen-
r         trations will  occur somewhat  more frequently than would be predicted.
j'                               •*
j          When  the results of this exercise are  compared  for all 49 sites,  the median
j          as  estimated from the plot was  found  to be higher  than  that  estimated from
].-         all  the  data  at  only  six  sites,  was  equal at  five sites,  and was less  at
;,.         38  sites.   However, at only three sites was  the change greater than 10  ug/1.
;          Considering the population  of all copper sites, the  average median is 47 ug/1
!'         and the  coefficient of variation  is  0.84  when  the estimates  are based on all
t          the data.   If the  estimates  are based  upon  the plots, the respective  values
["         ere 42 ug/1 and 0.24 respectively.   The significant  reduction in  the coeffi-
!          cient  of variation in this latter case deserves  comment,  because  it suggests
!          that  much  of the apparent  variability  from site to site  is due to data  arti-
          facts  such  as  detection  limit phenomena, outliers,  and/or sampling/analytical
          errors.   Similar comparisons  of the coefficients of variation for each site
           showed increases at 21  sites,  6 unchanged,  and decreases at  22 sites.   Con-
           sidering all  sites, the average  coefficient of variation is  essentially un-
           changed  (0.61  vs 0.63)  as  is  its variability (0.47 vs 0.49) .

          Eased  on the  results of  the analyses which  "nave been  performed,  the NURP
            indings are as follows-.

                   Lognormal  distributions adequately represent  both the storm-to-
                   storm variations in pollutant EMC ' s  at an urban  site, and site-
                   to-site variations  in  the  median  EMC's  which  characterize
                   individual  sites.


-------
— 7.
 n.m
 iii    ii
n.05 n.i  0.2   0.5   1
                                                   JL
                                                   JL
                J_
                                            JL
                                            J_
                                       10
20
30   40  50.  60   70    80
                                                                              90
95
                                            98   99
—I	1—
 99.8 99.9
                                99.99
                                 Figure  6-3.  Cumulative Probability Distribution

                                            of Total Cu at NH1  Pkg. Site

-------
     -   More detailed analysis to compensate for sampling errors  (e.g.,
        outliers  and  detection  limit  problems)  would  result  in  some
        adjustments in the statistical parameters tabulated later  on  in
        this  chapter.    The   data   summaries  presented   are  based  on
        statistics  computed  directly  from  the  log  transforms  of the
        data.

        Such  adjustments  would  not  have  any  significant  effect  on
        overall   results   nor  on   the  general  conclusions   reached.
        However, at a small percentage of sites,  the  parameter estimates
        for some pollutants would change  significantly.
                                      "                       .
        In  general,  estimates of  the site median  EMC  would be  least
        affected; estimates of variability  more  so.   It  is likely that
        the very  high  or very low  values  for coefficient  of variation
        (storm-to-storm variability) would  be  adjusted to  more  central
        values.

STANDARD POLLUTANTS

This grouping includes the following pollutants:

                    TSS - Total Suspended Solids
                    BOD - Biochemical Oxygen Demand
                    COD - Chemical  Oxygen Demand
                    TP'  - Total Phosphorus  (as P)
                    •SP  - Soluble Phosphorus (as P)
                    TKN - Total Kjeldahl  Nitrogen (as N)
                NO   -N - Nitrite + Nitrate (as N)
                    Cu  - Total Copper
                    Pb  - Total Lead
                    Zn  - Total Zinc

It  includes pollutants  of general  interest  which  are  usually  examined in
other studies  (both point  and nonpoint sources)  and  includes representatives
of  important  categories  of pollutants, namely solids, oxygen consuming con-
stituents, nutrients, and heavy metals.

Condensed Data Summary

Tables 6-1  through 6-10  summarize  the  NURF  results  for  these  pollutants.
Monitoring sites  are grouped in each of the tables according  to  dominant  land
use.  Broad  categories  have  been used;  residential,  commercial,  industrial,
urban open/nonurban  (other),  and mixed,  this  latter  category being  used  for
sites which had  no  predominant land use.   It  should  be. noted that the indus-
trial category does not  include  heavy  industry  sites,  but more  typically  re-
flects an  industrial park  type of  use.   As  a  result, most of these sites  are
more closely related to  a  commercial use  than  to the typical image called up
bv  the  term industrial  site.   For  subsequent  comparisons,  the  data  shown in
Tables 6-1 through 6-10 for the commercial  and industrial sites,  are  combined
and desianated as commercial land use.

-------
TABLE 6-1.  SITE MEAN  TSS  EMCs (mg/S,)






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TABLE 6-4.  SITE MEAN TOTAL  P  EMCs






1
1
4
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r.
7
n
9
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1 1
1 1

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T-l Mflrt
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nr.l U«.nrn l.""i Is


397-672
353-640
217-302
255-353
53R-753
717-2031
95-491
175-RR3 '
253-47I


1.14-705
706-340
169-32?
164-205
1HR-233
201-264
205-3SO
179-319
29" -166
1R3-2R?
76R-3RO
507-727
IP.4-227
101 -5H7
116-374
561-1739
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515-171.1
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190-555
201-379



1
2
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4
5
6
7
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9
10
1 1
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14
15
16
17
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19
20



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T01 Mnrth 4wp


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17
17
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1512
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7
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13
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1
2
3
4
5
6
7
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10
11
12
1.1
1"
15
16
1'
in
19
70
71
72
2.1
74
75
76
77
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79
30
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32
33
34
]<
36
37
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39


Site
COI Pin Ory r,r
COI Cherry
COI 116/Claude
nr.l n
n
17
14
15
16
17
18
19
20


Site
KSI Inland
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36
17
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76
601
164
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7030
1542
30
194
69
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3
40
3
11
12
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5
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68
72
58
68
81
23
33
38
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12
28
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32
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165
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43
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160
106
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47
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150
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56
13
37

17
35
74
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1
2
3
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5
6
7
8
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Wll state fair
land
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r
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inn
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inn
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100
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inn
96
91
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Area
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73
179
17
1
76
12
58
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29
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(•/A)
n
0
2
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n
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in
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91
69
21
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99

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77
of
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116


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H7-76K




78-50

58-111

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Site

1
7
3
a
5
6
7
R
r.«l Seavlnw
COI Pnnney r^trh
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HY2 f.nflllsn Or
NY2 West Hr
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HI3 Traver Cr
NY2 Sheriff (V,r>

Use
t
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inn
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98
97
91
90
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Area
(A)

633
405
78.416
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5.338
17.728
2.303
552

Pnp.
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f'/AI


0



1



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1
a
1
1
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6
7

of
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12
7
n
18
n
n
5
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Mean

las
137
-
5
8

33
39
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1.74
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.55
1.11
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91
124

5
7
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79
26
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dence limits

55-150
90-171

4-6
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70-3"





1
2
3
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land
t
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inn
180
56
52
1

Area
(A)

18
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72
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69
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75
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346
59

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55
103
179
17


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76-116
76-140
infl-296
24-56

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1.007
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1971-525?
3640.6370
4996-731?
5502-7463
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955-1509
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1369-4245
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801-1173
791-1572
1674-3474
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379-539
1447-1904
1790-5200
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7343-3406
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340
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Median


3159
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315
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883
765


	

2411-4139
I115-.176B
77R-I240
246-371
292-412
854-1279
796-981
628-93?


1
2
3
4
5
6
7
8
9
10
II

1.
16
17
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19

3

rSI Noland
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1
5
2
-

5

17
-


* >

61
7?
58
68
43
11
23
33
38
71
5




13
97

•* ''.
••-,
0
19
35
35
13
16
, 5
8
?3
6
21

73
13
70
15
15

• 	 ;

_
6994
?B?2
1490
623
145?
?44fi
1080
1631
845
1237


4741
7770
1111
1107
19
.*.


.55
.64
.53
.50
.35
.50
.64
.4?
.79
.1.1



.7^
.49
.31

^^ 	 :


6140
?37?
1316
551
1.169
?l«1
910
I50fi
111
951

IR07

1775
1249
1056

*~ "~"
;

5004.7533
7006-7805
1142-1516
447-705
Ilfl0-l5"9
I394..14.1?
615-134?
1 304 . | 740
647-1075
774-1740

1536-7115
30lo-4ior
1171 -7?on
1011-154?
9-0-1717

Co^,£l,l


SU..

1
2
3
4
5
6
7
n
9
10
CO) VIIU ItftKj
NCI 1013 (CIO)
HV.l Snutha
TM1 CRH
Ull Pll!tl»r
KSI 1C MB(c»lf
Fll Norms PV
Ull Stale F»!r

l.snd
Hit*
Cn»!
ino
100
100
100
100
100
100
96
91
74


(M

74
73
179
1?
1
26
1?
51
47
29

Pnp.
(•/Al

0
0
2
0
0
0
r.
-
-
10


IMP.

91
69
21
100
90
99

97
45
77

Mn.
nf
ORS

27
61
13
27
IR
15
25
17
1?
8
TKN

""*"

3657
1613
1256
1073
211?
646
107.1
1175
826
1656

r.ov

.15
. 70
.45
. 44
.66
.41
.61
.73
.14
.65

Mprtiar.

7715
1.111
1144
9.16
1761
',07
916
040
633
1319



7116-1541
115.-. 1501
"75-1414
115-107',
1.176. ,V54
400- I|4
755-HIO
770. 1J5.-
43.1-0?5
931-7061
Industrial

SH.P

1
2
3-
4
MA2 Adrllinn
I'M Indus Drain
'SI lenaia
Mil Gnce S.

li""11
Ind
100
ino
56
52

(A)

18
(3
72
75

Pop.
Oen
(•/A)

0
0

S

t
IMP.

69
64
tl
39

Nn.
nf
085

5
18
12
18
TKN
Mean

7092
1274
1385
1713
COV

.49
.57
.73
.56
Mndlai

1179
1107
1117
1493
90" Cnnfi.

1207-2924
891-1376
796-I56R
1705-1151

-------
TABLE 6-7.  SITE MEAN NITRITE PLUS NITRATE EMCs



1
2
3
4
5
6
7
R
i
in
11
i?
M
14
IS
ifi
17
IP
15
2n
71
72
2.1
24
25
?r
7.P
79
.10
.11
3?
lil
14
.15
3"
37
.in
.19


Site
mi Rio. Ory C,-
r.01 r.hrrr,
CHI llft/CUiMe
(1C.I Ouflpf
nr.i K.eridn..
Or.l 5'ral.l.nn
II. 1 John M
ITSI Ovorfnn
MA? Hnmlrc*
MTl Rnltnn tlltl
MH1 Homeland
MOI HI Wa
land
T
inn
100
inn
98
97
91
90
RO
Area
(M
633
105
?B.4I6
5.218
S.33B
17.728
2.303
552
Pop.
Oeo
0



1

-
t
IMP.
1
1
1
1
11
6
7
No.
of
OBS
12
7
0
30
31
0
5
33
"n?..r"
Mean
IS12
581

210
Bf2

1108
383
COV
.19
1.03

.60
.53

.17
1.02
Median
1383
405

206
763

1092
26B
901 Confi-
dence limits
|OR7-l7Sft
217-756

|71-?4f
656 -BRR

93n-12B3
Zn9-313
Hlviid

1
2
.1
4
5
6
7
P,
9
in
n
12
13
H
15
16
17
18
19
20
SH*
K5I Kolinil
«01 Hmo^n
III Mjttls »
Hit Wjv.rly
l»l St
Ull Vnnil Ctr
HA1 m 9
"A| Convent
"11 Grand 0 01
MI3 Pitt AA-S
»»2 tutor
M\ Ann*
«I3 out AA-«
Mil 
CAI "no.
TI.I ». Jcvilt
Til Wllllpr
COI »nrtl> Aye
L4nd
Hie
t


-




-







-
-

-

• rw
(«)
36
17
17
30
187
45
338
inn
453
2001
7R
nni
2871
IM
I2n?
203n
1542
3n
194
S9
Poq.
0»n
(•/»)
3
40
3
11
3
12
7
1
5
2
-
9
7
5
2
-
12


9
J
IMP.
68
72
58
68
•3
81
23
33
38
21
5
12
26
2B
4

-
13
97
50
No.
itl
OP.S
0
20
n
35
t 13
17
5
n
23
6
32
6
5
23
5
15
17
14
15
32
""2-3-"
"-

11.529

775
587
751
1.789
960
R83
284
2«8
I.26R
469
875
1 .033
616
l.lll
376
456
1,744
r.nv

4. no

.49
1.49
.»!>
,4R
.19
.44
-4R
.'2
.fin
.24
.13
.76
.*n
.36
.54
.47
.92
HnrlUn
.
2793

696
327
618
1613
R94
pn7
25«
2ni
inR6 ^
45n
Rn3
f!2l
571
1044
332
412
12R6
9m Confi-
dence I.
t
Cn»l
100
100
inn
ino
ion
ion
inn
96
91
74
Conotrcla!

Area
m

74
23
179
12
1
26
12
5R
47
29

Oen
(•/A)

0
0
2
0
n
0
0


10

t
1»".

91
69
21
100
90
99

97
«5
77

n'
085

27
61
0
2R
2R
15
26
n
12
12
""2.3""
Hnun

nan
HIP

708
on i
662
7RI
-
.156
7P3
r.nv

.Rn
.15

.fin
.04
.r,2
.61
-
.46
.50
Hi>rl!»n

895
9flO

504
615
5V
f>1?

.12.1
7n?
9n» Confl-
nVnrB 1. .mils

7n|-1143
P7n. 1094

470-7)2
4RPi-77n
414- 77R
.'•20-71!

257-mf,
540-R17





1
2
1
4



Site

HA2 AddHon
MM Indus Oraln
rSl Lcn»i<
MM Grace S.



t
ln
-------
TABLE 6-8.  SITE MEAN TOTAL COPPER EMCs
»«(*.ntl.l

1
.1
«
f.
7
1
•>
10
1?
1"
15
If.
17
IP
;i

•i
;•«
;'•
,-'.
.->
.'(!
7»
in
1 1
i;
1.1
.15
15
17
in
,0
5fl,

rni | if./f i*iiH"
Of! p,,fiPf
Of.? |.^^,(Hnn
pr.l <;irflffnn
II 1 ,tnhi. H
*!M Ovrr»n«
MA7 Mrmlorl
HP) MnmrlatH
HPI *-t «*•>
HP 1 Or '. Mill
»v| MWM
HY.l JVan^nn
WVT f _ Ooi-.h.
Wt 1 Pic h."il
WM 11* M i»n'.
rt | yni.o,, n,i'-.
!»t Ma-l
WM l.:'"nln"
trn rr
PC. 1 u<». ' i.-init
i.M K - nr-rt
n ; .'elm r, .
THl P|
Wfl) |.*Vf imi-.
II 1 M^rti-. r>.
(II rh,i.-t0r H,t,,
(ir.l raM-irlnr
rni A-,hi(t-v
IM 1 oi it-: I
nri --in.'M
nri -...,*-,...
1 *nH
inn
inn
inn
inn
inn
inn
inn
inn
inn
inn
inn
inn
inn
ion
inn
inn
inn
inn
inn
inn
inn
no
?>
or.
IT
*>;
11
01
?l
in
*>i
ff
fir.
,5
.".
• r.
IM
(.7
1*'
17
^n
w
5"
H
17
,,

ISf
l^p
fifl
5?
M
1
'7C
.w
m
*l
'•J
11
11
m?
?n
*.'
11
i;1'
,M
lin
"
P»n
19
11

71
in
ft
5
in
1?
1.1

5
in
3
,s
17

1
in
n
.1 •

in
1 1
1?
1!


'"
1 1
1"
^
T

7«
-
.1.1
1?
.M
15
51
70
*n

?.?.
.in
71
so
SI
r.
in
S7
1.1
?1
.17
in
.1.1
.17
.17
Ifi
.11
7?
,.
„
.«
No.
H
IK
71
H
.1*
1?
n
n
70
n
n
n
0
n
0
n
i?
n
n
1 1
5
7
.«
II
5
If
1?
0
0
A
n
i
Tot.l Cnpwr
"'""
15
7B
.
3"
B3
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in;
7.

.
-



A


?n
.17

«3
51
7?
45
10
?«
50
in?
10
71
30
rov
1.AR
. 71

.ss
.as
.so

. 7fl
,31
, 7R
.





,lfi •


1.5"
."•.I

.B«
.AO
..!«
.75
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.71
.?'
.35
»rHi..

77

.1.1
« '
ni

Rn
?n






A


15
.n

1.1
57
,-|
15
7
75
«5
77
?n
?nt Con'nf
MII r.^^n/i o m
M | ,1 P i ( t fl A . 5.
WV? f.^rf^i
MA | Anna
MI 1 C.rar.P fl
**(.!' Swfff. Olin
:,0] M*.*rfr
r.A] Knni
n. t N. .v^tiff
ft! UfM*r
CHI North ftvn


Unrl
I




















Arpa
f«)
.Ifi
I 7
17
31
•IS
i.W
inn
iro
mm
7f>
SOI
lf,1
l?n?
?n.in
1M?
.in
i?"
A9
Mi.rd
'
Pop.
f'/fl)
.1
in
_i
n
i?
7
1
s
?

0
5
?

i?


<»


»
IMP.
fR
7?
51
KR
ftl
7.1
1.1
.11
?.\
S
1?
7"
ri
-

13
07
sn


Ho.

9
?n
37
IK
n 4
7
7
1.1
n
n
!»

P
n
n
if
15
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Tnf


An
ftl
(in
IS

n?
ins
in


M
M


Oft
7
A
77

*1 Cop


,.1R
,n*
,ni
. T'"

.4I>
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r,t


.n.
. M


t.M
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.M
.R.l

rr


IT*
ftl
17
M

inn
OR
.-ft


«
1,1


r,f.
ft
r.
r,0




.1fi-S7
Afi-R?
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(0-lfi

M-M1
J|.|tn
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,n.;.
1 l-t'


H.or,
t ,c
A.r
IP. 71



1
3
A
5
A
.7
R
0
10


*...,
rni vuu itAiM
wr,i loi.i fr.noi
NVI -,otit>axto
WM fost. nrfirr
NHl Pig lot
THI rnn
.Wit Binflor
fjl IT. M(.|.r»lf
F|. 1 llorm» Pk
WM St.at? F*l«-


I
100
inn
inn
inn
inn
inn
inn
fit,
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71


m
74
7.1
170
1?
1
75
17
5»
11
71
omoin-f; i


n
0
n
7
n
n
0
-

10
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1
1W.
91
59
?|
ion
90
99

97
«r.
77


n";
z'
0
n
.11
15
n
^
17
0

TO

.13
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101
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.B7
51


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11


tn.i
ifi

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i i,f ..-.
7n-J7



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in.'.i
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1
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.,.1 :h,.,nrll
Ji |f '""'."
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inf.
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i;
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1.13

S..1.W
i 7 . ;?n
7.. 10,1


P»n
C/M


1



IMP.

1
I
I
n
r-
7


Ol>'.
I?
n
n
0
n
n
n

Tot
MM"
17





rov
.33
1 09




rr
M"'M"r
75





U-f, .
11. 1P

-












1
i
1




f- 1 f.r
M«, «oo«r.on
Ml I r.r,>rp 5.



I^O'l
In/1
100
57





in
77
75


*,,.ri»

f/«)

J






dA
39




ORS

s
7



Io-


3A



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OH' font tHf"' f
^,.,.,

7f. - 1 1


-------
                            TABLE 6-9.    SITE  MEAN TOTAL  LEAD  EMCs   (ug/H)
PpsMrMlril

Stir
1

.1
A
$
f,
7
n
o
in
1 1
1?


15

1 7
11
;o
-n
--1
,V
"i
,'4
rfi
??
?n
70
in
_i|
17
i;
id


./c.i»,,A*
nr.i n.,f*rf
OT.t |.*k*Hrin»
nr.i st ••*»».««
11.1 ,lrhn N
*SI Ovprtf.,,
MB? llrnlnrl
MO) Rni ton Illl 1
MP| MfimpUnrl
Mfll Mf W.,Sh


NY| linn..*

«yl f Pfirh.
I»l Doniniwnnrt
Uftl r..l-,-rV
U[ 1 riifh.mi
UN i MM t,,n'.
n.; v.-.H..-, upc.
TV] l.,1(-l

nn wrr.ticinh
*TO ic - ornrf
11. 1 .inhn <;.
TNI P|
Wft] | ^kn Hill-,
1 1. 1 Mj ( f i •; f. .
fl.: r.h,»>-fo' "HT
Pr I fa>. if)f|r
mi AShii>-r

1 l.n-

I.Anrl
HSP
ors
inn

inn
inn
inn
inn
inn
inn
inn
ion
inn
inn

inn
inn
inn
inn
inn
inn
inn
inn
inn
99
17
01
T
'H

91
on
P.O
nn
RA


70
7P

Are*
m
33


1?
fifl
n
5^
fii
3.1
n
17B
is
4)
SI
39

10?
t'n
^?
19
I.?'


110
? 7

Pop.
n*n
(•/*)
19


.
71

' 1R
R
5
30
9
1?
55
13


IP
3
o

17

9
in
i

1R

17
?.?


i


in
15

i
(Mr.
41



.13

19
.in
16
51
79
79
76
?n


.in
71
29

51
6
40
57
71
.17
I"
11
17
.17
16
.11
77


?l
.14

"0.
ftf
ORS
IS


1
19
n
36
11
n
19
13
70
13
n
R

fl
n
MR

.15
1?
n
2?
c,
3
33
1 1
l?fi
37
1?
1
9

*
art
-"
in.i


.
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737
I3R

?"5
76
Rfi
461

Rfl

19.1

15?

inn
7fi

303
in6

717
44n
19?
595
19

«.!.!
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I6R
HI
cnv
.RR



.54

.73
.39

4.53
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.«fl
I.R6

1.36

.R9

.51
72
.67
i.ni
-
I.H
.17

.nn
61
.67
I.I?
1.6n

.7?

.67
.3?
.41
Mfdlan
117



700

191
i?n

59?
69
77
?in

5?

i«
.
136
77
90
5.1

?nn
1R4

169
37fi
159
.196
76

.151


160
130
lot Confident.
limits
in-191

151-79?

I«4.?4S

I5R-73I
104-157

795- linn
56-R6
65-92
119-399

76-103
.
n6-?in

l?6.|4(

75-107
.14 -"?

I4.1-7HO
157-716

I3R-70R

|4ri-l74
.lOR-SOR
|4-<7

25.1-574


I.I,'- 19«
In5-I6l
























Mi.pd


1
?
3
4
5
6
7
fl
9
in
II
1?
"

15
16
17

19
70

5 1(1!
KM Nnland
Mnl Mamprtrn
III Mattls »
M|| Ua»«rly
T«l 5f.
Ull Unnd r.tr
Mil pt 9
MA| Convent
Mil f.rand 0 Of
^113 Pitt AA-S
»Y? Cfdar
MAI Anna
"
Mil firac* N
MI3 Swi't. 9'l"
501 Miiadp
CAI Knn.

r|. | Wilder
Cnl Nnrth Avr


land
lll»
1














-







Area
(A)
36
17
17
.in
IH7
45
33R
100
«S3
?noi
76
«ni

164
1707
?o.in
154?

|94
69


pnn.
Oeo
(•/A)
3
in
3
II
3
1?
7
1
5
?



5
7

1?


9


t
IMP.
AR
7?
5P
Sfl
43
fll
?1
33
3H
71
5
1?
*
?R
A



97
sn


"0.
0'
ORS
9
?o
'1
?*
13
as
- 7
7
IR
fi
?R
4


4
74
7?

15
33

tot*1 I part
Mr-in
1S4
7?7
554
111
737
5*2
4,19
IIS
l?7
?!
75


t 'n

3fl3
495

05
.i5n

COV
.•19
-R?
1 .ns
1.09
.31
.9*
l.n?
.94
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1.63
1.75

'
1 . 3!>

1.13
.99

.R5
.R1
«,dian
147
17fi
.inn
75
??1
K?A
107
11.1
?1
11
1 7

10


754
151

*5
7^n
90> Cpn'trtijncr
Limirs
110-19S
J 11-71?
KO-47R
55- I"?
](**,. ?r,a
34P.-51 '
IW-'.'1
pn.7^:
fiS-17)

in
S3
72
75

'OP.
n»n
(•/A)

n
n

5

•t
IMP.

69
64
44
.19

No.
al
(IRS

n
13
6
1.1
Intal lead
Mean

.
116
-
115
rov

.
.77

.'6
Median

-
9?

9?
in' ConHdnncr
limits


66-171

66-l'P

-------
TABLE 6-10.    SITE MEAN TOTAL ZINC EMCs
.r,.*.,,,l

1
1
.1


'".
in
1 1
It
i;
M
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-------
 These tables  (one for each pollutant)  list  each  of the appropriate  sites  in
 the data  base,  grouped  according to general  land  use category.  Some  pert-
 inent  site  characteristics  are  identified:   drainage   area,  population
 density, and the percentage  of  the  total  area  covered  by  impervious  surfaces.
 The  number  of  monitored  storms at  each site  is  tabulated.   Urban  runoff
 quality is summarized by the mean and median  EMC for  all  storms monitored  at
 the site, the storm-to-storm variability  of  EMC's  (defined by the  coefficient
 of variation) , and the 90  percent confidence limits for the site median EMC.

 Transferability of Data

 The urban runoff  loading  site  EMC  data were carefully examined in  an  effort
 to determine'whether specific groupings of results  would  suggest the presence
 of consistent patterns of  similarities and/or differences  that  could be used
! to support estimates of  urban runoff  characteristics at unmonitored  locations
 and sites.

 Variability of  EMCs  at  a  Site.  Inspection and analysis  of the individual
 site coefficient of variation  entries  in Tables  6-1  through 6-10 shows that
 with very  few  exceptions  (usually associated  with   constituents  that  were
 monitored in fewer than 10 storm events)  the  coefficients  of variation fall
 in the range of 0.5  to 1.0.   This applies to all constituents except TSS, for
 which the range in coefficients of variation is more like  1 to 2.

 The frequency of occurrence  of any EMC of interest can be  estimated readily
 from the coefficient of variation by  using  the procedures  outlined  in Chap-
 ter 5.   Thus, for TSS, 90 percent of the individual  storm events at a given
 site will have  EMCs that  do  not exceed a value of roughly 3 to  5  times the
 median EMC value  for  that site.   For  the other  constituents,  90 percent  of
 the individual  storm  events  at a site will have  EMCs less than about  2  to
 3 times the  median  EMC value  for  that  site.   More  refined estimates  and
 values for other exceedance  probabilities can be  readily  computed  using the
 relationships presented  in Chapter 5.

 Effect of Geographic Location.   Figures  6-4 through  6-13  indicate  the range
 of median .EMC's  at  individual  sites,  grouped  by project.   The   land  use
 category of  the site  is  indicated  by the  letter  R  for  residential,   M for
 mixed,  and  C for commercial/industrial,  and  the  plotting  position  is  the
 median value as given by  the data  in  Tables  6-1 through 6-10.  The ends  of
 the bars for  each project are  the  highest  and lowest 90  percent confidence
 limits for site median EMCs  at  the project  for the constituent in  question.
 Inspection of Figures 6-4 through  6-13  indicates  that,   for any given con-
 stituent,  each  project  can  be  put  into one  of three  rather  general  cate-
 gories:  (1)  low EMCs and tightly grouped;  (2} average characteristics;  and
 (3)  wide range  and high EMCs.   Using the numbers  1,  2,  and  3  as shorthand,
 project  categories  for   each  constituent  are  summarized  in  Table 6-11.
 Although no  site is category consistent for all constituents,  WASHCOG  (DC1),
 Tampa (FL1) ,  Lansing  (Mil),   and Ann  Arbor   (MI3)   tend   to have  lower  and
 more tightly  grouped  EMCs  than  the  others  while Kansas  City  (KS1),  Lake
 Quinsigamond  (MAI), and Baltimore (MD1) tend to have e wider range and  hiaher
 EMCs  than the  others.  Thus we  can conclude  that .some  projects represented in
 the  database  appear,  from the  monitorinc  sites   selected,  to  tend towards
 somewhat  higher or lower  EMC median  values  and ranees than the bulk  of the
 projects.  However, there  are no distinct geographical patterns  revealed.
                                    6-20

-------
 CA1
 cot
 DC1
 FL1
 111
 112
 KS1
 MAI
 MA2
 MD1
 Mil
 MI3
 NCI
 NH1
 NY1
 ii Y2
 NY3
 SOI
 TN1
 TX1
WAI
 WI1
0 1
|
B1R
.
CRMMR
1C C
IMRM
I RC
IRMRR R
1C M
IM-MM
1
R~Vl
1
1 R
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1 \
\L

i * n
00 2
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CR
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RR II
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R
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1
C R 1

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7


                    200
                             300
                          CN
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                          or
             1=12471203?
                                     400
500
                                                     600
     Figure  6-4.  Range of TSS  EMC Medians (mg/1)  by Project
                              BOD
DC1
Fll
KS1
MI1
MI3
NC1
NH1
SD1
TN1
WI1
n
D 5 10 15 20 25
i ' i
[ R

1 R C MRM
•


1 C CR MR *i
-JM MM 1 I


IRC I
1 C I

1 1 M 1
R M R C ] i
R R R C C 1
1 i
1


                        10
                                 15
                                          20
                                                   25
                                                                  41
    Figure 6-E.   Range  of BOD  EMC Medians  (mg/i)  by  Project
                               6-21

-------
 CA1
 C01
 DC1
  FL1
  111
  112
 KS1
 MA1
 MD1
  Mil
  MI3
 NCI
 NH1
  NY3
 SD1
  TN1
  TX1
 WA1
  WI1
5 5


| R RRR
M C RH


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IMJ


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1 R 1

IRRI
i R R Cl

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D 75 10
1
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1 R 1
II
M
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1
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1 C |
R 1

fl C R
RR 1

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1
0 12

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£* 1180

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167
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               25
50
75
100
125
150
        Figure  6-6.  Range of COD  EMC Medians (mg/1)  by Project
                          TOT. P
CA1
C01
DC1
 Fll
 IL2
MAI
MA2
MD1
Mil
MI3
NC1
NH1
NY1
NY2
SD1
TN1
TX1
WI1
O.b 1.0 1
rm
RRR R C M
I R R RRR R I
|R CMMR I
1 R 1
1 M R M R
1 C
1 R
ICMMMMI 1
|M M M
MR C 1
1 C 1 1
I R R
IMJ
1 R M R C I
MR R
1 RRMCC I
0.5 1.0 1
5 2.
Z)



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I


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i


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0 2
















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5 3.




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D





4.2 4.'
>/RRRl









.0
      Figure  6-7.  Range  of Total F EMC Medians  (mg/1)  by Project

-------
                    SOL. P
t
CA1
C01
DC1
FL1
111
112
KS1
MAI
MD1
MM
NCI
NH1
TNI
WAI
2

1 Rl

LJ
MRMRC



r
IMM


1 R
"jj
1 2
0 4

1CR
RRR RR

[ RRM
|
1. cc
1
t R
MM C
|R

M C
1 	 |
0 4
0 6
1
R 1!
	 1


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M
M
n
1


R
0 6
0 8
R
A 1


R 1

1
R
A

O

i
0 8
0 10
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1
M
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0 1
0 12






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M R



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10 1
0 1'













20 1
0







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'




40
                                                             R|349
Figure 6-8.   Range of Soluble P  EMC Medians  (mg/1)  by Project
                          TKN
t
CA1
C01
DC1
FI1
IL1
112
KS1
MA1
M01
Mil
MI3
NC1
NH1
NY1
NY2
NY3
SD1
TNI
WAI
WI1

11

.

1 RCMRM 1



r
1 RR
IMM
IM M 1


1 R
IMI
IRC



(RRC

0 21

RR C
1 R R 1

1 RR
1
ICCRRM 1
M MR
M
MCM I

1 R
1 C
J

R

R C
IR Rl
C

0 30
1
1
R M
1 I


R

R r
R


(



1
M
M

n

0 4(
R
R


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J

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1
R
.
C

0 50
I
1 1

1
1
\














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0 60

D


D


i









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~1

0








?
-------
[
CA1
C01
DC1
FL1
IL2
KS1
MA1
MD1
MM
NC1
NH1
NY3
TNI
WA1
WI1

11


|R RRR
ICMRR R


1 A
IR
1



1 R

TRR c

)0 21

I RR
R R |
J
I R

II M
R
MM n
1 R

r
M
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N02 + 3-
)0 3C
R
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1
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1

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791
M£ C 12882

li I973



i t H247




         100
                  200
                           300
                                   400
                      500
                        600
Figure  6-10.  Range  of NO   -N EMC  Medians  (mg/1)  by Project
                         Cu
(
CA1
C01
DC1
FI1
111
K51
MAI
MA2
MD1
MM
M13
NC1
NH1
NY1
NY2
NY3
SD1
TNI
TX1
WA1
WI1

) 200 400 61
1 	
ICRRMRRI
1R RRRR R
[CMMRR |l
1 1 M R
| C CM
1 M R M
1C R |
l| R RM
1 M MMM C
IMM MM
1 1 CR I
LRRI
1 M 1
|C R R |
1
CRM
RR I
RR|
ICC RRMCR 1
1
10 81


RR |
R


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r
R




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1







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1 C 11820





         20D
                400
600
800
100G
1200    1400
rig-ore  6-11,   Range of  Total Cu  EMC Medians  (vg/'l) by  Project

-------
                       Pb
           50
                   10G
        150
        200
250
CA1
C01
DC1
I12
KS1
MAI
MA2
MM
MI3
NY 2
S01
TNI
,. '



[ M 1



| RM R RCR
[R R RR R {/392R598



314) H396R 501
| C M C R RV 378
| M R M R |
C R
MMM M C I
[M MM |
|_M_J

1 Nl 1



1C R R M |


1


           60
100
150
                                     200
                          250
Figure 6-12.   Range of Total Pb EMC  Medians (yc/1) by  Project
                        Zn
CA1
C01
DC1
FU
111
KS1
MA1
MA2
MD1
Mil
MI3
NC1
NH1
NY1
NY 2
NY3
SD1
TN1
1X1
WA1
wn

i
1 M 1 1


1 R RR C R M 1
1 R RRR RR i
! £ MRMtt




MR R R 1


JCC R I
[ M R M MR 1

i
1C R I


, ! C MMM M 1
IM MMI
IR C I


1 C 1
T RR 1
1 M 1

9.9
1 R RM RftRH2.2


LC R fi 1


IRMC R 1

M I


1 R R 1
IRRI
LCCRRMC i




I


Figure  6-13.   Kange of Total  Zn EMC Medians  rgg/1) by project

-------
           TABLE 6-11.   PROJECT CATEGORY  SUMMARIZED BY CONSTITUENT



TSS
BOD
COD
Tot. P.
Sol. P.
TKN
N02+3-N
Tot. Cu
Tot. b
Tot . Zn
( 	 i
G
U
•3
_
3
1
2
2
2
2
2
2
^ t i 	 ,
u
Q
^
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a
2
"5
1
1
1
1
1
!—!
r. .
i
2
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1
-
1
1
I
1
1
r— i
M
H
2
_
'S
2
-
2
—
2
2
-
r-:
a:
^
' 3
7
3
3
3
2
-
2
1
3
H 1 t— ' —
<

3
_
2
3
2
2
3
3
2
2
C i H
2 £
,
__
,
^
J
-
"
3
3
3
3
T
_l
2
1
2
' 2
I
1
1
1
2
fi
1— !
2
1
1
-
1
1
• 1
2
-
-
-
n
>!
2
2
_
1
2
-
2
-
-
1
3
( 	 t
2
tH
3
2
2
2
2
1
1
2
. 2
2
i — i
H-i
s
2
2
2
2
-
1
1
-
2
2
It must  also be  realized  that had  any particular  project monitored  other
local sites (or additional  sites)  its categorization  could well change.   This
can be seen  qualitatively  by  perusing Figures 6-4 through  6-13  and  mentally
dropping the highest or lowest site  from each  grouping.   Although some  loca-
tions, such as Tampa,  will  undoubtably and  appropriately  be influenced by the
relatively low  EMCs  and  tight groupings found there in  estimating  probable
values for other urban sites in the area, there is little to warrant attrib-
uting similar  characteristics to  other locations in  the  same  geographical
region.   For the other locations  it would appear that individual site differ-
ences eclipse any possible  geographic ones.

Effect of Land  Use Category.   The  data in  Tables 6-1 through  6-10 were pre-
sented by land  use category;  residential, mixed,  commercial, industrial, and
open/non-urban.  The  question to be  addressed here  is  the extent  to  which
such site categorization can  be  used to assist in predicting EMC parameters
for unmonitored sites.   Two approaches  were  used.   In  the first,  the site
data for each project with more than three  sites  were  normalized by  dividing
the site median and its  upper and lower SO percent  confidence  limits by the
average  project median value for  the  constituent in  question.  This procedure
simply  allows   all  constituents  to  be  viewed on  a  common  scale   that  is
centered at  unity.   An  example  of  the  result is given in Figure  6-.14.   A
legend is provided in Figure  6-14 (a)  showing  the  lower 90 percent confidence
limit, the upper  90 percent confidence limit, and the location of  the  point
estimate of  the median within this   confidence  interval  for  a hypothetical
constituent.   Sites that  fall  to  the  right  of  the unity line have higher EMCs
than average  for this location,   while sites   that  fall   to the  left of the
unity line have lower EMCs than  average.   Thus,  the  interpretation is that
for this  location,  Site  #1 is the "dirtiest"  (has  the   highest  EMC value) ,
Site #3   is  the  "cleanest",   and  Site  £2  is  in  between,  being   somewhat
"dirtier" than  average.   Since  the  90 percent  confidence  limits for  these
three sites  no not overlap,  we  know,  that  this difference is statistically
sianificant.

-------
                            1.5
                                    2.D
SITE* 1
SITE * 2
SITE » 3

__^_^ *~
upptmos CM
el i»n

IDEICI IIMI1
                 MV Different  Sites
  (a) Significantly
0
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,-vui« n.
t-iic an c.
t-1lKt
t-CHMIV
i-»»BURY
•-•ORIH •«.
C-VKU n.
H-BI6 MY t.
R-ntit
R-CNfffl
R-ueraY
M-IORIH »«.
c-vui> n.
H-B1B mi C.
lUllllt
R-CKtWY
B-«SBUIY
n-«mii MI.
c-mi» n.
K-IS mi c.
K-11M
K-cmiKi
R-»umt
M-IOIITH Ml
c-vuun.
R-BB DRY C.
R-1IK
R-CHtWY
n-UBimi
H-MRTH »«.
c-vnu n.
B-BtC DH1 t.
R-11IIC
R-CHIMIY
R-MBUR1
M-IORTH »«
c-«u» n.
R-BK mi t.
R-nuc
R-CHERtlY
R-ASBURY
W-WRTH *Vt.
c-viu* n.
R-BIG MY C.
R-neic
R- CHI RBY
D.5 1.0 1.5 2.0
t— *
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>- •
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| TOT. ZN
|
                                                          O.E    1".C    1.5    2.0
               .*>,
   (b) Sites with
       Difference
            Figure
                      Significant
(c)  EMC Data  from Denver  (CO1)
                   6-l4.
                                 of Normalized  EMC Medians  et.  Denver  (COD
                                         6- 2 7

-------
The actual data for the Denver (CGI) project are presentee in Figure 6-14(c).
With the exception of  nitrate + nitrite, there  is  little  tc nc statistically
significant difference  among  the  majority  of the  sites fcr each constituent
examined.   The lack cf consistency among  the  sites  over  the  various  con-
stituents  is  apparent.   One can  observe  that the Cherry  site  (residential)
tends to plot  at the lowest position for all constituents, suggesting that it
is the  "cleanest,"  the Asbury site  (also  residential)  tends,  to  plot  at the
highest  position,  suggesting  that  it  is   the   "dirtiest."   The  Eig  Dry
Cottonwood site, which  is  also residential,  tends  to fall between these two.
Careful  examination  of  other site  data  does  not  provide  any  evidence  tc
explain  this  difference in response for sites in  the  same  land use categcry
at  the  same   location.    Thus,  based  on  the  information  presented  in
Figure 6-14 (c), one  is forced to conclude that  land  use  category  does not
provide  a  useful basis for predicting differences  in site  EMC  values,  at
least for this project.

When the foregoing type of  analysis  was applied  to the other  applicable NURP
projects,  the  results  were the  same.  As another  example,  the range of nor-
malized  EMC   medians   at   Tampa   (FL1)  and  WASHCOG   (DC1)  are  shown  in
Figure 6-15.   These   are   essentially  similar  tc  the Denver  results  just
discussed.

The WASHCOG  date presentee  in  Figure 6-15(b)  suggest that  there  is  little
consistent difference among residential land  use sites at that project.  The
data  from  Champaign/Urbana (IL1)  presented in  Figure 6-16 suggest just the
opposite.  As  a part of this project's  experimental  design,  two site  pairs
were selected.  The  sites  of  each pair  were expected to respond in a  similar
fashion.  That they do  and  that the  responses of the two  pairs are different
from each  other for  most constituents is  apparent, in  Figure  6-16.  However,
there is no consistency in  the pair  responses.   Fcr  example,  the Kettis pair
has significantly  higher EMC values for  T£S,  COD,  and  Total Pb,  while the
John Pair  is higher in  Total P.   The residential land  use category for  these
sites provides no explanation of these differences in  response.

Eased upon the foregoing  approach,  we can conclude  that,  while there can be
differences in  the responses  of different  sites at  a  given location,-  signif-
icant differences dc not  appear  to be widespread, and where  they occur, the
site  land use category  is virtually  useless  in  trying   to understand or
predict them.

The second approach  to examining  the effect, of  lane use  category en  the EMC
parameters of  s. site makes use cf  the  observation,  discussed earlier,  that
Geographic location  has no discernible  effect  on  size 'response.   Since site
t.c Site  variability • was shewn tc be verv well  represented by the  logncrmel
distribution,   analysis  procedures similar to these  describee previously for
characterizing an individual site were  applied.   Table 6-12  lists  the median
EMCs for all  sites v;ithin  each  land use category.   The coefficient  of varia-
tion quantifies the  variability  of  site characteristics  within the land use
category.  To  the extent  that the si-es included  in this  database  provide  a
"representa-cive" sair.pie c:: the land u.ss  classifications.,  then the  infcreation
summarized by  I'-abl^  £-1.'   indica'css  -he eff.ec"  cf  lane  use  cr. urban  storm
rur.cff -cllutanv. cischarces.

-------
                                                  0.5
                                                        1.0
                                                             1.5
                                                                   2.0
0
R-VOUIG
M-WDOIR
M-JESlin
B-CHMTIB
C-»OR*«
R-VOUHG
H-«inn
H-JESUn
R-CH«BTIB
C-IIORM*
R-tOUHG
M- WIDER
M-JISUH
R-CHARtiR
C-HORMA
R-rount
M-WUDER
M-JESim
R- CHARTER
C-liORll»
R--.<>•' .
t-
* 	 1
^
, £/
1 >_ <
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1— «f 	

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1SS




TOT. P

SOL. P
TKH
N02 + 3-«

TOT. CU

TOT. Pb

TOT. 2K
            1.0
                  1.5
                       2.0
                                                   0.5
                                                         1.0
                                                              1.5
                                                                    2.0
(a)   Tampa Sites
(b)   WASHCOC- Sites
        Fiaure  6-15.   Ranee of  Normalized  EMC Medians  et  FL1 and  DC1
                                      6-29

-------
(
R MATTIS S.
M-MATTIS N.
R-JOHN N.
R-JOHN S.

R_ MATTIS S
M MATTIS N
R mHN N
R— IflHN S

R-MATTIS S
M MATTIS N
D IflHU M
n — j u n n n .
R— IfiHW S

R— MATTIS S
MM ATTIC U
— MAI Ho nl.
D inMit M
n — junn n.
D_ mHM S

R— MATTIS S
M MATTIS M
— W1AI llo n.
o mUM M
n — jufin n.
D inuu c

R— MATTIS S
MMATTIC M
RinuN M
D inHiu 9

) 0














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COD




TOT. P




TKN




TOT. CU




TOT. Pb


        0.5
1.0
1.5
2.0
Ficure 6-16.  Ranee  cf  Normalized EMC Medians  at  IL1
                         6-30

-------
TABLE 6-12.  MEDIAN EMCs FOR ALL SITES
         BY LAND USE CATEGORY
Pollutant
BOD
COD
TSS
Total Lead
To t a 1 Coppe r
Total Zinc
Total Kjeldahl Nitrogen
NO -N -t- NO -N
Total P
Soluble P
•
f
1
mg/£



ug

,


-
/!.


Residential
Median
10.0
73
101
144
33
135
1900
736
383
143
cv
0.41
0.55
• 0.96 '*
0.75
0.99
0.84
0.73
0.83
0.69
0.46
Mixed
Median
7.8
65
67
114
27
154
1288
558
263
56
CV
0.52
0.58
1.14
1.35
1.32
0.78
0.50
0.67
0.75
0.75
Commercial
Median
9.3
57
69
104
29
226
1179
572
201
80
CV
0.3.1
0. 39
0.85
0.68
0.81
1.07
0.43
0.48
0.67
0.71
Open/Nonurhan
Median
-
40
70
30
-
195
965
543
121
26
CV
-
0.78
2.92
1.52
-
0.66
1.00
0.91
1.66
2.11

-------
Some caution in the interpretation  of  the  information presented  in  Table  6-12
is  in  order since statistical confidence  limits  are net  given.   These  are
indicated  in  Figure  6-17  (e through k),  which  illustrates land use  differ-
ences graphically, with additional  statistical detail derived from the basic
parameters listed in  Table 6-11,  to assist in  interpretation and comparisons.
The box  plots  which  compare characteristics of all  sites  within a land  use
category identify the land use, median EMC,  its  90  percent  confidence  limits,
and the  10, 25, 75 and 90 percent quantities for the sites.   Careful  perusal
of  these box plots leads  one to  the conclusion that only  the 'open/non-urban
land use category appears  to be  significantly different overall.   Responses
of  the  other  land use categories  are varied  and  inconsistent among  con-
stituents.   This  may  be  seen in a somewhat different  way by  observing  the
plotting  positions of  the  land  use categories  presented  in  Figures 6-4
through  6-13.   Here   also,  there are  no  consistent  tendencies.   There  are
undeniably  some trends.   For example, in Figure 6-7 commercial sites occupy
the lowest  plotting position at  each project for  total phosphorus  (Mil  and
one Wll  site are  exceptions), which certainly suggests  that there  might  be a
land use category difference for  this  constituent.

Review of Figure  6-17(j),  however,  suggests that while a trend to lower total
phosphorus EMC values is apparent as one  goes from residential, to mixed, to
commercial  land  uses, the  statistical  significance may  not be great.   The
actual  site  median total  phosphorus  EMC probability  density  functions  for
each  land   use  are  presented in  Figure 6-18.   Here   it  can  be  seen  that
although three different pdfs can  be  drawn for residential,  mixed,  and  com-
mercial  land use  'categories,  their degree of overlap is, so great  that there
is  little  statistical significance to the  apparent difference.   Since  this
was the  strongest tendency  towards  land  use effect,  we  must  conclude  that
using this approach there  is again  no truly discernible and consistent effect
of  land  use on the quality of urban runoff.

The one  exception is  the open/non-urban category which, as its  name suggests,
includes  atypical sites.   The  data  in  Table  6-12  and  the  box plots of
Figure 6-12 suggest that  the  pdfs  for this land use  category are  quite dif-
ferent from those of  the  other  land use  categories,  and  this is in fact the
case.  Figure 6-18 shows it dramatically for total phosphorus.

Thus, regardless  of the analytical  approach taken, we are forced to conclude
that,  if land use category effects  are  present,   they are  eclipsed  by the
storm  to storm variabilities and  that,   therefore,  land  use category is of
little general use to aid in predicting  urban  runoff  quality  at unmonitored
sites or in explaining site tc site differences where monitoring data  exist.

Correlation Between EMCs  and Runoff  Volume.   To  examine  the possible  rela-
tionship between  the  event mean concentration of a particular constituent and
the runoff volume, linear correlation  coefficients (r)  were calculated.  The
null hypothesis that  the  two variables are  linearly unrelated was tested at
both  the 90  and  95 percent  confidence   levels.   Since  it  is possible  for
correlation to be either positive  or  negative,  the two-tailed  test was  used.
Failure  tc  reject the null  hypothesis is interpreted  as meaning that linear
dependency between the two variables in the population  has not  been shown.

-------
                      LEGEND
              GROUP A    GROUP 6
                                        20

                                        18 -

                                        16 -

                                        14


                                        12




                                         8

                                         6

                                         4

                                         2
                                                                              BOD
                                                                RESIDENTIAL
                                                                               11
                                                                             MIXED
                                                                     11
                                                                 COMMERCIAL
                                                                    SITES
                                                                       1
                                                                     OPEN
                                                                      SITE
(a)
                                    (b)
 BOO
 400
 300
 200
 100
          33
       RESIDENTIAL
         SITES
                         TSS
 19
MIXED
SITES
    14
COMMERCIAL
   SITES
OPEN
SITES
                                        160


                                        140


                                        120


                                        100


                                         80


                                         ED


                                         40


                                         20


                                          0
                          33
                       RESIDENTIAL
                         SITES
                                                                                     COD
 16
MIXED
SITES
    13
COMMERCIAL
   SITES
OPEN
SITES
                                                         (d)
                     Figure 6-1".   Boy.  Plots  of  Pollutant EMCs  for
                                      Different Lend Uses

-------
100r
|
90 j-
60
70
= en
z e 60
-*• &
sst-
S S « = 50
z t- i
LAJ **• e
tg£
"•-c 40
u:
30
20
10











•
•












\
\














'/
{
r
i








^





i

° 23
RESIDENTIAL
SITES









TOTAL
COPPER

T
I
«2
c3
0

2
UJ
G
" ~ ~ " U - - J ^
1 / \ 1 =
w \/ '
X 6
[* ~ ~ . "t 1
1
U 10 2
MIXED COMMERCIAL OPEN
SITES SITES SITES
                                                            S>-i
                                                                   500 r
                                                                   400
                                                              •c   300
                                                                    200
                                                                    100
(e)
                                                             (f)
                                                                                                    TOTAL LEAD
                                                                              30
                                                                          RESIDENTIAL
                                                                             SITES
                                                                                    1
                                                                16
                                                              MIXED
                                                              SITES
                                                                  11
                                                              COMMERCIAL
                                                                 SITES
                                                               7
                                                              OPEN
                                                              SITES
      500
      400
      3DO
      200
       100
                    TOTAL
                    ZINC
                26
            RESIDENTIAL
               SITES
MIXED
SITff
    13
COMMERCIAL
   SITES
 4
OPEN
SITES
                                                                     5000
                                                                     4000
                                                                     3000
                                                                      2000 [
                                                                      1000
                                                                             TKN
    32
RESIDENTIAL
   SITES
 16
MIXED
SITES
    14
COMMERCIAL
   SITES
                                                                                         8
                                                                                        OPEN
                                                                                        SITES
                         :':. o u r £  t -1 . .
                  tsox  Plots  c-r  ;
             fferent  Land Uses

-------
                              NITRITE
                                AND
                              NITRATE
                         17
                        MIXED
                        SITES
  ..- 11
COMMERCIAL
   SITES
                      6
                    OPEN
                    SITES
      1000


       900


       800


       700

   —
!o|   600
I Pz
: «%.
(|11 600


' e H   400
 «o

       300


       200


       100


         0

 LAND USE
 NO SITES
                                                    TOTAL PHOSPHORUS
                                                               34         19         14         8
                                                           RESIDENTIAL    MIXED   COMMERCIAL    OPEN
                                                                                   &         &
                                                                                INDUSTRIAL  NON URBAN
  (i)
                         (j)
Is.
       250
       200
       150
       100
   16
RESIDENTIAL
  SITES
 14
MIXED
SITES
                                    SOLUBLE
                                  PHOSPHORUS
 COMMERCIAL
   SITES
                                               6
                                              OPEN
                                              SITES
  (k)
                      Figure  6-17.   Box  Plots  of  Pollutant  EMCs foi
                                Different  Lane Uses  (Cont'd)

-------
URBAN OPEN
    &
NON URBAN
 (121
 CV = l.fifi
                                                          URBAN LAND USE
                                                       COMMERCIAL  (201)
                                                       MIXED        1263)
                                                       RESIDENTIAL  (383)
                                                          1000
 CV
0.67
0.75
O.R9
  3000
                         SITE T.P. CONCENTRATION (pg|l)
        Figure 6-18.   Site  Median Total P EMC Probability  Density
                    Functions for Different Land Uses

-------
The rejection of the null hypothesis means that there is evidence  of a  linear
• ii-pendency between the  two  variables in the population, but  it does not mean
that a cause-and-effeet relationship has been established.

"•neral guidelines  for the use  of  this test  suggest  that  it  be used with
i-hution for  values  of  n  less  than ten  due  to the  high uncertainties  asso-
r-inted with  estimates  of  population variance  with  small  samples.  Further-
more, when n  is 2 a perfect correlation will  result but is  meaningless.   To
include as many sites as possible  in  this examination, all  constituents  for
-which n was 5 or greater were  included.  At  the other extreme,  when n  is very
Jorge, say over 100, correlation coefficients are  almost always  significant
Jn.u can be so weak that they are meaningless.   For n =  100  the critical value
 !  r  at  the  90 percent confidence  level is 0.164,  meaning that  the correla-
 ion explains less than 3 percent of the concentration  variability.

   total  of  67 sites from 20 of the NURP projects were  examined  for possible
 correlation  for nine  constituents.   Of the 517 linear correlation  coeffic-
 ients,  calculated  (not  all   constituents  were  measured   at  all  sites),
  Hi (22 percent)  were  significant  at  the  95 percent  confidence level  and
  M (30 percent)  were  significant at the 90 percent  confidence level.   Of the
   values  that were  significant, 83 and 87  percent were negative at the 90 and
  J-. percent   confidence  levels  respectively.   When sites   with   fewer  than
  1) events were  dropped,  the  foregoing was essentially unchanged.   Greater
  vtoil in terms of  the number of significant  linear correlation by constit-
  rnt  is  provided in  Table 6-13.  There  it can  be seen  that  the  greatest
   ndency for  positive  values  of  r occurs with  TSS,  followed  by  soluble
   lusphorus.   The correlation  coefficients  for the  other  7  constituents  all
 bUongly tend to be negative.
 kj
  >>»MI the results are  examined by sites, however,  a clearer picture emerges.
  Illiough it can be correctly  argued  that unless a correlation coefficient  is
 l*.6tistically significant the  number  is meaningless, it also follows that  in
 Mich a  case they  are  as likely  to  be  positive  as negative.   On the other
 j*nri, if all  the  correlation coefficients  (whether significant or not) have
      same sign, it  suggests  a  tendency for that site.  The  sign  of  the  corre-
 lation  coefficient  (if  greater  than  0.1)   for  each  site  and  constituent
  »nn\ined is given in  Table 6-14.   Giving appropriate  weight to  si-gnifica-nt
   values but  considering others as well,  some 37 of the  sites tend to have
  »?Mt>tive correlations,  13  tend to be positive,  and the remaining  17 tend  to
  »c mixed.   Perusal of Table 6-14 reveals that  this  tendency for  sites to have
  oilier  positive   or  negative  correlation   coefficients   is  quite  strong,
jr;:**prcially  for sites  with  a large number cf significant correlations.   Sites
       erosion,  scour,  system lag, and  such  are present could be  expected  to
       .t a tendency towards  positive correlations.   Sites lacking such effects
i'-H'u'ld be  expected to have negative  correlation due  to dilution  associated
     h larger' runoff events.

      magnitude of  the correlation  coefficients  is  indicated in  Table 6-15.
    • (joints  stand  out  in  particular.   First,  the  r  values are net  very  large,
     i.'Kiinc   crounc  0.55.   This  means  that  the  correlation  is  only  able  to
     iiiir:  abcut  30 percent,  cf  'the  concentration  variability.   The few  high
    itn•;.  are  alwavs  associated   with very few  observations  (n<10)  for which the

-------
TABLE 6-13.  NUMBER OF SIGNIFICANT LINEAR
       CORRELATIONS BY CONSTITUENT
(a) ALL SITES
TOTAL #
POLLUTANT OF SITES
TSS
COD
TOT. P
SOL P
TKN
N02 + 3-N
TOT. Cu
TOT. Pb
TOT. Zn
TOTAL
PERCENT
67
64
67
34
64
57
49
*%
56
517

90% SIGNIFICANT CORRELATION
TOTAL #
13119%)
24 138%)
20 (30%)
10 (29%)
19 (30%)
17 (30%)
17 (35%)
15 (25%)
19 (34%)
154
30%
#NEG.
4
23
16
6
18
15
15
13
18
128
83%
#POS.
9
1
4
4
1
2
2
2
1
26
17%
95% SIGNIFICANT CORRELATION
TOTAL ft
1 (10%)
19 (30%)
15 (22%)
7 (21%)
14 (22%)
13 (23%)
13 (27%)
12 (20%)
16 (29%)"
116
22%
# NEG.
3
19
12
4
14
11
12
11
15
101
87%
# POS.
4
0
3
3
0
2
1
1
r
15
13%
Ib) SITES WITH n > 10
TSS
COD
TOT. P
SOL. P
TKN
N02 + 3-N
TOT. Cu
TOT. Pb
TOT. Zn
TOTAL
PERCENT
56
52
53
23
50
41
31
45
37
388

9 (16%)
21 (40%)
17 (32%)
8 (35%)
17 (34%)
14 (34%)
13 (42%)
13 (29%)
14 (38%)
126
32%
4
20
15
5
16
12
12
12
13
109
87%
5
1
2
3'
1
2
. 1
1
1
17
13%
7 (12%)
16 (31%)
12 (23%)
6 (26%)
12 (24%)
12 (29%)
12 (39%)
11 (24%)
11 (30%)
99
26%
3
16
11
4
12
10
11
.10
10
87
88%
4
0
1
2
0
2
1
I
1
1
12
12%

-------
                          TABLE  6-14.   SIGN OF CORRELATION COEFFICIENTS BY SITES



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NY1 CARll R.
NY2 CEDAR
NY3 CRANSTON
E. ROCH.
SODTHGATE
TN1 CBU
R1
R2
SC
TX1 HART
R'WOOD.
WAI LAKE H.
SURREY D.
WI1 BURBANK
HASTINGS
LINCOLN
POST 0.
RUSTLER
STATE F.
WOOD C.



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 • INDICATES R POSITIVE R VALUE
 - INDICATES A NEGATIVE R VALUE
©INDICATES « SIGNIFICANT R VALUE
 Bl»NK INDICATES EITHER R LESS THAN 0.1 OR NO DATA

-------
                                   TABLE 6-1.5.    CORRELATION COEFFICIENT VALUES  BY  SITE

fftl KNOX
S. "IFW.
r.m AsniiRY
R. DRY C.
CHF.RRY
N. AWE.
RODNEY
VILLA IT.
11R/H
nni miFiF.F
FAIRIDGE
IftKFRIOGE
STF.FWICK
STRflTTON
WFSTLEIGH
FI.1 CHARTERIH
YOUNG
NDRMA P.
I1 1 JOHN N.
JOHN S.
MATTIS N.
MftTTIS S.
KS1 HIM

^, =» •" *
O- O- "^ O Q- rsi
C/} O >— _J z oi t_' )_' . |_J
(ST) .in
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.17
@
0 C«T) (7?) (Tz)(52)(7j) 0 0
© ©
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©
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-.7
@ ..39 0 0
(.fiz) '.si ii (.fin) -.51 (BT) ..sfi
ii
n
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..IB t.ti) II II II
'.Ri)(.5!^ ii (.in) n (.in) (.16) u
(.BI)('.SS'I n (.53") n (.31) (-.««) n
n u


KS1 LENAXA
METCALF
NfllANO
OVERTON
MAI ANNA
CONVENT
JORDAN
LOCUST
RT. 9
MA2 ADDISDN
HEMLOCK
MD1 ROLTON
HAMPDEN
HOMELAND
MT. WASH.
RES. Hill
MM GRACE S.
GRACE N.
GRAND
IND. OR.
WAVERLY
NCI 1013
1023
NH1 PKG.
f* 3 .e z
0. Q_ £ " °- ^
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II II (S7)

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NY2 CEDAR
NY3 CRANSTON
E. ROCH.
SOtlTHGATE
TN1 CRD
R1
R2
SC
TX1 HART
R'WOOD.
WA1 LAKE H.
SURREY D.
WI1 BIIRBANK
HASTINGS
LINCOLN
POST 0.
RUSTIER
STATE F.
WOOD C.




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( ) INDICATES 95% LEVEL OF SIGNIFICANCE. OTHERS ARE AT THE 90% LEVEL
 II INDICATES AN UNMEASURED CONSTITUENT
 BLANK INDICATES NO SIGNIFICANT CORRELATION

-------
test  is  suspect  since  one or  two events  may  dominate  the  correlation  or
otherwise cause it to be  overstated  due to uncertainties in  parameter  esti-
mation.  Second, only 25 percent of the sites account  for over  two-thirds  of
the significant correlations.   In  fact, 33 of  the  67  sites had at most one
significant correlation,  16  had 2  or  3,  and  16 hac  4  or more  significant
r values.

Data  for the  sites  with many  significant  correlations  are  presented  in
Table 6-16.   It  can'  be  noted  that  the  r values  for  all  constituents  are
around 0.55.  Thus, there  is no overall tendency to have strong correlations
for some  constituents  and weak correlations for others.   On a site  by site
basis, the  strength  of the apparent  correlation varies  inversely with n  as
does  the  significance  requirement.  Discounting the  sites  with very  low  or
high  values of  n, however, the r  values  for  the remainder are  a-gain around
0.55, which is the average for all 19 of these sites.   Turning  to land use,
it  is significant that  half  of the sites  with  many significant correlations
have  a large commercial/industrial component.   Discounting sites with a small
number of observations (n _< 12), the sites in Table 6-16 are smaller  (average
size  is  41 acres  vs 126 acres  for all sites) ,  more  impervious  (average  of
65 percent  vs  40 percent for all  sites) ,  and  have  higher  runoff  •coef-
ficients  (0.5 vs 0.3 for  all  sites).   Thus,  one could conjecture  that their
responses might tend to be somewhat  less  random and more ameanable to  deter-
ministic  analysis  (i.e., with  conventional  modeling approaches).   Since they
represent only  around  25  percent  of the total  number  of sites,  however, and
the correlations  are  rather weak,  any effect of EMC  correlation with  runoff
volume can be ignored without  serious overall error.

This  finding  of  no  significant linear correlation between  EMCs  and  runoff
volumes  is  important for  several  reasons.  First,  in stormwater monitoring
programs  there  is  a  natural  and  appropriate  bias that favors  emphasizing
resource  allocation to larger  storm events.  This was generally the case with
the NURP  projects  as  well. However,  because  of differences  in local meteor-
ological  conditions,  degree of site imperviousness, and  other factors,  there
are appreciable differences in the average sizes of storms monitored by site
in  the NURP  database.   Since no  significant  linear  correlation  was  found,
such  biases and differences are not expected  to influence  EMC comparisons  tc
any appreciable extent.

Secondly,  the  probabilistic  methodologies  for  examining  receiving  water
impacts  identified in Chapter  5 assume, as  they are now  structured,  that con-
centration and  runoff volume  are  independent  (i.e., that there is no signif-
icant correlation).  Although  the  methods  can be modified to  account for such
correlations  if  they  exist,  the finding  of  no significant correlation indi-
cates that such refinement is  not  warrantee at  this  time.

Other Factors.   We have  not  exhaustively analyzed  all  potential effects  of
other factors that might  influence and hence modify our interpretations  and
conclusions  regarding site differences.   Factors   such  as slope,  population
density,  soil  type,  seasonal  bias  in monitored   events,  and  precipitation
characteristics   (average  rainfall   intensity,   peak   rainfall   intensity,
rainfall   duration, time  since last •  stor~; event,  etc.)  all  have  a  potential

-------
TABLE 6-16.  SITES WITH  MANY SIGNIFICANT CORRELATIONS

r.oi NORTH AVE.
VILLA IT.
DC1 WESTLEIfill
FI.1 CHARTERIH
11,1 MATTIS N.
MATTIS S.
KS1 LENAXA
MA
1 LOCUST
ME)
1 RES. HILL
NCI 1013 ICRHI
NH1 PKfi.
NY3 E. ROCHESTER
TNI con
R1
WA
1 LAKE H.
SURREY n.
WI1 P.O.
RUSTLER
STATE FAIR
AVERAGE •'
AVERAGE r
CO
CO
1 —
-

-
-
-
-
-

.80

-
. -

-
-.48
.82

-
-
-.39
-.37
-.47
.34
.58
tn
-.58
-,70
-.32
-.62
-.64
-.61
-.70

-

-.79
-.58
-.58
-.79
-
-

-.33
-.34
-.28
-.55
-.48
.33
.58
1 — "
0
I —
-.47
-.58
-
-.54
-.59
-.55
-.51

.91


-.46
-
-.84
-.62
-

-
-.30
-.24
-
-.47
.29
.53
Q_
o
CO
-.42
-.67
-
IJ
II
IJ
U

-

U
II
II
. U
-.47
-.62

U
U
U
U
U
.31
.55
g
-.72
-.69
-
-.68
-.48
-.53
-

-

-.58
-.57
-.49
-.70
-.56
-

-.34
-.21
-.46
-.39
-
.30
.55
rn
0
-.52
-.44
-.39
-
II
U
U

-.82

-
-.67
-.46
II
-
-

U
U
-.53
-.37
-.72
.30
.55
13
-.47
-.46
-.84
-.54
-.40
-.34
-.80

-

-.55
-.32
-.50
U
-.51
.72

U
II
U
U
IJ
.31
.56
_D
-.42
-.55
•f-
-.67
-.46
-.46
-

.78

-
-.29
-.41
-.72
-.51
.85

-.29
-.18
-.23
-
-
.28
.53
c:
-.46
-.65
-.44
-.56
II
II
-

-

-
-.54
-.58
-.72
-.65
.82

-.37
-.23
-.
-
-
.32
.57
CD

-------
influence en  the median  arid variability  of  pollutant  concentrations at  a
site.

On  the  basis  of limited  screening,  however,  we have  concluded that  such
factors do not appear to have any real consistent significance in explaining
observed  similarities  or  differences among  individual  sites.   Therefore,
although more detailed and rigorous  analysis and evaluation of the NURP data-
base may  well provide  additional useful  insight and  understanding  of  the
influence of  such  other  factors,  we do  not believe  that the  basic  findings
and conclusions presented in this  report  will be significantly altered'by the
results of such' efforts.   Furthermore, the  value  of  any  such insights as may
be  developed  are likely  to  have  limited  influence  on general  decisions on
control  of  urban  runoff.   For example,  the  finding  of  a  strong  seasonal
effect  on  EMC values would  have  little  influence on  a decision  to require
detention basins in all newly developing urban  areas,  nor  would it be likely
to influence their design.

Urban Runoff Characteristics

Having  determined,  as discussed  in  the preceding section,  that geographic
location, land use category, or other factors appear to be of little utility
in  explaining  overall  site-to-site  variability or predicting the character-
istics  of  unmonitcred  sites,   the  best  general  characterization  of urban
runcff can be obtained by pooling  the site data for all sites  (other than the
open/non-urban ones) . ^ This approach is appropriate,   given the  need for a
nationwide  assessment and  the  general  planning  thrust   pf  this   report.
Recognizing that there tend  to be exceptions to  any generalization, however
realistic and appropriate,  in  the   absence of  better information  the  data
given in Table G-17  are  recommended  for  planning  level  purposes as  the best
description of the characteristics of urban runoff.
         TABLE 6-17.  WATER QUALITY CHARACTERISTICS OF URBAN RUNOFF
Constituent
TSS (mg/1)
i
BCD (mg/1)
COD (rag/I)
Tot. P (mg/1)
Sol. P (mg/1)
TKN (mg/1)
NO, _-N (mg/1)
Tot. Cu (yg/1)
Tot. Pb (pg/1)
Tot. En (UQ/'I)
Event to Event
Variability
in EMC's
(Coef Var)
1-2
0.5-1.0
0.5-1.0
0.5-1.0
0.5-1.0
0.5-1.0
0.5-1.0
0.5-1.0
0.5-1.0
0 . I'-'i . 0
Site Median EMC
For
Median
Urban Site
100
c
65
0 . 3 3
0 . u 2 '
] .50
0.6E
For
90th Percent ile
Urban Site
300
15
140
0.70
0.21
3.30
1
24 ! 03
144 25C
160 500

-------
Coliform Bacteria

Coliform bacteria  counts  in urban  runoff were monitored  for a  significant
number cf storm  events  bv  seven  of  the NURF projects at  17  different  sites.
Data were collected  at twelve of these  sites for more  than five and up  to
20 storm events.   Date, on  either*  Fecal  Coliform or  both  Fecal and Total  '
Coliform counts  are  available  for  a total  of  156 separate  storm  events.
Although the data base for bacteria  is thus considerably more restricted  than
for other pollutants, useful results have been obtained.

Table 6-18 summarizes the results of  an  analysis  of  these data.   Some vari-
ability exists from  site  to site,  and data are too  limited to  identify any
land use distinctions.  However,  results  from the different sites  and proj-
ects  are  consistent  in showing  a very  dramatic  seasonal effect.   Coliform
counts in urban  runoff during the  warmer periods cf  the year  are  approxi-
mately 20 times  greater than those  in  urban runoff that occurs during colder
periods.

The  substantial  seasonal  differences  which are  observed do  not correspond
with comparable  variations  in urban activities.   This  suggests that seasonal
temperature effects  and sources of  coliform unrelated  to those traditionally
associated with human health risk may be  significant.

In addition to the summarized data presented here, special study reports pre-
pared by the  Long  Island  and  Baltimore projects address  the  issue of animal
and  other sources  of coliform bacteria using  information  derived from  field
monitoring and  the  technical  literature.  The Baltimore NURF  project  also
conducted small  scale  site studies  which simulated washoff  by  storms  and
identified that  quite  substantial  differences in coliform  levels can result
from  the  general  cleanliness of   an  area,  which  they  associate  with  the
socio-economic   strata  of   the   neighborhood.   A  special   study  by    the
Long Island NURF project examined salmonella counts in urban runoff and  in an
adjacent  shellfish  area  influenced  by  urban  runoff.    The  Knoxville,  TN
project also  conducted  a  special  study on Salmonella.   These project  reports
may be obtained  through NTIS.

Other  issues  related to  bacteria  as  a  health risk  were  raised and  warrant
further investigation.  A better understanding is needed of the  contribution
cf • domestic  animals  or such  wildlife as  may  be. expected in  urban areas to
observed coliform levels.

Though high  levels cf  indicator microorganisms were found  in urban  runoff,
the  analysis  ss  well as current  literature  suggests  that indicators  such as
fecal  ccliform   may  not be  useful  in  identifying  health risks,  from  urban
runoff pollutions.

PRIORITY POLLUTANTS

 :5ckground

 ne  KURF priority  pollutant monitoring project was concuctec  tc  evaluate  the

 utants in urbar.  runcff.   .-. total of  111  vrbar: runcfi 'samples were  collected

-------
        TABLE 6-16.  FECAL COLIFORK CONCENTRATIONS IN URBAN -RUNOFF
Project
and
Site
DC1 Burke
Westleigh
Stedwick-
MD1 Homeland
Mt Wash
Res Hill
NCI (CBD) 1013
Res 1023
NH1 Pkg Lot
NY1 Carll
Unqua
SD1 Meade
-TNI CBD
' Rl
R2
SC


All Sites*
Warm Weather
Site
No.
Obs
1
1
2
7
1
1
11
2
20
12
.* 7
9
7
6
6
7
76
Events
11
Median
EMC
(1000/
100 ml)
4.6
46
10
11
130
281
15
23
0.3
24
11
57
54
56
19
12


21
'C . V .
_
-
-
1.8
-
-
1.6
-
0.5
0.9
1.6
0.7
1.5
2.0
. 6.2
2.8


0.8
Cold Weather
Site
Nc.
Obs
1
2
1
_
I
1
e
4
-
15
4
-
7
4
4
4
52
Events
o
Median
EMC
(1000/
100 ml)
0.02
0.35
0.2
_
3.3
330
1.0
2.6
-
1.4
0.9
-
1.0
1.6
0.5
0.9


"-
c.v.
_
-
-
_
- '
-
0.6
1.1
-
1.5
14
-
1.4
1.9
2.4
1.7


C.7
Notes:
        *  For  general  characterization  of urban  runoff,  exclude  the
           following sites:

           - . NH1 - A  small (0.9A) Parking Lot;  concentrations low and
              atypical.

              Four  sites   with   only   one  observation   for  season;
              variability  is too high for  any  confidence in representa-
              tiveness of e single value.

-------
at 61 sites;  (two storm events per site) in 20 of the NURP  projects  that par-
ticipated in  this  phase  of the program.  These  sites  were predominantly in
the  residential,  mixed,  or  commercial land  use  areas  as defined  earlier.
Thus, the results  of  this  effort  cannot be  attributed  to  runoff  from  indus-
trial facilities or complexes.   Furthermore,  an  especially  exhaustive quality
control component, over and above  the standard NURF  QA/QC effort,  was imposed
on the priority pollutant portion of the program, resulting  in  the  rejection
of nearly 14  percent  of  the  data.   Therefore, there is a  high  level of  con-
fidence in the results of this  project.

Since only two  samples were  collected  at  each site, no  meaningful  site  sta-
tistic could-he calculated.  Therefore the data  were.pooled for  analysis.   In
view of the discussion in the preceding section,  however, this approach seems
to be justified.

A  detailed  compilation  of  NURP  priority  pollutant analytical  results  in-
cluding  city  and  site where the  sample was  collected,  date of  collection;
discrete or composite sample, pH,  and pollutant  concentration can be found in
the final report on the NURP Priority Pollutant  Monitoring Program soon to be
issued by the Monitoring and Data Support Division  of  the  agency.  A summary
of the findings taken from the  December 5,  1983  draft of that report follows.

Pollutants Not Included in NURP.  Asbestos and dioxin  were excluded from the
NURF program.  However,  standard  laboratory methods will reveal the presence
of dioxin at  concentrations  of  1  to 10 pg/1, and most  laboratories did scan
their chromatograms  for  the possible  presence  of  this  pollutant.   All  such
scans were negative, and on this basis dioxin is included  as "not detected".

Results Not Valid.  The  NURP results  for  seven  priority pollutants cannot be
considered  valid.    Recent  EPA  investigation  has  revealed   that  standard
methods are not appropriate for the measurement  of  hexachlorocyclopentadiene,
dimethyl  nitrosamine,  diphenyl nitrosamine,  benzidine, and 1,2-diphenylhy-
drazine.  Two othc-r pollutants, acrolein  and  acrylonitrile,  must be analyzed
within  three days  of sample  collection.   Such a time  constraint  was  an
impractical one for the NURP program.

Pollutants Detected in Runoff

Seventy-seven priority  pollutants  were detected  in  the  NURP urban  runoff
samples.   This   group   includes   14  inorganic  and  63 organic  pollutants
(Table 6-19).

Inorganic Pollutants.  As a group, the toxic metals are  by far  the most prev-
alent priority  pollutant  constituents of urban  runoff.   All  14  inorganics
(13 metals,  plus  cyanides;  asbestos  excluded)   were  detected,  and  all but
three  at  frequencies of  detection  greater than  30 percent.  Most often
detected  among  the metals  were copper,  lead,  and  zinc,  all  of which were
found in  at least  91  percent of the  samples.   Their concentrations  were also
=imong the highest  for any  pollutant,  and reached a maximum  of  100, 460, and
1,400 pg/1,  respectively.    Other  frequently  detected  inorganics included
irsenic, chromium, cadmium, nickel,  and cyanide  (Table €-20).  Twelve of the
:hirteen  toxic metals (antimony  excluded)  were also sampled in  the   special
                                    €-46

-------
 M'.l.F 6-IS.   SUMMARY OF ANALYTICAL CHEMISTRY _ FINDINGS  FROM
              NURF  PRIORITY POLLUTANT  SAMPLES'


-includes  inforrriation  received through  September 30,  1983}
	 - 	
pollutant

• It-iri
-.-.., rhlorocyclohexane (o-BHC)
-..ichlorocyclohexane U-BHC)
'•-i a) . „.,, ,
,...,rhlorocyclohexene 1-,-BHL)
..ii-iiio ) (lindane)
....rhlorocyclohexane U-BMI. j
vita)
"' €



' •'.!••< ri
...u.MiHan (Alphs)
!,-i,-.Milfari (Betel
...iiUan suHate
- ! 1:
- HI aldehyde
:..,-hlor epoxide
''7?^7,8-tetrachlorodiben20-
•.'.hpne
IlinRGANlCS

nnr.v
•nir
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Cities Where Detected*
Holdinc times exceeded

7,fi,22,?6
7,f-
7,6,22,26
7,26
2,8,21,26
Not detected
26
*
?6 27
7,?6,27
Not detected
Not detected
Not detected
Not detected
7.F..27
7,26
7
Not included in NURP prc-arem
Not detected

7 ?1 26
?'• 7 12 19 20 21 2? 26 T'7
Not included in NURP prooram
7 ,12,20,21
i, 2 ,3, 7, 12, 20, 21, 27
i,£,7,6,i:,17,lS,?0.?.l,22.26,
27,26
1,2 ,3.1, 7 ,6, 12, 17, 19,20,?], 2;.
23,26,27,28
1,8,19,22,26,27
! 1,2, 3.1.7 ,8,12, 17. 19.?0.?1.2::
26,28
7,20,26
f.3,7,]2.?0.21,26,?7
7,19,2;

7
j 1.2,;. 7 .12. 17. 19,20.21. 22.
i 23,27,26


Freoutr,.;;,- nf
Detection1'

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20
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17

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91

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Fence of Detected
Concent rat ions (ug/l)L

0.002T-0.1M
0. 0027-0. 1M
0.01F.-0.1K
0. 007-0. 1M
0. 001-0. IM
O.OH-IO

0.007-0.027
c-.in
fi.oo7-n.i
0.008-0.2
I
C.Ol-O.lM
0. 0031-0. 1M
10M

•
[
2.6-23A
i-sn.t

1-19
0.1M-11
i . i on 1
i
I 11.-100

?-300
6-16D
i
i n.6-i.;
1-18?
2-77
0.2K-C;.f-
1-11
ir-?ico


 'IA'ED COMPOUND?

 •i']l (Aroclnr  lO'f;
 ;:•;! (Arodcr  t'if'l :
 •-'.:• (Aroclor  VL~-\ !
  ;*J? 'Aroclor  I't^'i
 •.-4f. (Arocior  IZ'S)
 i;".i (Aroclor  1J511;
 ;:'hO (Aroclor  126-0 i
KM detecT.ec-
Not dei.e'.iec
Not cetected
Hc-i ceteciec
Hc-t detected
ijot cettciec

Kc-t ritisctf'0

-------
TABLE  6-19.    SuKMARY OF  ANALYTICAL  CHiMlS'rwY  Fj.MDJ.NGS
               NURF PRIORITY POLLUTANT  SAMPLES:   {Ccnt'd;
 (Includes  infcritiction  received throucn  Septemjj
                                 —i"
  Iv-t h.ni". hri.iiii.-  (iili.-:liyl hriinniji'i
  Mi-thcllt: . .."hluiu-  Imothyi ( I; lui'idi; J
  Mi-; n.-Mr-, <]i rhl.»r.>- ( mrl.ny Irni
  l-'i.-t ii.mr .  ') i(h I Mrt.hnimij-
  Ki-th.in. .  i,i-ibn.ii:»i  -  !l.rni!io*i."-iii;
             iihli.i-:.-  U'lil'ii'i'liirm
           triihli.i-:.- (c
Iml di'tl-Cli-il
Iml di;letii"!
«,i",??
                                       .l/",;;U,iL
  i.U	 lu---- :-; •<'•'•



  [ilicnf . irii-hii-i-,--

  F i-oiiitiio, ! .L'-dli.lii.in
  frrpc-T-.e, ! .J-duhln/i
  i-.u'.cdlfiii- ,  tif i-£rhi-.r.
                      .
  Eihi'-r, t'is(;-ch'iiirnf ;V.yi )
  t.lhi-r. Lis (\: -chlor-ju-...-'.'.!'";-;-
  M.tit-r, L'-chiiirceth.v! vin;, 1
i.'i.i. oevc-cif-ri
ii^1 do'.t-c ii.-
-------
TAELE 6-19.  SUMMARY OF ANALYTICAL CHEMISTRY FINDINGS FROM
         NURP PRIORITY POLLUTANT SAMPLES1 (Cont'd)

(Includes information received through September 30, 1983)
Pollutant
V!I. PHEN015. AND CRES01S
90. Phenol
91. Phenol , 2-chloro-
9?. Phenol , 2,4-dichloro-
93. Phenol, 2,4,fc-trichlorcj-
91. Phenol, pentachloro-
9b. Phenol , 2-ni t rp-
96. Phenol , 4-nitro-
97. Phenol , 2,4-dinitro-
96. Phenol, 2,4-dimethyl-
99. m-Cresol , p-chloro-
100. o-Cresol 4 ,6-dinitro-
Vlii. PHlHALME ESltRl
;0i. Phthalete, dimethyl
101. Phthalate. difthvl
102. Phthalate, di-ri-'butyt
]0<. Phthclotf, di-n-oclyl
]0b. Phthdlote, biv(f-fthylhe/yVi
10f.. PhthaUte, butyl ber.ryl
IX. POtYCYCLIC AROMATIC HYDROCAP.F.rm;.
107. Acenaphthent ,»
108. Acenaphthyler.e
109. Anthracene
110. Benro (a) anthracene
111. Eenzo (b) fluoranthenf
IK'. Benzo (k) f luorantherit
113. Benzo (g,h,i) peryUne
114. Benzo (a) pyrenf
Hi. Chrysene
lit. Dibenzo U,h) anthracene
117. Fluoranthene
116;. Fluorene
119. Inotno (l,i,3-c,d; pyrene
120. Naphthalene
l?i . Phcndiithrene
l?t. Pyrene

Cities Where UeiectedL
|
fl,7,?6
n
Not detected
Not detected
«,8,19,?0, 26,27,26
B
«, 7, 8, 20, 26,26
Not detected
«,7, £,26
4
Not detected

e
3,4,17,20,21
4,22,24
B, 20, 26,27,26
4,12,19,22,21,26
2,6,26

Not detected
Not detected
2,17,20,21,26,28
1,21,27
26,27
2,21,27
21 .
2,21,26,27
2,7,17,21,26,27
21
2, 6,12, 17, 21, 26,27, 2t
26
21
1,24,26,26
2, 8, 17, 20,21, 26,27, 26
2, 3,8, 12, 17, 21, 26, 27, 2fc

Frequency of
Detection'

1«
1


19
1
10

6
1


i
6
6
6
22
6


f
7
4
b
j
1
6
10
'i
If.
1
1
c
12
li
1
kcnoe of Oetected
Concentrations Ug/>:)~

H-13T
",
L.


n-iii
1M
n-37

1T-10K
1.5A


H
1-1011
0.51-11
0.4T-2G
41-62
1-iOM



i-101'i I
1-10K
1-;
4-14
^
1-10K
O.tT-iOK
1 '•
0. 31-21
1
4
0.61-2.3
0.31-10K
O.Jl-lfc


-------
           TABLE 6-1S.    SUMMARY  OF ANALYTICAL  CHEMISTRY  FINDINGS FROM
                         NURP PRIORITY  POLLUTANT  SAMPLES1   (Cont'd)

            (Includes  information received  through  September  30,  1983)
                      Pollutant
                                                 Cities  Where Detected'
                                       Frequency of
                                       Detection3
                                               Range of Detected
                                               Concentrations (uQ/t)1'
   X.  NITROSAMINES AND OTHER NITROGEN-CONTAINING COMPOUNDS
      123.   Nitrosamine, dimethyl  (DMN)
      \?t.   Nitrosamine, diphenyl
      125.   Nitrosamine, di-n-propyl
      126.   Benzidinf
      127.   Benzidine, 3,3'-dichloro-
      126.   Hydrazine, 1,2-diphenyl-
      1?9.   Acrylonitrile
          Standard methods inappropriate
          Standard methods inappropriate
          Not detected
          Standard methods inappropriate
          Not detected
          Standard methods inappropriate
          Holding times exceeded
1   Based on 12]  sample results received as of 9/30/83, adjusted for quality control  review.
2   Cities from which data  are available:
      1.  Durham, NH
          Lake Ouinsigamond, MA
          Mystic River,  MA
          Long Island, NY
          Washington, DC
          Baltimore, MD
          Knoxville, TN
          Glen Ellyn, It
          Austin, TX
20.  Little Rock, AR
21.
22.
23.
24.
26.
27.
26.
Kansas City, K$
Denver, CD
Salt Lake City, UT
Rapid City, SD
Fresno, CA
Bellevue, WA
Eugene, OR
    3.
    4.
    7.
    8.
   12.
   17.
   19.
   Numbering of cities conform^sto NURP convention.

Percentages rounded to nearest whole number.
Some reported concentrations are qualified by  STORE! quality control remark  codes, to wit:  A « Value reported  is the
mean of two or more determinations; G • Value  reported is the maximum of two or more determinations; L « Actual value
is known to be greater then value given; M * Presence of material  verified but not quantified; T =  Value reported is
less than criteria of detection.  One value in this column indicate; one pcsitive observation or that all observations
were equal.
No longer included as a priority pollutant.
                                                      6-5C

-------
         TABLE 6-20.   MOST FREQUENTLY DETECTED PRIORITY  POLLUTANTS
                        IN NURP  URBAN RUNOFF SAMPLES1


   Priority Pollutants Detected  in 75 Percent or More  of the NURP Samples

         Inorganics                            Organics

    30.  Lead (94%)               None
    36.  Zinc (94%)
    28.  Copper (91%)

Priority Pollutants Detected in  50 percent to 74 percent of the NURP Samples

         Inorganics                            Organics

    27.  Chrominum (58%)          None
    23.  Arsenic (52%)

Priority Pollutants Detected in  20 percent to 49 percent of the NURP Samples

         Inorganics                            Organics

    26.  Cadmium (48%)      105.  Bis(2-ethylhexyl) phthalate  (22%)
    32.  Nickel (43%)  .„      3.  a-Hexachlorocyclohexane  (20%)
    29.  Cyanides  (23%)

Priority Pollutants Detected in 10 percent to  19 percent of the NURP Samples

         Inorganics                            Organics

    22.  Antimony  (13%)      12.  a-Endosulfan  (19%)
    25.  Beryllium (12%)     94.  Pentachlorophenol  (19%)
    33.  Selenium  (11%)       7.  Chlordane  (17%)
                              5.  -y-Hexachlorocyclohexane  (Lindane)  (15%)
                            122.  Pyrene  (15%)
                             90.  Phenol  (14%)
                            121.  Phenanthrene (12%)
                             47.  Dichloromethane  (methylene  chloride)  (31%)
                             96.  4-Nitrophenol  (10%)
                            115.  Chrysene  (10%)
                            117.  Fluoranthene (16%)


    1   Based  on 121 sample  results  received as of  September 30, 1983,  adjusted
        for quality control  review.   Does  not include  special  metals samples.
                                     6-5:

-------
metals  project  in  order  to  determine  the relationships  among  dissolved,
total,  and  total recoverable  concentrations.  The  discussion and result  of
this separate effort are in a  subsequent section  of  this  chapter.

A comparison  of  individual urban runoff  sample  concentrations undiluted  by
stream  flow  (i.e.,  end of pipe  concentrations)  with EPA water quality  cri-
teria  and  drinking  water  standards  reveals numerous exceedances of  these
levels, as  shown in Table  6-21.   Freshwater acute criteria were  exceeded  by
copper concentrations in 47 percent  of the samples and by lead in  23 percent.
Freshwater  chronic  exceedances  were  common for  lead  (94 percent),  copper
(82 percent), zinc  (77 percent),  and cadmium (48  percent).   One organ oleptic
(taste and odox)  criteria exceedance was observed.  Regarding human toxicity,
the  most  significant  pollutant  was  lead.   Lead  concentrations  violated
drinking water criteria in 73  percent of the observations.

Whenever an exceedance is noted above, it does not  necessarily imply that an
actual  violation of  criteria  did or  will  take  place in  receiving  waters.
Rather, the  enumeration  of exceedances is  used  as  a  screening procedure  to
make  a  preliminary  identification of those pollutants for  which  their pres-
ence  in urban  runoff  requires highest priority  for  further evaluation.   Ex-
ceedances of  freshwater chronic  criteria levels may not persist  for  a  full
24-hour period,  for  example.   However,  many  small  urban streams  probably
carry  only  slightly diluted runoff  following  storms, and  acute  criteria  or
other exceedances may in fact  be  real in such circumstances.

Among the inorganics, the most frequently detected  pollutants are also those
which  are found  at  the highest concentrations,  which most frequently exceed
water   quality   criteria   and which  are   the   most  geographically  well-
distributed.  One additional  observation  can be  made  concerning  the samples
from  Washington,  D.C.   These  samples  accounted   for  & preponderance  of the
detections  of  many  of  the less frequently detected inorganics,  including
antimony, beryllium, mercury,  nickel, selenium, and thallium.  No sampling or
analytical irregularities have been  identified which explain this result.

Organic Pollutants.   In general, the  organic  pollutants  were detected less
frequently  and  at  lower  concentrations  than  the  inorganic  pollutants.
Sixty-three  of  a  possible 106 organics  were  detected.   The  most commonly
found  organic  was  the plasticizer bis  (2-ethylhexyl)  phthalate  (22 percent)
followed by  the  pesticide a-hexachlorocyclohexane  (u-BHC)  (20 percent).  An
additional  11  organic pollutants were reported with detection   frequencies
between 10  and 20 percent; 3 pesticides,  3 phenols,  4 polycyclic aromatics,
and a single haloginated aliphatic (Table 6-20).

Criteria exceecances  were  less  frequently  observed  among  the crganics than
the   inorganics.    One .unusually  high  pentachlorophenoi  concentration  of
115 yg/1 resulted  in  the only exceedance  of the organoleptic criteria  (Ta-
ble 6-21).   This  observation  and one  for  the  chlordane  exceeded the fresh-
water  acute criteria.   Freshwater chronic  criteria exceedances were observed
for pentochlcrophenol, bis  {2-ethylhexyl)  phthalate,  y-hexachlorocyclohexane
(Lindene) ,  c-endosulfan, and  chlordane.   All other  organic exceedances were
in  the human  carcinogen  category and were most serious  for a-hexachloro-
cyclohexane  (t-EHC),  Y'hexachlcrocyclchexane  (v-EHC  -or  Lincane), chiorcane,
phenantnrene , p-yrene , and cnrysene .

-------
   TABLE  6-21.   SUMMARY OF  WATER QUALITY  CRITERIA  EXCEEDANCES  FOR
      POLLUTANTS DETECTED  IN  AT LEAST  10  PERCENT  OF NURP  SAMPLES:
                    PERCENTAGE  OF  SAMPLES  IN WHICH  POLLUTANT  .
                            CONCENTRATIONS  EXCEED  CRITERIAj
Pollutant
i. Ptsiicmts
3. o-He»achlorocyclohe»anf
5. >-He>achlorocyclohexane (Lindane)
7. ChlorCane
IT. o-F.n
VH. PHFNOIS AND CRE5015
90. Phenol
9£ . Phenol, pentechloro-
96. Phenol , 4-nitro-
VI! I. PHlHAim tSIERS
lOt. Phthelate, bis(2-ethylhe»yl'i
i>. . POivrvcuc AROMATIC HYDROCARBONS
Hi. Chrvsene
]]7. Fluoranthene
l?i. Phenanlhrcne
1?J. Pyrene
Frequency nf
Detection ('. )

?0
15
17
19

13
I?
1?
if.
5E.
91
?:•
9«
"3
11
9«

11

• 1«
19
10

??

10
16
r,
15
Detection^/
Samples1

21/106
15/100
7/«?
9/«9

11/106
«5/B7
11/94
11/91
47/81
79/87
16/71
75/80
39/91
10/86
88/94

3/28

13/91
21/111
11/107

15/69

11/109
17/109
13/110
16/110
r.riteric F.>ceeciences (':'
Nnne






X













X

X




I


FA.



?





F.

47

?3


1£




r








FC


e
17
10



f
IE
1*
t?
??
C£
c
=
77




11'


??•





nL





















1








HH









1


4
73
21
10














HCL

8,18,20
0.1C.15
17,17,17



52.52,52
12.1?, 12









0,0,11







10,10,10

12,12,12
15,15,15
OK







1

1
1


73

10














Indicate* FTA or FTC value substituted *r»erf FA or FC  criterion not  available (see below).

Besefi on 1?] sample results receives e« of September 3D, 1SB3, adjusted for quelitv control review.

NumDer o* time* detected/number of  ficcepteblc samples.

     Freshwater ambient ?"-hour instantaneous ma>imum criterion ("acut*:" criterion).
Freshwater ambient ?4-hour averaoe criterion ("chronic" criterion).
lowest reported  freshwater acute toxic concentration.  (Used only when FA is not available.!
lowest reported  freshwater chronic to>ic  concentration.  (Used only  when FC  is not available.
Icste end odor  (uroanoleptic ) rritprior..
Non-Cercinoaenic human health criterion for incest ion of contaminated water  and orcar.ismi.
Protection of human health from cercinooenic effect; for inqestinn nf contarr.ineiec water  ?.nc
Primary drinkino water criterion.
 FC
Flf
FK
 01
 HM
 HC
Fr.trip;  if: thi; column indicate exceedence* r-f the human carcinooen

number*  crf cumulative, i.e., all  10*"" exceedances are  included in 10"  exceedar.cef, snc  el
exceeflencei.
Where herdne.jF  dependent, herdnesf. nf 100 mg.M CaCfs.  eauivalpni assutneC.
[MffereTd criteria are written for the trivalent and he>e-velent fnrm; nf chromium.  For pur
M'umec to be in the less tnxlc trivelent form.
                                                                                        f ": ,  respect i

                                                                                        ere  inclucec
                                                                                                         e'iy .   the

                                                                                                         in 10"

-------
An additional 50 organic pollutants were found in one  to  nine percent  of the
samples.  These frequencies of detection are low, and  the  pollutant is noted
in Table 6-22.

Among the PCE group, there was only a single detection of  one FCB type among
all the  samples.   Approximately  two-thirds  of  the nalogenated aliphatic com-
pounds were detected.  Among those cities reporting  these compounds, the city
of Eugene,  Oregon,  figured prominently.  For  example, eight pollutants from
this group  were  found' in  Eugene  only.   None of the pollutants in the  ethers
group were detected.

Monocyclic  aromatics were  rarely detected  in the  samples.   However,  many
reported detections of benzene and toluene, two commonly reported pollutants,
had to be withdrawn due to contamination problems.

Of the 11 phenolics, four have not been reported in  urban runoff, while  three
have been  observed  only  once.    The  remaining four  have been  found  fairly
frequently  but  at  low  concentrations.   Exceedances  of  criteria  were  noted
only for pentachlorophenol.

All  the  phthalate esters  were  detected at  least once in  the NURP program,
with bis  (2-ethylhexyi;  found most  frequently.   Several  times the reported
concentration exceeded the lowest observed freshwater acute toxic  concentra-
tion for this pollutant.   Given  the  significant  blank contamination problems
with  the  phthaiates,  however,   these   findings  must be   interpreted  with
caution.             ••>

Only  two of  the polycyclic  aromatic  hydrocarbons  were  not  detected in  at
least one sample.   Crysene, phenanthrene,  pyrene, and fluoranthene were each
found at  least  10 percent of the  time.  All the  observed concentrations  for
the first three  of  these  pollutants  exceeded the  criteria for  the  protection
of  human health  from  carcinogenic effects  (there  are no  such criteria  for
fluoranthene).  Results for the polycyclic  aromatics were generally free from
quality control problems.

There were  no detections  of  nitrcsamines   or  other nitrogen-containing  com-
pounds.   Due to methodological  end  holding time problems, however,  results
for  only  two compounds can be  used.   Moreover, for  one  of these  compounds,
3,3-dichlorobenzidine,  performance evaluation results were unacceptable  in
several cases.

Pollutants Not Detected In Urban  Runoff
 Some  43  priority  pollutants  were not detected  in  any acceptable  runoff  sam-
 ples  (Table 6-22).  All of these pollutants  are  crganics.   This  group of  sub-
 stances  r.houic be  considered to  pose  a  minimal   threat  to  the quality  of
 surface  waters from runoff contamination.

 While  the  priority  pollutants which were  not  detected are of less  immediate
 concern  than  those  pollutants found often,  they cannot safely  be eliminated
 from  all  future  consideration.    Many  of  these pollutants  have  associated
 wattr  quality  criteria wrier, are below the  limits  c-f  detection of  routine

-------
           TABLE 6-22.  INFREQUENTLY DETECTED ORGANIC PRIORITY
                 POLLUTANTS  IN NURP URBAN RUNOFF  SAMPLES1


Priority Pollutants Detected in  1 percent to 9 percent  of  the NURP  Samples

     51.  Trichloromethsne  (9%)
    120.  Naphthalene  (9%)
     98.  2,4-Dimethyl phenol (8%)
    109.  Anthracene  (7%)
      2.  Aldrin  (6%)
      6.  6-Hexachlorocyclohexane  (6%)
      9.  DDE  (6%)
     11.  Dieldrin  (6%)
     17.  Heptachlor  (6%)
     58.  1,1,1-Trichloroethane  (6%)
     65.  Trichloroethene  (6%)
     85.  Ethylbenzene (6%)
    102.  Diethyl phthalate  (6%)
    103.  Di-n-butyl  phthalate  (6%)
    104.  Di-n-octyl  phthalate  (6%)
    106.  Butyl benzyl phthalate (6%)*
    114.  Benzo(a)pyrene  (6%)
       4.   6-Hexachlorocyclohexane (5%)
      53.  Trichlorofluoromethane 05%)2
      66.  Tetrachloroethene  (5%)
      78.  Benzene (5%^
      79.  Chlorobenzene (5%)
     111.   Benzo(b)fluoranthene  (5%)*
      64.   1,2-trans-dichloroethene (4%)
     110.   Benzo(a)anthracene (4%)
      19.   Isophorone  (3%)
      52.   Tetrachloromethane (carbon tetrachloride)  (3%)
      56.   1,1-Dichloroethane (3%)
      87.   Toluene (3%)
     112.   Benzo(k)fluoranthene  (3%)
      18.   Heptachlor epcxide  (2%)*
      59.   1,1,2-Trichloroethane  (2%)*
      60.   1,1,2,2-Tetrachloroethane  (2%)*
      63.  1,1-Dichloroethene (2%)
      68.  1,3-Dichloropropene (2%)*
     113.  Benzo(g,h,i)perylene  (2%)
      10.  DDT '(!%)*
      43.  PCB-1260  (1%)*
      48.  Chlorodibromomethane  (1%)*
      49.  Dichlorobromomethane  (1%)*
      50.  Tribromomethane  (bromoform)  (1%)*
      57.   1,2-Dichloroethane (1%)*
      67.   1,2-Dichloropropane  (1%)*
       91.   2-Chloropheno3  (1%)*
       95.   2-Nitrophencl  (1%)*
       99.   p-Chloro-m-creosol (1%)*
      ]C>1.   Dimethyl phthalate (1%)*
      116.   Dibenzo (a,h) anthracene  (!%)'•
      :-18.   Fluorene  (1%)'
      319.   Indeno(1,2,^-cd)pyrene

-------
                   INFREQUENTLY DETECTED ORGANIC PRIORIT
       POLLUTANTS IN NURF URBAN RUNOFF SAMPLES1  (C
                  jllutants Net Detected in NURF Samples
 t;.   DDD
12.   p-Endcsulfan
14.   Endcsulfan suifate
15.   Endrin
16.   Endrin eldehyde
21.   Toxaphene
37.  -FCE-1016
38.   PCE-1221
39.   PCP-1232
40.   PCE-1242
41.   PCE-1248
42.   PCE-1254
44.   2-ChloronaphthaIene
45.   Erorr.oiriethane (methyl bromide)
46.   Chlcromethane  (methyl chloride)
54.   Dichicrccifluoromethane  (Freon-12)
55.   Chloroethane
61.   Hexachloroethane
62.   Chloroethene (vinyl chloride)
69.   Kexachlorobutadiene
71.   Bis(chloromethyl) ether2
72.   Bis(chioroethyl) ether
73.   Eis(chlorcisopropyl) ether
74.   2-Chloroethyl vinyl ether
75.   4-Brorricphenyl phenyl ether
76.   4-Chiorophenyl phenyl ether
77.   Bis(2-chloroethoxy) methane
80.   1,2-Dichlorobenzene
81.   1,3-Dichicrcbenzene
82.   1., 4-Dichlcrobenzene
65.   1,2,4-Trichlorobenzene
64.   Hexachlorcbenzene
86.   Nitrobenzene
8E.   2,4-Dinitrotoluene
69.   2,c-Dinitrotoluene
92.   2,4-Dichlorcphenol
93,   2,4,6-Trichiorophencl
97.   2 , 4-Diriitrophencl
00.   4., t-Dinitrc-o-cresol
     Acenaphthene
     A c e n aph t h y1e n e
     Di-n-propyi nitrosamine
     3 , C- ' -Dichlorobenzidine

-------
            TABLE 6-22.   INFREQUENTLY  DETECTED ORGANIC PRIORITY
             POLLUTANTS  IN  NURP  URBAN  RUNOFF  SAMPLES1  (Cont'd)
    Priority Pollutants  Not  Analyzed  for  or  Withdrawn  for  Methodological
                     Reasons or Holding Time Violations

      . 1.   Acrolein
      20.   TCDD (Dioxin)
      24.   Asbestos
      70.   Hexachlorocyclcpentadiene
   '  123.   Dimethyl nitrosamine (DMN)
     124.   Diphenyl nitrosamine
     126.   Benzidine
     128.   1,2-Diphenyl  hydrazine
     129.   Acrylonitrile

*  .Detected in only one  or two samples.

   Based on  121  sample  results received  as of September 30,  1983,  adjusted
   for quality control review.

2  No longer on the priority pollutant list.
analytical methods.  Soifle of  these  substances may in fact  have  been present
in the  NURP  samples.  Four priority  pollutants not detected  in  runoff were
found in  street dust  sweepings  from  Bellevue, Washington,  suggesting that
further urban runoff samplings  can  be expected to  detect  more priority pol-
lutants.  More  sensitive  analytical  methodologies -must be  used  and dilution
effects considered before it can be  said with assurance that these pollutants
are not found in  urban stormwater runoff at  levels  which,  without dilution,
pose a threat to human health or aquatic life.

ODD, chloromethane,  I,2-dichlorobenzene, and 2,4-dichlorophenol were detected
in runoff  samples  at least  once, but  these  observations had to be withdrawn
for quality  control  reasons.   Therefore, among the  net.  detected pollutants,
these four can  be considered to have  a  slightly  elevated  possibility of ac-
tually being present in the runoff samples.

•RUNOFF-RAINFALL RELATIONSHIPS

A runoff coefficient (Rv), defined as  the  ratio of  runoff  volume to rainfall
volume, has  been  determined  for  each  of the monitored storm events.  As with
the EMCs,  the runoff coefficient  values  at  a particular site are, with  rela-
tively  few  exceptions,  well  characterized  by  a  lognormal  distribution.
Table 6-23 summarizes the statistical  properties  of  Rv' s at  the loading sites
in the data  base.

Figure 6-18  illustrates the  relationship between  percent impervious area  and
the median runoff  coefficient for the  site.   Sites which monitored  fewer than
5 storms ere  excluded.  The upper clot  {£',  croues  the results  from  16  of  the.

-------
         TABLE 6-23.   RUNOFF  COEFFICIENTS FOP  LAND USE SITES
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            0   10   20  30  40  50  60   70   80   90  100
                          % IMPERVIOUS

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Figure 6-19.  Relationship Between Percent Impervious Area
               and Median  Runoff Coefficient

-------
20 projects  investigated.   The lower  plot  (b) groups  results  from  the  re-
maining four projects (KSI, MI], TNI, TX1).   The reason for the difference is
unexplained.  However,  the separate grouping  is  based on the  fact  that  the
relationship for these  sites  is internally  consistent  and significantly dif-
ferent than the bulk of the project results.

Figure 6-20  illustrates the  same . impervious  area/runoff coefficient  rela-
tionship, but shows the 90 percent confidence limits for median Rv's.

POLLUTANT LOADS

Although the EMC median concentration  values  are  appropriate for many appli-
cations  (e.g.,,assessing  water quality impacts in  rivers and streams), when
cumulative  effects  such  as  water  quality  impacts  in  lakes  and comparisons
with other  sources on a long-term basis  (e.g.,  annual  or seasonal loads)  are
to be examined, the EMC mean concentration values should be used.  Taking the
EMC median  and  coefficient of variation values given  in Table 6-17, we have
converted  them  into  mean  values using the  relationship given  in Chapter 5.
These EMC  mean  concentrations  and  the values used  in  the load comparison to
follow are  listed in Table 6-24.

The range  shown' for site  mean concentrations  for  both  the  median  and  90th
percentile  urban sites  reflects the  difference in means depending on whether
the higher  or lower value of coefficient of variation  listed  in Table 6-17 is
used  to  describe event-to-event  variabilitv  of  EMC's  at urban  sites.  The
                     i^ft*                     "*
range  in  values shown  for use in  the load  comparisons  beJLow reflects the
median and  90th percentile site mean concentrations, using the  average  of the
range caused by coefficient of variation effects.
            TABLE 6-24.  EMC MEAN VALUES USED IN LOAD COMPARISON
Constituent
TSS (mg/1)
BOD (mg/1).
COD (mg/1)
Tot. P (mq/1)
Sol. P (mg/1)
TKN (mg/1)
N0_ _^-N (mg/1)
Tot. Cu (ug/1)
Tot. Pb (ug/1)
Tot. Zn (yc/i)
Site Mean EMC
Median
Urban Site
141 - 224
10-33
73-92
0.37 - 0.47
0.13 - 0.17
1.68 - 2.12
0.76 - 0.96
38 - 48
161 - 204
~[ " c _ 22 6^
90th Percentile
Urban Site
424 - 671
37 - 21
157 - 198
0.78 - 0.99
0.23 - 0.30
3.69 - 4.67
1.96 - 2.47
' 104 - -132
79- _ 4pc:
559 .- 707 '
Values Used in
Load Comparison
180 - 548
12-19
82 - 178
0.42 - 0.88
0.15 - 0.28
1.90 - 4.18
. 0.86 - 2.21
45 - 118
182 - 443
202 - 633

-------
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                      % IMPERVIOUS
                   (a)   16  Projects
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        % IMPERVIOUS

Projects  (KSi,  Mil, TNI,  TK1)
i'icure 6-20,. .  90 Percent Confidence Limits  rcr Medier
                  Runoff Coefficients

-------
It is £ straightforward! procedure to calculate  mean annual  load estimates for
urban runoff constituents on a Kg /He basis by  assigning appropriate rainfall
end  runoff  coefficient values and  selecting  EMC mean  concentration  values
from Table 6-2.4.  In and of themselves,  however,  such  estimates seem to be of
little utility.   Therefore,  it was  decided  to do a  comparison of  the  mean
annual loads from urban runoff with  these of  a  "well run"  secondary treatment
plant.  We chose to use TS£ = 25  mg/I,  BOD =  15 mg/1 ,  and  Tot; F = 8 mg/'l for
the  effluents  from  such plants for  the  purposes  of  this   order  of magnitude
comparison.  For  a  meaningful comparison  for  a specific  situation,  locally
appropriate values should be used.   Based  upon Table  6-24, the corresponding
urban runoff mean concentrations  used were TSS  = 180 mg/1,  BOD = 12 mg/1, and
Total P = 0.4 mg/1  as  typical   and  TSS =  548 ug/1,  BOD  =   19 mg/1,   and
Tot. P =0.88 mg/1 as a "worst case" for comparison purposes.

The  value of 0.35 was  selected as a typical  mean runoff -coefficient.   It is
the  median of  the NURP  mean runoff   coefficient  database  for  the  twenty
projects discussed earlier;  their average  is 0.42,  but we believe that this
number is overly weighted by the  disproportionate number of highly impervious
sites in the database.  Assuming an  average  population  density of 10 persons
per  acre   (the  average of  the NURP  sites)  and  a  mean  annual  rainfall of
40 inches per  year,  urban  runoff  averages  104 gallons per  day  per capita.
This  is  also  a reasonable  estimate of  sewage generation  in  an • urban  area.
Therefore, as  a first  cut,  the  ratio  of mean  pollutant  concentrations of
urban runoff and POTW effluents will also be  the ratio of  their annual loads.
Thus, we have;
           TSS = -    ~  7 ;  BOD =    =  0.6 ,-  Tot .  F =    -  = 0.05
                  ^5              lb                    c

using typical urban runoff values, and;
using the "worst case" values.  These numbers  suggest  that annual loads  from
urban runoff are approximately one  order  of  magnitude  higher than those  from
c. well run secondary treatment plant for TEE, the same order of magnitude for
BOD, and an order of magnitude less for Tot.  F.

If  the  hypothetical  urban area just describee were to  go to advanced waste
treatment and achieve an effluent quality of TES = 10 mg/1, BOD =  5  mg/1, and
Total F = 1 mg/1  and no  urban  runoff  controls  were  instituted,  the  mean
annual load reductions to the receiving water woulc be:

     TSS - ,£ ~ ™ =: 7% ; BOD - f-
           180 + 25 ~ ' '  '  """ ~ 12 + 15

for our typical case,  and;
           545 -r 25

-------
for our  "worst case."   On  the  other  hand,  if  urban  runoff  controls that
reduced TSS by 90 percent,  BOD by 60 percent, and Total P by 50 percent were
instituted, (typical results from a well-designed detention basin) ,  the mean
annual load reductions to the  receiving  water would  be:
for our typical case, and;
Thus, if these pollutants are causing  receiving water  quality problems,  con-
sideration  of  urban  runoff  control appears  warranted  for  TSS, both  urban
runoff  control  and AWT might be  considered for BOD,  and  only AWT  would  be
effective for Total P.

The foregoing should be viewed as illustrative of a preliminary screening for
trade-off  studies  that  can  be  performed  using  appropriate  values  for  a
specific urban area,  rather  than  as description  of any particular real-world
case.   They are,  however,  believed useful in  providing order  of  magnitude
comparisons.  Local values  for  annual  rainfall,  runoff coefficient,  or point
source  characteristics that are different than those used in the illustration
will of course  change the  results shown; although in  most ca'ses the changes
would   not  be  expected  to  cause  a  significant  change  in  the  general
relationship.

As a final  perspective on urban runoff loads, Table 6-25 presents an estimate
of  annual  urban runoff loads,  expressed as Kg/Ka/year,  for comparison with
other  data  summaries  of  nor.point  source  loads  which  state  results in this
manner.   Load  computations  are based  on site mean  pollutant concentrations
for the median urban  site and on  the specified values  for annual rainfall and
runoff  coefficient.  Typical values for mean  runoff  coefficient  Abased  on
NURP data)  have been  assigned for residential land use  (Rv =  0.3), commercial
land use  (Rv = 0.8),  and for an aggregate urban area which is  assumed  to have
representative  fractions  of the  total area  in  residential, commercial, and
open uses  (Rv =  0.35).

Several useful  observations  can  be made.   The annual  load estimates  which
results are  comparable  to  values   and  ranges  reported in  the literature.
Although  the findings presented  earlier in this  chapter  indicated that  the
lane  use category  does not  have  a  significant  influence  on  site  concentra-
tions  of pollutants,  on  a  unit  area basis  total pollutant  loads are  sig-
nificantly  higher  for commercial   areas  because  of  the  higher  degree  of
imperviousness  typical of  such  areas.   For broad  urban areas, however,  the
relatively  small fraction of land  with  this  use considerably mitigates  such
an  effect.

Finally,  the  annual loads shown by  Table 6-25 "nave been  computed on the basis
of  a  40 inch  annual  rainfall volume.  For  urban  areas in  regions with higher

-------
              TAELE e-25.   ANNUAL UREAN  RUNOFF  LOADS KG/HA/YEAR
•

Constituent
Assumed Rv
TEE


BOD
COD
Total P
Sol. P
TKN
NO' _-N
2+J
Tot . Cu
Tot. Pb
Tot . Zn


Site Mean
Con.mg/1
-

180


12
62
0.42
0.15
1.90
0.86

0.042
0.182
0.202



Residential
0 . 5
^. - r,


36
250
1.2
0.5
5.6
2.6

0.12
0.55
0.62

' J

Commercial
0.6
1460


98
666
3.4
1.2
15.4
7.0

0.35
1.48
1.64



All Urban
i
0.25
640


43
282
1.5
0.5
6.6
3.6

'o: 15
0.65
0.72

    NOTE.  Assumes 40 inches/year rainfall as a long-term average.
or  lower rainfall,  these  load  estimates  must  be  adjusted.   The  results
presented earlier suggest that  pollutant  concentrations  are not sensitive to
runoff volume; however,  total loads (the product of concentration and volume)
are strongly  influenced by the  volume  of  runoff.   For estimates using equiv-
alent site conditions  (Rv},  loads for areas with  other  rainfall amounts are
obtained by  factoring  by  the ratio of  local  rainfall volume  to the 40 inch
volume  used  for the  table.   Planners  who  believe  that the  average annual
runoff  coefficients. in their  local areas  are  substantially  different from
those used in the table can make similar adjustments.

-------
                                 CHAPTER  7
               RECEIVING WATER  QUALITY EFFECTS OF URBAN RUNOFF
INTRODUCTION

The effects of urban  runoff on  receiving  water  quality are very site speci-
fic.  They  depend  on the type,  size,  and hydrology of  the  water body, the
designated beneficial use and  the pollutants  which  affect that  use, the  urban
runoff (URO)  quality  characteristics,  and  the  amounts  of URO  dictated by
local rainfall patterns and  land use.

A number  of the NURP projects  examined receiving  water  impacts in some de-
tail, others less rigorously.   Because  of  the uniqueness  of URO water  quality
impacts,  individual project  results are considered  best used  for confirmation
and support, rather than as  a  basis for broad generalizations.

Accordingly, this chapter is structured to address  each of the  principal cat-
egories  of  receiving  water  bodies separately;  streams   and  rivers,  lakes,
estuaries and  embayments,  and  groundwater aquifers.   Some can  be  addressed
more thoroughly  than  ot'h'ers  at this time.   The  approach taken  to develop  a
general,  national scale  screening assessment of the significance of  URO pol-
lutant discharges is to compute anticipated effects using analysis methodolo-
gies  identified  in  Chapter 5,  where   these  are appropriate  and to  compare
anticipated effects indicated  by such  generalizations  to  specific experiences
and conclusions drawn by relevant individual  NURP projects.

As with any generalization, there will be exceptions.  Specific local situa-
tions can be  expected which  are either more or less  favorable  than  the •gen-
eral case.  The  results presented herein should therefore be  interpreted as
representative estimates  of  a  substantial percentage  of urban runoff sites,
but not all of them.

Receiving waters have distinctive general characteristics which  depend on the
water body  type  (e.g.,  stream,  lake,  estuary)  and  relatively unique  individ-
ual characteristics which depend  on geometry and  hydrology.   Given a minimum
acceptable  amount of  data on  water bodies and  their setting,  it appears pos-
sible  tc  make useful  generalizations  regarding the  quantitative effects of
urban runoff  on  concentrations  of  various pollutants  in  the receiving waters
and to craw inferences concerning  the  influence urban runoff may have on the
beneficial  uses  of  the water  bodies.   However extending the  results of such
an analysis to an assessment  of the prevalence of urban  runoff  induced  "prob-
lems" on  a  national scale cannot be  accomplished  in  a  way  would provide an
acceptable  level of  confidence  in  any  conclusions  drawn  therefrom.   In  addi-
tion to the importance of local hydrology,  meteorology,  and urban character-
istics,  the emphasis  placed  on  each  of the  three  elements  that  influence
problem definition;

      (j)  Denial or  serious impairment of beneficial use;

-------
Flowinq streams  carry  pollutant discharges  downstream with the  stream flow.
For intermittent  stormwater discharges,,  a  specific stream location  and  the
biota  associated,  with  it are  exposed  to a  sequence  of discrete;  pulses  con-
taminated by  the  pollutants which  enter with urban  runoff.   Because  of  the
inherent  variability of  urban runoff  (URG),  the  average concentrations  in
such pulses  vary,  as do  their duration and;  the  interval  between successive
pulses.  Table 7-1 summarises  average values  for  storm duration and intervals
between stc-rm events for  selected, locations  in the  U.S.,  based en analysis of
lone .term  rainfall  records  using  a  methodology   (SYNOF)  presented in  an
i^rlier  NU--F document   -the-  NURP  Data   Management  Procedures Manual).   The
information presented provides  '- cense  of the temporal aspects of such inter-
           c- £. c; -. ;"; r
                                  tne  intermiti
              hours ^v-si"."
                         exposure patterns to which
;.   For many  locations,  storm pulses ere produced
ihrer-  days or more,  on avcreqe-.
.:. '.; robabaiistic methodology  ha?: been used to examine  the  concentration char-
: ct-ristics of the storm rulses  ;--roduced  in  streams,  civen the variabiiitv of
             processes  which are dirt:otl'.; inv
                            Stream
                                    :low rates.  run-
            es, ana concentrations  var1
                                         and result in variable stream concen-
•:r;:.-.icn£.  rcr streams.. it is not  the  runoff  volume per se that is important.
The combination of stream and runoff flow rates  (together with runoff  concen-
"rc.ticni  determine  the-  pollutant  concentration  in the  stream  pulse.    The
duration  cf  the  runoff  event  and the  stream  velocity  dictate  the  spatial
•-::••:t•;r.t  of the  storm pulse  in  the  stream.   The  analysis presented  in  this
section  addresses  the  frequency and magnitude of  pcllutant concentrations in
-:';-.•;• ;.nstrearr: storm pulse= •.•;hioh  are  produced,

~.un '•••:  j.nd Stream Flow Rs.tes
                                                             race

-------
TABLE 7-1.  AVERAGE STORM AND TIME BETWEEN STORMS FOR
       SELECTED LOCATIONS IN THE UNITED STATES
Location
Atlanta, GA
Birmingham, AL
Boston, MA
Caribou, ME
Champaign-Urbana , IL
Chicago, IL
Columbia, SC
Davenport , IA
Detroit, Ml
Gainesville, FL
Greensboro, SC
Kingston, NY
Louisville, KY
Memphis , TN
Mineola, NY '*
Minneapolis, MN
New Orleans, LA
New York City, NY
Steubenville, OH
Tampa , FL
Toledo, OH
Washington, DC
Zanesville, OH
Mean
Denver , CO
Oakland, CA
Phoenix, AZ
Rapid City, Sp
Salt Lake City, UT
Mean
Portland, OR
Seattle, WA
Mean
Average Annual Values in Hours
Storm
Duration
8.0
1 . 2
6.1
5.8
6.1
5.-?
4.5
6.6
4.4
7.6
5.0
7.0
6.7
6.9
5.8
6.0
6.9
6.7
7.0
3.6
5.0
5.9
6.1
6.1
9.1
4.2
3 "
e.o
7.8
6.5
15.5
21.5
18.5
i
Time Between
Storm Midpoints
94
85
68
55
80
72
66
9€
57
106
70
80
76
89
89
'87
89
77
78
93
62
80
77
81
144
320
286
127
132
202
63
101
92

-------
 Figure 7-1 (a).  Regional Value of Average  Annual Streaitiflow  (cfs/sq mi)
      .025
j-'icure v-1(b;.   Regional Value  of  Average Storm ivent  intensitv (inch/hr)

-------
Variability of daily stream flows was determined for  a  smaller sample  (about
150 sites) of the stream sites.  Variability of storm event  average  intensi-
ties was  determined  for  ell  of the  rain gauge locations in  the  current  data
base.  These results, are summarized  in Table 7-2.

Total Hardness of Receiving Streams

Where the  beneficial use of principal  concern  is  the protection  of  aquatic
life, the  URO pollutants of major concern  appear  to be  heavy metals,  partic-
ularly copper, lead and zinc.  The potential toxicity of these pollutants are
strongly  influenced  by total  hardness,  as indicated by Table  5-1  in  Chap-
ter 5.  Other beneficial uses  deal  with pollutants and  effects  that  are not
influenced  by  total hardness  or (as  with drinking  water  supplies) do not
modify the assigned  significance of heavy metal concentrations  on the  basis
of total hardness.

As with stream flow  and  precipitation,  distinct regional patterns also exist
for receiving water total hardness concentrations.  Figure 7-2 delineates the
national  pattern of regional  differences.  These  patterns  impose  an  addi-
tional regional  influence  on the potential of  urban runoff  to create problem
conditions in streams and rivers.

Technical  Approach To Screening Analysis

The magnitude and frequency of occurrence  of  intermittent  stream concentra-
tions  of   pollutants  of  interest,  that  result from  urban   runoff,  has been
computed using the probabilistic methodology discussed in Chapter  5.

The  input data  required for  application of the methodology includes repre-
sentative  values  for the mean  and  variability of  stream  flow,  runoff  flow,
and runoff pollutant concentrations.   The material presented earlier in this
chapter provides  the basis for  assigning  values  for the  flows;  the results
summarized in  Chapter 6 provide  the  basis for specifying  pollutant concen-
tration inputs.   In  order  to translate the  probability distribution of stream
concentrations  (which  is the basic  output of the analysis methodology)  to  an
average  recurrence   interval,  which is  considered  to provide  a more under-
standable  basis   for  comparisons,  the average  number of storms per.year  is
also  required.   This is  estimated directly from the  average  interval between
storm  midpoints  generated by  the  statistical analysis of  hourly  rainfall
records.

For  a general screening on  a  national  scale,  an  estimate  of typical  values
for a  selected geographic  location  must  be made.   This  he?, been  done,  end  the
set  of input values considered to be typical of  geographical  location  are
described and summarized below.  The values used  should  be  considered rea-
sonably representative of  the  majority  of  sites in  the  area,  but it  should be
recognized that  not  all potential sites  will have  conditions either  as  favor-
able  or unfavorable  as those listed.

We have worked with  a  limited  sample  in assigning  typical values,  h greater
cete  base on  rainfall  end  stream flow would permit  greater  spatial definition

-------
HARDNESS AS CaC03
IW PARTS PER MILLinW
           tlnilnr fin

      IH31  fin- 120
Over 240
                 Figure 7-2.   Regional Values for Surface  Water Hardness

-------
than shown in  the  results.   Specific  regions or states  could,  with develop-
ment of a more detailed spatial definition of stream  flows  and  rainfall,  .ex-
tend  the  analysis  presented  to provide  a  considerably more  comprehensive
assessment of  problem potential  for  local  areas.    This  would  involve  the
development  of input parameters  (rainfall and  streamflow)  readily  derived
from available long  term  USGS  stream  flow records and  USWS rainfall records
and their use  in the methodology with quality  parameters based either on the
NURP analysis presented in Chapter 6,  or on local monitoring activities.

The analysis methodology  presently  available permits  computation of the pro-
bability distribution of  instream concentrations, incorporating the effect of
upstream  (background)  concentrations  of the pollutant  of  interest.  The re-
sults  presented -here assume upstream concentrations  of zero, principally be-
cause  of our  inability  at  present to  make  reliable estimates  of typical
values for  the magnitude and  variability for pollutants  of interest, espe-
cially on  the broad national scale being  examined.   As a result,  the  summa-
ries  will show  the effects of  urban  runoff  contributions  only.   In cases
where  the background is small relative to the URO contribution,  the summaries
will  represent actual conditions quite closely.  However, where  background  is
high  and has  appreciable variability,  the  implications of  the  URO contribu-
tion  will be  overstated, particularly  the inferred  improvement which could
result from  control  of URO.

 In order to  perform a national screening  of  regional  influences on urban  run-
 off impacts, eight  geographical regions  illustrated by Figure  7-3  have  -been
 delineated.   Using the  information  summarized  by Figures 7-1 and 7-2,  typical
 values  for  the  pertinent  rainfall/runoff and  stream  parameters have  been
 assigned for each of the regions.   Table 7-2 summarizes the values for these
 parameters  which are used in the  screening analysis.
                      TABLE 7-2.   TYPICAL REGIONAL VALUES
1



j
£
~)
4
t
6
7
e
[vent Average
Re infa 11 Intensity
M.esn
(in/hr)
0.0*
0.10
0.06
0.055
0.04
0.02
0.045-
0.025


1.00
1.35
1.35
1.25
1.10
1.10
l.?0
0.85
Averane
Number
of
Events/year
110
100
90
no
62
7C
30
80
Average
Runoff Flow Rate
Mean [vent
(cf s/sq mi }
5
n
10
/
L
L
:.
;


0.65
1.15
1.15
1.05
0.95
0.95
1.00
0.75
Stream Flnw Rate
(L'ci 1 v Avq Flow; \
Mean
(cf S/sq mi }
i.75
i.25
1.00
0 . 7 5
0.35
G.0£
0.0:
i.50


!.25
1.25
'1.25
1.25
'; f. '.
j.-t
1.25
i 5.25
Stream
Total
Hardness
(mg/1)
• 50
50
50
200
200
300
200
50
  Average  stream flow and rainfall  intensity  were taken from  the  plots,  which
  are  based on sources previously described.   The estimate  for  variability of
  daily  stream flows  (coefficient of  variation)  is based en computed values for
  a sample  of  about  150 perennial streams.   Results for a number of regional

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Geocirapli.tr: Roiq.ions Select'^ for Screening Analysis

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groupings indicated median  values  for coefficient of  variation to  fall  be-
tween approximately 1 and 1.5.  Since  there  were no clear  regional  patterns
apparent, a  uniform value  for  coefficient of variation  of stream  flows  of
I./.5 was assigned.

The coefficient of variation of rainfall  intensities was  taken directly from
the statistical analysis of the rainfall  records  examined.   This was reduced
by 15 percent to  provide estimates of  the coefficient  c-f  variation of runoff
flow rates,  based .on a recent published report, "Comparison of Basin Perform-
ance  Modeling  Techniques",  Goforth,  Heaney  and  Huber,   ASCE  JEED,  Novem-
ber 1983, using the SWMM model on a long-term rainfall record.

The quality  characteristics of urban  runoff used in  the  screening analysis
ere listed  in  Table 1-3,  and  are  based  on  the  results summarized  in Chap-
ter 6.   The  analysis  results  have  been  rounded  in  the selection  of repre-
sentative site median EMCs  and  are interpreted as being representative of an
array of urban sites discharging into the receiving stream being analyzed.

Average  site conditions are based on  the  50th percentile  of all urban sites.
Since the date analysis indicated that sites at some locations tend to clus-
ter at either the higher or lower ends of the range for all sites, high range
and low  range  site conditions  were  also  selected for use  in the screening
analysis.  High range site conditions are nominally based on the 90th percen-
tile of  all  site  median concentrations;  the  low range on the  10th percentile
site.   The variability  of  EMCs from storm to storm at any  site is based on
the median  of  the  coefficients of variation  of EMCs  at  sites monitored by
NURP.   This  value was  used  for the low range  and average site condition  and
was increased nominally for the high range site condition.
              TABLE 7-3.  URBAN RUNOFF QUALITY CHARACTERISTICS
                       USED IN STREAM IMPACT ANALYSIS
                          (Concentrations in pg/1)


Low Ranae of
Site Conditions
Average
Site Conditions
High Range of
Site Conditions
COPPER
Site Median
EMC

15
"2 c

SO
Coef
Var

0.6 '
0.6

0.7
LEAD
Site Median
EMC

50
135

350
Coef
Var

0.75
0.75

0.85
ZINC
Site Median
EMC

75
165

450
Coef
Var

0.7
0.7

0.6
An  illustrative  example  ci & s-ite-sp'ecific  application of  the probabilistic
analysis methodolcqv emcicveo is presented  in  order to:
         .illustrate the nature of  the  cciriputaticr:?.! results produced;

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     2.   Assist in the  interpretation of the tabulations presented  later
         which  summarize   results  of   the  national  scale   screening
         analysis;

     2.   Indicate how magnitude/frequency  of instream concentrations may
         be  interpreted  for  inferences  concerning  the   absence   or
         presence of a "problem" and  where .a problem  is  concluded  to
         exist, its degree of severity; and

     4.   Demonstrate how  alternative URO control options  may be  eval-
         uated in  terms of their expected impact  on  water quality and
         potential effect  on problem severity.

From selected  representative  values for  mean and  variability of  stream  and
runoff conditions, the  probability distribution  of  resulting  instream  concen-
trations during storm events can be computed.  Figure 7-4  illustrates a  plot
of such an output.   Uncertainty  in  estimates  for specific  inputs  can be  ac-
commodated by  sensitivity  analyses  which  incorporate upper and  lower bounds
for specific parameter values.   Results are then presented as a band rather
than a specific projection.  The probabilities which are the  basic output of
the analysis may be converted to average  recurrence intervals to  provide  what
is believed to be a more understandable basis  for interpreting ' and  evaluating
results.

Figure 7-5 presents  Results  converted  to  the  average recurrence interval at
which specific  stream  concentrations  will  be produced  during  storm runoff
periods.

The significance  of  s  particular magnitude/frequency pattern of stream  con-
centrations caused  by  urban runoff can be  evaluated by comparing them  with
concentrations which are   significant  for the  beneficial  use  of  the water
body.  In the  example  presented, we have excluded  comparisons with drinking
water criteria  on the basis  that urban  streams are not  generally  used as
domestic water  sources,  and  in  any event, the  criteria relate to   finished
water, and surface water supplies almost  invariably receive treatment.

Protection of aquatic  life  is selectee for the  screening analysis  of  the im-
pact of urban  runoff because  it  is believed to  be  the  predominant potential
beneficial use  for  urban  streams  on  a  national scale.   The concentrations
which result from urban runoff are compared with stream target concentrations
associated with different  degrees  of  adverse  impact, as discussed and tabu-
lated in Chapter 5.

In  the  site  specific  situation  illustrated,  the  stream concentrations of
copper caused by  untreated  urban runoff  discharges exceed  the "EPA  Maximum"
criterion more than  ten times per year on average.   The concentration level
suggested by the NURP analysis to be the  Threshold level of adverse  biologi-
cal impacts is exceeded an  average  of  five  times per year (recurrence inter-
val 0.2 year), and significant mortality  of more sensitive biological  species
occurs about  once  every three years on average.   Although this  stress level
may not be  great  enough to  result  in  a  total  denial  of the  use, there  are
many who would argue that  it  represents  an  unacceptably severe decree of  im-
pairment of this beneficial use.

-------
               9E
                                                       COPPER

                                                STREAM TOTAl HARDNESS * 60 mgll
  0.1
                          10          50          90
                      PERCENT OF STORM EVENTS EQUAL TO OR LESS THAN
Figure 7-4.   Probability Distributions  of Pollutant Concentrations
                        Durina  Storm Runoff Periods
                                                       COPPER
                                               STREAM TOTAl HARDNESS • 60 tngll
                                                 DRAINAGE AREA RATIO " IOC
    D.I
                           MEAN RECURRENCE INTERVM YEARS
   Ficure  7-5.   Kecurrence  Intervils  fcr Pcliutcnt Concentrati onr-

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The projection labeled "treated urban runoff" may  be  taken tc represent  the
in-stream result for either the  originally  considered  discharge following  the
application of controls which effect a 60 percent reduction, or of  an  uncon-
trolled urban runoff site with lower levels of copper  in  the runoff.   In this
case, threshold levels are  reached  only  once every  3  or 4  years on  average,
and  significant mortality  levels  are virtually  never reached.   Even  though
the ambient "EPA MAX" criterion is exceeded once or twice  a year on average,
one might conclude that the implied degree  of stress  is  tolerable  and  is  not
interpreted to represent  a significant  degree of  impairment of the  use.

The Threshold and  Significant Mortality levels are  estimates, which have been
explained earlier.  In addition, the "acceptable" frequency at which specific
adverse effects can be tolerated is subjective at  this  time, since there  are
no formal guidelines.  However, an  approach of  this nature must be  taken in
any  evaluation  of  the  significance of  urban  runoff and  the importance of
applying  control  measures.   There  are  two reasons why  this  is  necessary.
First, because  of the stochastic nature of the  system we  are dealing with,
virtually any target  concentration  we  elect to  specify will be exceeded at
some  frequency,  however rare.   Secondly,   from  a practical  point  of view,
there are limits to the capabilities of controls, however rigorously applied.
In the illustration presented, the untreated urban runoff site-assigned urban
runoff copper  concentrations equivalent tc the average urban site.   Since
NURF analysis data  indicate that the  copper  in urban  runoff has  a  soluble
fraction  of  about 4fi percent,  the level of removal  used  in the example  re-
flects a control efficiency approaching the practical limit.  Receiving water
impacts are significantly reduced, but not  totally eliminated.

Results of Screening Analysis

A projection of stream water quality responses has  been made for each of the
eight  geographical  areas  shown by Figure 7-3.    The  rainfall, runoff,  and
stream  flow  estimates  used  in  the  computations  are  those  summarized  in
Table 1-2.  The urban runoff quality characteristics used  are those  presented
in Table  7-3.

To consolidate  screening analysis results  for  easier comparison, results are
not  presented  as  continuous  concentration/frequency curves as used  in the
illustrative  example  presented above.   Instead, the comparison  plots which
follow  show  only  the  recurrence  interval at  which   specified   biological
effects  level-s  are  exceeded.   The  concentrations which correspond with these
effects  are strongly  influenced  by  stream total  hardness, and  hence  vary
regionally.  Table  7-4,  based on information presentee  in Chapter  5, summa-
rizes  the  stream  target   concentrations   used   in   the  screening  analysis
summary.

Analysis  results  are presented  for Copper  (Figure 7-6},  Lead  (Figure 7-7) and
Zinc  (Figure 7-8).  Each  individual bar represents  a different geographical
region,  and  the analysis is performed  for two  drainage  area  ratios.  Since
regional  stream  flow  differences  ere  based  on  unit  flows  (cfs/sq  mile  of
drainage  eree) ., actual flew in  £ receivi.no  stream at  z particular  location  is

-------
      TABLE  7-4.  REGIONAL DIFFERENCES IN TOXIC CONCENTRATION LEVELS
                          (Concentrations in yq/i)
I
Pollutant
Copper


Lead


Zinc


Stream
Total Hardness
vg/1
50
200
300
50
200
300
50
200
300
Geo-
graphic
Regions
1,2,2,8
4,5,7
6
1,2,3,8
4,5,7
6
1,2,3,8
4,5,7
6
EPA
MAX
12
42
62
74
400
660
180
570
800
Suggested Values For
Threshold
Effects1
20
80
115
150
850
1400
38C
1200
1700
i
Significant Mortality'1
(e) (b)
50 i
180 I
265
350
1950
3100
870
2750
3850
90
350
500
3200
17,850
29,000
3200
8.000
11,000
     3   Threshold Effects - mortality of  the  most  sensitive  individual
        of the most sensitive  species.


     2   Significant Mortality
        Level  (a) - mortality  of  50  percent  of  the  most  sensitive
        species.
        Level  (b) - mortality  of  the  most   sensitive  individual  of
        25th percentile sensitive species.
a  function of  both the  unit  flow  rate and  the .size  of  the contributing
drainage area.  The "drainage area ratio" (DAR) used in the analysis is
             DAR =
Urban Area Contributing Runoff	
Stream Drainage Area Upstream of Urban Input
It  is  a  measure  of  the  location  of  the urban area relative to the headwaters
of  the receiving stream.

The  shading  scheme  used  on  the bars  duplicates that  used earlier  in  the
illustrative  example  (Figure 7-5) ,  and identifies the recurrence  interval  for
each  of  the  target concentrations.  For  example,  instream copper concentra-
tions  during  storm  runoff periods  in  geographic  region 1,  with  average  site
conditions  for copper  concentrations  in . urban  runoff, and  a  DAP = 30,  are
projected to  be as  follows  (middle plot,  Figure 7-6).

         EPA  MAX -  ambient  criterion  is  exceeded  at  a   frequency  of
         C.02  veer  !=  50 times/year')  or about every other storm  event  or.
         average.

-------
KKIUTUT
                     snt ma amury
                      tow M«ct srns
im ma OUHITT
                                                                                                            HUH MICE SITES
                                     I "
                                     I
                                     i  '
                                     i
 1  Z 1 4 5 • 7 1 «  |  •  1 7 ] « I I 7
    nu - in    «H)8»«pinr   nix - ion
               s  -
               SK
               i
               i   ,
               8
                                                                                      1  I 3 « 5 t 7 »
                                                                                                        1 2 3 «  5 6  7
                                               DM - II    ORIBMme    OM <
                      1 J 3 • S I 7
                         DM - II
1 ? 3 4 5 I 7 •
   n*« - iim
                 Figure 7-6.   Exceedance Frequency for  Stream Target Concentration
                                                   COPPER

-------
I    "'"    I
                       SITt DUB OIXUTT.
                        IBW «««6t Snit
                                         r   "«•  ^
                                                                    tnt (in noucry
                       stTi u«n amtrrr
                        mc» mGE strts |

5(1


n.i

-
:

i
t

uL



1


-

•

el.
|

t t t T


1 1 1 1


-







1




1
8



3
^



4 S 1 7 I
t f t t t


1 1 1 | 1
3  4 5 « 7 II •  ,	-I J 3 4 S ( 7  «
nun - 10    lUOGmpmc    nut - too
          mini
                                                                   I 3 4 S I 7 I
                                                    I  I I  I
                                                                                8      so
                                                                                2

                                                                                    I  "
                                                                                    2  '
                                               I }  3 4 S I 7 I •  |   • 1 7 3 4 S  8 7 I
                                                  DM . to    8HI6MMIIC    gu . tun
                                                                                            1 » 3  « 5 t 7
                                                                                                               1  I 3  4 S I 7 I
1  I 3 4 5 8  7 • i  |  •  1  ? 3 * 5 « 7
   DM " 10    BBIWWWC    n» - 1(10
                   Figure  7-7.   Exceedance Frequency  for  Stream  target  Coficentratibrv
                                                         LEAD

-------
                           SITE URO OimiTY
[   tnt    |            | inw PMCE SITES I          [    imc    \
                                                                    sirt QUO oumrt
                                                                      «vni6i SITES
                                                                      SITE unn nuniiTY
                                                                     I HIGH HIKE SITES
3 in
        2 3 1 fi fi 7 fl
                           3 « s « 7 B
                              I»11
                        -1 7 .1 1 5 fi 7
1
a  i
                                          s
                                          m
                                          S ».'
                                                    3 « 5 g 7 i
                                                                  1  I ! 4 5 I I a
                            tcm
                                                   i, i i  '. I
          "•" - '"      ornim
                                                 I 7 .1 < 5 B 7
                                                    nun - in
                 B .  ,  . I  1 3 » 5 fi ' «
                  GEOGMPHIC.    n«n - inn
                                                                                    s
                                                                                    s
                                                                                    I-
                      Figure  7-8.   Exceedance  Frequency  for  Stream Target Concentration
                                                          ZINC

-------
        Threshold  concentration   levels   at  which   adverse-   biological
        stress for short  duration  exposures is  projected  to occur have  a
        recurrence interval  of  about  0.05  years (20  times/year).

        Significant mortality levels are  exceeded at  intervals  of about '
        0.5 year  (twice/year) for  the less severe effect,  to  about once
        in 5.5 year for the  more severe  impact  specified.

The plot is terminated at an upper level  for  recurrence interval of 50  years.
Although  the  analysis procedure  computes specific  recurrence  intervals  in
excess of  this  value, a realistic  interpretation  suggests that  such  condi-
tions are  for practical purposes  quite  unlikely to  ever be reached  or  ex-
ceeded.   At computed recurrence intervals of  about 10 years or more estimates
are not considered to be reliable  and are very  probably conservative.  There-
fore, indicated mean recurrence intervals in  excess of 10 years probably {and
50 years certainly) should be interpreted as  "unlikely" or "highly unlikely".

Discussion

An  inspection of  the screening  analysis  results   (Figures 7-6  through  7-8)
indicates the reason  why it  is unrealistic to  attempt a  broad generalization
on  whether  urban  runoff  is, or  is  not   a "problem" in  rivers  and streams.
Water quality impacts can  vary  widely,   depending  on regional  rainfall  and
stream  hydrology, urba« ' site  quality characteristics,  drainage  area ratio
 (reflecting the size  of the receiving stream relative to the urban area) , and
the  total hardness of  the  receiving stream.   While the  screening analysis
results provide an informative and useful perspective on the  issue,  it should
be  recognized that any specific site may differ considerably  from  the  typical
.conditions  used  to.characterize  rainfall and  stream flow for  the area,  and
further,  that local  variations in runoff quality  characteristics within the
range defined by  the  NURP data can also have significant  influence.  The dom-
inant  indication  of  the analysis  is  that  the  problem  potential for urban
runoff  is highly  site-specific.  Nevertheless  some useful  generalizations can
be  made.

Perhaps  the major factor which dictates whether urban  runoff discharges  of
copper,  lead, or  zinc will  adversely impact  aquatic  life is the  natural hard-
ness  of the  receiving  streams.   As a  result, the  southeast end gulf coast
 areas are consistently indicated  to be more  sensitive than other areas of  the
 country.   Of  the' remaining  soft water areas,  the  northeast   is somewhat  less
 sensitive;  the  Pacific northwest  markedly less.   This  is attributed  to  sig-
nificantly  lower storm intensities in these areas,  coupled  in  the  northwest
with  appreciably  higher  stream flows.

Drainage  area ratios have   an  important effect,  reflecting  as  they  do  the
magnitude of  stream  flow at the  urban  location.   The effect is  much  greater
 for geographical  regions with  high unit  flow (cfs/sc  mile)  than  for  lower
 stream  flow regions.

 Finally,  the  quality  characteristics  of the  urban  sites have  e.  significant
 influence.   Stream concentrations  differ markedly  depending on  whether  the
 local urban sites tend to cluster toward  the lower  or higher  end of the range
 of  site median  concentrations  indicated  bv the KURF date base-.

-------
A comparison  of the  relative  position  of the  bars  on Figures 7-6,  7-7  and
7-8,  is  sufficient to indicate  the  comparative sensitivity to urban runoff
pollutant  discharges.   However,  it  is  also  desirable to  decide whether  a
given stream effect constitutes  a serious degree of  impairment of an aquatic
life  beneficial use.   There  are no  formal  guidelines,  and  .interpretations
that  are  either more  liberal  or more restrictive than  those  suggested below
may be  preferred by  others dealing  with  specific  stream segments.   For  the
interpretation  of  the  national  scale  screening  analysis,  the  following deci-
sion  basis  has  been used  to  identify the  situations  in which  urban runoff is
likely to  result in  a water use "problem",  (i.e.,  cause  an unacceptable  de-
gree  of use impairment):

        Threshold  effects -  (mortality of the  most  sensitive  individual
        of  the  most sensitive  species) occur more often than  about once
        a year  on  average.

        Significant mortality -  using the lower of the two levels  (i.e.,
        50 percent mortality of  the most sensitive species)  , occurs more
        often than about once every 10 years on average.

Using these guidelines for assessing the occurrence  of  problem  situations,
copper  is shown to be the  most  significant of the three  heavy  metals con-
sistently  found in urban runoff  at elevated concentration levels.  Where site
concentrations  are at  the high range of observed urban  site conditions, prob-
lems  are  expected  in^all geographic  regions at a  DAR  =  10^,  and  in all geo-
graphic   regions  except  region 8  at  DARs  as  high  as  100.   When  site
concentrations   are in the  average   range  of  observed  conditions,   problem
situations  are   restricted to  geographic  regions 2  and  3  (plus  region 1  at
DAR = 10) .   When  site  copper  concentrations  are  in  the  lower  range   of
observed  site  conditions,  problem situations  are   restricted  to geographic
regions 2  and  3 at low DARs.   They  are marginal  (significant mortality once
every 5 years)  but remain a problem according to the definition adopted.   The
 "marginal"  attribution  is  used here,  because the more  severe  degree  of
significant mortality  (most sensitive individual of  25th  percentile  sensitive
 species)  is indicated  by the analysis virtually never  to  occur.

Thus, copper  discharges  in  urban runoff  are indicated  to represent  a signif-
 icant threat to aguatic life  use  in  regions 2 and   3  (southeast  and  Gulf
Coast)  under  almost all  possibilities for urban site  runoff  quality.   In  re-
 gion  1  (northeast), problems would be expected at  all but the  lower  range of
 site  concentrations.   In the hard' water  areas  (regions 4,  5, 6,  7)  problems
 are  expected  only  where  site  runoff quality if in  the high end  of  the  range
of  observed site median concentrations.

 It  should be  noted that the analysis has been  based on  total  copper concen-
 trations  in urban  runoff.• Toxic effects  are usually considered to be exerted
by  the soluble  form of the  metal,  and EFA defines an  "active"  fraction based
 on  a  mild digestion  which  converts some  of  the   inactive  particulates  to
 soluble  forms,  to  account for  transformations  which may  occur  in the natural
 water systems.   Copper  in  urban  runoff  has  £ typical  soluble  fraction  of
 about 50 percent,  and the  active  fraction  would   therefore fall  somewhere
 between  50 and   100 percent  of  the total  concentration used  in--the  analysis.
 The   analysis has  beer: performed  usinc   the  total  fraction, since  adecuate

-------
infcrmaticri  is  not • avaiieDie  at present  to  reliably  adjust  these  values. '
However, although the problem assessment presented above may be somewhat con-
servative, further  refinement  alone  these  lines would  not  change the infer-
ences drawn from the screening analysis results.

Zinc,  like  copper, has  an  indicated  soluble  fraction  in  the  order  of
50 percent, and the screening analysis indications will also be unaffected by
this  consideration.   It is  indicated  to be  unlikely  to pose  a significant
threat  to aquatic  life  in  most  urban runoff  situations.   Exceptions -are
restricted to  soft  water  areas in the east  and  south,  lower DARE,  and  sites
with high zinc concentrations in urban runoff.

Lead  results  mus-t  be viewed with greater  caution,  because  soluble fractions
in  urban  runoff  are   indicated  to  be quite  low  (less  than  10 percent).
Problem  indications are therefore likely to  be  reasonably conservative,  i.e. ,
overstate  the  problem potential.  Problem  situations may  be expected  to be
restricted to  soft water  areas  in the  east and Gulf  areas when urban  sites
have  average site  concentrations and  DARs  are low,  and  even  at  high DARs
when  site concentrations  are  in  the  high range.  Lead is not  indicated  to be
a  threat to aquatic  life  in the hard  water areas of  .the  country  or in  the
Pacific  northwest,  except  for  the   combination cf  low DAR  and  high  site
concentration.

In perfermine  the  screening  analysis, upstream concentrations were  assumed to
be  zero; that  is,  the receiving  stream had  only a  diluting effect on  the
urban  runoff pollution.  In  actual  cases 'background  concentrations  will  be
greater  than zero,  and in some instances upstream  contributions (e.g.,  agri-
cultural runoff, another  city) could be  significant and result in more 'severe-
conditions than  those  identified in  the  screening  analysis.

On  the basis cf the foregoing,  it appears  appropriate to  identify  copper as
the  key toxic  pollutant in urban runoff,  for the following reasons:

         Problem  situations anticipated  for lead  and  zinc  do  not  occur
         under  any  conditions for which copper  does  not  show up  as  a
         problem  as well - and with  more  severe impacts.   On  the  other
         hand,  copper  is  indicated  to be  a  problem in. situations  where
        'lead or  zinc are  not. .

         Based, on  the  ratios  between concentrations  producing  increas-
         ingly severe effects, copper  is suggested to  be  a more generic
         toxicant.   It has an  effect en a bread range of  species.    This
         is   in  contrast  to  lead and  zinc  for  which  ?.   substantially
         greater  degree cf  species  selectivity  is  indicated.  Some  spe-
         cies are  sensitive,  others   relatively  insensitive  to lead  ant
         zinc.

         From the  NURF data,  locations  which  tend tc have sits ~\~:~:it:r
         concentrations in  the  low,   average,  or  high end of  the r;M".:--
         nave generally consistent ;.:attern=  fcr e.aor.  c-J  the thrcr  :••--.•.•••
         metals.

-------
        Control measures which produce  reductions  in  copper  discharges
        to receiving waters  could be expected  to  result in  equivalent
        reductions in zinc,  end greater  reductions  in lead,  by virtue  of
        its significantly greater  particulate  fraction.  •

Copper is  accordingly  suggested  to be an effective indicator for all heavy
metals in  urban runoff relative   to  aquatic  life.   It  might  be  used as  the
focus   for  control   evaluations,   site  specific   bioassays,    monitoring
activities, and the like.

It should be noted that while immediate water column impacts  of  lead  are  not
as  significant  as those  for  copper,  the high  particulate  fraction  of  lead
would tend to result in greater accumulations  in the stream bed.   This aspect
has  not  been  addressed by the NURP  program  in  sufficient  detail  to  warrant
any comment on its potential significance.

The  results of  the screening  analysis summarized by Figures  7-6 through  7-8
are  approximate,   because  they   are   influenced  by the   suitability  of  the
typical values for stream and runoff flows  which were  assigned.  This however
can  be refined  by the  use of appropriate values which can  be developed  from
readily  available  data bases, and thus  adjusted for  local  variations  which
are  to be  expected.  A second issue relative to the reliability of  the  pro-
jections is the validity of the  computations,  given that the input parameters
arc  representative.  This has been confirmed  by  a number of validation tests,
                     **
discussed  in the NURF supporting  document referenced earlier, which addresses
the  stream analysis methodology.

The  remaining  issue for evaluating  the  reliability  of the  indications' of
problem potential produced by the screening analysis is the reasonableness of
the  intermittent  exposure concentration levels,  which  have  been associated
with  various biological  effects  levels, and  the guidelines adopted  for this
discussion, which determine  whether  or not  a  problem   is  expected.  While
rather tenuous at this time, the  information  available does provide support.

Two  of  the NUR? projects examined aquatic life  effects  in streams receiving
runoff from monitored sites.

         Believue, . WA concluded  that  whatever adverse  effects were  ob-
         served  were  attributable to  habitat  impacts   (stream bed scour
         snc  deposition)   as   opposed  tc  chemical  toxicity.  For this
         project,  heavy  metal concentrations  in  the   monitored urban
         runoff  sites were typical of  the  average for  a 11  urban  sites.
         The  screening  analysis  results under  these  conditions dc  not
         indicate  the expectation of a problem.

         Tampa, FL  conducted extensive  bioass.ay  tests  but failed  to  show
         any adverse  effect  of water column concentrations  of pollutants
         in  urban  runoff.  The screening analysis  results  presented  in
         Figure 7-6  indicate  marginal  problem condition? at  low  DAK  for
         this geographic  region.   At  this- project however,  all monitored
         sites  sncv; heavy metal  concentrations  significantly  lower  than
         the low  ranee  conditions  used  in  the  screeninc  analvsis.   When

-------
        the  screening  analysis  is  repeated using  site  concentrations
        representative of Tampa  monitoring results, a problem  situation
        is not predicted, even at DAKs  lower  than is probably  the  case
        for this location.
LAKES
Because lakes provide  extended  residence times for pollutants,  the  signifi-
cant time scale for evaluating urban runoff impacts is at least seasonal,  and
usually annual or longer, rather than the storm event scale used for streams.
The screening methodology identified in Chapter 5,  uses annual nutrient loads
to assess the tendency for development of undesirable eutrophication effects.

Figure 7-9 illustrates the effect of  urban  runoff  on  average lake phosphorus
concentration.  The very significant influence of area ratio is evident.  The
larger the urban  area  which  drains  into a lake of a  given size, the greater
the annual loading, and  the  higher  will  be the lake phosphorus concentration
and the eutrophication effects produced.

The phosphorus concentrations characteristic of the urban sites surrounding a
particular lake are also seen to be significant.  The  three bands shown re-
flect the range of possibilities, based  on the NURP data.  The same basis is
used to estimate  the  phosphorus loads from average urban  sites  and  those at
the higher  and lower  ends of  site conditions, as  was described  for heavy
metals  in  the previous  section.   In  this  case, because  it  is  annual mass
loads which  are  of interest, site median 'cpncentrations have been converted
to site mean values for use in the computations.
                                               V
Lake  phosphorus  concentrations are  also  influenced by  the  annual  runoff
volume  (annual  precipitation  end  runoff  coefficiehst).   The  results  illus-
trated  are  based  on an  annual  rainfall  of 30 inches  a-qd  an overall  average
runoff coefficient of  0.2.   Plotted  results may  be scaled up or down  in pro-
portion to the ratio between  local values for  these parameters and those u-sed
in the illustration.

Finally,  the lake morphology and hydrology  influence the outcome;  specific-
ally  depth   (K)  and residence time  (i).   This  is  reflected by  the  width of
each  of the bands, which  are based  on  a range of  values for  H/T  (1 to  10)
estimated to be fairly typical  for  lakes  in urban  settings.

If an average lake phosphorus concentration of  20  yg/1  is  used as  a  reference
concentration to  assess  the  tendency  for producing undesirable levels  of bio-
stimulation, it is apparent  that only  lakes with rather  small  area ratios  are
likely  to be unaffected  by urban runoff  nutrient discharges.   Since  the three
bands represent different concentration  levels of  phosphorus in  urban  runoff,
qualitative  inferences may be drawn concerning the beneficial use impacts of '
control activities.   More  detailed  estimates may of  course  be made  by use of
the methodology with  site specific  parameters.

The  salient feature'  of  the   situation,  as generalized  by the  analysis  sum-
marized  by  Figure  7-9,  is  that  the  problem  potential  of  urban runoff  for
lakes  is  quite site  specific.  The  illustration considers  only  urban runoff
loads;  in   an  actual  situation, all   nutrient   sources (point  end  nonpoint)

-------
   1000
c

p
<
c
c-
V.
c.
it
c
              URBAN SITE QUALITY

                CHARACTERISTICS
               SITE MEAN TP CONCENTRATION ugll
                                                                           HIGH RANGE

                                                                           AVERAGE

                                                                           LOW RANGE
                                              ANNUAL RAINFALL  =  30 iniyear

                                            RUNOFF COEFFICIENT  =  0.2
                                               DEPTHIRESIDENCE

                                               RATIO FOR LAKE
K!T=  1 to 10 miyr
                                              SETTLING VELOCITY Vs =

                                               (TOTAL Pi
                                                                                          100C
                                                URBAN
                                             LAKE SURFACE AREA

-------
would be considered, and this would tend to modify  the  relative significance
of urban runoff on lake conditions.

Several of the NURP'projects addressee impacts on lake quality in some depth..
These projects include the following:

        Irondequoit  Bey,  NY - Lake has  been highly  eutrophic,  due  to
        point and nonpoint discharges.  Sewage treatment  plant and com-
        bined  sewer  overflow discharges  have  been  removed,   so  that
        residual  sources  are recycle from  lake  sediments  and nonpoint
        sources,  including urban  runoff, from the  contributing drainage
        area.  Further reductions are consider-ed necessary to meet tar-
        gets.   (Area ratio is high at this location.)

        Lake George, NY - Lake is oligotrophic;  the study addressed the
        concern  that  urban  runoff  from  present and potential future de-
        velopment would unacceptably  accelerate  degradation of  existing
        water quality.  (Area ratio is low at this  location.)

        Lake Quinsigamond, MA - Urban runoff was determined  to  be one  of
        a  number of  sources preventing water quality  objectives from
        being  met.   Some  control of  urban runoff  phosphorus loads was
        recommended  as one  of the  elements  of an  overall mana-gement
        plan.
                       i*
 Each of the  above  situations is sufficiently  unique,  and  the mix of urban
 runoff and other load  sources is sufficiently  different to suggest  that it  is
 inappropriate  to attempt  a  broad generalization.   The interested  reader may
 refer  to  the  individual  project  documents which  are available  through NT1S
 for more  information.

 ESTUARIES  AND EMBAYMENTS

 These  water bodies  are normally of sufficient size and  complexity that simple
 screening   analyses  have  not been  considered to   be  sufficiently useful  or
 effective to justify their  use.

 The Long  Island, NY  NURP project examined and confirmed  that  urban runoff
 sources of  coliform  bacteria  are  the  principal   contributors to the water
 column concentrations that  result in  closure of  shellfish beds in a number of
 embayments  (principally the  Great South Bay) .  Estimates of control activi-
 ties that would  allow the  opening of presently  closed areas were also made.
 The reader is referred to the project documents  for further  information.

 The significance of urban runoff  and  other nonpoint source  loads on eutrophic
 levels in the  Potomac estuary is being  investigated under  a  study  which is
 not associated with the NURP program.  However,  among other  objectives of  the
 WASHCOG NURP project, estimates of urban  nonpoint source loads have  been  de-
 veloped to support this study.

 Although  specific   situations where  urban  runoff is  significant  have  been
 identified, n'c  general assessment .for  water bodies  of this type can be madf
 at  this time.

-------
:: si?, no...  wY and  Fresno,  Ck NUKJr  projects  e:i-:a.:".inec; -this  issue  thrrcv.gh
 z.'ists  utiiisinc recharge br.sins  ranginc  f::or;.  recer.t  instEllaticns
  v.'i'!J.ch  ha'.'S  bee;":  ir:  service  in  excess  c:^  20 '-'i^.rs,    .R  sornevb^^
.  ccncclidation c£  the  salient findings  c:1  these.  tv.?c  projects  is
 :;.-::Io'v,   The interested reader is  referrec  ^c  the i"di':.'idua.l  ;::o;c-ject
 /•:,^-;'."=.  r.--^i;^;:-;.s  -chrouch   NTI;..  ::c:-.  '::'•;   :.;-•: :T-:?.:V:.   istf.i;..:  -imc.

                                    tested £;•;.£• found  -c
                        in  cne  upper  sci..
                       function cf  the  Jen;

-------
No   significant   differences   in   interception/retention   of
pollutants  is  apparent  for  basins with  bare versus  vegetated
recharge  surfaces.   However  vegetation does  apparently  help to
maintain  infiltration rates normal for the soil type.

Surface  soil  accumulations  of  priority pollutants  in  dual pur-
pose  installations  used  for both recharge  and recreational use
warrants  further  investigation to determine  whether such prac-
tice creates unacceptable health risks or requires appropriately
designed  and conducted maintenance procedures.

-------
                                  CHAPTER  8
                            URBAN  RUNOFF CONTROLS
INTRODUCTION

This  chapter  summarizes the  information developed  by  the individual  NURP
project  studies' relating to  performance characteristics  of selected  tech-
niques  for  the  control of  urban  runoff  quality.   The  number  of  control
practices addressed  here  is  considerably  smaller than the array of  best
management practices  suggested  in prior studies  and  publications.  This  is
not  intended  to  exclude consideration  of  other  approaches.   However,  the
techniques discus-sed  in this  chapter may be  taken as an  expression of con-
trols considered  by  the agencies involved  to be potentially attractive and
practicable  at  localized planning  levels.   They represent  the  practices for
which performance data  were obtained under  the  NURP program and which  can be
analyzed and evaluated in this report.

Most  of  the  NURP  projects  provide  in  their  project  reports  a  detailed
analysis and evaluation*of the controls that were studied.  These reports are
available through NTIS.  In addition to  this  information source,  an analysis
was  performed  by  EFAs  NURP headquarters  team,  using  results available from
all project studies.  The objective  was  to  provide an overview  and a generic-
description  of performance  characteristics  in a  format  considered   to  be
useful  for  planning  activities.  Thus,  in  addition to  providing  a consoli-
dated  summary  of project  results,  this  chapter presents  a summary  of the
results  of  applying  analysis  methodologies  developed  under the  NURP program.
Further  detail on the former can be obtained by reference to relevant project
report  documents; a  more comprehensive development of the latter is provided
in  separate NURP documents  ("Detention  and  Recharge  Basins for  Control of
Urban  Runoff  Quality",  and  "Street   Sweeping  for Control  of  Urban   Runoff
Quality").

The  types of  control  techniques which  received  attention  (to  a  greater or
lesser   degree)  in  the  NURP  program  can  be grouped  into  four   general
categories.

         Detention Devices - These  include  normally dry  detention basins
         typically  designed for  runcff  quantity  control,  normally wet
         detention basins,  dual  purpose basins,  over-sized drain pipes,
       •  and catchbasins.

         Recharge  Devices - These  include  infiltration pits,  trenches,
         and  ponds;   open-bottom galleries  and  catchbasins;  end porous
         pavements.

         Housekeeping  Practices  -  These are prir.cipc.lly-  street  sweepinc..
         but  else  include  sidewalk  cleaning.,  litter  containers,  catch-
         basin  cleaning,  etc.

-------
        utner - These  incj.uoe  m
        grassec Ewaj.es.. wetiancs , etc.
DETENTION DKVICEE
General
Detention  oasins  provec  tc  oe one  ci  tne most  pcpu_ar appro-,rnes  ::
runoff quality  control selected at  the local  level;  based en  th;  ".ursber of
individual projects  which electee to study  them and  the number of de~enti.cn
devices tested  in  the study.  It is perhaps  instructive tc nets  ^hae nearly
ai]  the  detention  facilities  studied  were  either already  in place,  or re-
quired  only  modifications  of  cutlet  structures  before   initiation of  the
NURP-supported  studies.    Jn general,  detention  devices  proved to  provide  a
highly effective  approach tc  control  cf  urban runoff quality ,  although the
design concept has a  significant bearing  on  performance characteristics.

Table fc-1  lists the NURF  prcjects that  included detention  device? as elements.
of their study program.   Both  the number  of  devices,  and the number of storms
analyzed vary considerably,  as indicated  in Table 8-1.- depending  on project
priorities and  ether.relevant  activities.  As  a  result,  not all of the  sites
are incorporated in the  summary presented below.   The Washington Area Council
of Governments  (VJASHCOG/  conducted a particularly  thcrouch and. comprehensive
investigation  of   control techniques,  particularly  detention  basins.    They
have prepared several us;eful and informative  analyses of  performance results
on these devices.

Drv Basins
This  is  a  type  of  detention  basin .which is  currently i-  fairly  extensive
service  in  various parts of the  country.  The  performance objective  cf  such
basins it- commonly called ''peak shaving1', that  is,  tc  limit the maximum  rate;
of  runoff  to  some preselected magnitude,-  usually  a  maximum j-rre-deveiopment
rate.   The  purpose  is  tc  control  flooding  and  e rosier;  potential in  areas
dov;!':Strea;t:  cf  new development,   Such' basins  em'clov  5.  better;, cutlet navinc  =<
hydraulic  capacity  restricted  tc  tht  maximuTr  a 1 low able  ::lcv    Runoff  from
smaller  storms  flows along the bot-coir;  cf.  the basin e.nc  :.s  eischargec  v-ithcut
restrietic:':.   Flows  in  excess  of design  are backed -j.p  rr. t!".•:-. :;as:'.:':.  ti~.;:er--
                      ;.' o. t _ .. -r

-------
          TABLE 8-1.  DETENTION BASINS MONITORED BY NURF STUDIES
Project
C01 Denver
DC1 Washington, D.C.
IL2 N. Illinois
Mil Lansing
MI 3 Ann Arbor
NY1 Long Island
Site
North Ave
Burke
Lakeridge
Stedwick
Westleigh
Lake Ellyn
Dryer Farms
Grace St. N*
Grace St. S*
Waverly Hills
Pitt-AA
Traver
Swift Run
Unqua Pond
Design Type
Dry Basin
Wet Basin
Dry Basin
Dual-Purpose
Wet Basin
Wet Basin
Dry Basin
Wet Basin
Wet Basin
Wet Basin
Wet Basin
Wet Basin
Wet Basin
Wet Basin
No . Events
in/out
39/21'
60/35
49/41
48/34
41/45
29/23
2/8
23/21
20/22
35/30
6/6
5/5
5/5
8/8
*  These are oversized storm  drains  installed below  street  level.   Inverts  of
   control sections are below the general grade line,  so a permanent  pool  is
   maintained.
constructed drainage systems.  Runoff from an individual  storm displaces all
or part  of the prior  volume,  and the  residual  is  retained  until the  next
storm event.  This pattern may  or  may not be  modified by natural base  inflows
during dry weather depending on the local situation.

Detention basins  utilizing  this design  concept have been shown by the  NURP
studies to be capable of highly effective performance  in  urban runoff appli-
cations,  as  summarized  below.   Although   performance  characteristics  of
individual basins ranged from poor to excellent,  analysis shows these  differ-
ences to be  attributable  to the size of the basin relative to the connected
urban area  and  local  storm characteristics.   Performance date also indicate
that in addition  to removal  of  particulate forms  or  pollutants by sedimenta-
tion,  some  basins  exhibit  substantial  reductions  in  soluble  nutrients
(soluble  phosphorus,  nitrate +  nitrite  nitrogen).   This  is  attributed  to
biological processes  which  are permitted to  proceed in  the  permanent water
pool.

-------
There are a number of ways to characterize detention basin performance.  The
primary basis  selected 'by  NURF  for doing so  is  to define performance  effi-
ciency on  the basis  of  the total  pollutant  mass removed  over all  storms.
This provides  a  meaningful general measure for  comparison   is relevant for
water quality  effects associated with extended  time  scales  (e.g.,  nutrient
load  impacts  on  lakes) ,   and  conforms with  the  capabilities of  the  NURF
analysis methodology  developed  to provide a  planning-level  basis for  esti-
mating cost/benefit differences  in  size  or  application density of this  type
control.

Table 8-2 tabulates performance  in terms  of  reduction  in  pollutant mass loads
over all  monitored storm  events.   The analysis methodology  developed  under
the NURP program  activities  suggests  that performance should  be  expected  to
improve as  the overflow  rate (QR/A =  mean runoff  rate * basin surface area)
decreases and as the volume ratio (VB/VR = basin volume •=  mean runoff volume)
increases.  The  NURP basins used  in  the analysis are listed  in increasing
order of expected performance capabilities.

The  wide  range  of  relative basin  sizes  provided  by  this  data  base  is
apparent, and performance  is seen to  generally  correspond with expectations.
The  poorest performance occurs  in a basin  with an  average  overflow  rate
during  the mean  storm  of  about  six  times  the median  settling  velocity
(1.5 ft/hr) of particles in  urban runoff.  In addition,  less than 5 percent
of the mean storm runoff volume remains in this  basin  following the event,  to
be  susceptible  to  additional   removal   by  quiescent  settling  during  the
interval between storms.  The basins which exhibit high removal efficiencies,
at the other  end of  the scale,  have  size relationships which result in the
mean  storm displacing only  about  10 percent  of  the  available  volume,  and
producing  overflow rates  which  are  only  a  small  fraction  of  the median
particle settling velocity.

This rationale is  described  more completely in  the supporting NURP  document
on  detention  basins  identified  earlier.  The  testing  of  the  methodology
against  the NURP monitoring data  is  presented,  and  the basis for  the per-
formance projections  illustrated below is documented.

Figure 8-1  presents  a projection of  removal  efficiency of  urban runoff de-
tention  devices  as  a function  of  basin size  relative to  the  contributing
catchment  area  and regional differences  in typical  rainfall patterns.  The
removal rates .apply  for  TSS, which are all settleable,  and must be  factored
by the  particulate/soluble  fraction  of  other pollutants which have  signif-
icant soluble  fractions  in urban runoff.   It applies  for the  specific  basin
average depth and area runoff coefficient indicated (which are fairly typical
based on  NURP data).  However  performance  relationships could be  different
than indicated based  on relevant local values lor  the  controlling parameters.

An alternate approach for  characterizing  performance of detention basins con-
centrates on the variable  characteristics of  individual storm events and  how
these are  modified by the  detention  device.    A comparison  of the  mean  and
coefficient of  variation  of basin  inflow and  discharge concentrations pro-
vides  another  measure of  performance of en urban  runoff  detention device.

-------
                        TABLE 8-2.  OBSERVED PERFORMANCE OF WET DETENTION  BASINS
                                 REDUCTION IN PERCENT OVERALL MASS LOAD
Project
and
Site
sing
r?ir:p St. N.
sing
race St. S.
Arbor
itt-AA
Arbor
raver
A rbo r
•'ift Run
:[ Island
Tqua
T.ington, D.C.
?stleigh
7 i n q
iverly Hills
ike Ellyn
No.
of
Storms

18
18

6

5

5

8

32

29
23
Size Ratios
QP/A

8.75
2.37

1.86

0.30

0.20

0.08

0.05

0.04
0.10
VB/VR

0.05
0.17

0.52

1.16

1.02

3.07

5.31

7.57
10.70
Average Mass Removals - All Monitored Storms (Percent)
TSS

(-)
32

32

5

85

60

81

91
84
BOD

14
3

21

(-)

4

(TO

*

69
•
COD

(-)
.(-)

23

15

2

C=7)

35

69
•
TP

(->
12

18

34

3

45

54

79
34
Sol.P

(-)
23

(-)

56

29

*

71

70
•
TKN

(-)
7

14

20

19

(-)

27

60
•
N02+3

• (-)
1

7

27

80

(-)

•

66
•
T.Cu

<->
(-)

•

•

•

*

•

57
71
T.Pb

9
26

62

•

82

80

•

95
78
T.Zn

(-)
(-)

13

5

(-)

*
	
26

71
71
NIPC
Nnt-p.s:   (-)  Indicates  apparent  negative  removals.

             Indicates  pollutant was  not  monitored.

-------
/'Si
liillll (•
  f  •-•
                            . .1..:
                            n.ns
 L.
10
                                                                             BASIN DEPTH - 3.S FT
                                                                             RUNOFF COEF = 0.20
                                                                              RM -  ROCKV WIT
                                                                              NW -  NORTHWF.S
                                                                              NE =  NORTHEAST
                                                                              SE =
                                                                                                           "1
                                                                                                            1   s
n.s
i.n
                         HASIM SURFACE AREA AS % OF r.QMTRIBMTIMG CATCHMENT AREA
                            i.'.---'.-|-ionri'.l. l>.ij;'fe-.:>:enr:es in Dovi:.en-i::i.Mn Basin Performance


-------
This approach  provides  more useful  information  for subsequently  evaluating
the effect of  controls  on water quality impacts  on rivers and  streams.-  As
evident from the  discussion in Chapter 6,  reductions  in  the mean and  vari-
ability of  runoff concentrations  (and the  inferred reduction  in mean  and
variability of runoff rates) will have a significant beneficial effect on the
severity of impacts on flowing streams.

Table 8-3  summarizes  detention  basin performance  when  assessed  in  this
manner.  It should be  noted that in most cases more inlet  storm events were
monitored than  discharge  events, and  that  some inlet  events do not  have a
matching  discharge  event  and vice-versa.    Further,  for  the  larger  basins
where  storm  inflow  displaces  only  a  fraction of  the basin volume,  it  is
unlikely that  influent  and effluent for a specific  event  represent  the same
volume of  water.   The tacit assumption  in  this analysis is  that  the inflow
events which  were monitored  provide  a representative sample of the total
population of  all influent  event mean  concentrations (EMCs).   Similarly, the
monitored  effluent  events are assumed  to  be a representative sample of all
basin  discharge  EMCs.   The appropriateness  of this assumption  is obviously
more  uncertain where  the  number  of  individual  storm events  monitored  is
small.

For each  basin influent and effluent,  the arithmetic  mean and variance were
computed based on the  relationships for lognormal distributions. The percent
reduction  in  the mean concentration  and  the  coefficient of  variation  are
tabulated  (Table 8-3?.  Note  that  where the  number  of  monitored events  shown
in  this  table  differ from those listed in Table  8-2,  it  is because the mass
removal  computations  were restricted to  synoptic  storms  (i.e.,  matching
influent and effluent results were  available for an event) .

Performance characteristics are generally consistent  using either  approach,
even  though  each displays a  different type  of  information.   Performance
improves with  detention basin size relative tc catchment  size and hence  the
magnitude  of  the  runoff processed.  Giving greater weight to  the  sites  moni-
toring large  numbers  of storms,  indications ere that for most pollutants  wet
ponds  also generally result in a considerable  reduction in  the variability of
pollutant  concentrations.

A'significant exception to this tendency  to reduce variability is  shown  for
the soluble  nitrogen   forms  (NC>2  + NO3) .    The positive  remove]  efficiency
indicated  by  reduction of mean concentrations  must   be  attributed to  bio-
logical  processes  rather  than  sedimentation.   A  substantial  increase  in
variability  is consistently indicated  by  the  data.  Among the  heavy metals,
lead  which is nearly all in particulate form  shows  significant reductions in
variability.   Copper  end  zinc  which  have  high  (40  to  60 percent)  soluble
fractions  show an ambiguous pattern with regard to  changes in variability.

In c.  few  of  the  cases where  atypical results  are  indicated, unique  local
conditions suggest  plausible  explanations.   For  example,  at the  Ann  Arbor
 (Trsver)  site, erosion from an unstabilized bank at the  outlet of this newly
constructed  basin  is   attributed  to  the  peer suspended  solids  removal  ob-
served.   The  poor   remove. I  characteristics at  the Uncua site  for  TKK  and
nitrate  may be  associated with the  significant  wildfowl population  at . t.hih-
site.

-------

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-------
The ability of detention basins  to  reduce  coliform bacteria  concentrations  is
also of considerable  interest because  of  the significant impact these urban
runoff contaminants exert on recreational or shellfish harvesting  beneficial
uses.  Other  than at the  Unqua site of  the Long  Island  NURP project,  the
number of observations made for indicator bacteria  were  too few to support a
reliable  assessment  of  the  ability of  detention basins  to effect  quality
improvements.  However, extensive data of this nature were  secured on deten-
tion basin  influent  and effluent  during  all monitored  storms  at  the  Unqua
site.

Since coliform bacteria  have a  high rate  of die-off in  natural waters,  per-
formance  characteristics based  on  total mass reductions  are not particularly
meaningful.   The  Unqua site data  were analyzed  to evaluate performance  in
terms of  reductions in  concentration levels.  Over eight monitored storms at
this site, covering a wide range in storm size,  the mean EMC (MPN/lOtD ml) was
reduced by 94 percent for  total coliform, 91 percent  for fecal coliform, and
95 percent  for   fecal   streptococcus  bacteria.    Variability  of  bacteria
concentrations in the pond outlet  increased,  with effluent  coefficients of
variation  ranging from about  10  to  100  percent greater than  influents.
Accordingly,  detention  basins  employing  permanent  pools  (wet  ponds)  are
indicated to be capable of substantial reductions in indicator bacteria.

Dual Purpose Basins

In.the  absence of a  we!3? defined terminology,  we  have  adopted this designa-
tion  to define basins  that are normally dry,  and hence   retain  their full
potential for  flood  control, but  which have outlet designs that result in a
slow  release rate  for  detained  storm  flows.   Detention  time  is extended
considerably compared with that provided by dry basins employing conventional
outlet designs.

One of the detention basins examined by the WASHCQG NURP project,  was of this
type.   This  project  designates   such  designs  as  "Extended  Detention  Dry
Ponds."   The pond was converted from a conventional dry pond by replacing  the
outlet pipe with  a perforated riser enclosed in  a  gravel jacket.   The modifi-
cation was  designed  to detain  stormwater runoff  for  up to 24  hours,  instead
of the  1  to  2 hours typically observed in conventional dry  ponds.

For  undetermined  reasons,  average  detention periods during the study were in
the  order of 4  to 8 hours, and hence considerably  shorter than  the  design
objective.   Nevertheless,  based on monitoring of  more  than 30 storm  events,
the  removal  of particulate forms  of urban  pollutants was   typically  high and
comparable to the performance efficiency  of wet  ponds.

Observed  removals  for  this  site  (Stedwick)  are summarized  by  Table S-4,
showing percent reductions  i.n both mass and concentration  distributions.  The
principal differences in performance of dual purpose basins compared with wet
basins  are  suggested by  the available  data  to consist of the following:

        Soluble pollutants  (e.g.,  soluble F and  Nitrate/Nitrite) are not
        effectively  reduced because of the  absence of  a permanent poo]
        within which biological reactions  have  an opportunity to occur
        in  addition to  sedimentation,

-------
The  variability
                             pollutant  EMC's  does  not  appear
       modified to the  extent  that  this  occurs  in wet  ponds.
                TABLE 8-4.   PERFORMANCE  CHARACTERISTICS  OP  A
                        DUAL-PURPOSE  DETENTION  DEVICE

               (Stedwick Site  -  washinqton  Area NURF  Proiect)
Pollutant
TSS
COD
Total P
Sol F
TKN
Organic N
N0-_t-
• T. Cu
T. Pb
T. Zn
Percent Reduction In
Pollutant Mess
Load Over All
Monitored Storms
64
30
< 15
1
•
30
10
•
84
57.
Poll
EM
Mean
62
41
11
(4)
E
•
13
•
•
43
utant
C's
Coef Var
(31)
17
0
(13)
(11)
*
6
•
•
33
Although the performance characteristics of basins of this type are indicated
to b'.  somewhat  inferior to the  potential  offered by wet  ponds, there  are a
number  of  considerations which  make dual  purpose basins  highly  attractive
candidates for quality  control of  urban runoff.   These include .the fact that
flood  control requirements  are  likely  to be  more economically obtained than
with wet  basins  and that many  existing stormwater management  basins  may be
readily modified to significantly  enhance  their  capability  for improving the
quality of  urban runoff.   In  areas where  ordinances requiring conventional
stormwater  management   ponds  are  already  in  existence;   tho  only  changes
required would be ar. alternate specification of the outlet  desi
Costs
Tne inrormaticn presentee  here  is intended  tc  provide an  order of magnitude
estimate cf the cost of providing different  levels  of  control of urban runoff
pollutant cischarceS; when wet detention devices  are  usei  es ~he best manage-
ment practice  (BMP).   The  summary, is based  on  the  siz-;   versus  performance
relationship presented earlier :.r,  riourr;  -l?.-1 and cr. '^r.z ;!?.=• '.'ersu;? cost  re-
"i ^ — -. ,-.r. c f. ". •"' c ^2." :~ c — ^ T £ ;" ^-e "' ""'V-

-------
The  analysis  is  based  cm  cost  information  developed  by  the  WASHCOG  NURP
project and discussed in detail in one of their project reports produced for
the NURP effort.   Construction cost  estimates as a function of basin  volume
are  shown  by  Figure 8-2,  adopted from  this  source.   This  estimate  compares
quite favorably with a similar cost/size relationship  developed  previously by
the Soil Conservation Service (SCS).
                                                                          \
The cost relationship shown by this  figure applies to "dry  pond"  designs anfi
relates only to expected cost of  construction  activities.   For  specific cost\
estimates, the  results  derived from  Figure 8-~ should be modified  as  appro-
priate, in accordance with the following:

        The  highly* variable  capital cost  of land  acquisition  is  not
        included in the construction costs.

        Outlet modifications to provide a dual purpose basin design will
        increase construction costs by about 10 to 12 percent.

        Pond designs  which meet   the peak shaving requirements  of  con-
        ventional  (dry) pond designs, but  also provide  a  permanent pool
        of water may have  costs up to 40 percent greater  than indicated
        by the cost relationship shown by Figure 8-2.

        An  additional  allowance  equal  to  25 percent  of  construction
        costs  is  suggested to allow for planning, design, administra-
        tion, and  construction related contingencies.

        Operation  and maintenance  costs  are estimated  to involve an
        annual  expenditure  of  approximately  3 to  5 percent  of  base
        construction cost, that is, before application of the 25  percent
        factor  for design,  planning, and  administration.   The  total is
        composed  of  two elements:   2 to 3 percent of construction cost
        estimates  the  annual  cost of routine maintenance  and upkeep; an
        additional  1 to 2 percent  of  construction  cost  estimates the
        annualized  cost of  sediment removal  operations  for  a  10  year
        clean-out  cycle.

Planning  agencies often  distinquish between  "on-site"  controls,  which  are
applied  to  relatively  small  urban   catchments,  often  installed  by  the
developer  of an urban property, and  "off-site" controls,  which  involve  larger
basins  and serve  substantially larger  urban  drainage areas.  Because  of  the
appreciable  economy of scale  inherent  in  the cost  relationship defined  by
Figure  8-2,  this  factor  must  be  taken  into account   in  developing  cost/
performance  summaries  for  urban  runoff  quality  control using   detention
basins.  Accordingly, the control costs  presented below for wet basin  designs
indicate  the  differences  based on the  size  of the urban catchment  the basin
is  designed to  serve.

Figure  8-3 presents  a  planning level approximation of both present  value and
annual  cost  of wet detention basins.   Amoritizaticn of  costs  is based  on a
20  year basin  life and  an  interest rate of  10 percent.

-------
    inn.nno -
tn
er

CO
UJ
o
co
o
o
o
=>
oc
t~
to
^a
o
m,non -
      1,000
         i.nno
                                  10,000                          100,000


                                     VOLUME OF STORAGE-V (CUBIC FEET)
1,000,000
                   Figure  8-2.   Average Stormwater Management (Dry) Pond  Construction

                                   Cost Estimates Vs. Voli.iine  of Storage

-------
                         APPROXIMATE REMOVAL EFFICIENCY FOR TSS
                                                                                                        APPROXIMATE REMOVAL EFFICIENCY FOR TSS
 _
O O uj
,u C cc
        2000
        isnn
        innn
         500 -
                             30.5(1
                               %
                  n.ns
                              n.in
                                            (us
95%
                                                      SIZE OF URBAN /
                                                      AREA SERVEO  /
                                                      RV RASIN »  21) ACRES
                                                       n.sn
                                                                  /
                                OFJENTinN RftSIN SIZE
                               A PF.nnF.NTARE Of IIRflnN nRAINAKF ARF»I
                                                                                         200
                                                                                         ISO
                                                                                                  20-30
                                            3050
                                             •A
                                                                                                                                       no 90
                                                                                                                                                   95%
                                                                  SIZE OF URBAN
                                                                  AREA SERVED
                                                                  RY RASIN = 20 ACHES
                                                                                                   n.ns
                                                                                                             o.in
                                                                                                                            n.25
                                                                                                                                       n.sn
                                               DETENTION RftSIN SIZE
                                 IRASIN AREA AS « PERCENTARE Of linnAM nnAINACf
                                                BASIS WET BASINS- CONSTRUCTION COSTS 40% GREATER THAN FIRIIHE B 2
                                                     ANNUAL (MM COST-5% OF BASE CONSTRIICTinN COST
                                                     BASIN AVG DEPTH 3.5 FEET
                                                     INTEREST  RATE   10%
                                                     RASIN LIFE      20 YEARS
                                          Figure R-3.   Cost  of  Urban  Runoff  Control Usinig
                                                             Wet Det.ent.i.on  Basins

-------
The performance  levels  associated  with a particular basin  size  are shewn at
the top  of  the plots as  a  range for  long-term average  removal  efficiencies
for TSS.  The  ranee associated with & particular  size  reflects  the regional
differences in performance which can be  expected  (Figure  fc-i)  as a result of
regional differences in storm characteristics.  Approximate removal efficien-
cies for  pollutants other than TSS  can  be estimated by  factoring the indi-
cated TSS removal  by the; particulate  fraction of  the  pollutant  of interest.
The supplementary  NURF-  document dealing  with detention basins  provides in-
formation  to  permit  further refinement.   A  more  concise  local  summary of
cost/performance  relationships  can  be  developed  using  the  NURF data  and
analysis methods,  if  local  rainfall  and  land  use  characteristics,  and design
and planning preferences are utilized.

The  generalized  relationships  shown  by  Figure 6-3  can  be summarized as
follows, if an urban catchment size of 20 to 40 acres it- taken to  represent  a
typical  "on-site"  control   application,  and  an   "off-site"   application is
reflected by detention basins serving  640 to 1000 acres.
Control
Application
On- site


Off-site


Approximate.
Level of
Control
(I TSS. Reduction) •
Cost Per Acre of Urban Area
(Approximate)
Present
Value
50 ! $500 - $700
90

50
90
$1000 - $1500

• $100
$250
Annual
Cost
$60 - $80
$125 - $175
1
$10
$25
1 I
RECHARGE DEVICES

Control measures which enhance the infiltration  of  urban  runoff are indicated
hv the NURF'  studies to be techniques which  are practical  to apply and capable
of effective reductions  in urban runoff  quantity and quality.   This finding
is based  on  project  reports and  on the results  of  a  screening analysis using
a  probabilistic methodology  described in  a supplementary  NUKF  document  on
detention  basins.
The  issue  of' the  potential  contamination  of  grcuncwater  aquifers  due  to
enhanced  infiltration  of  urban  jjtcrrn  runoff  has  been  discussed   in  the
previous  chapter   dealing  with   receiving  water   impacts.    The  favorable
findings  support  further  consideration of this technique.  At the same time,
it  must  be  emphasized  that  specific  local  conditions,  may make  recharge
inappropriate.   Such conditions  can include  steep, slopes,  soil conditions,
cepth  to  groundwater,   and  the   proximity  of  water  supply wells.   Sound
planning  and  engineering  judgement  must  be  applied to determine the.  accept-
c..7 1-L 1 ~'•' C -  tfJlS CCr;"CJTC_ c-'C-£ rC£ C:";  i :";  o  _LCCc._  S. 1 " Uc. t 1 C T: .
         f  for -use.   rhesi  ranee  fro:
                                                                 cons j. s~ me

-------
large retention basins, to small  individual  on-site units which include  in-
filtration pits and trenches, percolating catch basins, and porous pavement.
The operating  principle  is  the same  regardless  of size  or design concept.
The important  elements are the  surface  area  provided for  sub-surface perco- •
lation and  the storage volume  of  the device.  Overall  performance  will  be
related to the size cf the recharge device  relative to  the urban catchment it
serves and the permeability  (infiltration rate) of  the  soil.

The context  in which  the  performance capabilities of  recharge devices  are
evaluated is  the  extent to  which  urban runoff is "captured"  and prevented
from discharging directly to surface  waters.  Pollutant  removals are  reduced
in direct proportion to the  runoff volume which is  intercepted and recharged.
Load reductions will be further enhanced if quality improvements occur .in the
portion of the runoff which is not  captured.  The  combination of soil infil-
tration rate and percolating  area  provided  determines  the "treatment  rate" of
a  specific  recharge  device.   When storm runoff is applied to  the device at
rates of  flow  equal  to or less than this rate, 100 percent of the runoff is
captured  during  that event.   At  higher applied  rates,  the fraction of  the
runoff flow in excess  of the  treatment  rate will  escape and  discharge to
surface waters.

Most recharge devices other than porous pavement  also provide storage volume.
This  improves  performance  capability because portions  of the  excess runoff
can be retained for subsequent percolation  when applied rates subside.  Over-
flow to surface water occurs only  when the  available storage is exceeded.

The  Long  Island  and  Metropolitan  Washington, D.C.  (WASHCOG)  NURP  projects
examined  the  performance  of on-site  recharge devices.   An interconnected
system of percolating catch basins in Long  Island  was  estimated to reduce
surface  water discharges  of  storm  runoff  by more  than 9S  percent.   The
WASHCOG project  found that  a  porous pavement  site produced  pollutant  load
reductions  on the  order  of  85   to  95 percent   depending on  the  specific
pollutant  considered.   An  infiltration  trench  studied  by  this  project
produced  reductions in the order of 50 percent.

The NURP  analysis methodology was  employed in a  screening analysis to assist
planning  evaluations by  establishing  the  relationship  between performance
level  and device  size and  soil  percolation rates.   Figure  8-4  presents a
planning .level estimate  of  the influence  of  size, soil characteristics,  and
regional  rainfall differences on the performance of recharge  devices.

The  upper plot  illustrates  the significant  effect regional  differences  in
rainfall  characteristics  can have  on the  performance  of identical  recharge
devices.  Basin depth,  soil  percolation rate/ and runoff coefficient for the
urban  catchment  are  the  same  for each case.   The  performance  differences
result from  differences in the  intensity and volume of the average storms in
each  region.   Easin  size  is  represented on the horizontal axis  by expressing
the  percolation  area  that  is  provided  as  a percentage  of  the  area of  the
contributing  urban  catchment.   For example,   a recharge device with  a  perco-
lating surface ares  equal to 0.10  percent  of an  urban catchment  represents a
desiqn  which  provides  (42,560 sq .ft/acre >:  0.10/100%  =)  42.5 square feet of
                                    B~±-

-------
                NORTHWEST

                /NORTHEAST/"
                       'SOUTHEAST
                                         AVERAGE DEPTH - E  FT.

                                   SOIL PERCOLATION RATE = 5  1NCHIHOUR

                                            RUNOFF COEF = Q.2E
  O.OE        .1C                      O.E        1.C

PERCOLATING AREA AS % OF CONTRIBUTING CATCHMENT AREA
                                                                      5.0
                                                       SREfcT S.AKES PRtCIF
                                                               WEAK   C.V,
                                                               0.25    U
                                                               0.6i     •/,
                                                               75     :.(•
                                                            BY = 6.i
                                                       =  SO'L FERC M.TE (INIHhi
                                                               DfFTK iFHTi
  O.Ot         .H                       fi.f

 PERCOUTIKC AREA if V C'i- GOISTHBl'llKC CMtKMEKT

-------
percolating  surface  area for  each  acre of  urban  catchment it  serves.   The
lone-term average  reductions in urban  runoff volume  ana  pollutant load which
can be expected will be approximately 35 percent in the southeast, 45 percent
in the northeast and 65 percent in the Pacific northwest.

The lower plot  illustrates  the much  more significant influence of the amount
of storage volume  provided  (incidated by basin average depth},  and the perme-
abilitv of the  soil through which the storm  runoff must percolate.  The rain-
fall  characteristics  used  in  this  analysis  are  typical of the  Great Lakes
region  of the  United  States  and  are  roughly  comparable  to those  in  the
northeastern part' of  the  country.   As  might be expected, the permeability of
the soil  in which  the recharge device is constructed has a dominant influence
on performance  capability.  However  significant compensation for  low percola-
tion  rates  can be achieved  by  increases   in  percolation area  and  storage
volume.

When  the  screening analysis results are  considered  along  with the favorable
results from the  NURP studies, the NURP  findings indicate  that with a  reason-
able  degree  of  design flexibility to compensate for  soils  with lower percola-
tion  rates,  recharge  devices provide a  very effective method  for control of
urban runoff.

STREET SWEEPING

End-of-piPe  urban runoff -"pollutant  concentrations  have been  commonly viewed
as  being  °- function of  two prime  factors -- accumulation of  contaminants  on
 street surfaces and rainfall/runoff washoff.  The postulated beneficial  ef-
 fect  of  street sweeping was  to  reduce  contaminant accumulation.  Prior  to
NURP, emphasis  of street sweeping  investigations  was placed on street surface
 mechanisms (e.g.,  accumulation and  washoff)  and sweeper  equipment performance
 in removing  street dirt.   While  these  studies provided valuable  insights  into
 the possible benefits of street  sweeping, measurements of  end-of-pipe concen-
 trations  are the only direct  measures of  street  sweeping effectiveness  in
 water quality  terms.

 Recoanizing  this,  NURP was designed  to provide a  large  data base  of urban
 runoff water quality  concentrations for both swept  and  unswept conditions.
 In addition, the NURP street sweeping projects gathered and evaluated data on
 atmospheric  deposition  (i.e., wetfall end  dryfall),  street surface accumula-
 tion end weshoff, and street sweeper removal rates and costs.   The individual
 prelect reports look at these other issues,  and  the results are not  repeated
 herein.  Of prime interest end provided below is  the effectiveness of street
 <=weepinc in reducing  end-of-pipe  urban runoff pollutant  concentrations  (and
 ultimately receiving water impacts).   The  findings- presented  below are based
 upon  the analyses performed  by  the  individual  projects,  as well  as other
 statistical  techniques,   and  are  generally  consistent  with  the  projects'
 conclusions.

-------
Five of the 28 NURP prototype projects had the evaluation of  street  sweeping
as a central element of their work plans.   These  projects were as  follows:


                     Project                   Number  of Sites

              Castro Valley, CA                        1

              Milwaukee, Wl                            £

              Champaign-Urbana, IL                     4

              Winston-Salem, NC                        2

              Bellevue, WA                             2
Long Island,  NY  and  Baltimore,  MD  also collected  limited  street  sweeping
data.  The experimental designs of the projects varied  in  detail,  but essen-
tially followed either a paired basin or serial basin approach to gather test
and  control  data, with  some  projects  using both  approaches.  The  general
concept was that during a test period street sweeping would be more intensive
(up to daily) and thorough (e.g.,  with operator training, parking bans, etc.)
than during control periods when the streets were to be swept as usual or not
at all.               -»

In the paired  basin  approach, two adjacent  or  close-by basins were operated
in a  "control"  or unswept mode  for certain periods  of time  to  establish a
baseline comparison,  and then street sweeping was performed in a "test" basin
while the other remained as a control.  The date provided an overall compari-
son between  basins  as well as  a  series of  synoptic  events for both basins.
In the serial approach, a basin was periodically operated in either a control
or test mode, with the periods adjusted so  that all seasons of the year were
represented  in  each  mode.  Here,  rather than  synoptic data  pairs,  one has
date strings for both "swept" and "unswept" conditions.

There  are  no well established or prescribed  procedures  for  evaluating the
possible reduction in runoff concentrations due  to street sweeping.   Issues
of concern  include  storm size and  intensity effects,  time since  last  rain,
ability to select truly paired basins,  seasonal effects, etc.  In an  attempt
to sort out these issues, an exploratory data analysis  was  performed,  and  the
following findings were established:

        Street sweeping  has  not been  found tc change  the basic proba-
        bility distribution of  event  mean concentrations.   That is,  the
        fundamental  assumption of random,  lognormal behavior is valid
        during sweeping operations.
                                                           .;.
        The  runoff quality  characteristics  of  a basin during swept  or
        unswept  conditions  is best  measured by  the  maximum  likelihood
        estimator of  the  median EMC,  with  the  uncertainty indicated  by
        the 80 percent

-------
        There  is  in most cases no significant correlation (and in a  few
        cases  a weak negative  correlation) between EMCs and  storm runoff
        volume.   EMCs and  storm  runoff intensities  are  also  generally
        uncorrelated (but  in  isolated cases exhibit a weak positive  cor-
        relation) .   The implication of these findings  is  that differ-
        ences  in  concentrations  between  swept  and  unswept  conditions
        will be  largely  unaffected by  the size of the storms  during  the
        monitoring  periods.  Because of  this independence between  con-
        centration   and  volume,  effects of  sweeping  on  E.MCs  will  also
        indicate  effects on mass  pollutant loads.

        EMCs  for synoptic  events  on paired  basins are,   in  general,  not
        significantly correlated  or in  some  cases  are weakly correlated;
        however,  over the  longer  term  (e.g., mean,  frequency distribu-
        tion,  etc.),  there are no  significant  differences between  the
        distribution of EMCs  of paired basins.  These results show that
        basins are  independent from storm to storm,  and thus,  compari-
        sons   between basins  should not  be  attempted  using  synoptic
        events,  but  the basins do  have  similar statistical  properties
        and thus can be considered paired.

To evaluate the  effectiveness of  street sweeping,  a series  of bivariate plots
were  constructed  for projects  using   the  serial  basin  approach.    The  site
median  EMCs  for swept  and unswept conditions  form  the data  pairs  of  the
plots.  Bivariate  plots are  presented  in Figure 8-5 for TSS, COD,  TP,  TKN,
and  Pb  concentrations,  respectively.   Each plot  contains  swept  or unswept
conditions for  multiple project  sites.   The assumption of  the analysis is
that  a  large  enough data  base was  collected to negate  any temporal effects
such  as seasonal,  land  use conditions, parking patterns,  and other possible
factors  (as   noted  earlier,  storm volume   and  intensity  effects  are  not
believed to be  significant).   Examining  the bivariate plots, it  is observed
that,  for  the  NURP  data,  the  median concentrations  are as  likely to be
increased  as  decreased  by street  sweeping.   Further,  street sweeping never
produced  a dramatic  (e.g.,  >50 percent)  reduction in concentrations   {or
loads).

Street  sweeping  performance,  as measured by the  percent change  in the  site
median  EMC, for  selected NURP sites -is graphically  displayed -in Figure  8-6.
The  results are for  five constituents   (TSS,  COD, TP, TKN, and Pb) at 10 sites
nationwide).  For  each site, the  median  EMC is  based   on  data  from  between
10 and  60  events,  with 30 events  typical.   Based on Figure  8-6  a  number of
important  observations  are evident.

        Performance  as  measured  by change in site median  EMC is highly
        variable.

        Where   reductions   occur,  they   generally   occur   for  ail
        constituents.

        Reductions  never exceed 50 percent.

-------
     (TSS  Concentrations'!
(TKN  Concentrations)
  ' 0     IOC     200    30(1
           UNSWEFT TSS Img/l)
       1.0    2.0    3.0     4.0
          UNSWEPT TKN Img/l)
      (COD Concentrations)
 (Pb Concentrations)
         50    IK'    ISC     200
           UNSWEPT COD Img/l)
   0     0.?     0.4     O.E  '   0.8
          UNSWEPT Pb Img/l)
      (TF Concentrations)
  O.E
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        o.:    o.<   o.t    0.6   i.o
           UNSWIPl IF.imo/l)
                c-: .   Eivc.ri.ate Flcts  cf Meciar.  iMCs  for
                   £wert  end  Unswer- Ccncitions

-------
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                                                    Pb
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 Figure 6-c.  Street Sweepinc  Ferfcrrnance

-------
Ir.  evaluating  the  results,   it  is  critical  that the  uncertainty  in  the'
estimate cf median EMCs based en limited  observed  data,  and thus  the  uncer-
tainty in performance  estimates, be  assessed.  This  is  especially true  for
the cases of apparent  increases,  in  concentrations indicated by  Figure  8-6.

For each of the  10  sites  considered,  the 90 percent confidence  intervals  cf
the site median EMCs were  computed  as  indicated in  Figure £-7.   This, analysis
indicates that  there  is generally no  significant  difference  between  median
EMCs for swept and unswept conditions.  The  implications  of this analysis of
uncertainty are as follows:

        Eased on statistical testing,  no  significant  reductions  in EMCs
        are realized by street sweeping.

        The  indicated  'changes  in  site  median   EMCs    (increases  or
        decreases)  are much  more  likely  due to  random  sampling than
        actual effects of  sweeping  operations.

        Benefits  of  street  sweeping  (if  any) are  masked  by  the  large
        variability of  the EMCs, therefore the benefit is certainly not
        large  (e.g.,  >50 percent), and an even larger site data base  is
        required to further identify the possible effect.

        In  the  above  qcntext,  the  hypothesis   that  street  sweeping
        increases EMCs is generally  not shown by the  data,  though  it
        could occur in  isolated, site specific cases.

Urban runoff loads are  the product cf  long term (e.g., annual)  runoff  volume
and  event  mean concentration.  Under this definition, statements,  concerning
EMCs  also hold for loads.

OTHER CONTROL APPROACHES

Several best management practices  (BMPs)  in  addition  to  those  discussed above
should  be  identified  on the basis that local planning  efforts  determined them
to be practical to apply  and to  have  the  potential  to-  provide  significant
improvements  in  the   quality  characteristics of  urban   runoff.   They  are
grouped together in  this  section  and  discussed  only  briefly,  principally
because,  for one reason  or  another,  sufficient   data to  characterize their
performance capabilities was  not developed during  the  NURF program.

Grass Swales
 Three-  press  swales  were  monitored b
 No significant  improvement•is urban runoff quality was  indicated for pollut-
 ants  analyzed.    Increases in  zinc concentration  which  were  observed  were
 attributed to mobilization of zinc  from the galvanized culverts which carried
 runoff  under-the driveways at  the  monitored residential  sites.   However the
 preject   study   report   concluded   that  modifications  -which  would  increase
 residence of runcff in  the  s^alesr  and enhance  inf i J.trat: o".-  capability cculc
 make  this EM? effective  for  control of urban runofi.

-------
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The  Durham,  New Hampshire  NURP project monitored performance  of a carefully
'designed  artificial  swale  which  received runoff  from a commercial  parking
lot.   Over 11 monitored storms,  both soluble  and particulate  fractions  of
heavy  metals  (Cu,  Pb,  Zn,  and Cd) were reduced  by  approximately 50 percent.
Reductions in COD, nitrate, and ammonia were on the order of 25 percent.  The
swale  did not  prove  to be effective  in  reducing  concentrations  or  organic
nitrogen,  phosphorus,   or  bacterial  species.   It  should be  noted that the
performance  capabilities  indicated  are   based  only  on , the  concentration
changes produced in the stormwater which passes completely through the swale.
To  the extent  that infiltration of a portion of the  runoff  is effected by a
swale,  load  reductions  would be increased  in proportion.

The  NURF  results  suggest that grass swales  represent  a  practical and poten-
tially effective  technique for control of urban runoff  quality; that design
conditions are  of  major significance;  and that additional study is necessary
to  establish such  parameters.

Wetlands

The  potential  of  either  natural  or  artificially  created wetland  areas  to
effect favorable  modification of  urban runoff  pollutant loads  (particularly
sediment,  nutrients,  and heavy metals) has  been widely suggested.  The NURF
experience  reinforces  this expectation,  but has not  developed the detailed
performance  data  to  permit  either  characterizing  general  performance  capa-
bilities  or  identifying general design principles  and  parameters.  Additional
study  will be required'to  develop  such information.

Miscellaneous

This  category  encompasses a  variety  of   BMPs  which were  identified at  the
local  level  as techniques of  quality control which  appeared to  be  relevant
for the  circumstances  which  were operative.   They  are  grouped under  this
category  because  (a) their  applicability tends  to  be  site-specific  rather
than general,  and (b) while their effectiveness as a BMP may be substantial
on  a relatively small  spatial  scale,  the broad-scale effect  on  urban runoff
loads  has not been possible  to document.

EMPs  in  this   category  include erosion  control practices  and  urban  house-
keeping practices.  As  an example of the former,  the Little Rock,  Arkansas
NURF project widened  and  stabilized  (with  rip rap)  a  segment of  an urban
stream to reduce erosion potential.   The  Baltimore NURF  project data clearly
indicated the  substantial  difference  in urban runoff  quality that can result
from the  general  level  of  cleanliness maintained in an urban neighborhood.

-------
                                 CHAPTER  9
                                CONCLUSIONS
INTRODUCTION

The Nationwide Urban Runoff Program has addressed such  issues as quantifying
the characteristic  of  urban runoff, assessing  the  water quality  effects on
receiving water bodies-attributable to  urban runoff  discharges, and examining
the effectiveness  of  control  practices in  removing  the pollutants  found in
urban runoff.   This chapter summarizes NURP's  conclusion relating  to these
issues and is based on the  results  presented  in Chapters 6,  7, and 8 of this
report.   Conclusions reached  by the individual  NURP projects  are also pre-
sented to further support the  results of the national level analysis.
                                            t                      *
URBAN RUNOFF CHARACTERISTICS

General
                    ,**
Field monitoring  was  conducted to  characterize urban runoff flows and  pol-
lutant concentrations.   This  was  done  for a variety  of  pollutants at a  sub-
stantial number of  sites distributed throughout the  country.  The  resultant
data  represent a   cross-section  of regional  climatology,   land  use types,
slopes, and soil conditions and thereby provide a  basis for  identifying  pat-
terns of similarities or differences and testing their significance.

Urban runoff  flows and  concentrations of  contaminants  are  quite  variable.
Experience shows that  substantial  variations  occur  within a  particular  event
and from one  event  to  the  next at a particular  site.   Due to  the high  vari-
ability of urban runoff, a  large  number of sites and storm events were  moni-
tored, and a  statistical approach was used to  analyze  the data.   Procedures
are available for characterizing variable data  without requiring knowledge of
or  existence  of   any  underlying  probability  distribution  (nonparametric
statistical procedures).  However,  where  a specific type of  probability dis-
tribution is  known  to  exist,  the  information content and efficiency  of sta-
tistical  analysis  is  enhanced.    Standard  statistical  procedures  allowed
probability  distributions   or frequency,  of  occurrence  to   be examinee  and
r.ested.  Since  the  underlying distributions were determined  to be adequately
represented by the  lognormal  distribution,  the  log  (base e)  transforms of al]
urban runoff data were used in developing  the statistical characterizations.

The  event  mean concentration (EMC) ,  defined  as the  total  constituent  mass-,
discharge divided by the total runoff  volume, was chosen as the primary wat.r-r
quality  statistic.   Event  mean  concentrations  were based  on  flow veic;htec
composite samples  for  each event  at each  site  in  the   accessible cr-i-.--.  !v.>s< .
EHC'E  were  chosen  £E  the primary  water quality  characteristic  subvrclec  Vi
Getcilec analysis,  ever,  though it is recocnizec that mas?  loadinc char^c.-ter-
istics cf urban  runoff  ie.c., pounds/acre  re;  i specified tinw' int-; rv;; j ;  :.:

-------
ultimately  the  relevant  factor  in  many situations.   The  reason  is  that,
unlike EMCs,  mass  loadings  are  very  strongly  influenced by  the amount  of
precipitation and runoff, and estimates of typical annual  mass  loads  will  be
biased by  the  size  of monitored storm  events.   The  most  reliable basis  for
characterizing  annual  or seasonal  mess loads  is on  the basis  of   EMC  and
site-specific rainfall/runoff characteristics.

Establishing the  fundamental  distribution  as iognormai  and  the availability
of  a  sufficiently  large  population of  EMCs to  provide reliability  to  the
statistics derived has yielded a number of  benefits,  including the ability to
provide:

     -  Concise summaries of highly variable data

        Meaningful  comparisons of  results  from  different sites, events,
        etc.

        Statements  concerning frequency  of  occurrence.   One can express
        how  often values  will be expected to exceed various magnitudes
        of interest *

        A  more  useful  method of  reporting  date  than the use of ranges;
        one  which is less subject to misinterpretation
                         1-,
        A  framework for examining  "transferability"  of data  in  a quanti-
        tative  manner

Conclusions

1.  Heavy  metals  (especially copper,  leac  and zinc)  are by  far the most pre-
    valent priority pollutant constituents found in  urban  runoff.  End-of-pipe
    concentrations  exceed EFA  ambient  water  quality .criteria and  drinking
    water  standards in many  instances.   Some of the metals  are present often
    enough and  in high enough concentrations to  be potential threats  to bene-
    ficial uses.

    All  13 metals  on  EFA's  priority pollutant  list were detected  in urban
    runoff samples, and  all but  three  at  frequencies  of  detection greater
    rhan  10 percent.   Most often detected  among  the  metals were copper, lead,
    and zinc,  all of which were  found  in at  least 91 percent of the  samples.

    Metal  concentrations in  end-cf-pipe urban  runoff  samples  (i.e.,  before
    dilution by  receiving water)  exceeded EPA's  water  quality  criteria  and
    drinking water  standards numerous  times.   For  example,  freshwater acute
    criteria were  exceeded  by  copper  concentrations  in  4" percent  of  the
    samples and  by lead  in  22  percent.   Freshwater  chronic exceedances were
    common for lead (94 percent),  copper (62 percent),  zinc  (11 percent) , and
    cadmium  (48  percent).   Regarding human toxicity,  the  most  significant
    pollutants  were lead and nickel,  and  for  human carciriogenesis  ,  arsenic
    anc  berylliuir,.   Lead concentrations vic-latec crinkinc  water  criteria in
     ~1  percent cf the  samples.

-------
    It  should  be  stressed  thet the exceedances noted above do not necessarily
    imply  that an actual  violation of  standards  will  exist  in the receiving
    water  body in question.   Rather,  the enumeration of exceedances serves a
    screening  function  to  identify those heavy metals whose presence in urban
    runoff warrants  high priority for further evaluation.

    Based  upon the much more extensive NURP data set for total copper, lead,
    and zinc,  the site  median  EMC values for the  median urban  site  are:   Cu =
    34  yg/1, Pb = 144  yg/i,  and  Zn =  160 yg/1.. For  the 90th percentile urban
    site the  values  are:   Cu = 93 yg/1,  Pb =  350  yg/1, and  Zn =  500 yg/1.
    These  values are suggested to be  appropriate  for planning  level screening
    analyses where data are  not  available.

    Some individual NURP  project sites  (e.g.,  at DC1,  MD1,  NH1) found unus-
    ually  high concentrations  of certain heavy metals  (especially  copper and
    zinc)  in urban runoff.  This was  attributed by the  projects  to  the effect
    of  acid rain on materials  used for  gutters, culverts, etc.

2.   The organic  priority  pollutants  were detected  less frequently  and  at
    lower  concentrations than  the heavy metals.

    Sixty-three  of  a  possible  106  organics were  detected in  urban  runoff
    samples.    The  most   commonly  found  organic  was  the  plasticizer  bis
    (2-ethylhexl)   phthalate    (22 percent),   followed  by   the   pesticide
    a-hexachlorocyclohexsne  (a-BHC)   (20 percent).   An additional  11  organic
    pollutants  were  reported  at  frequencies  between  10  arid  20 percent;
    3 pesticides, 3 phenols,  4 polycyclic  aromatics, and  a  single halogenated
    aliphatic.

    Criteria   exceedances  were  less  frequently  observed  among  the  organics
    than the  heavy  metals.   One unusually high  pentachlorophenol  concentra-
    tion  of  115 yg/1   resulted  in  exceedances  of  the  freshwater  acute and
    organoleptic criteria.  This observation  and one  for chlordane also ex-
    ceeded  the  freshwater   acute   criteria.    Freshwater  chronic  criteria
    exceedances  were  observed   for  pentachlorophenol,   bis   (2-ethylhexyl)
    phthalate, gamma-BHC,  chlordane,  and alpha-endosulfan.   All other organic
    exceedances were in the  human  carcinogen category and were  most serious
    for alpha-hexachlorocyclohexane  (alpha-BHC) ,  gamma-hexachlorocyclohexane
     (gamma-BHC or Lindane),  chlordane,  phenanthrene, pyrene,  and chrysene.

    The fact  that-'the  NURP  priority pollutant monitoring effort was limited
    to two samples at each site  leaves us unable to make many generalizations
    about  those organic pollutants which  occurred only rarely.   We can  spec-
    ulate  that their occurrences tend  to  be  very site specific as opposed to
    being  a generally  widespread phenomena,  but much  more data  would be .re-
    quired to conclusively prove this point.

I- .   Coliform bacteria  are present at high levels in urban runoff  and can be
    expected  to exceed EPA water  quality criteria  during  and  immediately
    after   storm  events in  many surface  waters, even these  r>rcvicinc  hiqh
    cecrees or ciiution.

-------
    Fecal  cciiform counts in urban runoff are typically  in the tens to hun-
    dreds  cf thousand  per  100 ml during  warm weather conditions,  with the
    median for all  sites being around  21,000/100 ml.  During cold weather,
    fecal  coliform counts are more typically in•the 1,000/100 ml range, which
    is  the median for  all  sites.  Thus,  violations  of fecal coliform stand-
    ards  were reported  by  a number  of  NURP projects.   High  fecal coliform
    counts may not  cause actual  use impairments, in  some  instances,  due to
    the location  of  the urban runoff  discharges relative  to swimming areas or
    shellfish beds end the  degree of dilution/dispersal and rate of die off.
    The same is true of total coliform counts, which were found  to  exceed EPA
    water  quality criteria  in  undiluted  urban runoff at virtually  every site
    every  time  it rained.

    The substantial seasonal differences  noted  above  do  not correspond with
    comparable  variations in urban activities.  The NURP analyses  as well as
    current  literature   suggest  that fecal  coliform  may   not  be  the most
    appropriate   indicator  organism   for  identifying  potential  health  risks
    when the source is stormwater runoff.

4.   Nutrients are generally present  in urban runoff,  but with a few individ-
    ual site exceptions, concentrations  do not appear  to be high  in compari-
    son with other possible discharges to receiving water bodies.

    NURP data for total'phosphorus,  soluble  phosphorus, total  kjeldahl  nitro-
    gen,  and nitrate plus  nitrite as nitrogen were carefully  examined.   Me-
    dian site EMC median concentrations in urban runoff  were  TP = O.33 mg/1,
    SF  = 0.12 mg/1,  TKN  = 1.5 mg/1,  and N02+3 - N = 0.6£ mg/1.  On an  annual
    load basis,  comparison with  typical monitoring data,  literature  values,
    and design objectives for discharges from a well  run secondary treatment
    plant  suggests  that mean  annual nutrient  loads   from urban  runoff  are
    around an order of magnitude  less than those from a POTW.

5.   Oxygen demanding substances are  present in urban  runoff at -concentrations
    approximating those in secondary treatment plant discharges.  If  dis-
    r.clved oxygen problems are present  in receiving waters of interest, con -
    sideration of urban runoff  controls as well as advanced  waste treatment
    appears to be warranted.

    Urban  runoff median site  EMC. median concentrations  of 9  mg/1  BODS  and
    65 mg/1 COD are reflected  in the NURP data,  with 90th percentile site EMC
    median values being  15 mg/1 BOD5 and  140  mg/1  COD.  These  concentrations
    suggest that, on an  annual load  basis, urban runoff is  comparable in mag-
    nitude to secondary  treatment plant  discharges.

    It  can be argued  that urban runoff  is typically  well  oxygenated  and
    provides increased  stream flow  and,' hence, in  view  of  relatively long
    travel  times  to  the  critical  point,  that dissolved  oxygen problems
    attributable  solely  to urban runoff  should not be  widespread occurrences.
    Kc NURF project specifically identified a lev DO condition  resulting from

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    urban runoff.   Nonetheless,  there  will  be  some situations  where  con-
    sideration of urban runoff  controls  for oxygen demanding  substances  in an
    overall  water quality management  strategy would  seem  appropriate.

6.  Total suspended solids concentrations in urban runoff are  fairly high in
    comparison  with  treatment plant discharges.   Urban runoff  control is
    strongly indicated where water quality problems associated with TSS,  in-
    cluding  build-up of contaminated  sediments,  exist.

    There are  no formal water quality  criteria for TSE relating to  either
    human health or aquatic  life.   The nature  of the  suspended solids  in
    urban runoff is different from those in  treatment plant  discharges,  being
    higher  in  mineral  and man-made  products  (e.g.,  tire and  street  surface
    wear particles)  and somewhat lower  in  organic  particulates.  Also,  the
    solids  in  urban  runoff  are  more  likely   to  have  other  contaminants
    adsorbed onto  them.   Thus, they cannot be  simply  considered  as  benign,
    nor  do  they  only  pose  an  aesthetic issue.   NURP   did  not examine  the
    problem of contaminated sediment build-up  due  to urban runoff, but  it
    undeniably exists, at least at some locations.

    The  suspended solids in  urban runoff can also  exert  deleterious  physical
    effects by sedimenting  over  egg deposition  sites, smothering juveniles,
    and  altering benthic communities.

    On an annual load ba_sis, suspended solids contributions from urban runoff
    are  around an order of magnitude or  more greater than those from second-
    ary  treatment  plants.   Control  of  urban  runoff, as  opposed  to  advanced
    waste treatment, should  be considered where  TSS-associated water quality
    problems exist.

7.  A  summary characterization  of  urban runoff has been  developed  and is
    believed to  be  appropriate for use  in estimating urban runoff pollutant
    discharges' from sites  where monitoring data  are scant or  lacking,  at
    least for planning level purposes.

    As  a result of  extensive  examination,  it was  concluded that geographic
    location,  land use category  (residential, commercial, industrial park, or
    mixed), or other factors (e.g.,  slope,  population  density, precipitation
    characteristics) appear  to be  of little utility in  consistently explain-
    ing  overall  site-to-site variability in urban  runoff EMCs or predicting
    the  characteristics of  urban  runoff discharges from unmonitored  sites.
    Uncertainty  in  site urban runoff  characteristics  caused  by high  event-
    to-event variability  at  most sites eclipsed any site-to-site  variability
    that might have been  present.   The finding  that  EMC  values  are  essen-
    tially -not correlated  with storm runoff volumes facilitates the  transfer
    cf  urban   runoff  characteristics to  unmonitored sites.   Although  there
    tend to be exceptions  to any generalization, the suggested  summary urban
    runoff  characteristics  given in  Table  6-17  of the  report  are  recommended
    for  planning level purposes  as the best estimates, lacking local  informa-
    tion to the  contrary.
                                      o_ c.

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RECEIVING WATER EFFECTS

General

The  effects  of  urban  runoff  on  receiving water  quality  are  highly  site-
specific.  They  depend  on  the type, size,  and  hydrology  of the water  body;
the  urban  runoff quantity  and quality characteristics; the  designated  bene-
ficial  use;  and  the  concentration levels  of the  specific pollutants  that
affect that use.

The  conclusions  which follow  are  based on screening  analyses performed  by
NURP,  observations  and conclusions drawn  by individual  NURP projects  that
examined receiving water effects in differing  levels of detail and rigor, and
NURP's three levels of problem definition.  Conclusions are organized on the
basis  of water body type:   rivers  and  streams,  lakes, estuaries  and embay-
ments,   and   groundwater   aquifers.   Site-specific   exceptions   should  be
expected,  but  the statements  presented  are believed to provide  an accurate
perspective on the  general tendency of  urban runoff  to  contribute signifi-
cantly to water quality problems.

Rivers and Streams

1.   Frequent exceedances of  heavy  metals ambient water quality  criteria for
     freshwater aquatic li
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   undertaken  with  two  species and resulted in no significant effects attri-
   butable  to  stormwater exposure.

   NURP screening  analyses  suggest  that the  potential  of  urban  runoff to
   seriously impair this beneficial use will be strongly influenced by local
   conditions  and the frequency  of occurrence of concentration levels which
   produce  toxic effects  under  the  intermittent,  short  duration exposures
   typically produced by urban runoff.

   While the application of  the  screening analysis  to the Bellevue and Tampa
   situations  supports  the absence of a problem situation in these cases, it
   also suggests that a significant number  of problem situations should be
   expected, rTherefore, although not the general,  ubiquitous problem situa-
   tion that  criteria  exceedances would  suggest,  there  are  site-specific
   situations  in which urban runoff could be expected to cause significant
   impairment  of freshwater  aquatic life uses.

   Because  of  the  inconsistency between criteria  exceedances and  observed
   use  impairments  due  to  urban  runoff,  adaptation  of  current   ambient
   quality  criteria to better reflect use impacts  where pollutant exposures
   are  intermittent  and   short  duration appears  to be  a  useful  area  for
    further  investigation.

3.  Copper,  lead and zinc appear  to pose  a significant  threat to aquatic life
   uses in  some  area.s  of  the country.  Copper  is  suggested to be  the  most
    significant of the three.

    Regional differences in surface water hardness,  which has a strong influ-
    ence on toxicity, in conjunction with regional  variations in stream flow
    and  rainfall  result in significant  differences in susceptibility to ad-
    verse impacts around the  nation.

    The  southern  and southeastern regions of  the country are  the most sus-
    ceptible to aquatic life effects due to  heavy metals,  with the northeast
    also a sensitive area,  although somewhat  less so.

    Copper is the major toxic metal in urban  runoff, with  lead and zinc also
    prevalent but a problem  in  more  restricted cases.   Copper discharges  in
    urban runoff  are,  in  all but the  most  favorable cases,  a significant
    threat to  aquatic life uses  in the  southeast  and southern  regions of the
    country.   In  the northeast,  problems  would  be expected only  in rathe,r
    unfavorable conditions (large urban  area contribution and  high site  con-
    centrations) .   In the remainder of the country  (and for  the other metals)
    problems would  only be expected under quite unfavorable  site conditions.
    These statements are based on total metal concentrations.

4.  Organic priority  pollutants  in urban  runoff do  not appear  to pose  a gen-
    eral threat to  freshwater aquatic life.

    This conclusion  is based on  limited  data on the frequency  with  which or-
    qanics are found  in urban runoff discharges and measured end-of-pipe con-
    centrations   relative  tc  published  toxic   criteria.     One   unusually
    high  pentachlorophenol  concentration of  115 ug/1  resulted  in   the  only
    exceedance  of  the crcanoleptic criteria.  This observation anc   one  for

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    chlordane   exceeded   the   freshwater   acute    criteria.     Freshwater
    chronic  criteria  exceedances  were   observed   for  pentochlorophenol,
    bis    (2-ethylhexyi)    phlhaiate,    Y~hexachlorocyclohexane    (iindane),
    a-endosulfan,  and chlordene.

5.   The physical aspects  of urban  runoff,  e.g.,  erosion and scour, can be  a
    significant cause  of  habitat disruption  and  can affect  the  type  of
    fishery present.   However,  this area  was  studied  only incidentally by
    several of  the projects  under the  NURP  program  and  more  concentrated
    study is necessary.

    The Metropolitan Washington Council  of Governments (MWCOG) NURP  project
    did an analysis of fish diversity in  the Seneca  Creek Watershed,  20 miles
    northwest of Washington,  D.C.   In this  study,  specific  changes in fishery
    diversity  were  identified  due  to  urbanization  in  some  of  the sub-
    watersheds.  Specifically, the number of fish  species present are reduced
    and the  types of  species present  changed  dramatically, e.g.,  environ-
    mentally sensitive species were replaced with  more tolerant species.  For
    example, the  Elacknose Dace  replaced  the Mottled Sculpin.  MWCOG con-
    cluded that the changes in fish diversity were  due to  habitat deteriora-
    tion caused by the physical aspects of  urban  runoff.

    The Bellevue,  Washington  NURP project concluded  that habitat  changes
    (streambed scour  and  sedimentation)  had a  more significant  effect than
    pollutant concentrations,  for the changes  produced by urbanization.

6.  Several projects identified possible  problems  in the sediments because of
    the build-up  of priority pollutants  contributed  wholly or  in  part by
    urban runoff.   However, the NURP studies in this area  were few in number
    and limited in scope,  and the findings  must be considered only indicative
    of the need for further study, particularly as to long-term impacts.

    The Denver NURP project  found significant quantities of  copper, lead,
    zinc,  and  cadmium in  river  sediments.  The  Denver Regional  Council  of
    Governments is concerned that during  periods of continuous  low flow,  lead
    may reach levels capable of adversely affecting fish.

    The Milwaukee NURP project reported the observation of  elevated levels  of
    heavy  metals,  particularly lead,   in the  sediments of  a river receiving
    urban runoff.

7.  Coliform bacteria  are present at  high  levels in  urban runoff and  can  be
    expected,  to exceed  EPA  water  quality criteria  curing  and immediately
    after  storm, events in most rivers and  streams.

    Violations of  the  fecal  coliform  standard were reported by  a number  of
    NURP  projects.   In some  instances,  high  fecal colifcrm  counts  may not
    cause  actual  use  impairments  due  to  the  location of .the urban  runoff
    discharge  relative to swimming areas  and the degree  of dilution  or  dis-
    persal and rate of die off.

    Coliform bacteria  are  generally accepted  to  be  a useful indicator of the
    possible presence  of  human pathogens when  the source of contamination  is
    sanitary sewage.  However, no such relationship has been demonstrated; for

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    urban runoff.   Therefore,  the use of  coliforms  as  an indicator of human
    health risk when the sole source of  contamination  is urban runoff, war-
    rants further  investigation.

8.   Domestic water  supply  systems  with  intakes located  on  streams in close
    proximity to urban runoff  discharges  are  encouraged to check for priority
    pollutants which have been detected  in  urban  runoff, particularly those
    in the organic category.

    Sixty-three of a possible  106 organics were detected  in  urban  runoff  sam-
    ples.   The  most   commonly   found   organic  was  the  plasticizer   bis
    (2-ethylhexl)   phthalate   (22 percent),   followed   by  the    pesticide
    a-hexachlorocyclohexane (a-BHC)  (20  percent).   An  additional  11  organic
    pollutants  were  reported  at  frequencies  between  10   and   20 percent;
    3 pesticides,  3 phenols,  4 polycyclic eromatics,  and  a single  halogenated
    aliphatic.

Lakes

1.   Nutrients  in  urban  runoff  may  accelerate eutrophication problems  and
    severely  limit  recreational  uses,  especially  in lakes.   However,  NURP's
    lake  projects   indicate  that  the  degree  of  beneficial  use  impairment
    varies widely, as does the significance  of the urban  runoff component.

    The Lake  Quinsigamond NURP project in Massachusetts  identified eutrophi-
    cation  as  a major problem in  the  lake,  with  urban  runoff being  a prime
    contributor of the critical nutrient  phosphorus.   Point  source discharges
    to the  lake have been eliminated almost entirely.   However,  in  spite of
    the  abatement  of point sources, survey  data  indicate  that the  lake has
    shown little  improvement  over the abatement period.  In  particular, the
    trophic status  of  the  lake  has shown no change, i.e.,  it is  still clas-
    sified  as  late mesotrophic-early eutrophic.  Substantial growth  is pro-
    jected  in the basin,  and  there is  concern that Lake  Quinsigamond will
    become  more eutrophic.  A proposed water quality management  plan for the
    lake  includes the objective of reducing urban  runoff pollutant loads.

    The Lake George NURP project in New York State also  identified increasing
    eutrophication  as  a  potential  problem if current development trends  con-
    tinue.  Lake George  is not classified ss eutrophic, but from  1974 to  1976
    algae production in  the lake increased logarithmically.    Lake George  is a
    very  long lake, and the  limnological differences  between the north and
    south  basins   provide  evidence  of   human  impact.    The  more developed,
    southern  portion of the lake  exhibits  lower  transparencies,  lower  hypo-
    limnetic  dissolved oxygen concentrations,  higher  phosphorus  and chlor-
    ophyll  £  concentrations, and a trend  toward seasonal blooms of blue-green
    algae.  These differences in water quality  indicators are associated with
    higher  levels  of  cultural  activities (e.g.,  increased  sources  of  phos-
    phorus)  in 'the  southern portion  of  the  lake's  watershed, and continued
    development will tend to accentuate  the  differences.

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The Lake  George  NURF project estimated that urban  runoff  from -developed
areas currently  accounts  for only 15.6 percent of  the  annual  phosphorus
loadings  to  Lake George  as  a  whole.   In contrast,  developed  areas con-
tribute  26.9 percent of the annual phosphorus  load to the  NURP  study-
areas at the south  end of  the  Lake.   Since  there are no  point source
discharges, this phosphorus loading is due solely to urban runoff.  These
data  illustrate the significant  impact  of  urbanization on  phosphorus
loads.

The NURP screening  analysis suggests  that lakes  for which the contribu-
tions  of  urban  runoff  are significant  in  relation  to  other nonpoint
sources  (even in the-absence of point source discharges) are indicated to
be highly  susceptible to eutrophication and that urban runoff control may
be warranted in  such situations.

Coliform bacteria discharges in  urban  runoff  have a significant negative
impact on  the recreational uses of lakes.

As was the case  with rivers and  streams,  coliform bacteria in urban run-
off can  cause  violations of criteria  for  the  recreational use of  lakes.
When unusually high  fecal  coliform counts  are observed, they may be par-
tially   attributable  to  sanitary sewage  contamination,  in  which case
significant health risks may be involved.
                           .*
The Lake Quinsigamond  NURP project in Massachusetts found that.bacterial
pollution  was  widespread  throughout  the  drainage  basin.   In all cases
where samples were taken,  fecal coliforms were in excess of  1O,000  counts
per  100  ml,  with conditions  worse in  the Belmont  street storm drains.
This project concluded  that the  very  high fecal -coliform counts  in their
stormwater are  at least partially due to sewage contamination  apparently
entering the stormwater system throughout the local catchment.

The  sources  of  sewage contamination are  leaking septic tanks,  infiltra-
tion from sanitary sewers  into storm sewers, and  leakage  at  manholes.   In
the  northern basin, the  high  fecal   coliform  counts  are attributed  to
known sewage contamination sources on  Poor Farm  Brook.   The  data from the
project  suggest  that it would be  unwise to permit body  contact recreation
in the northern  basin of  the lake during or immediately following signif-
icant  storm  events.   The  project concluded that  disinfection  at selected
storm drains should  be  considered in the future,  especially  if the  sewage
contamination cannot be eliminated.

The  Mystic River NURF project in Massachusetts  found various  areas where
fecal  coliform  counts  were extremely  high  in  urban  stormwater.   Fecal
coliform levels of  up  to .one million  with  an average of  178,000/100 ml
were  recorded  in Sweetwater  Brook,  a tributary  to Mystic  River,  during
wet  weather.   These  high fecal coliform levels  were specifically attrib-
uted  to surcharging in  their  sanitary  sewers,   which  caused  sanitary
sewage   to overflow  into  their   storm  drains  vie  the  combined  manholes
present  in this  catchment.   Fecal colifcrrr. levels above the  class E fecal
coliform standard of 200  per  100  ml were  found  in approximately one-third
of the  samples  tested  in  the upper and lower  forebeys of the Upper Mystic
Lake  and occasionally  near the lake's outlet.   In  addition,.  Sandy Beach,
c. c-ublic  swimn.inc   area  on Uroer Mvstic  Lake,   exceeded the.

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    coiiform criteria in  July of  1982,  and warnings  that  swimming may be haz-
    ardous to public health  were  posted for  several  days.   It  is important  to
    note that  sewage  contamination  of  surface waters is  a major problem  in
    the watershed.   The  project  concluded  that  urban runoff contributes  to
    the bacteria  load during wet  weather  but,  comparatively,  is  much less  '
    significant than the  sanitary sources.

Estuaries and Embayments

1.   Adverse effects of urban runoff in marine  waters  will be  a  highly  speci-
    fic local  situation.  Though  estuaries  and embayments were studied to a
    very  limited  extent  in NURP,  they  are  not  believed  to  be  generally
    threatened by urban  runoff,  though specific  instances where use  is  im-
  ,  paired  or  denied can be of  significant  local  and  even  regional  impor-
    tance.   Coliform  bacteria  present  in  urban  runoff  is   the  primary
    pollutant of concern, causing direct impacts  on shellfish harvesting  and
    beach closures.

    The significant  impact  of  urban runoff on shellfish  harvesting has been
    well documented by the Long Island, New York NURP project.  In this proj-
    ect,  stormwater  runoff  was identified  as  the major  source  of bacterial
    loading to marine waters and,  thus,  the indirect cause of  the denial of
    certification by the New York  State Department  of Conservation for about
    one-fourth of  the shellfishing  area.   Much  of this  area  is  -along   the
    south  shore, wher.r* the  annual commercial  shellfish  harvest  is valued at
    approximately $17.5 million.

    The Myrtle. Beach, South  Carolina NURP  project found that stormwater dis-
    charges from the City of Myrtle Beach directly onto the beach  showed high
    bacterial  counts  for  short durations  immediately after storm events.  In
    many instances these counts violated EPA water quality criteria for aqua-
    tic life and contact recreation.  The high bacteria counts, however, were
    associated with  standing pools  formed  at the end of collectors for brief
    periods following the cessation of rainfall  and before the runoff perco-
    lated  into the  sand.   Consequently,  the threat  to  public health  was  not
    considered great enough  to warrant closure of the beach.

Groundwater Aquifers

1.  Groundwater aquifers  that  receive  deliberate recharge of urban runoff do
    not appear to be  imminently  threatened  by this practice  at the two loca-
    tions where it was investigated.

    Two NURP projects  (Long  Island  and Fresno) are situated  over  sole source
    acquifers.  They  have been practicing  recharge with urban  runoff  for two
    decades or moire  at some  sites,  and extensively  investigated the impact of
    this practice on the  quality of their  groundwater.   They both found  that
    soil  processes  are  efficient in retaining, urbar. runoff  pollutants quite
    close  to  the land surface,  and concluded  that no  change  in the  use - of
    recharge basins  is warrantee.

    Despite the fact that some of these basins have been in  service for rela-
    tively  lone  periods of  time  and pollutant breakthrough  of  the upper  soil

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    pollutants is unknown.  r'urther -attention tc this  issue  is recommended-.
.-. limited number  cf  to-chnicues fcr the  oontrcl  of "urban  runoff ouality were
evaluated by  the  i-;UF.? program.   The set  is  considerably  smaller than prev-
iously published,  lists of  potential management practices.   Since the control
approaches  that  were  investigated  were  selected  at  the  local  level,   the
choices, may be  taken  as  an initial indication of  local perceptions  regarding
practicality and  feasibility  from  the  standpoint of implementation.

Conclusions

1.  There is  a  strong preference for detention  devices,  street  sweeping,  and
    recharge  devices as  reflected; by  the control  measures  selected at  the
    local level for detailed  investigation.   Interest was  also  shown in -grass
    swales, and,  wetlands .

    S'ix  NUF.F  projects monitored  the performance  cf a  total of  14  detention
    devices.    Five,   separate  projects  conducted;  in-depth  studies  cf   the
    effectiveness of  street sweeping on the  control of urban runoff quality.
    X  total of  !"•  separate  study  catchments were  involved  in  this  effoz't.
    Three NURP  projects,  examined either the  potential  of  recharge  devices to
    .reduce-  discharges of urban runoff  to  surface waters  or the  potential cf
    the,  practice  t-:  contaminate  groundwaters.   ?. total of  12  separate  sites
    were, covered  by  this effort.

    Grass  swale-s  were studied by  two- !\-UF;? projects.   Two  swales in existing
    residential areas,  and one experimental  swale- constructed to serve a com-
    mercial parking  lot  v;c;re  studied,

    ."-•.  number  of  !>rOF.P projects  indicated  interest  in  wetlands  for improving
    urban  runoff  quality at  early  stages  of  the  program.   Only one allocated,
    rr.onitcrinc:  activit"  to this control measure,  however,
     es-t by  individual  >"UR! projects,  but  none  or.  tnem  was  aiiocateo  tns
     necessary resources tc  be  pursued tc a po-int  which  allowed an evaluation
     cf their  abilitv  to  centred  polluticn  from  urban runoff.   Management
         ^iceo  '+.:'.  this  catec:cr'-:  include:  urba~.  housakeer inc  '£.•:...   litter
         ic-ifis ,  cat:?,  be.sin  c-leaninc..  ~~" -vrd:.nances',  and  tuhli"  l:'.formation
     r-etention bas:.ns are  capable  o-f providing very  effective removal  of  po'i-
     basir. i:". r-iatlcn  tc  tne urDa;":  ai'ic  serve'-"  nave  a  critica_ in^J.uen

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 when  basins  are  adequately  sized,  particulate removals  in  excess of
 90 percent (TS£,  lead)  can  be obtained.   Pollutants  with  significant  sol-
 uble  fractions  in  urban runoff show  lower  reductions;  on  the order of
 65 percent for  total P  and approximately 50 percent  for BOD, COD,  TKN,
 Copper,  and Zinc.  Results indicate  that biological processes which  are
.operative in the  permanent•pool  produce significant reductions  (50  per-
 cent  or  more}  in soluble  nutrients,  nitrate  and  soluble  phosphorus.
 These performance characteristics  are indicated  by both the  NURP  analysis
 results  and conclusions reached by individual  projects.

 'Dry basins,  (conventional  stormwater management basins),  which are  de-
 signed to attenuate peak runoff rates and hence only very briefly  detain
 portions o*f flow from the larger  storms, are indicated  by NURP data to be
 essentially ineffective for reducing pollutant loads.

 Dual-purpose basins  (conventional  dry basins  with modified  outlet  struc-
 tures which significantly extend  detention time) are suggested by limited
 NURP  data  to  provide effective reductions  in urban runoff  loads.   Per-
 formance may  approach  that of wet ponds;  however,  the  additional proc-
 esses which reduce soluble nutrient forms do not appear to be operative
 in these basins.   This  design  concept  is particularly promising because
 it represents  a  cost effective approach to combining flood  control and
 runoff  quality  control  and  because  of the  potential for  converting
 existing conventional stormwater  management ponds.
                  ,9t                          '
 Approximate costs of wet pond designs are estimated to be in the order of
 $500  to  $1500 per acre  of  urban  area  served,  for on-site applications
 serving  relatively small urban areas, and about $100  to $250 per acre of
 urban area for  off-site  applications  serving relatively  large  urban
 areas.  The costs reflect present value amounts which include both  capi-
 tal and  operating  costs.  The difference is  due to an  economy  of  scale
 associated with  large  basin  volumes.   The  range reflects differences in
 size required to produce particulate  removals in the  order of 50 percent
 or 90 percent.  Annual costs per  acre of urban  area served are  estimated
 at $60 to $175, and $10 to $25 respectively.

 Recharge Devices are capable of providing very  effective control of  urban
 runoff pollutant discharges to surface  waters.  Although continued  atten-
 tion  is  warranted,  present evidence  does  not  indicate  that  significant
 groundwater contamination will result from  this practice.

 Both individual project results and NURF screening  analyses  indicate that
 adequate]y sized recharge devices  are capable of providing  high  levels of
 reduction  in  direct  discharges of urban runoff to surface waters.   The
 level o.!  performance will depend on both  the  size of  the unit  and the
 soil pt r UK; !j wi. .1.1  be  restricted to areas where  conditions  are favorable.
 SoiJ   1 yp'-,  d'-'pi h  to groundwater,  land slopes,  and  proximity  of  water
 supply  wr'i.!.'   v.-j]J   f. 11  influence  the  appropriateness  of  this  control
 techninui .

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    Surface accumulations which result from  the  high efficiency of soils  to
    retain pollutants, suggest further attention in applications where dual
    purpose recharge  areas  also  serve as  recreational  fields or playground
    areas.

4.  Street sweeping is generally  ineffective  as a technique for improving  the
    quality of urban runoff.

    Five NURP projects evaluated street sweeping  as  a management practice to
    control pollutants  in urban runoff.   Four  of  these  projects  concluded
  •  that  street  sweeping was  not  effective  for this  purpose.   The  fifth,
    which  had  pronounced wet  and  dry seasons,  believed that sweeping  just
    prior to the rainy season could produce  some  benefit in terms of  reduced
    pollution in urban runoff.

    A large data  base on the  quality of  urban  runoff   from  street sweeping
    test sites was obtained.  At 10 study  sites  selected for detailed analy-
    sis, a total of 381 storm events were monitored under control conditions,
    and an additional 277 events  during  periods  when street sweeping opera-
    tions were in effect.  Analysis of these data indicated that no signifi-
    cant reductions in pollutant concentrations in urban runoff were produced
    by street sweeping.

    There may be special cases* in which street cleaning applied at restricted
    locations  or  times of.  year  could provide improvements  in  urban runoff
    quality.  Some examples that have been suggested, though not demonstrated
    by the NURP program, include periods following snow melt or  leaf fall, or
    urban  neighborhoods where  the  general  level  of cleanliness could be sig-
    nificantly improved.

5.  Grass  swales  can provide moderate improvements  in  urban runoff quality.
    Design conditions are  important.   Additional study could  significantly
    enhance the performance capabilities of  swales.

    Concentration  reductions  of  about   50  percent  for  heavy   metals,   and
    25 percent  for COD,  nitrate,  and ammonia were observed in one  of  the
    swales studied.   However the  swale  was   ineffective  in reducing  concen-
    trations  of  organic nitrogen,  phosphorus,   or  bacterial  species.   Two
    other  swales  studied failed to  demonstrate   any  quality improvements  in
    the urban  runoff  passing through  them.

    Evaluations by  the NURP projects involved concluded, however,  that  this
    was  an attractive control technique  whose performance could be  improved
    substantially by  application of appropriate  design  considerations.  Addi-
    tional study to develop such information was recommended.

    Design considerations cited included  slope,  vegetation type and  mainte-
    nance,  control  of flow  velocity  and  residence  time, and enhancement of
    infiltration.   The latter factor could   produce  load  reductions  greater
    than  those inferred  from  concentration  chances and  effect  reductions in
    those pollutant  species  which are  not   attenuated by  flow through  the
    swale.

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6.  Wetlands  are considered to be a promising technique for control of urban
    runoff  quality.   However,  neither performance characteristics nor design
    characteristics  in  relation  to  performance were  developed  by  NURP.

    Although  a number of projects indicated interest, only one assigned  NURP
    monitoring activity to a wetland.  This was a natural wetland, and flows
    passing though  it  were  uncontrolled.   Results  suggest  its potential  to
    improve quality,  but the  investigation was  not adequate  to associate
    necessary design factors to  performance  capability.  Additional attention
    to  this  control technique would  be  useful, and  should  include  factors
    such  as  the  need  for maintenance  harvesting  to prevent   constituent
    recycling.

ISSUES

A  number of  issues  with respect  to  managing   and  controlling urban  runoff
emerge  from the conclusions summarized above.   In some  instances they repre-
sent  the  need  for  additional  data/information or  for  further study.   In
others  they point to the need for follow-up activity by EPA,  State,  or  local
officials  to assemble  and  disseminate what  is   already known  regarding  water
quality problems caused by urban runoff and  solutions.

Sediments

The nature  and scope of> the potential  long-term threat  posed ^by  nutrient and
toxic pollutant accumulation in the sediments of urban  lakes  and streams re-
quires  further study.  A related issue is the safe  and  environmentally  sound
disposal  of  sediments  collected in  detention   basins  used  to control   urban
runoff.

Priority  Pollutants

NURP  clearly demonstrated that many priority pollutants can be found in  urban
runoff and  noted that a serious human health risk could exist when water sup-
ply intakes are  in  close proximity  to urban stormwater discharges.  However,
questions related to the sources,  fate, and transport mechanisms of priority
pollutants  borne  by urban  runoff  and their  frequencies  of  occurrence  will
 require further study.

 Rainfall  pH Effects

. The relationship  between pK and heavy metal  values in urban runoff has  not
been  established  and  needs  further study.  Several  NURP  projects (mostly  in
 the northeastern states) attributed high heavy  metals concentrations  in  urban
 runoff to the effects-, of acid rain.  Although it is quite plausible that acid
 rain increases tin-  level of pollutants in urban runoff and may transform them
 to more toxir and more easily assimilated forms, further  study is required to
 support this speculation.

 Industrie]  Hunoi :!

 No truly j nnust:':\ ,\",  :,jtr-:   i;3s opposed to  industrial parks)  were  included in
 any  of  th'1 K'MKi-  j.•!•••. ;.••-•:,.   /•  very  limited  body cf  data suggests,  however,
 that runoff • i om .1 m:i;::i • .; ,< • : ~:, t e <.- mav  have  sicnif icantly  hiqher contaminant

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levels than runoff from other urban  land  use  sites,  and  this issue should be
investigated further.

Central Business Districts

Data on the  characteristics  of  urban runoff  from  central  business districts
are quite  limited as  opposed .to other land  use  categories  investigated by
NURF.   The  date  do suggest,  however, that  some sites may  produce pollutant
concentrations in runoff  that are significantly higher  than those from other
sites in a given urban area.   When combined with their typically high degrees
of imperviousness, the pollutant loads from central business districts can be
quite high  indeed,.   The  opportunities  for  control in central  business dis-
tricts are quite limited, however.

Physical Effects

Several projects  concluded that  the physical  impacts  of  urban  runoff upon
receiving waters have  received  too  little attention and,  in some cases, are
more  important  determinants  of  beneficial use  attainment  than chemical pol-
lutants.  This contention requires much more detailed documentation.

Synergy

NURP did not evaluate  the synergistic effects that might result  from pollut-
ant concentrations  experienced  in stormwater runoff,  in association with pK
and temperature ranges that occur in the  receiving waters.  This  type  of  in-
vestigation  might  reveal that  control  of a  specific parameter,  such  as  pH,
would adequately reduce  an adverse  synergistic  effect caused by  the presence
of  other  pollutants  in combination  and be  the  most cost effective  solution.
Further investigations should include this issue.

Opportunities for Control

Based upon  the  results of NURP's  evaluation of  the performance of urban run-
off controls,  opportunities  for significant  control of urban  runoff  quality
are much  greater  for  newly  developing areas.   Institutional  considerations
and availability  of  space are the key  factors.  Guidance on this  issue in  a
form  useful  to  States and urban planning authorities  should be  prepared and
issued.

Wet Weather  Water  Quality Standards

The NURF  experience suggests that  EPA should  evaluate  the possible  need to
develop "wet weather"  standards, criteria,  or modifications to ambient crite-
ria  to reflect differences  in  impact  due to  the intermittent,  short dura-
tion  .exposures characteristic  of  urban  runoff  and  other  nonpoint  source
discharges.

Coliforni  Bacteria

The  appropriateness of  using   coliforrr. bacteric  &£  indicator organisms for
huir.cr. health risk  where  the  source  is exclusively urban runoff warrants  fur-
ther  investigation.

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Wetlands

The use of wetlands as a control measure is of great  interest  in  many areas,
but the  necessary information on  design  performance relationships  required
before cost effective applications can be considered  has  not  been adequately
documented.   The  environmental  impacts  of  such  use  upon  wetlands  is  a
critical issue which, at present,  has been addressee marginally, if at all.

Swales

The use  of grass  swales was  suggested by two NURP projects to  represent  a
very  promising  control  opportunity.   However,   their  performance   is  very
dependent upon design  features  about which information is  lacking.   Further
work to address this deficiency and appropriate maintenance practices appears
warranted.

Illicit Connections

A number of the NURP projects identified  what  appeared  to be illicit connec-
tions of  sanitary discharges,  to. stormwater sewer  systems,  resulting in high
bacterial  counts  and  dangers  to public health.   The  costs and complications
of  locating and  eliminating  such connections may  pose  a  substantial problem
in urban areas, but the opportunities for dramatic improvement  in the quality
of  urban  stormwater  discharges  certainly  exist  where  this  can  be accom-
plished.   Although not  emphasized in  the  NURP  effort,  other  than to•assure
that the  selected monitoring  sites  were  free  from sanitary sewage contamina-
tion, this BMP is  clearly a desirable one to pursue.

Erosion Controls

NURP  did  not  consider  conventional  erosion  control  measures  because the
information base  concerning  them  was considered  to  be  adequate.   They are
effective, and their use should be encouraged.

Combined Sewer Overflows

In  order to address urban runoff from  separate storm  sewers,  NURP'avoided any
sites  where  combined  sewers  existed.   However,   in  view  of  their  relative
levels  of contamination,  priority  should  be given  to  control  .of  combined
sewer overflows.

Implementation Guidance

The NURP  studies  have  greatly increased our knowledge  of  the  characteristics
of  urban runoff,  its  effects upon  designated;  uses,  and  of the  performance
efficiencies of  selected  control  measures.  They have  also confirmed earlier
impressions  that  some  States  and  local  communities have  actually  begun  to
develop  and  implement stormwater   management  programs  incorporating  water
quality  objectives.   However, such  management initiatives are,   et  present,
scattered  and  localized.   The  experience gained from such  efforts is  both
needed  and sought after by many other States and  localities.   Documentation,

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evaluation, refinement  and  transfer of management  and financing mechanisms/
arrangements,  of simple and reliable problem assessment methodologies, and of
implementation  guidance  which  can be used  by  planners end  officials  at the
State and  local level are urgently  needed' as  is a  forum  for  the sharing of
experiences by  those  already  involved,  both among  themselves  and with  those
who are about to address nonpcint source issues.

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