5927A
action
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.

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.
                                111

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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.
                                 v

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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-Clyde  Consultants were:  Gail B.  Boyd,  David  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  Plummer
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
   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
             Relationship Between NURP and WQM Plans	    4-17
                                     IX

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                         TABLE OF CONTENTS (Cont'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         RECEIVING WATER 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  	     8-2
             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

             Data 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
             Approach (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
             C01 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
             NHl 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/sg mi)  	     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"^
             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) Pond
             Construction Cost Estimates Vs. Volume of Storage  .  .   .    8-12
8-3          Cost of Urban Runoff Control Using Wet
             Detention Basins	    8-13
                                     XII

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                          LIST OF FIGURES (Cont'd)
Figure
8-4
8-5

8-6
8-7
Long Term Average Performance of Recharge Devices
Page
8-16
Table
 2-1
 5-1
 6-1
 6-2
 6-3
 6-4
 6-5
 6-6
 6-7
 6-8
 6-9
 6-10
 6-11
 6-12
 6-13

 6-14
 6-15
 6-16
 6-17
Bivariate Plots of Median EMCs for Swept and
Unswept Conditions 	    8-20
Street Sweeping Performance  	    8-21
Effect of Street Sweeping on Site Median EMC
Values	    8-23


                  LIST OF TABLES

                                                            Page
NURP Project Locations 	     2-7
Summary of Receiving Water Target Concentrations
Used in Screening Analysis - Toxic Substances
(All Concentrations in Micrograms/Liter, ug/£) 	    5-12
Site Mean TSS EMCs (mg/A)  	    6-10
Site Mean BOD EMCs (mg/£)  	    6-11
Site Mean COD EMCs (mg/£)  	    6-12
Site Mean Total P EMCs (ug/fc)  	    6-13
Site Mean Soluble P EMCs  (yg/£)  	    6-14
Site Mean TKN EMCs (pg/£)  	    6-15
Site Mean Nitrite Plus Nitrate EMCs (wg/fc)	    6-16
Site Mean Total Copper EMCs  (yg/£)	    6-17
Site Mean Total Lead EMCs  (yg/fc)	    6-18
Site Mean Total Zinc EMCs  (ug/£)	    6-19
Project Category Summarized by Constituent 	    6-26
Median EMCs for All Sites by Land Use Category 	    6-31
Number of Significant Linear Correlations
By Constiuent	    6-38
Sign of Correlation Coefficients by Sites  	    6-39
Correlation Coefficient Values by Site  	    6-40
Sites With Many Significant Correlations	    6-42
Water Quality Characteristics of Urban  Runoff  	    6-43
                                    Xlll

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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 Criteria*  	    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 ug/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
1977  (P.L.  95-217)  deleted  Federal  funding for  the  treatment of  separate
stormwater discharges.  The Congress stated that  there was  simply not enough
                                      1-1

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known about urban runoff loads, impacts, and controls to warrant making major
investments in physical control systems.

In 1978, 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\ a 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.
                                      1-2

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                                  CHAPTER 2
                                 BACKGROUND
EARLY PERCEPTIONS

As noted earlier, drainage is perhaps the single most important factor of the
urban hydrologic  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 volumes  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
19 percent  came  from  combined  sewers,   the  balance  coming  from treatment
plants.

In 1971, EPA  also conducted a study  in  Oakland  and  Berkeley, California, to
assess the infiltration  of  stormwater into  sanitary  sewers.   While only four
                                      2-1

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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  runofE 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).

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 sources 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) .   Rather,  ORD  has focussed
principally  on multi-purpose  analyses  and  controls, because  it  is  nearly
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impossible to  segregate benefits and  strategies of urban  stormwater runoff
pollution control from  drainage,  flood,  and erosion control.   Marty signifi-
cant results have been  obtained by ORD's effort, which  has dramatically in-
creased the technical literature in the area.

Data from ORD  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 to 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  to 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, and
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 to design and guide the development of the emerging NURP
program.  Also, three of the NURP projects were joint efforts with ORD  (i.e..
West Roxbury, 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  (Cate-
gory VI) was done 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 dollars).
One  state  alone identified  $80 billion  in  needs to  control  separate storm
sewer discharges.  In 1976, the Needs Survey was  conducted by the Agency, and
it was found that Category VI  would  require $66 billion to meet the goals of
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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  1969 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 stormwater 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 to  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  future 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.
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Figure 2-1.  Locations of the 28 NURP Projects
      TABLE 2-1.  NURP PROJECT LOCATIONS
EPA
Region
I



II




III


IV




NURP
Code
MAI

MA2
NH1
NY1

NY2
NY3

DC1

MD1
FL1
NCI
SCI
TNI

Project Name/Location
Lake Quinsigamond
(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
Tampa, Florida
Winston-Salem, North Carolina
Myrtle Beach, South Carolina
Knoxville, Tennessee

EPA
Region
V





VI

VII
VIII


IX


X

NURP
Code
IL1
IL2
Mil
MI2
MI3
wn
ARl
TX1
KS1
C01
SD1
UT1
CA1

CA2
OR1
WAI
Project Name/Location
Champaign-Urbana , Illinois
Lake Ellyn (Chicago Area)
Lansing, Michigan
SEMCOG (Detroit Area)
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 Selection

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  diversity  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
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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 arid
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.

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  (associated  with industrial,  energy,  and  agricultural  production
activities)  and  added surface particulates  (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  farmer, 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.

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
                                     3-3

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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  storm  flows could be
managed  and water  quality could  be  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   (SCS, 1975).

Other Federal agencies that have an  interest in urban runoff and its control
include the U.S. Geological Survey,  the Federal  Highway Administration, the
Federal Housing  Administration,  the Tennessee  Valley Authority,  and others
too numerous to mention.

State And Local Involvement

Although some  27 states  have adopted  floodplain management  legislation  to
protect property,  the  control  of urban  drainage has  traditionally  been  a
local matter.  Some  states have some form of erosion control  laws in force;
however few states have runoff rate/quantity legislation.  This  situation has
begun  to change  over  the  last decade,  and Maryland is one example where the
statewide legislation for  stormwater management is implemented at  the county
level.
                                     3-4

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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 cover 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 calls to public officials
                                     3-5

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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 inclxide
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.
                                     3-6

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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.
                                     4-1

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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.
                                                                                      to
                                                                                      o
                                                                                      CM
                 40%
                   EVAPO
                   TRANSPIRATION
                        NATURAL
                        GROUND
                        COVER
                                         38%
                                           EVAPO
                                           TRANSPIRATION
       10% RUNOFF
     25%
     SHALLOW
     INFILTRATION
                                            20% RUNOFF
                                                 10-20%
                                                 PAVED
                                                 SURFACES
  DEEP
  INFILTRATION
                 25%
21%
SHALLOW "    • DEEP
INFILTRATION    T INFILTRATION
           21%
                 35%
                   EVAPO
                   TRANSPIRATION
30% RUNOFF
                        35-50%
                        PAVED
                        SURFACES
                                         30%
                                          , EVAPO
                                           TRANSPIRATION
                                          55% RUNOFF

                                                75-100%
                                                PAVED
                                                SURFACES
       20%
       SHALLOW
       INFILTRATION
  DEEP
  INFILTRATION
15%
  10%
  SHALLOW
  INFILTRATION
5%
DEEP
INFILTRATION
    Source: J.T. Tour bier and R. Westmacott, Water Resources Protection Technology: A Handbook of 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
        Stormwater 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, changes in regulations  or engineering design standards, technical
assistance materials  for  landowners  or consulting  engineers, revisions  to
existing programs, or a written plan document.
                                     4-3

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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  local  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 programs.  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   -  Requirements   for  regular
        inspection and maintenance of stormwater facilities, including
        drains  and  retention or detention basins, may be enforced by
                                     4-5

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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 arid 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.
                 ANALYSIS
                   OF
                 TECHNICAL
                ALTERNATIVES/
  SELECT
             DETAILED
 TECHNICAL
ALTERNATIVES
              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?
   This material  is  largely  from the  draft document,  Planning for  Urban
   Runoff Control;  Financial and Institutional  Issues,  December 1981, pre-
   pared for FMAP 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 made.   An example of a preliminary matrix is given in Figure 4-4.
                                     4-7

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 PRELIMINARY
 FINANCIAL &
INSTITUTIONAL
  ANALYSIS
                  ANALYSIS
                    OF
                  TECHNICAL
                ALTERNATIVES;
 FINANCIAL AND
 INSTITUTIONAL
  ASPECTS OF
EACH ALTERNATIVE
                   SELECT
                  TECHNICAL
                ALTERNATIVES
 IN DEPTH
ANALYSIS OF
 SELECTED
ALTERNATIVE
                                 DETAILED
                                 DESIGN
                                           SUCCESSFUL
                                         IMPLEMENTATION
                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
ANO OPERATE
BASINS
   Figure 4-4.   Preliminary  Matrix for Selection of  a Control Approach
                            (Combined  Sewer Overflows)
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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 NEEDS
       - 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
                                                                                CO
                                                                                -=r
     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.
3  These elements were first defined in  Planning for Clean Water  Programs:
   The  Role   of  Financial  Analysis,   U.S. EPA's   Financial  Management
   Assistance  Program  by  the Government Finance Research  Center  of  the
   Municipal Finance Officers Association, September 1981.
                                      4-9

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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

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 un^nflated 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.5

Cost analysis  of  control alternatives  is  included  in  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 a  further  discussion of present  value  analysis,  see  pp 36 to  42  of
   Facilities  Planning  1981,  U.S.  Environmental  Protection Agency,  FRD-20,
   1981.
                                     4-10

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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 report6
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
   data provided by  the  projects are included in the  appendices  of this Re-
   port to show how the various projects prepared the data for submission.
                                     4-11

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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-tp-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.
                                     4-12

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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.   The 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.
                                     4-13

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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  no  additional
cost.
                                     4-14

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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 FOLLOWUP
FOR PROGRAM
TOTAL
AGENCIES
STATE



$2,000

$2,000
COUNCIL
OF
GOVERNMENTS



$ 5,500
$24,000
$29,500
DEPARTMENT
OF
POLLUTION CONTROL



$2,000

$2,000
DEPARTMENT
OF
PLANNING

$1,500
$ 800


$2,300
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   are  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 4-8 illustrates  an ability-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-
age annual household income,  and cost as a percentage of property taxes.
                                     4-15

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       A. TOTAL PROGRAM COST (ONE-YEAR PROGRAM)

       B. NUMBER OF HOUSEHOLDS AFFECTED

       C. COST PER HOUSEHOLD
           (A DIVIDED BY B)

       D. MEDIAN HOUSEHOLD INCOME

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

       F. AVERAGE ANNUAL PROPERTY TAXES

       G. COST AS A % OF PROPERTY TAXES
           (C 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  sensitix'ity  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 to  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  to 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.
                                      4-16

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RELATIONSHIP BETWEEN NURP AND WQM PLANS

Of the locations selected 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 the 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.
                                     5-1

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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  a 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 these data has been  to  develop a concise  summary of the
^teristics 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-
issessment 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.

 roximately two-thirds of the NURP  projects the occurrence of compounds
 s list of "Priority Pollutants" was investigated.   This program element
so  described under a  separate heading below.   A   number  of additional
   have also been addressed  in the program.  These are briefly discussed
                                5-2

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below 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 6.

     -  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   not  included
        herein.

Standard Pollutants

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

                        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

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 a 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,
                                     5-3

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geographic  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  from  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  log-normal and  have  the  same
median  are  shown.  The log transforms  of the   data  result in  normal  bell
                                     5-4

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                    MEAN
                  LOG VALUE
    (a)
                    VALUE
(b!
                                                 3.0
                                                 2 5
oS 2.0

H
oc o
  t—
    1 5
                                                 1 0
                                                   (c)
                                                     (d)
                MEAN AS
                MULTIPLE OF MEDIAN
                FOR LOG NORMAL
                DISTRIBUTIONS
                                                                  1.0
                                                                 COEF OF VARIATION
                                                                                 20
                                                                                         25
                                                                             90TH PERCENTILE AS
                                                                             MULTIPLE OF MEDIAN
                                                                             FOR LOG NORMAL
                                                                             DISTRIBUTIONS
                                                             0.5     10     1.5      2.D

                                                                    COEF OF VARIATION
                                                                                          2.5
              Figure  5-1.   Lognormal  Distribution  Relationships
                                            5-5

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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
=V
                                        (Coef 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:
  a

                          X =  exp (y,    + Z  an   )
                           a         Inx    a  Inx

where:

     Z    =  the standard normal probability

     u,   =  mean of log-transformed data
      Inx              ^

     a,   =  standard deviation of log-transformed data
      Inx                            ^

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              I	
                 ——.	 = 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.
                                     5-6

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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.

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.

Hydroroeteorological 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 data
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 NURP projects  examined the  site-specific impacts of
urban runoff on water quality  for a  variety of beneficial uses  and  receiving
                                     5-7

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water types.   These  results provide  important  information on the  extent to
which urban runoff constitutes a "problem" as well as "ground truth" measure-
ments against  which more  generalized techniques  can  be  compared.   Method-
ologies  employed  in  these  local  studies  vary  and  are  described in  the
individual project reports.  Relevant site-specific project results are cited
in Chapter 9.

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 quality  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 NURP 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 i:rban storm-
water runoff  or  the  cost  of  control  which would  ultimately  result.   The
available analysis methods do permit an assessment of a different kind.   NURP
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  do  so,  these
general  screening analyses  were  applied to  local  situations   which  exist
within  certain  of the  individual  NURP   projects.   Comparisons were  made
between  specific water quality  effects  or  broader  conclusions  relative to
problems derived from both local analysis  atnd general screening 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 quality
during and shortly after storm events.  Examples of this water quality impact-
include periodic  dissolved oxygen depressions  due to  oxidation  of contami-
nants,  or  short-term increases  in  the receiving  water  concentrations of  one
                                     5-E

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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 distinguish
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  of causing  adverse  environmental
impacts.    This  results,  in  part,  from  the  smoothing  obtained by  mixing
numerous sources which  have high frequency (short-term)  variability.
                                     5-9

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In view of the above discussion,  the  time  scale  used  by NURP 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,  NURP  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.

The  issue  (i.e.,  whether traditional ambient  criteria  are  excessively  con-
servative measures of  conditions  which  provide reasonable  assurances  of
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

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about 10 percent of  the time.  There are regional  and seasonal difference
but typical  values for annual  average  storm characteristics  in  the east«
half 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
These estimates  are  based on results from  an  analysis of long-term rainfc
records  for  40 cities  throughout  the  country.   Median  and 90th percent!
values are derived from data mean and variance based on a gamma distributic
which has  been  shown  to characterize  the  underlying distribution  of stc
event parameters quite well.

In the  semi-arid regions of the western half of the  country,  average stc
durations tend to  be comparable to the  above,  but  average intervals betwe
successive storms  increase substantially  (two  to  four fold) and  are high
seasonal.  With  urban  storm  runoff, therefore,  one  is dealing with polluta
discharges which occur over a  period of a  few hours every  several  days
more or  after  long dry periods.  In  advective  rivers  and streams,  the wat
mass influenced  by urban runoff tends to move  downstream in relatively di
crete pulses.  Because of the variability  in  the magnitude of  the pollute
loads from different storm events, only a  small percentage  of  these puls
have high pollutant concentrations.

There are currently no  formal  "wet weather" criteria and, thus,  no genera]
accepted way intermittent exposures having time scale characteristics typic
of urban runoff  can be related to use impairment.   In  the belief  that
would be inappropriate  to ignore such considerations in a general evaluata
of urban runoff, NURP  has developed estimates  for  concentration levels whj
result  in  adverse  impacts on  beneficial use when  exposures occur intermi
tently  at  intervals/durations  typical  of urban   runoff.   These  "effec
levels" were used to interpret the significance of the variable, intermitte
water quality  impacts  of urban runoff.   It should be  understood  that the
effects  levels do not  represent  any  formal position  taken by  EPA,  but i
simply the most  reasonable yardsticks available to  meet  the immediate nee
of the evaluation  of urban runoff.  As  used in the screening analysis proc
dures,  alternative values for  "effects  levels" may be  readily substitul
when either more accurate estimates can be  made,  or more (or less)  conser\
tive approaches are indicated in view of the importance of a particular wal
body or beneficial use.

Table 5-1 summarizes  information  on water  quality  criteria for a  number
contaminants  routinely  found  in  urban  storm runoff.   The data  present
include:

        Water quality  criteria  for  substances  on EPA's priority pollut-
        ant  list  (45 FR No. 79318, 11/28/80).  These  criteria  provide
                                     5-11

-------






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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 and stream  flows and is interpreted as the mean
                                     5-13

-------
                                                                   o
                                                                   o
                                I        \
                                  URBAN
                                   AREA   /
URBAN RUNOFF \
QR =FLOW V^
CR= CONCENTRATION
STREAM FLOW • • »> •

/
k-
•
I .
y L
                 UPSTREAM

            QS^FLOW
            CS = CONCENTRATION
     DOWNSTREAM
    (AFTER MIXING)
Q0~ 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.
                                   5-14

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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  and 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   resulting  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 dry  — is  simply  the  product  of
                                     5-15

-------
        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 of 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                  ,.
             	—:—	•  ,  j_	 = 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
             (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  of distributions  may   have  appreciable
uncertainty,  and in the natural water systems, distributions may be lognormal
                                     5-16

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over the bulk of the  range  but may deviate from the assigned distribution at
the extremes.   Computed stream concentrations  at long  recurrence  intervals
are likely to be  conservative, that is, overstated  because  there are likely
to be practical upper limits  for  runoff  concentrations and lower  limits to
stream flow.

It also 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-
ior, may  be  significant in  some  cases.   This  situation  would cause  the
average one year condition, for example, not  to repeat itself  every year but
rather to occur several times per year, at intervals greater than one year.

Other Receiving Waters

Other receiving waters of general  interest in assessing urban  runoff effects
include lakes, estuaries, embayments, and coastal zones.  The methods adopted
for lakes are briefly described below.  The other receiving  waters  generally
require site-specific and often complex analysis  techniques  (numerical meth-
ods, multi-dimensional modeling, etc.).  Given this, a generalized screening-
level assessment  was  not believed  to be  appropriate  for  this report.   A
number of  the  individual NURP  projects consider  these  coastal  water bodies
and report on the specific methods adopted and results obtained.

For lake eutrophication problems,  the time scale for analysis is considerably
longer  than  the  short  (event  scale)   periods  necessary  for   estuaries  and
rivers.   For  this  case,  annual average  loads  were  used  in  a steady-state
analysis performed using the type of empirical model advanced by Vollenweider
and others.   The EMC  data  developed  from NURP  monitoring  programs  can be
readily converted to  annual  loads directly from annual flows  or indirectly
based on annual rainfall.

For total  phosphorus, typically  the limiting  nutrient of  concern,  average
concentrations are calculated using the following formula:

                             P =   —¥1	 . 1000
                                 H/T •  u

The input values  include  pollutant mass loading  (W),  lake  physical charac-
teristics of depth  (H) and  residence time  (T)  and reaction rate coefficients
(u ).   The relative contribution of  all load  sources to lake total  P concen-
  s
trations can be defined by solving this equation for each of the sources.  By
comparing results in terms  of lake concentrations for initial  conditions  (no
control),  and then modifying  loads to  reflect various levels of control, al-
ternative control operations can be compared directly to effect on lake water
quality.

Some judgement  is involved in defining acceptable  lake water  quality  con-
centrations,  which  depend in  part  on   water  use  and  on regional norms  and
expectations.
                                     5-17

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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  described 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.
                                     5-18

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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
SWMM.  In  such  cases the local  soil permeability (the percolation  rate)  is
applied 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.
                               5-19

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                                  CHAPTER 6
                       CHARACTERISTICS OF URBAN RUNOFF
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
to 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-
tire  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 for a variety of pollut-
ants  at  a  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  81  sites in  22 different cities, and
includes more than 2300 separate storm  events.   The actual number  of events
                                     6-3

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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 data  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 of  representing the essential
characteristics  of the  data set in question,  and  (2)   the estimation of the
parameters of  the  population pdf that  the  observed datci 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
value on a subsequent trial  (either within or  outside  the  original data  set,
                                     5-2

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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 are  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 (g) 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 3-3.  For a given  sample size  and test,  fixing a  value for a also
determines a value  for g (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 consequences of 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  Kolmogorov-
Smirnof f D test.  The  a levels  for TSS,  Total  P,  TKN, Total Pb, 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 lognormal  distribution  quite  well  describes  the  data.   Because
BOD, Soluble P,  and Total Cu were measured at  fewer than  half  of the project
                                     6-3

-------
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  the  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 ug/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  ug/1)  is one-twentieth the
typical detection  limit  (20 yg/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  yg/1  and 0.37  for the  median  and
coefficient of variation  as  compared with  the  25 pg/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
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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/1) are presumably the  detection limit  of  the  analytical laboratory.
Of course in reality not all 27 values are 100  ug/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 ug/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
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-
trations will occur somewhat more frequently than would be predicted.

When the results  of  this exercise are  compared for all 49 sites,  the median
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
the data.  If the  estimates  are based  upon the plots,  the respective values
are 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).

Based on  the  results of the  analyses  which have  been performed,   the NURP
findings 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.

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        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  NURP 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
by  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 designated as commercial land use.
                                     6-9

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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  ether 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:   (I)  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 a wider range and higher
EMCs than the others.  Thus we can conclude that some projects represented in
the  database  appear, from the  monitoring  sites  selected,  to tend towards
somewhat higher or  lower  EMC  median values  and ranges than  the bulk  of the
projects.   However, there  are  no distinct geographical patterns revealed.
                                    6-20

-------
                            TSS
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     Figure 6-4.  Range of TSS  EMC Medians (mg/1) by Project
                              BOD
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     Figure  6-5.  Range of BOD EMC Medians  (mg/1) by  Project
                                6-21

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       Figure 6-6.  Range of COD EMC Medians (mg/1) by  Project
11
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                                 6-22

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) 21
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00 14
00
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f



         200
400
                      600
                    800
1000
1200   1400
Figure 6-11.   Range of Total Cu EMC Medians  (pg/1) by Project
                              6-24

-------
(
CA1
C01
DC1
IL2
KS1
MAI
MA2
Mil
MI3
NY2
SD1
TN1
) 5
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1 M R M R |
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MMM M C ]
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I M |

1 M |



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           50
100
                            150
200
                          250
Figure 6-12.  Range of Total Pb EMC Medians  (yg/1) by  Project
                       Zn
CA1
C01
DC1
FL1
IL1
KS1
MAI
MA2
MD1
Mil
MI3
NC1
NH1
NY1
NY 2
NY3
SD1
TNI
TX1
WAI
WI1



1 M 1


1 R RR C R M 1
1 R RRR RR I
1 C MRMR




MR R R 1


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| M R M MR 1



1 C R 1
1
1 C MMM M 1
IM MMI
IR C |

IIC 1

C


RR 1
1 I


1 R RM Rf


CR R 1

IRMC R 1

M 1


1 R R 1
IRRI

ICCRRMC I







                                                        9.9
Figure 6-13.  Range  of  Total Zn EMC Medians  (yg/1) by Project
                             6-25

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



TSS
BOD
COD
Tot. P.
Sol. P.
TKN
NO. -N
2+3
Tot . Cu
Tot. b
Tot. Zn
iH
O
o
3
-
3
1
2
2
2

2
2
2
i-l
U
Q
1
_
1
2
3
1
1

1
1
1
1-1
ij
Pn
1
2
1
1
-
1
1

1
1
1
r-1
»J
H
2
-
3
2
-
2
_

2
2
-
t-H
W
«
3
3
3
3
3
2
_

2
1
3
i-l
<
s
3
-
2
3
2
2
3

3
2
2
i-i
Q
s
1
-
3
3
-
3
3

3
3
3
H
H
S
1
2
1
2
2
1
1

1
1
2
00
H
s
1
1
—
1
1
1
2

-
-
—
n
><
Z
2
-
1
2
-
2
_

-
1
3
1-1
2
EH
3
2
2
2
2
1
1

2
2
2
H
H
S
2
2
2
2
-
1
1

-
*^
t.
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 90 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
significant.
                                    6-26

-------
                                                           0.5    1.0    1.5    2.0
             0.5
SITE » 1
SITE » 2
SITE # 3
                             1.5
                                     2.0

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R 10% CONFIOEK
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0 1.5 2.
  (a) Significantly Different Sites
             0.5
                     1.0
                             1.5
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SITE # 2
SITE tt 3



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                                                           0.5
                                                                1.0    1.5
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  (b) Sites with No  Significant
      Difference
(c)  EMC Data from Denver (C01)
           Figure 6-14.   Range of Normalized EMC Medians at Denver  (CO1)
                                         6-27

-------
The actual data for the Denver (C01) project are presented in Figure; 6-14(c).
With the exception of  nitrate + nitrite,  there  is  little to no statistically
significant difference  among  the  majority of the  sites  for each constituent
examined.   The  lack of 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  Big  Dry
Cottonwood site, which  is  also residential,  tends  to fall between these two.
Careful  examination  of  other site  data  does  not provide  any evidence  to
explain this  difference in response for sites in  the  same  Land use category
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  to the  Denver  results  just
discussed.

The WASHCOG  data presented 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 (ILl)  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.  For  example,  the Mattis pair
has significantly  higher EMC values  for TSS, 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.

Based 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 do 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 land use  category on the EMC
parameters of a site makes use of  the  observation,  discussed  earlier,  that
geographic location has no discernible  effect on  site response.  Since site
to site  variability  was shown to be  very well represented by  the  lognormal
distribution, analysis  procedures similar to those  described  previously for
characterizing an individual site were  applied.   Table 6-12  lists the median
EMCs for all  sites within  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 sites  included  in this  database  provide a
"representative" sample of the land use classifications, then the information
summarized  by Table 6-12  indicates  the  effect of land  use  on urban storm
runoff pollutant discharges.
                                    6-28

-------
                                                    0.5    1.0    1.5    2.0
       0.5    1.0    1 5
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(b)   WASHCOG Sites
        Figure 6-15.   Range of Normalized  EMC Medians  at FL1 and  DCl
                                       6-29

-------
        0.5
1.0
1.5
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R MATTIS S.
M-MATTIS N.
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                         6-30

-------
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-------
Some caution in the interpretation of the information presented in Table 6-12
is  in  order since  statistical  confidence limits  are  not given.   These are
indicated  in  Figure 6-17  (a 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 WI1  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 to  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  to reject the null hypothesis  is interpreted  as  meaning  that linear
dependency between the two variables in the population has not been shown.
                                    6-32

-------
                      LEGEND
          90%
         VALUE
          75%
         VALUE
                              STATISTICAL
   OF THE
   MEDIAN
    90%   \
 CONFIDENCE^
                                              „

                                          nftWut
             GROUP A    GROUP B
                                                                              BOD
                                                                RESIDENTIAL
                                                                   SITES
                                                 11
                                                MIXED
                                                SITES
                                              11
                                          COMMERCIAL
                                             SITES
                                                                                                  OPEN
                                                                                                  SITE
(a)
                            (b)
 500
 400
 300
 200
 100
                         TSS
          33
      RESIDENTIAL

(C)      SITES
                     19
                    MIXED
                    SITES
    14
COMMERCIAL
   SITES
OPEN
SITES
160
140
120
100
f 80
60
40
20
0
COD
-r
-
T

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1C
33 16 13 5
RESIDENTIAL MIXED COMMERCIAL OPEN
SITES SITES SITES SITES
                                                        (d)
                    Figure  6-17.   Box Plots  of  Pollutant  EMCs  for
                                     Different Land Uses
                                               6-33

-------
100

90
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RESIDENTIAL MIXED COMMERCIAL OPEN
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                                                              500
                                                              400
                                                               300
                                                               200
                                                               100
                                                                                            TOTAL LEAD
                                                                       30
                                                                    RESIDENTIAL
                                                                      SITES
                                     16
                                    MIXED
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                                                             11
                                                         COMMERCIAL
                                                            SITES
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                                                                                                       SITES
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                  TOTAL
                   ZINC
                                                               5000
                                                               4000
                                                               3000
                                                               2000
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                                                                                              TKN
              26
           RESIDENTIAL
             SITES
                          12
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                         SITES
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OPEN
SITES
   32
RESIDENTIAL
  SITES
 18
MIXED
SITES
    14
COMMERCIAL
   SITES
 8
OPEN
SITES
 (g)
                                                         (h)
                     Figure  6-17.    Box  Plots  of Pollutant  EMCs  for
                                Different  Land Uses  (Cont'd)
                                                6-34

-------
      2000

      1800

      1600

     1400


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                             NITRITE
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                         SITES
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RESIDENTIAL MIXED COMMERCIAL OPEN
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                                                                                          INDUSTRIAL  NON URBAN
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                                  SOLUBLE
                                PHOSPHORUS
             16         14          8          6
          RESIDENTIAL     MIXED    COMMERCIAL     OPEN
            SITES       SITES      SITES       SITES
                    Figure  6-17.   Box  Plots  of Pollutant EMCs  for
                              Different  Land Uses  (Cont'd)
                                             6-35

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

General  guidelines  for the  use of this  test suggest  that it be  used with
caution  for  values  of n less  than ten due  to the high  uncertainties asso-
ciated 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
large, say over  100, correlation  coefficients are  almost always significant
but can be so weak that they are meaningless.  For n = 100 the critical value
of r  at  the  90 percent confidence level is  0.164,  meaning that the correla-
tion explains less than 3 percent of the concentration variability.

A 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),
116  (22 percent)  were significant  at the  95 percent  confidence  level  and
154  (30 percent)  were significant at the 90 percent confidence level.  Of the
r values that were significant, 83 and 87 percent were negative at the 90 and
95 percent  confidence  levels  respectively.  When sites with  fewer  than
10 events were  dropped, the  foregoing  was  essentially  unchanged.   Greater
detail in terms  of  the number  of  significant linear  correlation by constit-
uent  is  provided in Table 6-13.  There  it  can  be seen that  the greatest
tendency  for positive  values  of r  occurs  with  TSS,   followed by  soluble
phosphorus.    The  correlation coefficients for the  other  7 constituents  all
strongly tend to be negative.

When the results are examined by sites,  however, a clearer picture emerges.
Although it can be correctly  argued that unless  a correlation coefficient is
statistically significant the number  is meaningless, it  also follows that in
such  a  case   they are as likely  to  be positive  as  negative.  On  the other
hand, if all  the  correlation coefficients (whether significant  or  not)  have
the 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
examined is  given  in Table 6-14.   Giving  appropriate weight to significant
r values but  considering others as well, some 37 of  the  sites  tend  to have
negative correlations, 13 tend  to be  positive, and the  remaining 17 tend to
be mixed.  Perusal of Table 6-14 reveals that this tendency for sites to have
either  positive  or  negative  correlation  coefficients  is  quite  strong,
especially for sites  with a  large  number  of  significant correlations.   Sites
where erosion, scour,  system lag, and such  are present  could be expected to
exhibit a tendency towards positive correlations.   Sites lacking such effects
could be  expected  to  have  negative  correlation  due  to  dilution associated
with larger runoff events.

The magnitude of the correlation coefficients  is  indicated  in  Table 6-15.
Two points stand out  in particular.   First,  the r values  are not very large,
averaging around  0.55.   Phis means  that  the  correlation  is  only able  to
explain  about 30 percent,  of  the  concentration  variability.   The  few  high
values are always associated  with very few observations  (n<10) for which the
                                    6-37

-------
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
59
56
517

90% SIGNIFICANT CORRELATION
TOTAL ft
13 (19%)
24 (38%)
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 #
7 (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
1
15
13%
(b) 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
1
1
12
12%
                  6-38

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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 18  had 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  again 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 to
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 warranted 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  storm event, etc.)  all  have a potential
                                    6-41

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                                                        6-42

-------
influence  on  the  median and  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  unmonitored  sites,   the  best  general  characterization of  urban
runoff 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  of  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 6-17  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)
BOD (mg/1)
COD (mg/1)
Tot. P (mg/1)
Sol. P (mg/1)
TKN (mg/1)
Tot. Cu (yg/1)
Tot. Pb (yg/1)
Tot. Zn (pg/1)
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
0.5-1.0
Site Median EMC
For
Median
Urban Site
100
9
65
0.33
0.12
1.50
0.68
34
144
160
For
90th Percentile
Urban Site
300
15
140
0.70
0.21
3.30
1.75
93
350
500

-------
Coliform Bacteria

Coliform bacteria  counts in  urban  runoff were  monitored for  a  significant
number of  storm  events  by  seven of the NURP projects  at  17  different sites.
Data were  collected at twelve  of  these sites for  more  than five and  up to
20 storm events.   Data  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  of  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 NURP  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 NURP project examined salmonella  counts in urban runoff and in an
adjacent  shellfish area  influenced  by  uroan   runoff.   The  Kncxville,  TN
project also conducced 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
of domestic  animals or such  wildlife  as  may be  expected in urban  areas to
observed coliform levels.

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

PRIORITY POLLUTANTS

'ackground

 he NURP priority pollutant monitoring  project was  conducted to evaluate the
 resence,  concentration, and potential water  quality impacts of  priority pol-
 utants in urban  runoff.  A total of 121  urban runoff samples were collected
                                    6-44

-------
         TABLE 6-18.  FECAL COLIFORM 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
No.
Obs
1
2
1
_
1
1
8
4
-
15
4
-
7
4
4
4
52
Events
9
Median
EMC
(WOO/
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


1
C.V.
_
-
-
_
-
-
0.6
1.1
-
1.5
14
-
1.4
1.9
2.4
1.7


0.7
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 a single value.
                                    6-45

-------
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 NURP 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  hLgh  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 be 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
NURP program.  However, standard laboratory methods will  reveal the presence
of dioxin  at  concentrations  of 1 to 10 yg/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 detected1".

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 othe_- 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  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.   Their concentrations were also
among the highest  for any pollutant,  and reached  a maximum  of  100,  460,  and
2,400 yg/1,  respectively.   Other   frequently detected  inorganics  included
irsenic, chromium, cadmium, nickel, and  cyanide  (Table 6-20).   Twelve  of the
:hirteen  toxic metals  (antimony  excluded) were also sampled in the  special
                                    6-46

-------
TABLE 6-19.  SUMMARY OF ANALYTICAL CHEMISTRY FINDINGS FROM
             NURP PRIORITY POLLUTANT SAMPLES
(Includes information received through September 30,  1983)
Pollutant
I. PESTICIDES
1. Acrolein
2. Aldnn
3. o-Hexachlorocyclohexane (a-BHC)
(Alpha)
4. B-Hexachlorocyclohexane (6-BHC)
(Beta)
5. Y-HexachlorocyClohexane (Y-BHC)
(Gamma) (Lindane)
6. 6-Hexachlorocvclohexane (6-BHC)
(Delta)
7. Chlordane
8. ODD
9. DDE
10. DDT
11. Dieldrin
12. o-Endosulfan (Alpha)
13. B-Endosulfan (Beta)
14. Endosulfan sulfate
15. Endrin
16. Endrin aldehyde
17. Heptachlor
18. Heptachlor epoxide
19. Isophorone
?0. TCDD (2,3,7,8-tetrachlorodibenzo-
p-dioxi n)
21. Toxaphene
11. METALS AND INORGANICS
22. Antimony
23. Arsenic
24. Asbestos
25. Beryllium
26. Cadmium
27 . Chromium

28. Copper

29. Cyanides
30. Lead

31. Mercury
32. Nickel
33. Selenium
34. Sliver
35. Thallium
36. Zinc

HI. PCBs AND RELATED COMPOUNDS
37. PCB-1016 (Aroclor 1016)
38. PCB-1221 (Aroclor 1221)
39. PCB-1232 (Aroclor 1232)
40. PCB-1242 (Aroclor 1242)
41. PCB-1248 (Aroclor 1248)
42. PCB-1254 (Aroclor 1254)
43. PCB-1260 (Aroclor 1260)
44. 2-Chloronaphthalene
Cities Where Detected2

Holding times exceeded
4,7,26
7,8,22,26

7,8

7,8,22,26

7,26

2,8,21,26
Not detected
26
7
26,27
7,26,27
Not detected
Not detected
Not detected
Not detected
7,8,27
7,26
7
Not included in NURP program

Not detected

7,24,26
2,3,7,12,19,20,21,22,26,27
Not included in NURP program
7,12,20,21
1,2,3,7,12,20,21,27
1,2,7,8,12,17,19,20,21,22,26,
27,28
1,2, 3, 4, 7 ,8, 12, 17, 19, 20, 21, 22,
23,26,27,28
4,8,19,22,26,27
1,2,3,4,7,8,12,17,19,20,21 ,22,
26,28
7,20,28
2,3,7,12,20,21,26,27
7,19,23
3,17,27
7
1,2,3,7,12,17,19,20,21,22,
23,27,28

Not detected
Not detected
Not detected
Not detected
Not detected
Not detected
2
Not detected
Frequency of
Detection3


6
20

5

15

6

17

6
1
6
19




6
2
3




13
52

12
48
58

91

23
94

9
43
11
7
6
94








1

Range of Detected
Concentrations (ug/z)1*


0.002T-0.1M
0. 0027-0. 1M

0. 018-0. 1M

0. 007-0. 1M

0.004-0.1M

0.01L-10

0.007-0.027
0.1M
0.007-0.1
0.008-0.2




0.01-0.1M
0.003T-0.1M
10M




2.6-23A
1-50.5

1-49
0.1M-14
1-190

1L-100

2-300
6-460

0.6-1.?
1-182
2-77
0.2M-0.8
1-14
10-2400








0.03

                           6-47

-------
TABLE 6-19.  SUMMARY OF ANALYTICAL CHEMISTRY FINDINGS FROM
         NURP PRIORITY POLLUTANT SAMPLES1 (Cont'd)

(Includes information received through September 30, 1983)
Pol lutdnt
IV. hlALOGE^,ATEn ALIPHATICS
45. Methane, bronio- (methyl bromide)
46. Methane, chloro- (methyl chloride)
47. Methane, dichloro- {methvlene
chloride)
48. Methane, chl orodibromo-
49. Methane, dichlorobromo-
50. Methane, tribromo - (bromoform)
51 Methane, trichloro- (chluroform)
52. Hcthane, tetrachloro- (rarbon
tetrachlonde)
53. Methane, truhlorof luoro-1'
54 Methane, di chl orodi f 1 uoro-
( F reon-12) "^
55. Ethatie, chloro-
56. Ethane, 1 , 1-dichloro-
57. Ethane, 1 ,2-dichloro-
58. Ethane, 1 ,1 , 1-trichloro-
59. Ethane, 1 , 1 ,2-tr ichloro-
60 Ethane, 1 ,1 ,2 ,2-tetrachloro-
61. Ethane, hexachloro-
62. Ethene, chloro- (vinyl chloride)
63 Ethene, 1 ,1-dichloro-
b4 . Ethene, 1 ,2-trans-dichloro-
65. Ethene, trichloro-
66 Ethene, tetrachloro-
67. Propane, 1 ,2-dichloro-
68. Propene, 1 ,3-dichloro-
69. butadiene, hexachloro-
70. Cycl opentadi ene , hexachloro-
Cities Where Detected-^

hot detected
Not detected
4,17,??

28
28
28
4,17,20,22,23,27,28
4,28

2,4,24,28
Not detected

Not detected
4,28
28
4,2,7,22,24
28
4
Not detected
Not detected
28
20,28
2,4,8,24,28
8,17,22,28
28
28
Not detected
Standard methods inappropriate
V. ETHERS
7i. Ether, bi s(cMoromethyl ) 'J hot detected
72. Ether, bi s(2-chloroethyl ) Not detected
73. Ether, bi s(2-chloroisopropyl ) Not detected
74. Ether, 2-chloroethy 1 vinyl [lot detected
75. Ether, 4-bron'nphenyl phenyl Mot detected
76. Ether, 4-chl orophenyl phenyl Not detected
77. B's(^-chloroethoxy) methdne Not detected
VI. HOtiOCYCLIC ARMOMATICS (EXCLUOIIIG PHENOIS, CRESOLS, PHThALATES)
IK. benzene
79 Benzene, chloro-
80 Benzene, 1 ,2-dichloro-
83. Benzene, 1 ,3-dichloro-
82. Benzene, 1 ,4-dichloro-
83. Benzene, 1 ,2 ,4-trichloro-
84. Benzene, hexdChloro-
85. Benzene, ethyl -
86. Benzene, mtro-
87. Toluene
88. Toluene, 2,4-diriitrc-
89. Toluene, 2,6-dinitro
4,17,27
7,20,26,28
Not detected
Not detected
Not detected
Not detected
Not detected
4,8,17,20,26,28
[Jot detected
4,17
Not detected
Not detected
Frequency of
OetectionJ



11

1
1
1
9
3

5



3
1
(,
2
z


7
4
6
5
1
2











5
5





f

3


Range of Detected
Concent rat ]ofis (i,fj/. }"



5-14. 5A

2
2
1
0.2T-12L
1-2

0.6T-27



1.5A-3
4
1.6-1011
2-3
^0-3


I 5-4
1-:;
0.3T-12
1M-43
3
1-2











1-13
1G-10M





1 -2

3-1


                            6-48

-------
TABLE 6-19.  SUMMARY OF ANALYTICAL  CHEMISTRY FINDINGS FROM
         NURP PRIORITY POLLUTANT  SAMPLES1  (Cont'd)

(Includes information received  through September 30, 1983)
Pol lutant
VII PHENOLS AND CRESOLS
90. Pnenol
91 Phenol , 2-chloro-
9?. Phenol, 2 ,4-dl chloro-
93 Phenol, 2 ,4 ,6- tri chl oro-
94. Phenol, pentachloro-
95 Phenol , 2-m tro-
96. Phenol , 4-m tro-
9 /' Phenol , 2,4-dimtro-
98. Phenol , 2 ,4-dimethyl -
99. m-Ciesol, p-cMoro-
100 o-Cresol 4,6-dimtro-
1 11 I . PHTHALATE ESTERS
101. Phthalate, dimethyl
102. Phthalate, diothyl
103 Phthalate, di-n-butyl
104 Phthalate, di-n-octyl
105. Phthdlate, bi s(2-ethyl hexy! )
106. Phthdlate, butyl benzyl
l>. POKCYCLlC AROMATIC HYDROCARBONS
iO/. Ac enaphthene
108. Acenaphthylene
109. Anthracene
110. Bpnzo (a) anthracene
111. Benzo (b) fluoranthene
112. Benzo (k) tluoranthene
in Benzo (g.h.i) perylene
114. Benzo (a) pyrene
115. Chrysene
116. Dibenzo (a,h) anthracene
117. Fluoranthene
118. Fluorene
119. Inaeno (l,2,j-c,d) pyrene
120. Naphthalene
121. Phonanthrene
122. Pyrene
Cities Where Detected'

4,7,26
28
'lot detected
Not detected
4, 8, 19, 20, 26, 27, ?8
p
4,7,8,20,26,28
Not detected
4,7,8,26
4
Not detected

8
3,4,17,20,21
4,22,?4
8,20,26,27,28
4,12,19,22,21,26
2,8,26

Mot detected
Mot detected
2,17,20,21,26,28
2,21,27
26,27
2 ,21,27
2 1
2,21,26,27
2,7,17,21 ,26,27
21
2,8,12,17,21,26,27,28
28
21
4,24,26,28
2,8,17,20,21,26,27,28
2,3,8,12,17,21,26,27,28
Frequency of
Detection^

14
1


19
1
10

8
1


1
6
6
6
22
6



7
4
5
2
1
6
10

16
1
1
9
12
15
Range of Detected
Concentrations (pg/1. )""

1L-13T
2


1T-11B
1M
1T-37

1T-10M
1.5A


1L
1-10M
0.5T-11
0.4T-2C
4T-62
1-10N



1-10C
1-10M
1-S
4-14
5
i-ioc,
0 6~-10H
:1
G.3T-21
1
4
0 8T-2.3
(1.3T-10M
0 3T-16

-------
           TABLE  6-19.    SUMMARY OF  ANALYTICAL  CHEMISTRY FINDINGS FROM
                        NURP PRIORITY POLLUTANT  SAMPLES1   (Cont'd)


            (Includes  information  received  through  September 30,  1983)
Pollutant
X. NITROSAMINES AND OTHER NITROGEN-CONTAININC
123. NUrosamine, dimethyl (OMN)
124. Ni trosamine , diphenyl
125. Nitrosamine, di-n-propyl
126. Benzidine
127. Benzidine, 3,3'-dichloro-
128. Hydrazine, 1 ,2-diphenyl -
129. Acrylomtnle
Cities Where Detected2
COMPOUNDS
Standard methods inappropriate
Standard methods inappropriate
Not detected
Standard methods inappropriate
Not detected
Standard methods inapproonate
Holding times exceeded
Frequency of
Detection3

Range of Detected
Concentrations (ug/l)1*

1   Based on 121 sample results received as of 9/30/83,  adjusted for qua'ity control  review.

2   Cities from which data are available:

      1. Durham, NH                 20.  Little Rock, AR
      2. Lake Quinsigamond, MA        21.  Kansas City, KS
      3. Mystic River, MA            22.  Denver, CO
      4. Long Island, NY             23.  Salt Lake  City
      7. Washington, DC              24.  Rapid City, SO
      8. Baltimore, MO              26.  Fresno, CA
     12. Knoxville, TN              27.  Bellevue,  WA
     17. Glen Ellyn, IL              28.  Eugene, OR
     19. Austin, TX

     Numbering of cities conforms to NURP convention.
UT
3  Percentages rounded to  nearest whole number.
h  Some reported concentrations are qualified by STORE! quality control remark codes,  to wit:  A = Value reported is  the
   mean of two or more determinations; S = Value reported is the maximum of two or more determinations; L = Actual  value
   is known to be greater  than value given; M = Presence of material  verified but not  quantified; T = Value reported  is
   less than criteria of detection.  One value in this column indicates one positive observation or that all  observations
   were equal.
5  No longer included as a priority pollutant.
                                                   6-50

-------
         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.  ot-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.
                                    6-51

-------
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 odor)  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  a  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  (ot-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 exceedances  were  less  frequently  observed  among  the  organics than
the  inorganics.    One  unusually  high  pentachlorophenol  concentration  of
115 ng/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 pentochlorophenol,  bis  (2-ethylhexyl)  phthalate, y-hexachlorocyclohexane
(Lindane), a-endosulfan, and  chlordane.   All other  organic exceedances were
in  the  human  carcinogen  category  and were  most serious  for  a-hexachloro-
cyclohexane  (a-BHC),  •y-hexachlorocyclohexane  (y-BHC or  Lindane), chlordane,
phenanthrene, pyrene, and chrysene.
                                    6-52

-------
    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 CRITERIA1
Pollutant
1. PESTICIDES
3. a-Hexachlorocyf lohexanp
5. Y-Hexarhlorocyclohexane (Lindane)
7. Chlordanp
1J. a-Endosulfan
II. METALS AND INORGANICS
?2. Antimony
23 . Arsenic
25. Beryllium
26. Cadmium-
27. Chromium-16
28. Copper5
29. Cyamdes
30. Lead'
32. Nirke!5
33. Selenium
36. Zinc5
IV. HALOGENATED ALIPHATICS
47. Methane, dichloro-
V!I. PHENOLS AND CRESOLS
90. Phenol
94, Phenol, pentachloro-
96. Phenol , 4-nitro-
VIII. PHTHALATE ESTERS
105. Phthalate, bi s(2-ethylhexyl )
IX. POLYCVCLIC AROMATIC HYDROCARBONS
115. Chrysenp
117. Fluoranthene
121 . Phenanthrene
1?2. Pvrene
Frequency of
Detection (° )

20
15
17
19

13
52
12
48
58
91
23
94
43
11
94

11

14
19
10

22

10
16
12
15
Detections/
Samples^

21/106
15/100
7/42
9/49

14/106
45/87
11/94
44/91
47/81
79/87
16/71
75/80
39/91
10/88
88/94

3/28

13/91
21/111
11/107

15/69

11/109
17/109
13/110
16/110
Criteria Exceedances (' \
None






X













X

X




X


FA



2





8

47
3
23


14




1*








FC


8
17
10



6*
48
1*
82
22
94
5
5
77




11*


22*





OL





















1








HH









1


4
73
21
10














HC'

8,18,20
0,10,15
17,17,17



52,52,52
1?,12,12









0,0,11







10,10,10

12,12,12
15,15,15
DW







1

1
1


73

10














Indicates FTA or FTC value substituted where FA or  FC criterion  not available (see bellow).
Based on 121 sample results received as of September 30,  1983, adjusted for quality control review.
Number of times detected/number of acceptable samples.
 FA  - Freshwater ambient 24-hour i nstantaneous maximum cri ten on ("acute" en ten on).
 FC  = Freshwater ambient 24-hour average criterion  ("chronic" criterion).
FTA  = Lowest reported freshwater acute toxic concentration.  (Used only when FA is not ava"" 1 able. ^
FTC  = lowest reported freshwater chronic toxic concentration. (Used only when FC  is not available.1
 OL  = Taste and odor forganoleptic)  criterion.
 HH  = Non-Carcinogenic  human health  criterion for ingestion of contaminated water  and organisms.
 HC  ~ Protection of human health from carcinogenic  effects for ingestion of contaminated water and organisms
 DW  = Primary drinking  water criterion.
Fntries in this column  indicate exceedances of the  human  carcinogen value at the 10 ,10 , and  10   risk level,  respectively.  The
numbers are cumulative, i.e., all 10~ exceedances  are included  in 10  exceedances, and all 10  exceedances are  included in 10
exceedances.
Where hardness dependent, hardness of 100 mg/1 CaCO, equivalent  assumed.
Different criteria are  written for the trivalent and hexavalpnt  forms of chromium.  For purposes  of this analysis, all chromium is
assumed to be in the less toxic trivalenT form.
                                                  6-53

-------
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 PCB group, there was only a single detection  of one PCB type among
all the samples.  Approximately  two-thirds  of the  halogenated 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-ethylhexyl)  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  phthalates,   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  nitrosamines  or other  nitrogen-containing com-
pounds.  Due  to methodological  and 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 riot  detected in any  acceptable runoff sam-
ples (Table 6-22).  All of these pollutants are  organics.  This group of sub-
stances  should  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
water  quality  criteria which are below the limits of  detection of   routine
                                    6-54

-------
           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.  Trichloromethane  (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.  B-Hexachlorocyclohexane  (5%)
     53.  Trichlorofluoromethane  (5%)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 epoxide  (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 (1%)*
     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-Chloropheno:  (1%)*
     95.  2-Nitrophenol  (1%)*
     99.  p-Chloro-m-creosol  (1%)*
    101.  Dimethyl phthalate  (1%)*
    116.  Dibenzo(a,h)anthracene  (1%)*
    118.  Fluorene  (1%)*
    119.  Indeno(l,2,3-cd)pyrene  (1%)*

                                   6-55

-------
       TABLE 6-22.  INFREQUENTLY DETECTED ORGANIC PRIORITY
        POLLUTANTS IN NURP URBAN RUNOFF SAMPLES1 (Cont'd)
         Priority Pollutants Not Detected in NURP Samples

  8.  ODD
 13.  g-Endosulfan
 14.  Endosulfan sulfate
 15.  Endrin
 16.  Endrin aldehyde
 21.  Toxaphene
 37.  PCB-1016
 38.  PCB-1221
 39.  PCP-1232
 40.  PCB-1242
 41.  PCB-1248
 42.  PCB-1254
 44.  2-Chloronaphthalene
 45.  Bromomethane (methyl bromide)
 46.  Chloromethane (methyl chloride)
 54.  Dichlorodifluoromethane (Freon-12)2
 55.  Chloroethane
 61.  Hexachloroethane
 62.  Chloroethene (vinyl chloride)
 69.  Hexachlorobutadiene
 71.  Bis(chloromethyl)  ether2
 72.  Bis (chloroethyl) ether
 73.  Bis(chloroisopropyl) ether
 74.  2-Chloroethyl vinyl ether
 75.  4-Bromophenyl phenyl ether
 76.  4-Chlorophenyl phenyl ether
 77.  Bis(2-chloroethoxy) methane
 80.  1,2-Dichlorobenzene
 81.  1,3-Dichlorobenzene
 82.  1,4-Dichlorobenzene
 83.  1,2,4-Trichlorobenzene
 84.  Hexachlorobenzene
 86.  Nitrobenzene
 88.  2,4-Dinitrotoluene
 89.  2,6-Dinitrotoluene
 92.  2,4-Dichlorophenol
 93.  2,4,6-Trichlorophenol
 97.  2,4-Dinitrophenol
100.  4,6-Dinitro-o-cresol
107.  Acenaphthene
108.  Acenaphthylene
125.  Di-n-propyl nitrosamine
127.  3,3'-Dichlorobenzidine
                               6-56

-------
            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.  Hexachlorocyclopentadiene
     123.  Dimethyl nitrosamine (DMN)
     124.  Diphenyl nitrosamine
     126.  Benzidine
     128.  1,2-Diphenyl hydrazine
     129.  Acryloriitrile

*  Detected in only one or two samples.

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

^  No longer on the priority pollutant list.
analytical methods.  Some  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, 1,2-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  not  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 6-19 illustrates the relationship between percent  impervious area and
the median runoff coefficient  for the site.   Sites which monitored fewer than
5 storms are   excluded.  The upper plot (a)  groups the  results from 16 of the
                                    6-57

-------
w
H
CO
W
CO
Q
O
CO
E-i
CJ
M
tw
CM
W
O
U
O
a
CM
 I
W
                                                       6-58

-------
         o
         E
         LL.
         O
         u
I.U
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
n








0
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0
0 .
•
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6






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«






a
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              0   10   20   30   40   50  60  70   80  90  100
                            % IMPERVIOUS
                       (a)   16 Projects
I.U
0.9
0.8
<£ 0.7
i—
1 0-6
iz
g 0.5
o
fe 0.4
« 0.3
0.2
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0


             0   10   20  30  40  50  60  70   80   90  100
                           % IMPERVIOUS

            (b)   4 Projects  (KS1, Mil, TNI,  TX1)
Figure  6-19.   Relationship Between Percent Impervious Area
                and Median  Runoff Coefficient
                             6-59

-------
20 projects  investigated.   The  lower  plot  (b) groups  results from  the re-
maining four projects (KS1, Mil, 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 6-37,  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 variability  of  EMC's  at urban  sites.   The
range  in  values shown  for use  in  the load  comparisons  below 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 (mg/1)
Sol. P (mg/1)
TKN (mg/1)
NCL -N (mg/1)
2+3
Tot. Cu (ug/1)
Tot. Pb (ug/1)
Tot. Zn (ug/1)
Site Mean EMC
Median
Urban Site
141 - 224
10 - 13
73 - 92
0.37 - 0.47
0.13 - 0.17
1.68 - 2.12
0.76 - 0.96
38 - 48
161 - 204
179 - 226
90th Percentile
Urban Site
424 - 671
17 - 21
157 - 198
0.78 - 0.99
0.23 - 0.30
3.69 - 4.67
1.96 - 2.47
104 - 132
391 - 495
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
43 - ]18
182 - 443
202 - 633
                                    6-60

-------
         0   10  20  30  40   50   60  70  80  90   100
                        % IMPERVIOUS
                    (a)   16 Proiects
        1.0
        0.9
        0.8
        0.7
        0.6
        0.5
     it 0.4
        0.3
        0.2
        0.1
          0   10  20  30  40   50   60   70   80   90  100
                         % IMPERVIOUS

         (b)  4  Projects  (KS1, Mil,  TNI, TK1)
Figure  6-20.   90  Percent  Confidence  Limits  for Median
                   Runoff Coefficients
                           6-63

-------
It is a straightforward procedure to calculate mean annual load estimates for
urban runoff constituents on a Kg/Ha basis  by assigning appropriate rainfall
and  runoff  coefficient values  and selecting  EMC  mean  concentration  values
from Table 6-24.  In and of themselves, however,  such estimates see;m to be of
little utility.   Therefore,  it was  decided to do  a comparison of  the  mean
annual loads from urban runoff with those of a "well run" secondary treatment
plant.  We chose to use TSS = 25 mg/1,  BOD = 15 mg/1, and Tot.  P = 8 mg/1 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 = -if =  0.8 ;  Tot.  P = ^~ ~  0.05
                  2b              ID                    o

using typical urban runoff values, and;

          TSS - 548  s 22   BQD = 19 ^  1>3   Tot>  p = 2,88 ^ ^
                 2.b               ID                     o

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

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


     TSS =    -     * 7% ; BOD =         = 37% ' Tot' p -- ^ 83%
for our typical case, and;


     TSS =       lf * 3% ? BOD " lfr-15 = 29% '•  Tot' p = oTeir-a * 79%
                                    6-62

-------
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:
    TSS .          = W , BOD .
for our typical case, and;

   Too _ 548 - 55 __     _      _ 19-8  ^     _         _ 0.88 - 0.44 ^
   TSS ~ 548 + 25 ~ 86° ;  B°D - 19 + 15 ~ 32* ' T°tal P ~  0.58 + 8   ~ 5%


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 cases  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/Ha/year,  for  comparison with
other data  summaries of  nonpoint 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  (based 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
land 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 have been computed on the basis
of a 40  inch  annual rainfall volume.  For urban areas in regions with higher
                                    6-63

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              TABLE 6-25.  ANNUAL URBAN RUNOFF LOADS KG/HA/YEAR
Constituent
Assumed Rv
TSS
BOD
COD
Total P
Sol. P
TKN
N02+3-N
Tot. Cu
Tot. Pb
Tot. Zn
Site Mean
Con.mg/1

180
12
82
0.42
0.15
1.90
0.86
0.043
0.182
0.202
Residential
0.3
550
36
250
1.3
0.5
5.8
2.6
0.13
0.55
0.62
Commercial
0.8
1460
98
666
3.4
1.2
15.4
7.0
0.35
1.48
1.64
All Urban
0.35
640
43
292
1.5
0.5
6.6
3.6
0.15
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.
                                    6-64

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                                   CHAPTER 7
                RECEIVING  WATER QUALITY  EFFECTS  OF  URBAN  RUNOFF
 INTRODUCTION

 The  effects of urban runoff on  receiving  water quality are very  sdte  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 others 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  to make  useful  generalizations  regarding the quantitative effects  of
 urban  runoff on concentrations of various pollutants in  the receiving  waters
 and  to draw 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;

      (1)   Denial  or serious  impairment  of  beneficial use;
                                      7-1

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     (2)  Violation of ambient water quality standards; and

     (3)  Local perception;

will result in a high  degree  of  site-specificity to the determination of the
existence of a problem.

RIVERS AND STREAMS

General

Flowing 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 (URO),  the average  concentrations  in
such pulses vary,  as  do their duration  and the  interval  between successive
pulses.   Table 7-1 summarizes average values for storm duration and intervals
between storm events for selected locations in the U.S., based on analysis of
long  term rainfall  records  using  a  methodology  (SYNOP)  presented   in  an
earlier NURP  document   (the  NURP Data  Management  Procedures Manual).   The
information presented provides a sense of the temporal aspects of such inter-
mittent pulses and, by inference, the intermittent exposure patterns to which
stream biota  are  subjected.   For many  locations, storm pulses  are produced
for about six hours every three days or more,  on average.

A probabalistic methodology has  been used  to  examine  the  concentration char-
acteristics of the storm pulses produced in streams, given the variability of
the relevant processes which  are directly  involved.   Stream flow rates, run-
off flow rates, and concentrations vary and result in variable stream concen-
trations.   For streams, it is not the runoff volume per se that is important.
The combination of stream and runoff flow rates  (together with runoff concen-
tration)  determine the  pollutant concentration  in the  stream  pulse.   The
duration  of  the  runoff  event and  the stream  velocity  dictate  the  spatial
extent  of the storm  pulse in the  stream.  The  analysis  presented  in this
section addresses  the  frequency  and  magnitude  of pollutant concentrations in
the instream storm pulses which are produced.

Runoff and Stream Flow Rates

The local combination  of stream  and runoff flow  rates  for an urban location
are, as indicated, important  determinants  of  the stream concentrations which
will result.   For  long-range projections,  the  most appropriate  data sources
for characterizing these parameters are long-term stream flow gauging records
(USGS)  and long-term rainfall records  (USWS).

Figure 7-1 (a)   illustrates  the  regional  variation  of  average  daily  stream
flows expressed as cfs/sq mile of drainage area, based on  long-term (50 years
or  more)  gauging   records  at over  1000  stations.  Figure 7-1(b)  presents  a
somewhat  simplified  regional pattern  for  average  rainfall  intensity.   The
data base for  this  plot  is  considerably smaller,  consisting   of  rainfall
records   (usually   10  to  30  years of  record)  for approximately  40 cities.
Localized peturbations exist, but are smoothed out by contours presented.
                                     7-2

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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, MI
Gainesville, PL
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, SD
Salt Lake City, UT
Mean
Portland, OR
Seattle, WA
Mean
Average Annual Values in Hours
Storm
Duration
8.0
7.2
6.1
5.8
6.1
5.7
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
4.3
3.2
8.0
7.8
6.5
15.5
21.5
18.5
Time Between
Storm Midpoints
94
85
68
55
80
72
68
98
57
106
70
80
76
89
89
87
89
77
79
93
62
80
77
81
144
320
286
127
133
202
83
101
92

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 Figure  7-1(a).   Regional Value of  Average Annual Streamflow (cfs/sq mi)
 .025
                                      03
                        045
                          .055
                            .065
                                                                     .105
                                                                   125
                               .075
Figure 7-1(b).   Regional Value of Average Storm Event Intensity (inch/hr)
                                     7-4

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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 all 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 has been done, and 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.   A greater
data base on rainfall  and stream flow would permit greater spatial  definition
                                     7-5

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                                                 7-6

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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




I
L
3
4
5
6
7
8
Event Average
Rainfall Intensity
Mean
(in/hr)
0.04
0.10
0.08
0.055
0.04
0.03
0.045
0.025

C. V .
1.00
1.35
1.35
1.25
1.10
1.10
1.20
0.85
Average
Number
of
Events/year
110
100
90
110
63
70
30
80
Average
Runoff Flow Rate
Mean Event
( c f s / s q mi)
5
1?
10
7
5
4
5
3

c .v .
0.85
1.15
1.15
1.05
0.95
0.95
1.00
0.75
Stream Flow Rate
(Dai ly Avq Flows)
Mean
(cfs/sq mi )
1.75
1.25
1.00
0.75
0.35
0.05
0.05
4.50

c.v .
1.25
l.?5
1.25
1.25
1.25
1.25
1.25
1.25
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 on computed values for
a sample of about 150 perennial streams.  Results for  a number of regional
                                     7-7

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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
1.25 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 of 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
are listed  in Table 7-3,   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 data 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 yg/1)



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

15

35

90
Coef
Var

C.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

0.8
An illustrative example  of  a site-specific application  of  the probabilistic
analysis methodology employed is presented in order to:
     1.  Illustrate the nature of the computational results produced;

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

     3.  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 a 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  selected  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 degree of im-
pairment of this beneficial use.
                                    7-10

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  100
                 99
                          90
                                                  10
                                                         COPPER
                                                 STREAM TOTAL HARDNESS = 50 mgll
                                                   DRAINAGE AREA RATIO = 100
                 1         10          50          90
                       PERCENT OF STORM EVENTS EQUAL TO OR LESS THAN
Figure  7-4.   Probability Distributions  of Pollutant Concentrations
                        During Storm  Runoff Periods
                                                       COPPER
                                               STREAM TOTAL HARDNESS - 50 mgll
                                                 DRAINAGE AREA RATIO - 100
                            1       2         5
                           MEAN RECURRENCE INTERVAL YEARS
  Figure  7-5.   Recurrence Intervals for  Pollutant  Concentrations
                                     7-1]

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The projection labeled  "treated  urban  runoff"  may be taken  to  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 averacje,
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  controJ  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  vie;w,
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  to the average  urban  site.   Since
NURP analysis data  indicate that the  copper in urban  runoff has  a soluble
fraction of  about  40  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 7-2.  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 levels 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 presented 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 diffe;rent geographical
region, and  the  analysis is performed  for  two drainage  area ratios.  Since
regional  stream  flow  differences  are  based  on unit  flows  (cfs/sq mile of
drainage area), actual flow in a receiving stream at a particular location is
                                    7-12

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       TABLE  7-4.  REGIONAL DIFFERENCES  IN  TOXIC  CONCENTRATION  LEVELS
                           (Concentrations in  yg/1)

Pollutant
Copper


Lead


Zinc


Stream
Total Hardness
yg/i
50
200
300
50
200
300
50
200
300
Geo-
graphic
Regions
1,2,3,8
4,5,7
6
1,2,3,8
4,5,7
6
1,2,3,8
4,5,7
6
FPZX
MAX
12
42
62
74
400
660
180
570
800
Suggested Values For
Threshold
Effects1
20
80
115
150
850
1400
380
1200
1700
Significant Mortality2
(a) (b)
50
180
265
350
1950
3100
870
2750
3850
90
350
500
3200
17,850
29,000
3200
8000
11,000
        Threshold  Effects  -  mortality of the  most sensitive  individual
        of the most sensitive species.


        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
drainage area.
both  the  unit  flow rate
The  "drainage  area  ratio"
and  the  size  of  the  contributing
(DAR)  used  in the  analysis  is
                   Urban Area Contributing Runoff
                 — ~ ~ ~~: - - - - - --- -     -_-,™™.L-.,.— _..      —
                   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  DAR = 10, are
projected to be as follows  (middle plot, Figure 7-6) .

        EPA  MAX - ambient  criterion  is  exceeded  at   a   frequency  of
        0.02 year (= 50 times/year) or about  every  other storm event on
        average.
                                    7-13

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        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 tc 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  arid  streams.
Water  quality impacts can  vary widely, depending on regional  rainfall and
stream  hydrology,  urban  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 and  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/sq  mile)  than for  lower
stream flow regions.

Finally, the  quality  characteristics  of the urban sites have  a  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 by the  NURP data base.
                                    7-17

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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 thar  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  aquatic  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  is 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  EPA 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  a  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 been  performed using  the  total  fraction,   since  adequate
                                    7-18

-------
information  is  not  available  at present  to  reliably  adjust  these  values.
However, although the problem assessment presented above may be somewhat con-
servative, further refinement  along  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 DARs,  and sites
with high zinc concentrations in urban runoff.

Lead results must  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  of low DAR  and   high  site
concentration.

In performing 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 of  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  on a broad range  of species.   This
        is  in  contrast  to  lead and  zinc  for  which   a  substantially
        greater degree  of  species selectivity  is indicated.   Some  spe-
        cies are  sensitive,  others relatively  insensitive  to  lead and
        zinc.

        From the  NURP  data, locations  which tend  to  have site  median
        concentrations   in  the  low,  average, or high  end  of  the  range
        have generally  consistent patterns  for each of  the  three  heavy
        metals.
                                    7-19

-------
        Control measures which  produce reductions in  copper  discharges
        to receiving  waters  could be  expected to result  in  equivalent
        reductions in zinc, and 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
are representative.  This has been confirmed by a number of validation tests,
discussed in the NURP 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 NURP projects examined aquatic  life  effects in streams receiving
runoff from monitored sites.

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

        Tampa, PL conducted extensive bioassay 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 conditions at low  DAR for
        this geographic region.   At this project however,  all monitored
        sites show  heavy metal concentrations significantly  lower than
        the low  range  conditions used in  the  screening analysis.   When
                                    7-20

-------
        the  screening  analysis  is  repeated  using  site concentrations
        representative  of  Tampa  monitoring results, a problem  situation
        is not  predicted,  even at DAHs  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  concentrations  have been converted
to site  mean values for use  in the  computations.

Lake  phosphorus  concentrations  are  also  influenced  by  the  annual  runoff
volume   (annual precipitation  and   runoff  coefficient).   The  results  illus-
trated are  based  on  an  annual  rainfall of 30 inches and  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 used
in the illustration.

Finally, the  lake morphology and hydrology influence  the outcome; specific-
ally depth  (H)  and residence  time  (T) .   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  and  nonpoint)
                                    7-21

-------
   1000
3-

z
o
o
o
BE

O
o.
en
             URBAN SITE QUALITY

               CHARACTERISTICS
              SITE MEAN TP CONCENTRATION )jg/l
                            HIGH RANGE


                            AVERAGE


                      CT1  LOW RANGE
                                          ANNUAL RAINFALL  = 30 inlyear

                                        RUNOFF COEFFICIENT  = 0.2
                                           DEPTH/RESIDENCE

                                           RATIO FOR LAKE
                  H|T= 1 to  10m(yr
                                          SETTLING VELOCITY Vs  = iflmlyr

                                           (TOTAL P)
                                                                                 1000
                                  RATIO
   URBAN AREA

LAKE SURFACE AREA
  Figure 7-9.   Effect of Urban  Runoff on Lake Phosphorus  Concentrations
                                         7-22

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

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

     -  Irondequoit  Bay,  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  considered 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 management
        plan.

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 NTIS
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, no general assessment  for water bodies of this  type can  be made
at this time.
                                    7-23

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GROUNDWATER AQUIFERS

Much of  the  precipitation which falls on an  area  either percolates directly
into the ground,  or  does  so after relatively short  overland  flow distances.
This condition  is essentially  uncontrollable and distinctly  different  from
the case where  urban runoff from impervious  areas is  deliberately collected
and routed to a recharge device which causes it to percolate to groundwaters.

This type of control approach is a practical  and  effective  technique for re-
ducing pollutant  loads which would  otherwise reach  surface  waters  as  dis-
cussed in Chapter 8.  The concern addressed here  is  with the  extent to which
groundwater aquifers may be contaminated by this practice.

The Long Island, NY and Fresno, CA NURP  projects  examined this issue through
extensive tests utilizing recharge  basins ranging from  recent installations
to  others  which  have  been  in  service  in  excess of  20 years.   A somewhat
simplified consolidation  of the salient findings of  these two  projects  is
presented below.  The interested reader is referred to the individual project
report  documents, available  through  NTIS,   for  the  important  details  and
qualifications.

        Most pollutants  of importance  in urban runoff  are intercepted
        during  the  process  of  infiltration   and   quite   effectively
        prevented  from  reaching  the  groundwater  aquifers  underlying
        recharge basins.  The pollutants tested and  found  to  behave in
        this manner  include  the heavy metals, an  appreciable  number of
        the  organic  priority pollutants and  pesticides,  and  coliform
        bacteria.

        Chlorides,  which  are   sometimes present  in  urban  runoff  at
        elevated  concentrations due  to road  deicing practices,  are not
        attenuated during recharge.

        Pollutants accumulate  in the  upper  soil  layers.  The  concen-
        trations found are a function of  the  length  of time a basin has
        been in service.  Effective  retention of  pollutants takes place
        with all  soil  types tested,  ranging from clays to  sands.  The
        depth of pollutant penetration is affected by soil type; however
        in no  case did  contaminant  enrichment  of  soil  exceed several
        meters  depth,  and  highest  concentrations were  found  near the
        surface.

        The limit of the ability of  the soil to retain the pollutants of
        interest is unknown.  Additional  study of  this aspect is appro-
        priate.  However  given  the  long service periods  of a  number of
        the recharge basins  studied,  this does not  appear  to represent
        an imminent concern.

        At both of these NURP  locations, groundwater surfaces  were at
        least 20 feet,  and often appreciably more, below the base of the
        recharge device.  The  indicated findings may not be  applicable
        at locations with shallow depths to groundwater.
                                    7-24

-------
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.
                       7-25

-------
                                  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 discussed  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  EPAs 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  or  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  runoff 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; and porous
        pavements.

     -  Housekeeping Practices - These are principally  street  sweeping,
        but also  include sidewalk cleaning,  litter containers,  catch-
        basin  cleaning,  etc.
                                     8-1

-------
        Other - These include  the  so-called  "living filter" sipproaches,
        grassed swales,  wetlands, etc.

DETENTION DEVICES

General

Detention basins  proved to be one of the most popular approaches  to urban
runoff quality  control  selected at the  local  level,  based on the  number of
individual projects which  elected  to  study them and  the number  of  detention
devices tested  in  the study.   It is perhaps  instructive to note  that nearly
all  the  detention facilities  studied were either  already  in place,  or  re-
quired  only  modifications  of  outlet structures  before initiation of  the
NURP-supported  studies.   In general,  detention  devices proved to  provide  a
highly effective  approach  to  control of urban runoff  quality,  although  the
design concept has a significant bearing on performance characteristics.

Table 8-1 lists the NURP projects that included detention devices 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  other relevant  activities.  As  a  result, not all  of  the sites
are incorporated in the summary presented below.   The Washington Area Council
of Governments  (WASHCOG) conducted a  particularly  thorough  and comprehensive
investigation of  control  techniques, particularly  detention basins.   They
have prepared several useful  and informative  analyses of performance results
on these devices.

Dry Basins

This is  a type  of detention  basin which is  currently in fairly  extensive
service in various parts  of the country.  The performance  objective of such
basins is commonly called "peak  shaving", that is,  to limit the  maximum rate
of runoff  to some preselected magnitude, usually  a  maximum  pre-developmerit
rate.   The  purpose is  to  control  flooding  and erosion  potential  in  areas
downstream of new development.  Such  basins  employ a bottom  outlet having a
hydraulic capacity  restricted  to  the maximum  allowable  flow.   Runoff from
smaller storms  flows along  the bottom of the  basin and is  discharged without
restriction.   Flows in  excess of  design  are  backed up in  the basin tempor-
arily and ponding occurs  only during larger storms and for relatively short
periods of time.  This class of retention basin is thus normally dry.

Performance  of  such  basins,   from a pollutant  removal  aspect,  range from
insignificant to quite poor.  Accordingly, the limited data available are not
discussed in this chapter.

Wet Basins

This designation  covers detention  basins which maintain a  permanent pool of
water.   They may vary  considerably  in  appearance,  ranging  from natural
ponds or small  lakes dedicated urban runoff  control to  enlarged sections in
                                      3-2

-------
           TABLE 8-1.  DETENTION BASINS MONITORED BY NURP 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 data  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.
                                     8-3

-------
There are a number of ways  to  characterize  detention basin performance.   The
primary basis  selected  by NURP 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  NURP
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  -5-  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  timess 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 for 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 an urban  runoff detention device.
                                     8-4

-------
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-------
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 to  catchment size and  hence  the
magnitude of the runoff processed.   Giving  greater  weight  to the sites moni-
toring large numbers of storms,  indications are 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 -t-  NC^) .   The positive removal  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  and  zinc which  have high (40 to 60  percent)  soluble
fractions show an ambiguous pattern with regard to changes in variability.

In  a  few of  the cases where  atypical results are indicated,  unique local
conditions suggest  plausible  explanations.   For example,   at  the  Ann Arbor
(Traver)  site, erosion from an unstabilized bank at the outlet of this newly
constructed basin  is  attributed  to the  poor  suspended solids removal  ob-
served.  The  poor  removal characteristics  at   the  Unqua  site  for TKN  and
nitrate may be  associated with  the  significant wildfowl population  at this
site.

-------
             TABLE  8-3.   OBSERVED  PERFORMANCE OF WET DETENTION BASINS
                    (PERCENT  REDUCTION  IN  POLLUTANT CONCENTRATIONS)
(a)   Mean  EMC
Project
and
Site
Lansing
Grace St. N.
Lansing
Grace St. S.
Ann Arbor
Pitt-AA
Ann Arbor
Traver
Ann Arbor
Swift Run
Long Island
Unqua
Washington, D.C.
Westleigh
Lansing
Waverly Hills
NIPC
Lake Ellyn
No.
of
Storms
(1)

23/20

18/17

6/6

5/5

5/5

8/8

40/40

35/30

25/20
Percent Reduction in Mean EMC
TSS

(6)

22

38

0

83

34

83

87

92
BOD

(26)

4

17

(66)

11

COD

15

(3)

23

12

(3)

(TOC=26)



52



33

52

64
TP

(10)

6

28

37

(38)

38

59

69

61
Sol.P

(26)

0

(2)

63

21



70

56

62
TKN

11

(5)

11

19

25

(31)

19

30

•
N02+3

(1)

(20)

8

28

77

(10)

28

54

82
T.Cu

(9)

25

•

•



•

10

53

88
T.Pb

39

14

59

•

86

78

•

93

91
T.Zn

(9)

7

22

19





10

58

87
(b)   Coefficient of Variation of  EMCs
Project
and
Site
Lansing
Grace St. N.
Lansing
Grace St. S.
Ann Arbor
Pitt-AA
Ann Arbor
Traver
Ann Arbor
Swift Run
Long Island
Unqua
Washington, D.C.
Westleigh
Lansing
Waverly Hills
NIPC
Lake Ellyn
No.
of
Storms
(1)
23/20
18/17
6/6
5/5
5/5
8/8
40/40
35/30
25/20
Percent Reduction in Coef of Variation of EKCs
TSS
14
(7)
17
14
(5)
(87)
46
38
44
BOD
49
(59)
(6)
(109)
39
(TOC=
•
5
•
COD
35
39
10
58
50
66)
(26)
69
41
TP
(7)
13
28
(3)
(150)
47
15
34
71
Sol.P
(13)
0
(84)
42
0
•
20
26
48
TKN
30
20
37
(150)
20
19
41
(8)
•
N02t3
0
21
0
(82)
(150)
(66)
(280)
(198)
(115)
T.Cu
0
17
•
•
•
•
0
(22)
60
T.Pb
45
18
53
•
26
65
•
34
19
T.Zn
(31)
15
(5)
0
•
•
(14)
(36)
41
       Notes:  (1)  In/Out; numbers are approximate, and vary with pollutant.  Removals in parentheses indicate
                  negative removal.

              Dot  (•) indicates pollutant either not monitored or number of observations is too small for
                  reliable estimate  of percent  reduction.
                                               8-8

-------
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/100 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  well 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 WASHCOG 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 8-4,
showing percent reductions in 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 P and Nitrate/Nitrite)  are not
        effectively reduced  because of the  absence  of  a permanent pool
        within which biological  reactions have an opportunity to occur
        in addition to sedimentation.
                                     8-9

-------
     -  The  variability  of  pollutant  EMC's  does  not  appear  to  be
        modified to the extent  that this occurs in wet ponds.
                TABLE 8-4.   PERFORMANCE CHARACTERISTICS OF A
                        DUAL-PURPOSE DETENTION DEVICE

               (Stedwick Site - Washington Area NURP Project)
Pollutant
TSS
COD
Total P
Sol P
TKN
Organic N
N°2+3
T. Cu
T. Pb
T. Zn
Percent Reduction In
Pollutant Mass
Load Over All
Monitored Storms
64
30
< 15
1
•
30
10
•
84
57
Pol!
El
Mean
63
41
11
(4)
8
•
13
•
•
42
.utant
IC's
Coef Var
(31)
17
0
(13)
(11)
•
6
•
•
33
Although the performance characteristics of basins of this type are indicated
to be  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,  the  only  changes
required would be an alternate specification of the outlet design.

Costs

The information  presented here  is  intended to provide  an order of magnitude
estimate of the cost of providing different levels of control of urban runoff
pollutant discharges,  whan wet detention devices  are used as  the best manage-
ment practice  (BMP).   The  summary  is based on  the size versus  performance
relationship presented  earlier in Figure 8-1 and on the size versus cost re-
lationships presented below.
                                    8-10

-------
The  analysis  is  based on  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 and
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.  Amoritization  of costs is based  on a
20 year basin  life and an interest rate of 10 percent.
                                    8-11

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The performance  levels  associated  with a particular basin  size  are  shown at
the top  of  the plots as  a  range for long-term average  removal  efficiencies
for TSS.  The  range  associated with a particular  size  reflects  the  regional
differences in performance which can be  expected  (Figure  8-1)  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  NURP  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  NURP  data  and
analysis methods,  if  local rainfall and  land use  characteristics,  and design
and planning preferences are utilized.

The  generalized  relationships shown  by  Figure  8-3 can  be  summarized  as
follows, if an urban catchment size of 20 to 40 acres is 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
(% TSS Reduction)
50
90
50
90
Cost Per Acre of Urban Area
(Approximate)
Present
Value
$500 - $700
$1000 - $1500
$100
$250
Annua L
Cost
$60 - $80
$125 - $175
$10
$25
RECHARGE DEVICES

Control measures which enhance the infiltration of urban runoff are indicated
by the NURP 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 NURP document  on
detention basins.

The  issue  of  the potential  contamination  of groundwater  aquifers  due  to
enhanced  infiltration of  urban  storm  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,
depth  to  groundwater,   and  the  proximity  of  water   supply  wells.   Sound
planning and engineering judgement  must be  applied to  determine the accept-
ability of this control approach in a local situation.

however, where local conditions premit,  a wide variety of design concepts are
available  for  use.   These  range  from  off-site  applications consisting  of
                                    8-14

-------
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 of 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 99 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.  Basin 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 area equal to 0.10 percent  of an urban catchment represents a
design  which  provides (43,560 sq ft/acre x 0.10/100% =) 43.5 square feet of
                                    8-15

-------
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 0.05       .10                  0.5       1.0

PERCOLATING AREA AS % OF CONTRIBUTING CATCHMENT AREA
                                                                                      5.0
                                                                        GREAT LAKES PRECIP
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                                                                      H = HASIN DEPTH (FEET)
                          O.OS       .10                    0.5        1.0

                         PERCOLATING AREA AS S OF CONTRIBUTING CATCHMENT AREA
  Figure 8-4.   Long  Term Average Performance of  Recharge Devices
                                            8-16

-------
percolating  surface  area for  each  acre of  urban catchment it  serves.   The
long-term average reductions in urban  runoff volume  and 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-
ability 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  a 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.

Recognizing  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  and dryfall),  street surface accumula-
tion and washoff, and street sweeper removal rates and costs.  The individual
project reports  look at these other  issues,  and  the  results are not repeated
herein.  Of prime interest and provided below is the effectiveness of street
sweeping  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.
                                    3-17

-------
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, WI                            8

              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 data 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
data 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  to 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 90 percent confidence interval  of the  median.
                                    8-18

-------
        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 EMCs  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   rioted  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   all
        constituents.

        Reductions  never exceed 50 percent.
                                    8-19

-------
      (TSS  Concentrations)
(TKN  Concentrations)
                                           4.0
                                           30
                                           20
        100    200    300    400
            UNSWEPT TSS Img/l)
       1.0    2.0    3.0     4.0
          UNSWEP1 TKN Img/l)
      (COD Concentrations)
(Pb Concentrations)
         50    100    150     200
           UNSWEPT COD Img/l)
       0.2     O.t    0.6    0.8
         UNSWEPT Pb Img/l)
      (TP Concentrations)
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       Figure 8-5.   Bivariate Plots of Median EMCs for
                  Swept and Unswept Conditions
                                 8-20

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WISCONSIN
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WASHINGTON
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WASHINGTON
RESIDENTIAL
NORTH CAROLINA

CBD
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Figure 8-6.  Street Sweeping Performance
                  8-21

-------
In  evaluating  the  results,  it  is  critical  that  the uncertainty  in  the
estimate of median EMCs based  on limited obs;erved 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 of
the site median EMCs were  computed as indicated in Figure 8-7.  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:

     -  Based 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   context,  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 of 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 NURP program.

Grass Swales

Three grass swales were monitored by the Washington,  D.C.  area NURP project.
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
project  study  report   concluded  that   modifications which  would  increase
residence  of  runoff  in  the  swales and enhance infiltration capability could
make this BMP effective for control of urban runoff.
                                     5-22

-------
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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 NURP 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 NURP
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.

BMPs  in  this category include  erosion  control  practices and urban  house-
keeping practices.   As an  example of  the former, the Little  Rock, Arkansas
NURP project  widened  and  stabilized  (with  rip  rap)   a  segment  of an  urban
stream to reduce  erosion potential.   The  Baltimore NURP  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.
                               3-25

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                                 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.

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  examined  and
tested.   Since the  underlying  distributions  were determined to be  adequately
represented by the lognormal distribution, the log  (base e) transforms of all
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 water
quality  statistic.   Event mean concentrations  were  based on  flow weighted
composite samples for each event  at  each site  in  the accessible  data base.
EMCs were  chosen  as the primary  water  quality characteristic  subjected to
detailed analysis, even  though it  is  recognized that mass  loading  character-
istics of urban runoff  (e.g.,  pounds/acre for a  specified  time interval)  is
                                     9-1

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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  mass loads  is  on  the basis  of  EMC and
site-specific rainfall/runoff characteristics.

Establishing the  fundamental  distribution  as lognormal 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 data than the use of ranges;
        one which is less subject to misinterpretation

     -  A framework for examining "transferability" of data in a quanti-
        tative manner

Conclusions

1.  Heavy metals  (especially  copper, lead  and zinc)  are by far the most pre-
    valent priority pollutant constituents found in urban  runoff.  End-of-pipe
    concentrations exceed EPA 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 EPA's priority pollutant  list  were  detected in  urban
    runoff  samples,  and  all  but three at  frequencies of detection  greater
    than 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-of-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  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).  Regarding  human   toxicity,  the  most  significant
    pollutants  were  lead and nickel,  and  for human carcinogenesis,  arsenic
    and beryllium.  Lead concentrations violated drinking water  criteria in
    73 percent of the samples.
                                     9-2

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    It should be stressed that 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 pg/1, Pb = 144 ng/1, and Zn = 16° yg/1.  For the  90th percentile urban
    site the  values  are:   Cu  =  93 ug/lr 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-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 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.

3.  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  those providing  high
    degrees of dilution.
                                     9-3

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    Fecal coliform counts in  urban  runoff are typically in the  tens  to hun-
    dreds of  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 and the degree of  dilution/dispersal  arid 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 riot  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  = 0.33  mg/1,
    SP = 0.12 mg/1,  TKN =1.5 mg/1, and N02+3  - N  = 0.68 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-
    solved 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 BOD5  and
    65 mg/1 COD are reflected in the NURP data, with 90th percentile  site EMC
    median values being  15 mg/1  BODS  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.
    No NURP project, specifically identified a low DO condition resulting from
                                     9-4

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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 TSS 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 basis, 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
    of 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.
                                     9-5

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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

I.  Frequent exceedances  of  heavy  metals  ambient water  quality  criteria for
    freshwater aquatic  life are produced by urban runoff.

    The Denver  NURP project found  that  in-stream concentrations  of  copper,
    lead,  zinc,  and cadmium exceeded  State  ambient water  quality standards
    for the South Platte River during essentially all storm events.

    NURP screening  analyses suggest  that  frequent  exceedances  of both EPA
    24-hour and  maximum water quality  criteria  for  heavy metals should  be
    expected on a relatively general basis.

2.  Although a significant number  of problem  situations  could  result  from
    heavy  metals in urban  runoff,  levels  of freshwater  aquatic life use
    impairment suggested  by  the  magnitude  and frequency of  ambient  criteria
    exceedances were not observed.

    Based upon the magnitude and frequency of freshwater aquatic life ambient
    criteria exceedances, one would expect  to  observe impairment   of  this
    beneficial  use  in  most streams  that  receive  urban  runoff  discharges.
    However, those  NURP project studies  which examined this issue  did not
    report significant use impairment problems associated with urban  runoff.

    The  Bellevue, Washington NURP  project  concluded  that toxic  effects  of
    urban runoff pollutants did not appear to be a significant factor.

    The  Tampa,  Florida  NURP  project conducted  biological  studies  of the
    impact  of  stormwater  runoff  upon  the  biological  community  of  the
    Hillsborough  River.   They  conducted animal bioassay experiments  on five
    sensitive  species in  two samples of urban runoff  from the Arctic Street
    drainage basin.  Thirty-two bioassay experiments were completed including
    22 acute tests  and  10 chronic   tests.    Neither  sample of  stormwater was
    acutely  toxic to  test  organisms.  Long-term  chronic  experiments were
                                     9-6

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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.   Therefore,  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  areas 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  rather
    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-
    ganics are found in urban runoff discharges and measured end-of-pipe con-
    centrations  relative   to   published  toxic  criteria.    One   unusually
    high pentachlorophenol  concentration of  115 yg/1 resulted  in the  only
    exceedance  of the organoleptic criteria.   This  observation and  one  for
                                     9-7

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    chlordane  exceeded   the  freshwater    acute   criteria.     Freshwater
    chronic  criteria  exceedances   were   observed  for   pentochlorophenol,
    bis    (2-ethylhexyl)    phlhalate,   Y~hexachlorocyclohexane    (lindane),
    a-endosulfan,  and chlordane.

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  Blacknose 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 during  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  coliform 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
                                     9-8

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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 aromatics, 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 as eutrophic, but from 1974 to 1978
    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 ja 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  NURP  project estimated that urban  runoff  from developed
areas currently  accounts  for only 13.6 percent of  the  annual  phosphorus
loadings to  Lake George as  a  whole.   In contrast, developed  areas con-
tribute 28.9 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  10,000 counts
per  100 ml,  with conditions  worse  in  the  Belmont street  storm drciins.
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 NURP 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  via   the  combined manholes
present in this catchment.   Fecal coliform levels above the  class B fecal
coliform standard of  200 per 100 ml were found in approximately one-third
of the samples tested in the upper and  lower forebays of the Upper Mystic
Lake  and occasionally near the lake's  outlet.   In addition, Sandy Beach,
a public  swimming  area on Upper Mystic Lake,  exceeded the State fecal
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    coliform 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, where  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 more  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  urban runoff  pollutants quite
    close to the  land surface,  and  concluded  that no change in the  use of
    recharge basins  is warranted.

    Despite the fact that some  of these  basins  have been  in service for rela-
    tively long  periods of time and pollutant  breakthrough of the upper soil
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    layers has not  occurred,  the ability of  the  soil to continue  to retain
    pollutants is unknown.  Further attention to this issue  is recommended.

CONTROL EFFECTIVENESS

General

A limited number of  techniques  for the control of urban  runoff  quality were
evaluated by  the  NURP 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.

    Six NURP  projects  monitored the  performance  of  a total  of  14 detention
    devices.   Five  separate projects  conducted  in-depth  studies  of  the
    effectiveness of street sweeping  on  the control  of  urban runoff quality.
    A  total  of 17 separate  study  catchments were  involved in  this effort.
    Three NURP projects examined either  the potential of recharge devices to
    reduce discharges of  urban  runoff to surface waters  or  the  potential of
    the practice  to  contaminate groundwaters.  A  total  of  12 separate sites
    were covered by this effort.

    Grass swales were  studied by two  NURP  projects.  Two swales in existing
    residential areas, and one experimental swale constructed to serve a com-
    mercial parking lot were studied.

    A  number  of  NURP projects  indicated interest in wetlands  for improvir-g
    urban runoff quality  at  early  stages of the program.  Only one allocated
    monitoring activity to this control measure, however.

    Various other management practices were identified as having local inter-
    est  by  individual  NURP projects,  but   none  of   them was allocated the
    necessary resources to be pursued to a  point  which  allowed an evaluation
    of  their ability  to  control  pollution  from  urban  runoff.   Management
    practices  in this  category  included  urban  housekeeping  (e.g.,,  litter
    programs,  catch  basin cleaning,  pet ordinances) and public information
    programs.

2.  Detention basins are  capable of providing very effective removal of pol-
    lutants  in  urban runoff.   Both the design concept  and the  size of the
    basin in  relation  to  the urban area served have  a  critical  influence on
    performance capability.

    Wet  basins  (designs  which  maintain a  permanent water  pool)  have the
    greatest performance  capabilities.  Observed  pollutant  reductions varied
    from excellent to very poor in  the basins which were monitored.  However,
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    when basins  are  adequately  sized,  particulate  removals  in  excess  of
    90 percent (TSS, 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 of 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.

    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.

3.  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 NURP screening analyses indicate that
    adequately sized recharge devices are capable  of providing high levels of
    reduction in direct discharges of urban  runoff  to surface  waters.   The
    level of  performance  will depend on both the size of the unit and the
    soil permeability.

    Application will  be restricted to areas where conditions  are favorable.
    Soil type,  depth  to  groundwater,  land  slopes,   and  proximity  of  water
    supply  wells  will  all  influence  the  appropriateness  of this  control
    technique.
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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 changes  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  pH  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  the level of pollutants in urban runoff and may transform them
to more toxic  and more  easily assimilated forms, further study is required to
support this speculation.

Industrial Runoff

No truly  industrial sites  (as  opposed to  industrial parks)  were included in
any of  the  NURP projects.  A  very  limited  body of data  suggests,  however,
that runoff from industrial sites may  have  significantly higher 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 bv
NURP.   The data  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 pH
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 NURP  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.

Coliform Bacteria

The appropriateness  of using  coliform bacteria  as  indicator  organisms  for
human 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 addressed 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,  at 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 and officials  c\t 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  nonpoint source issues.
                                       9-18       «U.S. OOVERHMENT PRISTWO 0??IOS : 1984 0-421-082/520

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