PRELIMINARY RESULTS
OF THE
NATIONWIDE URBAN RUNOFF PROGRAM
UJ
EXECUTIVE SUMMARY
Water Planning Division
U.S. Environmental Protection Agency
Washington, D.C. 20460
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PRELIMINARY RESULTS
OF THE
NATIONWIDE URBAN RUNOFF PROGRAM
March 1, 1982
EXECUTIVE SUMMARY
WATER PLANNING DIVISION
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
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DISCLAIMER
This report has been reviewed by the U.S. Environmental
Protection Agency and approved for release. Approval 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, contractors, or
subcontractors.
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EXECUTIVE SUMMARY
GOALS AND OBJECTIVES OF THE NURP PROGRAM
The overall goal of NURP is to develop information that will help provide
local decision makers, states, EPA, and other interested parties with a
rational basis for determining whether or not urban runoff is causing water
quality problems and, in the event that it is, for postulating realistic con-
trol options and developing water quality management plans, consistent with
local needs, that will lead to implementation of least cost solutions. It is
also hoped that this information base will be used to help make the best pos-
sible policy decision on Federal, State, and local involvement in urban
stormwatar runoff and its control.
As a water quality management planning effort, the primary NURP objective is
to develop water quality management plans that will be appropriate, accepta-
ble, affordable, and focused on local needs. This requires information that
will allow determination of:
• The extent to which urban runoff is a contributor to water qual-
ity problems as compared to other sources and/or background
loads,
• The effectiveness of control short of treatment in reducing
water quality problems where they exist, and
• Whether best management practices for control of urban runoff
are cost effective in comparison to alternative options.
The overall intent is to initiate programs at the local level for preventa-
tive measures for the control of pollution from urban runoff. The Water Qua-
lity Management program established demonstration projects to help facilitate
this effort and to ensure that all pollution sources were being addressed in
relation to the extent of their contribution of pollution. Through implemen-
tation of these locally derived programs to prevent and to control urban run-
off pollution, one can minimize future high cost corrective actions.
At the national level, a primary NURP objective is to assess urban runoff
on a nationwide scale and attempt to determine:
• The nature of urban runoff problems where significant problems
have been identified,
• the causes of these problems (e.g., sources, transport modes,
impacts),
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• the severity of these problems, based on consideration of bene-
ficial uses and water quality standards, and
• opportunities for controlling urban runoff problems, including
descriptions of control measures, their effectiveness, costs,
and strategies for broad-scale implementation.
Detailed NURP objectives at the national level are:
• to develop the information base required to assess urban runoff
problems,
• to examine the adequacy of current dry-weather water quality
standards when used to judge the significance of storm-dominated
pollution problems,
• to provide technical support to related programs within EPA,
other federal agencies, and program participants at the state,
areawide, and local level, and
• to develop the information base required to identify, assess,
and implement effective controls.
NURP PROGRAM DESIGN
A key element of the NURP program is twenty-eight prototype projects being
conducted across the nation. The locations of these projects are indicated
in Table 1. NURP is also closely following the urban runoff efforts of cer-
tain projects being conducted by others (e.g., USGS), and these non-NURP pro-
jects are also listed in Table 1.
Individual project work plans were designed both to respond to local issues
and water quality management needs and to contribute to selected elements of
the broader information base needed to address transferability and national
scale perspectives. This was accomplished by active participation by EPA (at
both the headquarters and regional levels) i-n the development of individual
project work plans and the use of a matrix of overall input requirements to
ensure effective representation of an array of pertinent factors including
regional effects, climatological conditions, land use types, receiving water
bodies, water uses and problems, and control approaches. Since project can-
didates were at different stages as a result of prior 208 efforts and since
local match constraints precluded any individual project from completely
covering all aspects of concern, the matrix approach was also used to assure
that no information gaps or deficiencies would exist at the completion of all
planned NURP efforts.
One of the key monitoring and evaluation tools is the project progress report
(quarterly) in which each individual project sets forth its progress against
the plan for the covered period, problems encountered, how overcome, resource
expenditures for the reporting period and to date (and compared to plan), and
specific activities proposed for the next period. Copies are reviewed and
commented upon by the designated regional project officer, headquarters pro-
ject officer, and consultant team member. These comments are consolidated
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TABLE 1. NATIONWIDE URBAN RUNOFF PROJECT LOCATIONS
NURP PROJECTS
1. Duram, New Hampshire NH1
2. Lake Quinsigamond, Massachusetts MAI
3. Mystic River, Massachusetts MA2
4. Long Island, New York NY1
5. Lake George, New York NY2
6. Irondequoit Bay, New York NY3
7. Metro Washington, D.C. DC1
8. Baltimore, Maryland MD1
9. Myrtle Beach, South Carolina SCI
10. Winston-Sal em, North Carolina NCI
11. Tampa, Florida FL1
12. Knoxville, Tennessee TNI
13. Lansing, Michigan Mil
14. Oakland County, Michigan MI2
15. Ann Arbor, Michigan MIS
16. Champaign-Urbana, Illinois IL1
17. Chicago, Illinois IL2
18. Milwaukee, Wisconsin WI1
19. Austin, Texas TX1
20. Little Rock, Arkansas AR1
21. Kansas City, Kansas KS1
22. Denver, Colorado C01
23. Salt Lake City, Utah UT1
24. Rapid City, South Dakota SD1
25. Castro Valley, California CA1
26. Fresno, California CA2
27. Bellevue,. Washington WAI
28. Eugene, Oregon OR1
NON-NURP PROJECTS
29. Minneapolis, Minnesota MN1
30. Des Moines, Iowa IA1
31. Topeka, Kansas KS2
32. Reno, Nevada NV1
33. Salem, Oregon OR2
34. Dallas, Texas TX2
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and returned to the individual project with requests for clarification, re-
solution, etc. as appropriate. Comments also include evaluation of data and
its analysis, deficiency identification, and constructive comments for
offices.
Ancillary oversite by others has been structured into the program. The USGS
established a joint Advisory Technical Planning Committee through the inter-
agency agreement with EPA. This joint Federal committee is made up of re-
presentatives of the USGS (Reston and Bay St. Louis offices), EPA (OWPO and
ORD), the Federal Highway Administration, the Corps of Engineers, and the
Soil Conservation Service. To assist this joint committee, designated non-
federal observers have been assigned, including representatives of the
Chicago Metropolitan Sanitary District, Purdue University, Illinois State
Water Survey, and the City Engineer of Portland, Oregon. This provides a
balance of perspectives and helps assure that all concerns are represented.
They meet on a regular basis, review progress, and provide recommendations
which are communicated to all NURP projects. This represents a first level
of peer review for NURP.
OUTPUTS TRANSFERABLE TO LOCAL GOVERNMENTS
The following are things which NURP, upon completion, will be able to pro-
vide to local and State governments and which will be useful input for the
development and or implementation of the urban runoff element of water qual-
ity management plans:
A. Data base on concentrations and loads from urban runoff, with
transferability factors. Given that the monitoring of urban
runoff is costly and time consuming, and probably beyond the
capability of most State and local governments to do effec-
tively, the NURP data base will provide better estimates than
a limited local or State program.
B. Methods of analysis which are being developed will be useful
to others (especially where State and local governments do not
have capability for alternate approaches). Together with the
data base and appropriate local information, these will provide
a basis for: 1) evaluating effects of urban nonpoint sources,
and 2) comparing tradeoffs between point and nonpoint sources.
C. 28 Case Studies which will collectively provide useful informa-
tion to other local non-NURP projects on: monitoring, problem
identification, controls and evaluation, implementation, and
institutional aspects such as financing and management.
D. Other areas will include: information on which pollutants are
of more concern; conditions under which urban runoff will be
of more or less concern; effectiveness and costs of management
practices; and preliminary data on toxic pollutants in urban
runoff.
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CONCLUSIONS
It must be stressed that this is a preliminary report. A final NURP report
will be published in 1983. The conclusions given below are based on data ac-
quired between initial program start-up in 1978 through mid-1981 and analyses
performed on those data by both individual NURP projects and EPA.
At this stage, data acquisition is incomplete; most of the individual pro-
jects still have active monitoring programs. Analysis and interpretation of
data is even less complete, due to the inherent time lag required for lab-
oratory analysis and entry into the data management system.
Partial data analysis has been accomplished, and preliminary conclusions have
been drawn in some of the objective areas - both at the local level and the
national scale. In addition, certain screening analyses have been performed
making use of such data as are now available. These analyses provide a use-
ful start to an assessment of the significance of urban runoff as a contribu-
tor to water quality problems.
While some of the preliminary (national scale) conclusions which are pre-
sented below are believed to be sound, particular analyses were performed
more to illustrate approaches and procedures than to suggest actual results,
and these analyses are so identified. Lack of data at this time has pre-
cluded many important areas from even being addressed as yet.
Even for those analytical conclusions which are thought to be sound, the
limited data base on which they were based does not warrant suggesting that
they are all scientifically substantiated at this time.
A number of local projects have drawn tentative conclusions on a variety of
aspects related to the overall objectives. All are useful and informative,
and thought likely to hold up under further analysis, but like the national
scale activities, are based on incomplete data and have not been reviewed
thoroughly enough to suggest that they are all scientifically substantiated.
NURP fully expects that the important conclusions which will ultimately be
drawn at both local and national levels will be scientifically defensible.
NURP is not there yet, as a careful reading of this preliminary report will
confirm.
Consistent with the structure of the overall report, conclusions are organ-
ized in accordance with the three basic categories of loads, water quality
effects, and controls.
Loads.
1. Due to the highly variable nature of urban runoff, a large data
base significantly improves the confidence in any conclusions
drawn. NURP's emphasis on data acquisition has, even at this
interim stage, produced a data base which significantly exceeds
the total pool of data on urban runoff available from other
sources. Comparisons have been made with other sources which
extend the utility of the NURP data base.
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Urban runoff event mean concentrations of five pollutants ana-
lyzed to date have been demonstrated to have underlying proba-
bility distributions which are log normal. The statistical
parameters (mean and coefficient of variation) have been deter-
mined for COD, suspended solids, total phosphorus, lead, and
copper. Using the statistical properties of the fundamental
probability distribution, it is possible to do the following:
(a) Define urban storm runoff concentrations in a concise
way, and facilitate comparisons with other sources of
data.
(b) Separate the "random" components of the variability
in examining whether there are real, significant dif-
ferences in urban runoff quality based on location,
land use, or any of the other factors which have been
suggested in the past to influence runoff quality.
(c) Make statements concerning the frequency with which
concentrations of any particular magnitude will
occur.
(d) Interpret data from other sources which report ranges,
and apply an improved perspective to such information.
(e) Examine water quality impacts and evaluate such ef-
fects in terms of potential for significant threats
to beneficial use.
Some misleading conclusions that might be drawn with
respect to contaminant concentrations in urban runoff are
illustrated in Figure 1. In Figure l(a) the total NURP
pilot data set statistics are presented by zone, or geo-
graphic region. Indicated are the maximum likelihood
estimators for the mean, the median (the best indicator of
central tendency), and the upper decile (that portion
represented by only the upper ten percent of the events).
In Figure l(b) the same data sets are reproduced with the
lower decile (that portion represented by the lower ten
percent of the events), which is of little interest
insofar as water quality management is concerned, and the
upper decile (a range of relatively rare occurrence)
omitted. Although the copper data most dramatically illu-
strate the result, all constituents examined indicate the
misleading impression that simple range statements can
give. If one focuses on the median values, the change in
perception of concentration magnitudes is even more
striking.
Figure 2 provides an illustrative example of the rationale
which will be employed by NURP to evaluate the extent to
which pollutants discharged by intermittent, variable ur-
ban runoff events may impair assigned beneficial uses of
receiving waters. Applying the analysis methods adopted
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by the NURP program to the statistical characteristics of
pollutants in urban runoff developed from monitoring data
acquired by the 28 individual NURP projects, estimates can be
made of the frequency with which various concentration levels
in the water body will occur as a long term average. This
concentration/frequency distribution (see Figure 2-a) is
compared with various receiving water target concentrations,
for example those that relate to the specific beneficial use of
the water body, or those which reflect specific criteria or
different degrees of use impairment. The procedure may be
extended to illustrate the benefit to be expected in terms of
water use for different degrees of control of urban runoff (see
Figure 2-b).
3. It will be possible, when additional data have been analyzed,
to develop quantitative expressions which will express dif-
ferences in urban runoff quality as a function of factors such
as land use, geographical location, season of the year, etc.
The procedure adopted (examining subpopulations) appears to
provide a viable technique for so doing. Indications of reg-
ional, seasonal, and land use effects presented in Chapter 5,
should be considered tentative, because the data base for per-
forming such comparisons is still sparse. NURP expects, how-
ever, that some of the differences suggested will be confirmed.
For example, Denver and other locations with similar geography
will, because of climate and soil characteristics, continue to
exhibit higher concentrations of suspended solids and other
contaminants closely associated with them.
4. About one-half of the substances on EPA's priority pollutant
list sometimes occur in urban runoff. Heavy metals (especially
lead, zinc, and copper) are much more prevalent than organic
priority pollutants. Some of the metals are present often
enough and in high enough concentrations as to be considered
threats to beneficial uses.
5. Organic priority pollutants appear to be generally present only
in certain urban runoff discharges. Where present, and the
beneficial use is potable water supply, there is a significant
concern. Stream dilution and other mitigating factors may pre-
vent any real problem from developing, but communities with
water supply intakes in close proximity to urban runoff dis-
charges are encouraged to check for the relatively limited num-
ber of pertinent priority pollutants which have been detected
in urban runoff.
6. Total suspended solids concentrations in urban runoff from
available NURP data appear to be lower in general than sug-
gested by other studies.
Water Quality Effects.
Conclusions on the receiving water impacts of urban runoff will be presented
for each designated beneficial use for which it is believed that urban runoff
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will have a negative effect on water quality sufficient to cause impairment
or denial of the use.
Fresh water aquatic life.
1. The effect of oxygen demanding substances in urban runoff on
dissolved oxygen levels in receiving water has not been exa-
mined yet. This analysis will be done when sufficient data
become available.
2. The potential for suspended solids to have a significant dele-
terious effect has not yet been assessed. Thus analysis will
be done when sufficient data are available.
3. Organic priority pollutants do not appear to pose a general
threat to fresh water aquatic life. This is based upon the
limited available data on the frequency with which they are
found in urban runoff discharges and the measured end of pipe
concentrations relative to published toxic criteria.
4. At this time heavy metals appear to be the urban runoff con-
taminants that have the greatest potential for impacts on the
aquatic life beneficial use. This conclusion is based on the
fact that a number of heavy metals are consistently found in
urban runoff in high concentrations relative to suggested toxic
limits.
5. It appears reasonable to conclude that some degree of impair-
ment of this benefical use is probably common in many water
bodies which receive urban runoff. With some exceptions, how-
ever, the degree of any impairment that exists does not appear
to be of sufficient magnitude to generate serious local con-
cern. This conclusion is based on the following:
• The screening analysis suggests that local conditions
can be expected where the magnitude and frequency of
intermittent concentrations of some metals would have
adverse effects. Conversely, there will be local con-
ditions where adverse effects are very unlikely or
extremely rare occurrences. The governing local cir-
cumstances are storm flow characteristics and average
rainfall intensity, both of which vary with geographic
locality.
• Absence of evidence from NURP projects confirming im-
pairment of this beneficial use which is considered
significant at the local level. Bellevue, Washington,
with a high degree of local awareness and interest in
protecting a fishery, has concluded that chemical con-
stituents in urban runoff create no problem for their
sport fishery. Glen Ellyn (NIPC) documents high metals
concentrations which undoubtedly strongly influence the
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nature of the fishery which is present, but local opin-
ion does not characterize this as a problem, i.e.,
local residents do not consider the degree of use im-
pairment to -be significant.
• In an EPA examination of over 10,000 fish kills that
occurred from 1970 to 1979, only 265 were attributed to
runoff of any kind, and less than one-half of that num-
ber were associated with urban runoff.
6. Indications to date do not provide any basis for believing that
a denial of this benefical use is a widespread, general
occurrence.
Marine aquatic life.
1. Adverse effects of urban runoff in marine waters will be a
highly specific local situation. It is not a beneficial use
generally threatened by urban runoff, though specific instances
where it is impaired or denied can be of significant local and
even regional importance.
2. A significant impact of urban runoff on shellfish harvesting
has been well documented by the Long Island, New York NURP
project.
3. Coliform organisms present in urban runoff are the primary
pollutant indicator of concern.
Recreation.
1. Pollutants in urban runoff which pose the most significant
threat to this beneficial use are pathogenic organisms (as
possibly indicated by the presence of coliform bacteria), nu-
trients (particularly phosphorus), and suspended solids.
2. Coliform bacteria are present at high levels in urban runoff
and affect all types of water bodies — streams, lakes, bays,
estuaries, and oceans. Whether the potential for use impair-
ment is realized depends principally upon physical factors such
as the location of the discharge relative to swimming areas and
the degree of dilution and dispersal. In this sense, actual
use impairment will be a local condition. This problem has
been identified by a number of projects; however, data are not
yet available for characterizing the extent and severity of use
impairment.
3. Water bodies particularly s.usceptible to recreational use im-
pairment by nutrients are lakes. In the cases where at least
some information is presently available (Lake Quinsigamond,
Irondequoit Bay, Lake Austin, Lake George) it is apparent that
the degree of beneficial use impairment varies widely, as does
the significance of the urban runoff contribution. Detailed
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analysis which will permit establishing the relative signifi-
cance of urban runoff compared with other sources is not avail-
able at this time except for Lake Quinsigamond but can be
expected to be very site specific. At Lake Quinsigamond urban
runoff was found to be a significant source of the critical
nutrient phosphorus, such that a proposed water quality manage-
ment plan will include the objective of reducing urban runoff
loads. By contrast, very preliminary indications are that
nutrients in urban runoff are not causing any appreciable
negative impact on Lake Austin and controls do not appear war-
ranted, pending results of analysis of long term effects.
4. Adverse impacts on recreational use caused by suspended solids
have not yet been evaluated.
Public water supply.
1. Ground water aquifers do not appear to be threatened by pol-
lutants in urban runoff caused to percolate through the ground.
This finding is based on only one NURP project (Long Island)
which has specifically examined this issue and must be consi-
dered in that light.
2. Lakes and impoundments that receive urban runoff and also serve
as water supply sources are being addressed in NURP, but at
this time results available are too limited to warrant drawing
preliminary conclusions of a general nature.
3. Rivers or streams which serve directly as water supply sources
with intakes in close proximity to urban runoff discharges are
probably rare nationwide, but some do exist. From information
and preliminary analysis developed to date, it is inferred that,
where water supply intakes are in close proximity to urban
stormwater discharges, a serious enough potential for adverse
impacts exists that careful examination of the situation is
prudent. The principal contaminants of concern suggested by
preliminary results include heavy metals, a limited number of
the organic priority pollutants, and coliform bacteria. Al-
though the potential problem is present, there are mitigating
factors which reduce the likelihood that a problem situation
will actually exist at any given location. The present status
of our analysis does not warrant any firm conclusions to be
drawn with regard to the prevalence of actual problem situa-
tions of this type. However, based on the fact that local fac-
tors can significantly reduce the potential, and the belief
that relatively few water supply intakes exist at stream loca-
tions dominated by urban runoff, NURP believes that any pro-
blems that do exist will be limited rather than widespread
occurrences.
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Control effectiveness.
1. Some detention basins are quite effective at reducing pollutant
concentrations in urban runoff, with reductions on the order of
90 percent or better reported. High removals of suspended
solids and1 heavy metals, especially copper, are noted, with
somewhat lower removal efficiences for phosphorus and chemical
oxygen demand.
2. Other NURP project detention basins do not appear to be per-
forming very well in terms of reducing effluent concentrations
and may not be capable of providing a significant water quality
improvement. The performance of some is quite variable, being
fairly good for some storm events (~ 50 percent reduction) and
quite poor for others. Some detention basins are consistently
poor performers.
3. The design features of detention basins play a very important
role in their performance in terms of reducing pollutant con-
centrations. Data suggest that basins designed to merely con-
trol water quantity (drainage) problems may not function well
in water quality terms. The installation of an arbitrary de-
tention basin could even exacerbate water quality problems. As
more NURP project data become available, it will be possible to
make definitive recommendations on detention basin design for
water quality improvement.
4. Street sweeping is effective for its original purpose, but it
does not appear to be universally effective in reducing urban
runoff pollution. Only one project out of six has been able to
show any water quality improvement as a result of even very
intensive (daily) street sweeping.
5. The effectiveness of street sweeping as a water quality BMP
should be measured in terms of actual pollutant reduction in
the runoff, not determined theoretically from estimates of
pounds removed from street surfaces obtained from examination
of street sweeper hopper contents, pounds remaining on the
street surface, etc.
6. Data are insufficient to allow firm projections to be made as
to those conditions under which street sweeping might be able
to provide a water quality improvement, but preliminary indica-
tions are that it might be limited to semi-arid parts of the
country with pronounced wet and dry seasons.
7. Data indicate that under certain conditions street sweeping may
actually increase urban runoff pollutant levels, but this con-
clusion must be considered highly speculative until more data
become available. A possible mechanism is that sweeping can
break up larger particles making them available for washoff by
smaller, less intense storms with less runoff volume for dilu-
tion. At its conclusion NURP will be able to make definitive
statements in this regard.
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8. Recharge Basins appear to offer promise as effective and
economical BMP's for reducing urban runoff pollution to surface
waters, without creating a threat of adverse impact on ground
waters. This conclusion is tentative, and is based on prelimi-
nary data from monitoring efforts on one device, and screening
analyses to examine applicability. Applicability can be ex-
pected to vary on the basis of site-specific conditions such
as soil percolation rates, depth to water table, topography,
proximity to water supply wells, and the like. Preliminary
indications are, however, that recharge basins could have rela-
tively broad applicability.
GENERAL DISCUSSION
In summary, the possibility of having water quality problems caused by urban
runoff varies in type and degree. Whether or not a problem may truly exist
is strongly influenced by a variety of local, site-specific characteristics.
These include:
Local climatology and hydrology;
• Type of water body which is the principal recipient of urban
runoff;
• The particular beneficial use desired; and
Local attitudes, resources, values — especially values as
applied specifically to individual water bodies in an area.
The NURP screening analysis to date suggests that there are a lot of places
where urban runoff is unlikely to result in problems (quantifiable problems
reflected in standards violations or use impairment). The same screening
analysis also suggests that there should be a significant number of locations
where urban runoff could theoretically result in the occurrence of a quanti-
fiable problem. Some "possibilities of problem situations" would have to be
discounted on the basis of the actual beneficial uses. For example, "pro-
blems" based on drinking water standards not being met would be problems only
if the receiving water is actually used as a drinking water source. Local
attitudes or alternatives could further reduce a theoretical or potential
problem to the category of no problem from a practical standpoint.
NURP is unable, at this time, to estimate the probable relative distribution
of sites in the nation which fall into the above alternate categories. Its
analysis efforts are continuing to try to make this determination. At this
time, however, NURP is not highly optimistic about its ability to be able to
make a credible generalization of this type. However, some rather sweeping
generalizations that will be true more often than not are offered. The water
quality impact of urban runoff will be greatest in small urban impoundments,
especially those with no other influent flows. Aside from possible near-
shore effects, the water quality impact of urban runoff will diminish with
impoundment size and, consequently, so should the potential for occurrence of
water quality problems. Similarly, the water quality impacts of urban run-
off will be greatest in small streams, especially those that headwater in the
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urban area. As stream flow and size increase, the potential for water qual-
ity impacts caused by urban runoff should decrease as should problem poten-
tial. Furthermore, in this regard, swiftly flowing streams should be less
vulnerable than more sluggish ones. Bays and estuaries are so complex that
even such rather simplistic generalizations as the foregoing are difficult to
justify and the same is true of the near-coastal oceans.
There are plateau and threshold effects for many pollutants that influence
their impact on a given receiving water and, consequently, the strategy for
their control. As an example, consider the case where the Level of a toxic
substance is four times the LC-50 value for a species of fish associated with
the desired beneficial use. If urban runoff is the only source of the toxi-
cant, and if the implementation of a given control measure results in a
50 percent reduction in loads, the money spent would have been wasted insofar
as attainment of the designed beneficial use is concerned. To be sure,
pounds of pollutants would have been removed at a (perhaps) cost-effective
rate of so many dollars per pound, but there would still be none of the
sought-after fish in the water and, consequently, the desired beneficial use
would still be denied. Similarly, the removal of a contaminant that is at
such low levels that it is not interfering with a designated beneficial use,
simply because the substance is present in urban runoff, results in the
incurrence of costs but produces no benefit because the beneficial use was
not being impaired in the first place.
While the tools are available for conducting cost-effectiveness analyses and
the procedures are rather straightforward, NURP is not so fortunate in the
area of benefit-cost analysis. Damage theory and utility cost tools exist,
but their application is far from straightforward and is subjective at best.
The Agency is currently attempting to remedy this situation, and successful
approaches, if found, will be applied by NURP.
Because of the local nature of water quality problems in terms of existence
and cause, and because in many cases much more attractive approaches than
control of urban runoff will be available for addressing problems where they
are found to truly exist, it does not appear desirable to adopt a universal
requirement for urban runoff control or treatment.
Urban runoff does appear to contribute significantly to certain water quality
problems in certain areas (there are a number of well-documented cases in the
NURP program), and there are situations where control of urban runoff is the
only realistic action that is available to address the problem. However, the
practicality of being able to solve some problems will be constrained in some
cases by technological limitations, in some cases by costs, and in some cases
by physical site constraints. Some examples of such constraints include:
Technological. Situations which require very high degrees of removal of
a pollutant may prove to be beyond the performance capabilities of con-
trol measures available. Example: Suspended forms of a contaminant
lend themselves to removal whereas, if the soluble component is a sub-
stantial fraction of the total, control measures may not be able to
reduce the total load sufficiently to achieve desired effects.
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Cost. The cost associated with reducing the overall load of a pollutant
from an entire urban area could prove to be prohibitive, even though
relatively cost effective when applied in restricted areas. Usually,
the overall urban runoff load must be addressed if the "problem" is to
be successfully attacked. However, it may provide real benefit to apply
efficient, cost effective controls serving only limited areas where it
can be done conveniently.
Physical Site Constraints. Even where efficient, cost-effective con-
trols may be available for reduction of the specific pollutants contri-
buting to a particular problem, the physical space to implement them
may not be obtainable. For example, Central Business Districts may be
a significant pollutant source, but provide little opportunity for
control.
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