United States
Environmental Protection
Agency
Water Engineering Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-85/038 June 1985
&EPA Project Summary
Characterizing and Controlling
Urban Runoff Through
Street and Sewerage Cleaning
Robert Pitt
A study was conducted in Bellevue,
Washington, to characterize urban run-
off and evaluate its control by street and
sewerage cleaning. The project was one
of a series conducted in the city from
1978 through 1983 to investigate
Bellevue's urban runoff sources, effects,
and potential controls.
The project reported here spanned
the period 1980-1983, and it complete-
ly monitored more than 300 urban
runoff events in two residential areas
during that time. Flow-weighted com-
posite samples were analyzed for a core
list of important constituents. Complete
flow monitoring results allowed detailed
descriptions of urban runoff quality and
quantity, and they permitted estimates
concerning the contributions of flows
and pollutants from different source
areas. Street surface and sewerage
particulates were also collected and
analyzed to determine the effectiveness
of street and sewerage cleaning.
Most of the heavy metals were deter-
mined to originate from street dirt, but
street cleaning improved the quality of
urban runoff by a maximum of only 10
percent. A specially modified street
cleaner was then tested and found to be
much more effective than the conven-
tional model in removing the small
particles of street dirt that are washed
off the streets by rains. Catchbasin
cleaning twice a year was estimated to
improve runoff quality by a maximum of
about 25 percent.
This Project Summary was developed
by EPA's Water Engineering Research
Laboratory, Cincinnati, OH, to announce
key findings of the research project that
is fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
A 2-year monitoring program was
conducted to examine the sources of
urban runoff flows and pollutants in
Bellevue, Washington. The study of these
elements enabled a comprehensive in-
vestigation of the direct effects of street
and sewerage cleaning on runoff quality.
A large number of storm events were
monitored under two extreme street-
cleaning frequencies to investigate pos-
sible improvements in urban runoff
quality. Urban runoff was studied in two
residential areas using automatic, flow-
weighted samplers and sonic depth
gauges to monitor runoff during storms
and dry weather. Street dirt samples
were obtained in conjunction with specific
street cleaning programs using special
vacuum collection procedures. Storm
sewer inlet and sewerage particulate
samples were also obtained periodically.
Significant decreases in street surface
loadings occurred with intensive, three-
times-a-week street cleaning, but large
improvements in the quailty of urban
runoff were not detected. The improve-
ments averaged only about 10 percent,
possibly because the light Bellevue rains
removed only some 15 percent of the
street loadings. The particulates that
washed off the streets were of the finer
particle sizes that are not effectively
removed by conventional street cleaners.
These particulates constituted only a
small portion of the total urban yields of
many pollutants, but street dirt washoff is
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a major contributor of many heavy metals
and organic priority pollutants. In addition,
the amounts of rainfall at the two loca-
tions differed by more than 20 percent at
least half of the time. These rain differ-
ences made basin calibrations difficult
and tended to mask variations in runoff
concentrations or yields that may have
been caused by street cleaning.
Study Area Description
Bellevue is a middle to upper middle
class suburban community near Seattle,
Washington. The city is decentralized,
with residential areas served by shopping
malls and numerous businesses along
arterial streets. No heavy industry exists
in Bellevue. The population growth has
been rapid in the past decade, and the
population was about 74,000 in 1980.
Though the growth of Bellevue has mostly
been in residential areas, recent develop-
ment has included construction of addi-
tional office buildings and hotels. The
area is within commuting distance of
Seattle. Bellevue receives about 1 m/yr
of rain, but substantially more rain falls
on the Olympic Peninsula to the west,
and much smaller amounts occur to the
east in Washington.
Two residential areas were studied in
this project—Surrey Downs and Lake Hills
(Figure 1). The communities are about 5
km apart, and each covers an area of
about 40 ha. Both are fully developed,
mainly as single family residences.
The Surrey Downs basin is about 38 ha
in size and includes the Bellevue Senior
High School in addition to single family
homes that were built in the late 1950's.
Most of the slopes in the basin are
moderate, with some steeper slopes on
the west side. The Surrey Downs basin
ranges in elevation from about 3 to 55 m,
and about 60 percent of it is pervious.
Back and front yards make up most of the
land surface area of the basin, and streets
make up about 10 percent. The streets
are generally in good condition, with
smooth to intermediate textures. The
curbs need repairing in a few locations.
Westwood Homes Road and 108th Street
have no curbs. The Surrey Downs basin
has little traffic, and the on-street parking
density is low. The storm drainage system
discharges into an artificial pond located
in an adjacent development. This pond
discharges into Mercer Slough, which
eventually drains to Lake Washington
and Puget Sound.
The Lake Hills catchment covers about
41 ha and contains the St. Louise parish
church and school in addition to single
Redmond
Larsen Lake
Phantom Lake
N
Figure 1. City of Bellevue, Washington, study sites.
family homes, also developed in the
1950's. Lake Hills has slightly more
pervious area than Surrey Downs, but its
lots are typically smaller. With a few
exceptions, the slopes in Lake Hills are
more moderate than those found in
Surrey Downs. The elevation of the Lake
Hills study area ranges from 80 to 125 m.
The street surfaces and gutter systems
are similar to those in Surrey Downs.
Most of the streets in Lake H ills also carry
low volumes of traffic and have low
parking densities, except for two busy
roads that cross through the area. The
Lake Hills storm drainage system outfalls
into a short open channel that joins Kelsey
Creek just downstream from Larsen Lake.
Kelsey Creek also discharges into Mercer
Slough.
Sources of Runoff and Pollutants
Sources and amounts of runoff, flows,
and receiving water conditions are all
affected by site-specific rain conditions.
Bellevue rains are quite different from
those in most other U.S. locations. They
occurred every 2 or 3 days during the
study period and were on the average less
than 6 mm each. Fewer than 10 percent
had volumes greater than 25 mm, and the
largest rain monitored was 100 mm. Dry
periods of more than a week are rare, but
they did occur. Storms during the wet
season generally yield twice the amount
of rain and last twice as long as those
during the dry season.
This project monitored about 400 rains
and all base flow volumes between eventsi
that occurred at the two main study"
-------
locations during 2 years of data collection.
Bellevue received about 1 m of rain during
each project year. Base flows represented
relatively large portions of the total annual
urban flows.
Important differences between the two
study sites occurred in quantity of rainfall,
base flow, and runoff yields. Overall, the
base plus stormwater urban flows from
Lake Hills were about 18 percent greater
than those from Surrey Downs when
normalized by area (figured on an equal
area basis).
For both study years and test basins,
only about 25 percent of the rain that fell
left the areas as runoff. Typically, the
small rains had the smallest runoff factors
(Rv: ratio of runoff volume to rain volume)
and the large rains had the largest factors.
Multiple regression analyses were
conducted to relate the Rv values to total
rain, average and peak intensity, and days
since last rain. Results showed that
rainfall volumes alone accounted for
about 95 percent of the individual Rv
values. The season of the year was
extremely important in determining actual
runoff and rainfall relationships. The
winter wet months of November through
February had Rv values some 35 percent
higher than those for the drier months of
March through October for similar rains.
Thus, there was no real need to adjust the
calculated Rv values for rain intensity or
length of preceding dry period. All that
needed to be considered was total rainfall
and season.
A model was developed to determine
the sources of runoff and their propor-
tionate contributions. The model was
based on the variations of Rv values for
different rain volumes. Source of runoff
considered included vacant lots, parks,
front and backyards, rooftops, driveways,
parking lots, and streets. The amount of
runoff contributed by each source de-
pended on its distance from the drainage
system, its size, and the type of surface
cover.
For all rains greater than about 2.5mm,
impervious surfaces contributed more
than 60 percent of the total urban runoff
flows. The remainder of the flows were
approximately evenly divided between
front and back yards. Vacant lots and
parks contributed very little flow because
of their limited presence in the test areas.
Street surfaces contributed about 25
percent of the total urban flows for most
rains causing runoff.
Quality of Stormwater Runoff
Collecting data on the quality of storm-
water runoff was a major aspect of this
project. Most of the analytical effort was
associated with a core list of important
constituents. The sampling procedures
involved collecting total storm flow-
weighted composite samples throughout
most of the events that occurred during
the 2-year sampling period at the Surrey
Downs and Lake Hills sites. Variations in
stormwater quality with total storm char-
acteristics were analyzed. Very few vari-
ations were observed in the total solids
concentrations for various storm char-
acteristics, and they were statistically
insignificant.
The runoff water quality at Bellevue
was much better than that at most other
U.S. locations, but the base flow quality
was worse than expected. The reason
was probably that the study basins were
completely urbanized and the base flows
consisted of percolated urban sheet flow
waters from previous storms that were
draining out of the surface soils. In basins
with undeveloped upstream areas, the
base flow would originate mostly from
the nonurbanized upper reaches and
would be of much better quality.
The mass yields for annual urban runoff
(Table 1) indicated an apparent difference
between the runoff in Lake Hills and
Surrey Downs when expressed on a unit
area basis, but the total annual storm
runoff plus base flow discharges from the
two basins were quite similar. A much
larger fraction of the total urban runoff in
Surrey Downs occurred as base flow
between rain events. The runoff events in
Lake Hills were more sharply defined, and
the base flows made up a much smaller
fraction of the mass yields for urban
runoff.
The relative contributions of pollutants
from various source areas (Table 2)
differed from the contributions of runoff
flows. During very small rains, most of
the runoff and pollutant discharges were
associated with the directly connected
impervious areas. As the rain total in-
creased (to greater than about 2.5 mm),
the pervious areas became much more
important. These patterns varied signifi-
cantly, depending on specific rain char-
acteristics and land uses. For most rain
events, total solids originated mostly from
the back and front yards. Street surfaces,
however, were expected to account for
most of the lead, zinc, and COD dis-
charges. Phosphates and total Kjeldahl
nitrogen were mostly contributed from
street surfaces, driveways, and parking
lots combined. Front and back yards
contributed slightly less than half of these
Table 1. A nnual Mass Yields for Baseflow and Stormwater Runoff (kg/ha)
Surrey Downs
Lake Hills
Constituent
Base
Flow
Storm
Runoff
Total
Base
Flow
Storm
Runoff
Total
Total solids
COD
Total Kjeldahl nitrogen
Total phosphorus
Lead
Zinc
110 205 315
11 90 100
0.60 1.8 2.4
0.11 0.40 0.51
0.03 0.26 0.29
0.06 0.24 0.30
76 280 360
9.9 110 120
0.20 2.7 2.9
0.04 0.69 0.73
0.02 0.45 0.47
0.027 0.31 0.34
Table 2. Percentage Distribution of Urban Runoff Pollutants from Various Source Areas*
Percent of Pollutant Contributed from Source Area*
Source Area
Streets
Driveways and parking lots
Rooftops
Front yards
Back yards
Vacant lots and parks
Total
Solids
9
6
<1
44
39
2
COD
45
27
3
13
12
<1
Phosphates
32
21
5
22
20
<1
Total
Kjeldahl
Nitrogen Lead
31 60
20 37
10 <1
19 <1
20 <1
<1 <1
Zinc
44
28
24
2
2
<1
"For 2.5- to 65-mm rains.
^Approximate.
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nutrients. Zinc contributions from roof-
tops (galvanized gutters) made up about a
fourth of the total zinc discharges.
Contributions of Street Dirt to
Urban Runoff Discharges
About 600 samples of street surface
accumulations were collected from the
test areas during the 2-year project. The
particulate loads for each sample were
plotted to observe changes in street
surface loadings with time and to deter-
mine the initial rates of deposition and
long-term accumulation. The deposition
rate is the amount of dirt that accumulates
over the first several days after a signifi-
cant rain or street cleaning. This rate is a
function of various characteristics of the
area; especially climate, land use, traffic
and street surfacetexture. The accumula-
tion rate equals the amount of dirt
deposited minus the amount removed by
rain, street cleaning, traffic-induced tur-
bulence or wind. Material blownfromthe
street can remain suspended in the air,
but most of it settles to the ground within
about 10 m of the roadway.
Each of the street surface samples was
separated into eight different particle
sizes. These size distributions showed
that the smallest particle sizes account
for only a small fraction of the total
material, especially during the wet season
when the rains were most effective in
removing the smallest particles. During
the dry season, the larger particle sizes
also accounted for relatively small frac-
tions of the total solids weight. Most of
the street surface particulates were asso-
ciated with particles in the middle size
ranges of 0.125 to 1.0 mm.
The initial accumulation rates (assumed
to be equal to the deposition rates) in the
test areas were estimated to vary between
1 and 6 g/curb-meter per day, with an
average rate of about 3 g. This rate
compares with accumulation rates ob-
served in other locations for smooth
streets in good condition. The frequent
rains do not remove all of this material
from the streets. The texture of the street
traps and protects particulates so that
typical street cleaning equipment and
rains cannot remove them. About 50 to
100 g/curb-meter of street surface par-
ticulates remain on the streets after
storms of about 6 mm or greater. Infre-
quent large rains may remove much more
of the street surface particulates than the
smaller rains common in Bellevue.
Chemical characteristics of street dirt
in the different study areas varied most
with respect to lead, especially when
comparing streets with varying traffic
levels. Particle size also had a significant
effect on concentrations of chemical
pollutants in street dirt. Chemical oxygen
demand, Kjeldahl nitrogen, and phospho-
rus concentrations all showed high con-
centrations associated with the smallest
particle sizes, small concentrations with
the intermediate sizes, and high concen-
trations with the large sizes. Lead and
zinc concentrations were the highest with
the smallest particle sizes which is typical
(based on other studies for heavy metals).
The contribution of the street surface
particulates to runoff water depends on
the ability of the rain to loosen and wash
these particulates from the street surface.
During the 2-year project about 25 pairs
of street surface loading values were
obtained within 2 days of rain. Figure 2
shows the percent and size distribution of
surface particulates washed from the
street in Lake Hills during both the dry
and wet seasons. The initial loadings
were significantly greater than the resid-
ual loadings for particle sizes smaller
than about 500 microns. The smallest
particle sizes had the greatest significant
washoffs, whereas particles greater than
about 500 microns had lower significant
washoff values. With the smallest particle
sizes, the washoffs varied from about 40
to 50 percent, whereas increases were
found in street loadings for the larger
particle sizes. The overall reduction in net
loading averaged about 16 percent. Even
more material may have been removed
during the rains and replaced at the same
time by erosion material.
Most of the material washed from the
street surfaces had particle sizes of less
than about 125 microns. Only about 10
percent of the washoff material was
greater than about 500 microns. The
largest particle sizes were notably absent
from the washoff material. A total of
about 8.5 to 10 g/curb-meter was re-
moved from the street surfaces during
the rains, with about 4 to 6 g/curb-meter
having particle sizes smaller than 125
microns.
Table 3 summarizes the approximate
annual street dirt accumulations, washoff
values, and fugitive losses to air for the
Surrey Downs and Lake Hills sites. In
many cases, the amounts involved were
substantially greater for Lake Hills than
for Surrey Downs. About 15 percent of
the annual street dirt accumulation was
washed from the streets and either
discharged or accumulated in the sewer-
age systems. About 10 percent of the
annual accumulation was lost to the air,
with much of this material settling out
near the roadway. The remaining street
dirt would build up over time on the street
surface or be removed by street cleaning
operations.
-10
Figure 2.
6350
1000 2000 6350
Panicle Sizes (microns}
Total
Percent and size distribution of surface particulates washed from the street in Lake
Hills during the wet and dry seasons.
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Table 3. Approximate Annual Street Dirt Accumulation, Washoff, and Fugitive Losses to Air
" (kg/ha)
Surrey Downs
Constituent
Total solids
COD
Total Kjeldahl nitrogen
Total phosphorus
Lead
Zinc
Accumu-
lation*
200
25
0.2
0.1
0.1
0.03
Washoff
30
3
0.04
0.02
0.02
0.006
Loss
to Air*
20
2
0.02
0.01
0.01
0.003
Accumu-
lation*
350
70
0.8
0.2
0.4
0.08
Lake Hills
Washoff
60
10
0.16
0.05
0.1
0.02
Loss
to Air*
20
3
0.05
0.01
0.02
0.005
*Using an average 2- to 5-day accumulation period.
^Calculated based on the deposition minus the accumulation rates times the average interevent
time period.
Sediment Accumulations in
Sewerage Systems and
Catchbasins
Sewerage system sediment loadings
were periodically observed in the Surrey
Downs and Lake Hills study areas. The
drainage systems were cleaned before
the project began, and the sediment
volumes in inlets and catchbasins were
observed nine times during 2 years. The
first observations in December 1979
showed light accumulations. The next
observations were made in August 1980.
Beginning in January 1981, observations
were made every 1 or 2 months until the
end of the project. The first year of
observations indicated steady accumula-
tions of sediment, but the loading re-
mained about the same during the second
year. Typically, about twice as much
polluted sediment was observed in the
storm drainage systems at any given time
as was noted on the streets. The flushing
of the sewerage sediments out of the
drainage systems and into the receiving
waters was not analyzed, but such an
event would probably not occur except
during large storms. The smaller storms
probably removed a small fraction of the
sewerage sediments.
The stable sediment volumes that
occurred during the second year were
about 60 percent of the available sump
volumes of the catchbasins and inlets.
Only about 12 mm of sediment was found
in the manholes with outlets on the
structure bottoms, whereas about 150
mm of sediment accumulated in the inlets
and catchbasin sumps. When analyses
were conducted for individual structures,
wide variations were observed. The depth
below the outlet appeared to be the most
important factor, but the larger-capacity
sumps did not always contain the largest
amount of sediment. Large sump capacity
would allow less frequent cleaning before
the stable volume was obtained and
smaller outlet-to-sump bottom distances
would be associated with greater scouring
during storms.
The chemical quality of the sediment
material in the catchbasins was also
analyzed. The chemical quality of this
catchbasin and inlet sump material was
very similar to that of the same sized
particles of street dirt. Thus most of the
catchbasin sediments were probably
street surface particulates that had
washed off the streets during rains but
were not discharged to the outfall.
About 100 liters/ha per year accumu-
lated in the Surrey Downs storm sewer
inlet structures, whereas only about two-
thirds of this amount accumulated in
Lake Hills. About 50 percent more inlet
structures per hectare exist in Lake Hills
as opposed to Surrey Downs, where the
accumulation rate per inlet structure was
generally more than double that of Surrey
Downs. Nine of the ten most heavily
loaded catchbasins in the first summer
inventory for Surrey Downs were located
on or just downstream from the two
streets in the study area that did not have
curbs and had extensive off-street sedi-
ment sources.
Very few pipes in either Surrey Downs
or Lake Hills had slopes of less than 1
percent. Since both study areas were
drained by steeply sloping pipe systems,
the accumulation of sediments in the
storm drainage systems was not great.
Urban Runoff Controls
The last phase in developing an urban
runoff control program is to examine
measures that can be used to reduce the
identified problem pollutants or flows
originating from the various source areas
that discharge to the receiving water. To
meet water quality objectives, a combina-
tion of several control measures may be
necessary. Complex procedures for ana-
lyzing decisions may also be necessary if
multiple objectives are important. This
part of the study evaluated the effective-
ness of street cleaning in controlling the
urban runoff problems in Bellevue.
Street cleaning tests were conducted
using two different cleaning frequencies:
No cleaning, and intensive 3-day-a-week
cleaning. For several months, one clean-
ing frequency was used in the Surrey
Downs main basin, and the other was
used in the Lake Hills basin. The frequen-
cies were then rotated. During another
period of several months, no street clean-
ing was conducted in either basin.
Street loadings ranged from about 40
to 300 g/curb-meter (with an average
value of about 115) during the period of
no street cleaning. The loadings were
reduced to about 20 to 200 g/curb-meter
(with an average of about 60) after street
cleaning (from about 650 to 400 microns)
because of the selective removal of the
largest particles by the street cleaners.
Rains, on the other hand, increased the
median particles sizes because they were
most effective in removing the finer
material.
This study collected more than 400
street dirt samples in the two test basins
immediately before and after the streets
were cleaned. Figure 3 compares the
initial and residual street dirt loads for a
wide range of loading conditions. Street
cleaning equipment cannot remove par-
ticulates from the street surface unless
the loadings are above a certain level.
This value was about 85 g/curb-meter in
the test basins. If the initial street surface
loading values were smaller than this
value, then the residual loadings typically
were about equal to the initial loadings.
Statistical analysis showed that the fre-
quent rains in Bellevue were probably
more effective than the street cleaning in
keeping the streets cleaned. The street
surface loadings after rains were usually
50to 100g/curb-meter. Typical mechan-
ical street cleaning equipment was quite
ineffective in removing small particles.
Particle sizes smaller than about 350
microns were not substantially affected
by street cleaning, and there was no
effective removal of street dirt particles
smaller than about 125 microns. Very
subtantial removals were observed in the
large particles, however. A decrease
occurred in median particle sizes as the
street cleaners preferentially removed
larger particles. These decreases were
especially important when the initial
median particle sizes were large.
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A series of special tests were conducted
during September and October of 1982 to
compare the effectiveness of a modified
street cleaner with that of a standard
mechanical street cleaner. Many modifi-
cations were made to a standard Tymco*
regenerative air street cleaner. The pur-
pose of these modifications was to reduce
respirable fugitive dust emissions during
street cleaning. The modifications in-
cluded partial hoods around the gutter
brooms, a pressure controller to better
regulate the air flows, and a venturi
scrubber with a settling chamber in the
street cleaner hopper. The water spray
bar was also disconnected. This modified
street cleaner was compared with both a
standard street cleaner that was used in
the previous full-scale tests and with an
unmodified version of itself. The results
of these special tests are also shown in
Figure 3. Both the modified and unmodi-
fied regenerative air street cleaners
showed substantially better performance
than the regular mechanical street clean-
er, especially for finer particle sizes. The
poor performance of the mechanical
street cleaners was aggravated by the
low loadings of these small particles. The
regenerative air cleaners were much
more suited to the low loadings of small
particles.
Bellevue street cleaning costs were
about $13/curb-kilometer. About 73 per-
cent of this cost was associated with
labor and labor overhead, about 18 per-
cent was associated with all of the
maintenance costs, and 18 percent was
associated with the disposal costs. Street
cleaner operating costs (including labor,
depreciation, tires, oil, and gasoline) were
about 64 percent of the total costs.
A large part of the data analysis done
during this project attempted to identify
differences in runoff concentrations and
yields caused by different street cleaning
operations. No significant differences
were observed in runoff yields or concen-
trations during periods of intensive street
cleaning. A very few exceptions occurred,
but they were probably due to other
factors.
The poor street cleaning effectiveness
is probably the result of the specific
Bellevue rain conditions. The rainfall and
resulting runoff volumes varies greatly
between the two test areas—by at least
25 percent for about half of the rain pairs.
These differences could have shielded
the effects of the different street cleaning
operations.
'Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use.
800
700--
• Mobil (Surrey Downs)
a Mobil {Lake Hills) -,
T: Tymco (Surrey Downs) standard regenerative air street cleaner™'
M: Modified Tymco (Surrey Downs) regenerative air street
cleaner
100
0 100 200 300 400 500
Initial Load (Ib/ curb-mile)
Figure 3. Street dirt loads before and after street cleaning.
600
700
800
Though street surface particulates con-
tributed less than 25 percent to runoff
yields in nearly all cases, they contributed
about 50 percent of the total runoff lead
yield. If the street cleaning operations
could control a substantial fraction of the
street surface particulates, then reducing
runoff particulates by street cleaning
might be important. Rains were most
effective in removing particles smaller
than several hundred microns in size.
These particle sizes are not abundant, but
they do contain the largest concentrations
of heavy metals and relatively large
concentrations of many nutrients. As
noted, however, mechanical street clean-
ing equipment is not very effective in
removing small particles. The regenera-
tive air street cleaners were more effec-
tive in this area.
The coordination of street surface
sampling, street cleaning operations, and
runoff monitoring during this project
allowed many data analysis procedures
to be used to investigate possible effects
of street cleaning on runoff water quality.
The use of two test basins and the rotation
of the street cleaning operations also
allowed one basin to be compared with
the other, along with internal basin
comparisons. No significant differences
were noted in the runoff concentrations
over the ranges of data that were common
to the various data sets.
Intensive street cleaning resulted in
about a 25- to 50-percent reduction in
street surface loadings. If the street
surface contributes about half of the total
runoff yield for a specific pollutant, then
intensive street cleaning may remove 10
to 20 percent of the pollutant discharge.
Precise runoff measurements and con-
sistent rainfalls over the test and control
basins would therefore be required to
detect these relatively small improve-
ments. Intensive street cleaning signifi-
cantly reduced only the large particle
sizes, and those particle sizes most
subject to washoff by rains were not
effectively reduced. This may result in
less than a 6 percent improvement in
runoff water quality for intensive street
cleaning. The regenerative air street
cleaner is expected to be about 1.25 times
more effective in reducing runoff yields.
Conclusions
Direct receiving water effects from
urban runoff pollutants were not signifi-
cant for most storms, but potential long-
term problems associated with urban
runoff may be associated with settleable
solids, lead, and zinc. These settled
materials may have silted up spawning
beds and introduced high concentrations
of potentially toxic materials directly to
the stream sediments. The oxygen deple-
tion observed in the interstitial waters
was probably caused by organic sediment
buildup from runoff events.
Flooding in the receiving waters has
increased significantly with urbanization.
-------
This flooding has affected several benefi-
cial uses of these waters (aquatic life
habitat and water conveyance, for ex-
ample).
For all rains greater than about 2.5 mm,
the impervious surfaces (streets, side-
walks, driveways, parking lots, and roof-
tops) contributed more than 60 percent of
the total urban runoff flows. The remain-
der of the flows were approximately
evenly divided between front and back
yards. Vacant lots and parks contributed
very little to the flows because of their
limited presence in the test areas. For
most of the rain events monitored, the
street surfaces contributed about 25
percent of the total urban runoff flows.
Most of the total solids in the urban
runoff originated from front and back
yards in the test areas; the street surfaces
contributed only a small fraction. Lead,
zinc, and COD, however, were mostly
contributed from street surfaces. Nutri-
ents (phosphorus and total Kjeldahl
nitrogen) originated mostly from street
surfaces, driveways, and parking lots.
Motor vehicle activity was expected to
be the primary contributor of most of the
toxic pollutants. Gasoline and diesel fuel
combustion products, lubricant and fuel
leakages, and wear of the vehicles af-
fected the street dirt material most signif-
icantly.
The maximum observed runoff event
discharged about 25 percent of all pollu-
tants that were on the street surfaces, the
catchbasins, and sewerage combined.
Thus most urban runoff pollutants were
not source-limited. However, those par-
ticulates that were most available for
washoff (the smallest particles) might be
source-limited. About half of the total
particulates from annual urban runoff
discharge might be residing on the street
surfaces and tied up on catchbasins and
storm drainage sediments at any given
time. If the Bellevue rain events could
remove more of this material, the urban
runoff discharges would be much greater
than observed.
Rains removed only a small fraction of
the total particulate loadings on the
impervious surfaces (about 15 percent).
Large particles were not effectively re-
moved, and only about half of the smallest
particles (less than 50 microns) were
washed off during rains. These small
particles were not very abundant, but
they had very high concentration of heavy
metals and nutrients. Most of the settled
particulates in the storm drainage inlets
and sewerage pipes also remained after
the observed storms.
Intensive street cleaning three times a
week produced significant decreases in
street surface loadings—from about 115
g/curb-meter down to about 60 g/curb-
meter. The median particle sizes also
decreased significantly with intensive
street cleaning. A regenerative air street
cleaner performed substantially better in
removing the finer street surface mate-
rials than did the regular mechanical
street cleaner.
Extensive data analysis showed no
significant improvements in runoff water
quality during periods of intensive street
cleaning. The street cleaning operations
tested are expected to improve runoff
quality by a maximum of only 10 percent.
The street cleaning equipment preferen-
tially removed the larger particles, and
the rain events removed the finer mate-
rials. Street cleaning did not very effec-
tively remove the available particulates.
Mechanical-broom street cleaning effec-
tively removed the larger litter from the
streets. Infrequent street cleaning may
result in significant increases in fugitive
dust losses to the atmosphere.
After an initial cleaning, nearly a full
year was needed for sediment to reach a
stable volume in the inlet structures. Only
about 60 percent of the total available
sump volumes in inlets and catchbasins
were used to detain particulates at the
stable volume. At any larger storage
levels, the rains effectively controlled the
volumes. Cleaning the inlets and catch-
basin sumps about twice a year is expect-
ed to reduce the lead and total solids
concentrations in urban runoff by 10 to
25 percent. COD, the nutrients, and zinc
might be reduced by 5 to 10 percent.
Based on this project, many recom-
mendations can be made about public
works practices in the Bellevue area, but
their effects on improving the urban
runoff quality would probably be quite
small. If intensive street cleaning were
implemented along with semiannual
catchbasin sediment cleaning, most pol-
lutants in urban runoff discharges would
be reduced by about 10 percent. Some of
the heavy metal discharges might be
reduced by as much as 25 percent. Even
though these reductions are quite small,
they could contribute significantly to
reducing the accumulation of these highly
polluted sediments in the smaller creek
systems, especially if the receiving water
flows were reduced.
Peak runoff flows could be reduced by
requiring the use of more pervious areas
in developed areas, or by the use of
appropriately sized and located detention
basins.
The full report was submitted in fulfill-
ment of Cooperative Agreement No. CR-
805929 by the City of Bellevue under the
sponsorship of the U.S. Environmental
Protection Agency.
* U.S GOVERNMENTPRINTINOOFFICE: 19M- 559-111/10858
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Robert Pitt is a Consulting Engineer, Blue Mounds, Wl 53517.
Richard Field is the EPA Project Officer (see below}.
The complete report, entitled "Characterizing and Controlling Urban Runoff
Through Street and Sewerage Cleaning, "(Order No. PB 85-186 500/AS; Cost:
$35.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Wastewater Research Division
Water Engineering Research Laboratory—Cincinnati
U.S. Environmental Protection Agency
Edison, NJ 08837
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45^68
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