SERA
                                 United States
                                 Environmental Protection
                                 Agency
                                  Municipal Environmental Research^
                                  Laboratory
                                  Cincinnati OH 45268
                                 Research and Development
                                  EPA-600/S2-82-048 August 1982
Project Summary
                                 Stormwater  Management to
                                 Improve  Lake Water Quality

                                 Martin P. Wanielista, Yousef A. Yousef, and James S. Taylor
                                   Many investigators have identified
                                 the urban environments as those pro-
                                 ducing high levels of water pollutants
                                 relative to other land uses. In a 59
                                 hectare (146 acre) urban watershed in
                                 Orlando, Florida, the Stormwater sys-
                                 tem discharges to an 11 hectare (27
                                 acre) lake. The lake water quality is
                                 characterized by frequent algal
                                 blooms, odor, and in general, reduced
                                 recreational activities. The lake is one
                                 of the focal points of the city's recre-
                                 ational/social programs.
                                   Stormwater  management proce-
                                 dures were established based on the
                                 runoff sampling program and a target
                                 mass pollutant reduction of storm-
                                 water runoff with special emphasis on
                                 phosphorus. Management of storm-
                                 water for the removal of phosphorus
                                 was accomplished by diversion for
                                 retention (filtration) of the first flush of
                                 pollutants.
                                   Lake water quality will be managed
                                 by the reduction of Stormwater mass,
                                 bottom mud inactivation, and littoral
                                 zone plantings. Approximately half of
                                 the water column phosphorus concen-
                                 tration was estimated to originate in
                                 the bottom muds and return to the
                                 water column primarily during anoxic
                                 conditions. Thus, a coagulant cover-
                                 age of the bottom muds will be used.
                                 The coagulant possibilities are alum
                                 sludge or alum.
                                   This Project Summary was devel-
                                 oped by EPA's Municipal Environmen-
                                 tal Research Laboratory. Cincinnati.
                                 OH, to announce key findings of a
                                 research  project that is fully  docu-
                                 mented in a separate report of the
                                  same title (see Project Report ordering
                                  information at back).

                                  Introduction
                                   Stormwater  may be a significant
                                  source  of surface  water  pollution in
                                  urban areas. Lake  impacts have been
                                  and  continue  to be studied on an
                                  international level by the National Eutro-
                                  phication Research Program in the
                                  United  States  and an international
                                  program with United States participa-
                                  tion.
                                   This summary presents Stormwater
                                  impacts on an urban lake and recom-
                                  mendations for  Stormwater and  lake
                                  management. The  impact  was  first
                                  defined by visual observation and storm-
                                  water was the major pollution source.
                                  There was no point sources of industrial
                                  or domestic wastewaters. Samples were
                                  taken of Stormwater, lake water, and
                                  bottom  muds and estimates made of
                                  mass loading and impacts to determine
                                  a combination of management practices.
                                   Some elevations of best management
                                  practices (BMP's) for urban Stormwater
                                  had been completed before this work.
                                  The critical relationship between a BMP
                                  and receiving water quality, however,
                                  had not been well documented, except
                                  for some dissolved oxygen responses in
                                  rivers.


                                  Watershed and Lake
                                  Characteristics
                                   The drainage area is the Lake Eola
                                  watershed  in Orlando, Florida.  The
                                  Stormwater system, which is separate
                                  from the sewage  system,  drains a

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watershed of approximately 59 hectares
(146 acres), composed of 33.7 hectares
(83.2 acres) of commercial  and 25.3
hectares (62.8 acres) of residential areas
discharging to an 11-hectare (27-acre)
lake.  In addition, 4.5 hectares (11.2
acres) of parkland surrounds the lake
and  are  not  considered part  of the
watershed because of infrequent runoff
to the lake. Streets  and parking  lots
comprise approximately  19.7 hectares
(49 acres) of  the watershed within a
total of about 49.3 hectares (122 acres)
of impervious lands. The pervious area
is only 9.7 hectares (24 acres), most of
which is in the residential areas.  The
land use is illustrated in Figure 1.
  Visual observation of the watershed
indicates a total of 35 parking lots with
an area of about 12 hectares (29 acres)
discharging stormwater.  Parking areas
were identified to select possible areas
for management of  stormwater  dis-
charged to the land-locked lake. One of
the parking lots was designated a samp-
ling location for runoff waters and  is
usually  maintained  between  26.5
meters (87.0 ft) and 27 meters (88.5 ft)
above sea level by well discharge and
pumping. It is a shallow lake with  a
mean depth of approximately 3 meters
(9.84  ft) and about 73 percent of the
total volume located within the 0 to 3
meter (0 to 9.84 ft) frustrum layers.
Most  urban lakes in central Florida
(more than 5,000) have similar physical
characteristics.
Benefits
  The benefits of the lake and its
surroundings are evident but difficult to
quantify. The lake is a focal point of
Orlando with frequent music concerts,
arts and  crafts shows, tourist visits,
children's park, and relaxation areas,
and is one  of the  main reasons the
downtown area continues its economic
security. The property surrounding the
lake brings  top  value  because of its
location. The dollar benefits from  lake
activity are estimated at $2.3 million per
year.


Lake Impacts
  From visual observation and analytical
data.  Lake Eola has  persistent algal
blooms virtually year round. Populations
of the macroscopic algae, Chara,  and
the filamentous green algae, Spirogyra,
covered up to 30 percent of  the  lake
surface during the summer rainy  sea-
son. Lake Eola water was found to be
somewhat alkaline with  pH ranging
from 8.4 to 9.5 (indicative of the rate of
algal  production). The average annual
value and the measured range of values
for pH, chlorophyll-a, inorganic  and
organic carbon, and Secchi disc trans-
parency are shown by Table 1.
  The average values shown in Table 1
are similar to values reported  in the
literature for eutrophic lakes.
                                                                                                               L_
1
                                                   Legend
                                              Commercial
                                              Residential
                                              Parkland
                                              Sampling locations
                                              Sub- watershed
Figure 1.   Lake Eola watershed land uses and sampling locations.

                                  2

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Table 1.    Values for Selected Parameters Measured in Lake Eola, Florida, Between
            July 1978 and August 1979
Parameter
Chlorophyll-a
Organic carbon
Inorganic carbon
pH
Secchi disc
No. of
Samples
64
67
68
57
32
Average
Value
25.4
10.9
18.8
8.85
106
Standard
Units Deviation
mg/m3
mg/L
mg/L

cm
8.8
6.7
6.4
—
13.0
Range of
Values
9.0 -
3.0 -
13.8 -
8.40-
90
36.4
29.1
40.6
9.5
120
  Concentrations of dissolved oxygen in
Lake Eola, although usually at or above
saturation near the surface, drop period-
ically during  the spring and summer
months to less than 1 mg/L in deep
areas of 4 meters (13.1  ft) or greater.
Phosphorus from the bottom sediments
is released up to a level of 250  mg/m2
after  2  months of anoxic conditions.
This anaerobically released phosphorus
has the potential for increasing water
column phosphorus by 11.6 /ug P04~3-
P/L, about 50 percent of the average
orthophosphorus concentration in the
lake(23//g/L).
  Extensive bioassay experiments indi-
cate that  when  the  concentration of
orthophosphorus in Lake Eola was less
than 0.10 mg/L, algal production was
regulated  by  adding  orthophosphorus
alone. Above this concentration, appar-
ently an excess of phosphorus was
available,  and algal growth was regu-
lated by the N/P ratio. In most cases,
however, the concentration of orthophos-
phorus was below0.04 mg/L, and most
likely algal production was  limited by
the concentrations of added phosphorus
alone.
  In addition to the enhanced algal
growth  conditions experienced during
the summer rainy months, runoff enter-
ing the  lake after prolonged periods of
drought may produce severe toxic effects
on aquatic life in Lake Eola. Contami-
nants are allowed to accumulate within
the watershed, and when a storm event
occurs, the mass loading to the lake is
many times larger than experienced
during frequent rainfall periods of time.
This influx of toxic and oxygen demand-
ing wastes can be lethal to many forms
of aquatic  life.
  Evidence of such a phenomenon was
recorded in March 1979 when a rain
event followed a dry period of 6 weeks.
 oncentrations of organic carbon as
.ligh as 400 mg/L were measured in
stormwater runoff  entering the lake
during this event. Two days later, dis-
solved oxygen concentrations had been
reduced from saturation near the sur-
face to 4 mg/L at a depth of 1 meter and
to near zero below 2 meters. Numerous
large-mouth bass averaging  1 to 2 kg
were found floating in the water, and
large masses of dead filamentous algae
had accumulated in thick mats over
much of the lake's surface. During 1979,
a total of six fish kills were reported. One
dead bass (about 2 kg) floating  at the
surface was brought to the laboratory,
processed and analyzed for metal con-
centrations in selected organs (heart,
gall bladder, liver, stomach) and flesh. It
appeared that nickel and  lead concen-
trated in the gills, iron concentrated in
the heart, and zinc and copper concen-
trated in the liver. At this time, however,
it is not known that these metals were
directly responsible for the fish kill.
  A pathogen isolation study was con-
ducted for 1 year with the collection of
129 water and sediment samples. Four-
teen  were composites of runoff, 32
were bottom samples, and 83 were lake
water. Clostridium was isolated from
the bottom sediments of  the lake and
Salmonella was isolated from the lake
water samples.
  Domestic ducks  in the Lake Eola
waters and park areas number approxi-
mately 20, with decreasing populations
noted over the past 5 years. Microbiol-
ogists at the Orange County Pollution
Control Agency have speculated during
site visits, that gas production from the
anaerobic sediments is increased in the
summer months. This anaerobiosis pro-
motes growth of the botulism organism
that produces a toxin that, in turn,
concentrates in the small  insect larvae
of the sediments. When ducks eat the
larvae they can die. After the autopsy of
two dead ducks, botulism was the
reported cause of death.
 Stormwater
   Stormwater pollutants and flowrates
 were first estimated by sampling storm-
 water relative to the hydrograph. In this
 hydrograph-related sampling program,
 eight rainfall/runoff events were quan-
 tified. Next, a composite sampling pro-
 gram was  completed with seven rain-
 fall/runoff events. One major question
 was the percentage of dissolved pollu-
 tant materials present in the runoff. The
 sampling  program  indicated that the
 dissolved nutrients and organics were
 approximately 50 percent or more of the
 total, while the dissolved fraction of lead
 was 20 percent. From the 15 runoff
 samples, estimates were made for aver-
 age mass  loading (as discharged) and
 average concentrations. Priority pollu-
 tants were  measured. Estimates of
 loading rates from both commercial and
 residential  areas were calculated from
 the runoff studies.
   The Lake Eola site loading data were
 compared with the loadings of SWMM/
 level I analysis and other national data.
 The suspended  solids  (SS) and  BOD
 data (Table 2) appear to agree, but total
 nitrogen loadings are higher in the Lake
 Eola watershed. Possible reasons are
 that the residential areas should  be
 classified as commercial when consider-
 ing loading rate data, the landscaping
 maintenance places an additional nitro-
 gen load, and the heavy rainfall (130 cm)
 is greater  than the national average.
 Most likely,  a  combination  of these
 reasons caused the increase.
   The commercial and residential land
 use pollution contribution  to the total
 was estimated to be 98 percent for SS,
 96 for BOD, 95 for total organic carbon,
 94 for total  Kjeldahl nitrogen (TKN), and
 91 for  total  phosphorus  (TP). Total
 contribution was defined as the sum of
 the contributions from stormwater, at-
 mosphere,  and ducks resident  on the
 lake.
  The sampling program and the lake
 impact work led to the following conclu-
 sions:  (1)  stormwater is the major
 external source of lake related pollution;
(2) phosphorus  and other  stormwater
pollutants require removal; and(3) sedi-
 mentation was possibly not the choice
 method  for stormwater management
because of the large  percentage  of
dissolved pollutants.


Target Phosphorus Reduction
  The major question is to what  degree
should the bottom sediment and storm-

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Table 2.    Loading Rate Comparisons fkg/ha-yrj
Data Source
 SS    5005
        roc
 TN
TKN   POt-P    TP
Lake Eola
Commercial
Residential

1076
827

196
87

1167
757

32.0
40.5

27.8
36.1

1.7
3.1

3.5
6.2
SWMM/Levell
 Commercial
 Residential
1255
 922
181
 45
16.7
 7.4
        4.3
        1.9
National A verages
Commercial
Residential

941
470

97
39

14.5
6.6

3.0
2.0
water be treated to economically reduce
nutrient enrichment, fish and duck kills,
and algal activity to an acceptable level?
Using the trophic state models, a target
reduction level of phosphorus loadings
into the oligotrophic/mesotrophic level
may reduce algal blooms. In addition, a
chlorophyll-a mean concentration of 7
/ug/L may indicate a mesotrophic state.
Table 3 illustrates the target level and
need  for an approximate  90 percent
reduction in phosphorus load and con-
centration.
  In the National Eutrophication Study,
total phosphorus concentration of less
than 10/ug/L in the water column was
noted as a  target reduction to classify
lakes as oligotrophic. A combination of
stormwater treatment and bottom sedi-
ment inactivation may produce a water
column concentration  of less than  10
fjg/L. The bottom sediments were esti-
mated to contribute 11.6 yi/g/L of the
average water column concentration of
23//g/L

Stormwater  Management
Selection
  Each stormwater management prac-
tice that could be defined  in terms of
cost and efficiency and was practical for
the watershed was evaluated for storm-
                 water control. Selecting the best combi-
                 nation of practices that  met cost and
                 efficiency constraints (least cost) could
                 be aided by a computer analysis.
                   Cost-efficiency curves (present value
                 dollars versus removal quantities) were
                 developed for each  subwatershed of
                 Lake Eola.  Removal  efficiencies  were
                 used from the literature and nonpoint
                 urban runoff programs. These efforts in
                 the central Florida area had defined the
                 efficiencies and costs for diversion/
                 percolation basins, swales, underdrains,
                 and vacuum sweeping nonpoint source
                 management  methods. In the highly
                 impervious urban areas, the cost of land
                 is expensive,  and  land intensive activ-
                 ities (detention and  retention basins)
                 are sometimes not aesthetically pleas-
                 ing. Thus,  street  sweeping  diversion
                 with retention underground, and catch-
                 basin cleaning  appeared probable for
                 the Lake Eola area. Dutch drains, rooftop
                 storage,  coagulation, filtration, and
                 solids concentrators were other manage-
                 ment methods being investigated. These
                 methods formed the basis for determin-
                 ing optimal combinations of practices. A
                 linear  programming  network routing
                 model was incorporated into a computer
                 program, and  the cost-efficiency curves
                 were estimated by "piecewise" linear
                 approximation.
Table 3. Target Reductions
Models Before
Vollenweider 2.33 g-P/m2/yr
Dillon 0.49g-P/m2
Larsen-Mercier 0.48 mg/L
OECD/ chlorophyll1 269 mg-P/m3
Target Reduction Levels
0.2 g-P/m2/yr
0.05g-P/m2
0.05 mg/L
70 mg-P/m3
'Reduction corresponding to a chlorophyll-a of 7 fjg/L.

                                  4
  One limitation on stormwater control
was the use of private property. Thus, it
was decided to do all  management
within the city right-of-way. The alter-
natives considered for management of
the stormwater were:

  1.  diversion  of stormwater to  the
     sanitary sewer system for treat-
     ment;
  2.  street cleaning by both broom and
     vacuum sweepers;
  3.  diversion of stormwater into perco-
     lation basins;
  4.  conversion of inlets to catchbasins;
  5.  coagulant addition with sedimen-
     tation (detention);
  6.  silt removal  from lake, and draw-
     down every 5 years;
  7.  natural  "living filter" treatment
     through littoral zones;
  8.  fabric bag filters;
  9.  detention  systems (on-line pass
     through);
10.  "best" combination of any or all of
     the above alternatives; and
11.  diversion of stormwater into infil-
     tration trenches near the lake.

  The first alternative was eliminated
because it was not considered as a
general solution for other areas and it
required the  replacing of over 7.00C
meters  (22,950 ft) of sanitary  sewei
lines, thus the capital cost of pipe anc
pumping stations was over $600,000.
  A "column study" was done to exam
ine detention and detention after coagu-
lation as a method for improving watei
quality. Because a significant amount o
the pollutants in stormwater were in the
dissolved or colloidal state, coagulatior
with detention  may be necessary t<
remove these types of pollutants. Deten
tion with significant holding times wil
remove suspended materials. The reduc
tion reported ranged from a high of 5:
percent for TSS to a low of 20 percen
for  lead. Alum coagulation  improvei
stormwater quality more than detentioi
alone. Reductions of TP  and TSS afte
alum coagulation  were in excess of 91
percent. Standard isoconcentration line
and regression equations relating per
cent removal to time, settling velocity
and the logarithm of time were devel
oped. The regression equations are eas
to use and were developed within
predictive error of less than 5 percen
The detention systems were judged to
expensive because of land area require
and the chemical costs. Detention afte
coagulation, however, may be feasibl
for other locations.

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  Before the percolation  alternatives
could  be  considered,  the infiltrative
capacity of the soils was estimated by
defining the type of soils and the loca-
tion of the water table. The water table
is at least 2 meters (6.56 ft) below the
ground surface for a ground elevation of
29  meters (95  ft) or  higher. Borings
close to the lake indicate the water table
is near elevation 27 meters (88 ft). In
addition, sandy soil is available to about
6.5 meters (20 ft) below ground level.
Percolation of stormwater is possible for
parking lot and street drainage for those
areas whose ground elevation is above
29  meters (95 ft).
  All  alternatives were evaluated for
estimated  cost and  yearly  pollutant
removal efficiencies. The  cost for the
natural "Living Filter" areas was  esti-
mated from local contractors and the
city of Orlando records. Native vegeta-
tion was selected and has been used in
other lakes. All other cost data  were
obtained from recently bid sewer pro-
jects.
  The  selected solution was based on
minimum present value cost and maxi-
mum removal efficiencies. The fabric
bag alternative had a lower capital cost,
but poor removals relative to other
alternatives. The  location  of the  best
management practices was  near parking
lots and  immediately before lake dis-
charge. Parking lot and street diversion
were designed to percolate the first 0.6
to 1.25 cm (0.25 to  0.5 in.)  of every
storm  chosen, resulting in a removal
efficiency of 90 percent on  a yearly
basis.  The resulting capital  cost for
stormwater management and lake res-
toration was approximately  $6,2507
hectare ($2,5007 acre) of watershed.


Results and Conclusions
  Presented here are the  results and
conclusions separated into  the areas of
stormwater, lake  impacts, sediments,
and selection of management practices.

Stormwater
  The stormwater pollutants and quanti-
ties were first estimated by  sampling
stormwater relative to the  hydrograph.
Eight rainfall/runoff events were quan-
tified in this manner. Next,  a composite
sampling program was  initiated meas-
uring seven rainfall/runoff events. From
the  15 runoff samples, estimates were
made for mass loading (as  discharged)
and average concentrations.  Loading
rate and average concentration   data
were estimated  for 19 water quality
parameters,  including data  for  10
metals. Results of the sampling program
are:

  1.  The dissolved portion of storm-
     water pollutants was equal to or
     greater  than 50  percent of the
     total except for  zinc, lead,  and
     chromium.
  2.  Loading rates of SS, BOD5, and
     dissolved phosphorus were com-
     parable to national averages. Load-
     ing rate data for nitrogen are
     higher than national averages.
  3.  The relative loading rates for each
     external (not including lake recy-
     cle) source  of pollution were esti-
     mated. Stormwater produced the
     greatest percentage  of  the total
     loadings.

Lake Impacts
  During this research, monthly water
quality analyses were performed in Lake
Eola and bioassay experiments  were
conducted to determine the  effect of
nutrients and stormwater additions on
algal productivity in this lake system.
Coagulation of stormwater to remove
nutrients and limit algal production was
also studied. From the results  obtained
in this research,  the following conclu-
sions were reached;

  1.  The input of stormwater in Lake
     Eola has damaged this  aquatic
     system.  Persistent algal blooms
     exist virtually year round. Bottom
     sediments have become covered
     with a layer  of loose flocculant
     material  and  anoxic conditions
     exist in areas more than 4 meters
     (13.12 ft) deep during the spring
     and summer.
  2.  When the concentration  of ortho-
     phosphorus in Lake Eola is less
     than 0.10 mg/L, algal production
     is  regulated by  the  addition of
     orthophosphorus alone. Above
     this concentration, it appears that
     an excess of phosphorus is avail-
     able, and algal growth is regulated
     by the N:P  ratio.  In most cases,
     however, the concentration  of
     orthophosphorus  is below  0.04
     mg/L,  and  algal production is
     limited by  the concentration of
     added phosphorus alone.
  3.  Although nitrogen was  able to
     stimulate algal production in lim-
     ited bioassay experiments, it will
     probably not be a limiting resource
     in Lake Eola when considered over
     a period of years because of the
     large  numbers of nitrogen-fixing
     blue-green algae that are charac-
     teristic of eutrophic systems.
 4.  Adding stormwater runoff to Lake
     Eola water in any  concentration
     increases algal production. A mix-
     ture of 25 percent stormwater
     runoff produces the largest stand-
     ing crop.
 5.  Coagulating stormwater runoff
     with alum reduces concentrations
     of both orthophosphorus and  ni-
     trate nitrogen by 80 to 95 percent
     and re moves certain heavy metals.
 "3.  Coagulating stormwater runoff
     significantly reduces phosphorus
     and most metals. Thus, the treated
     stormwater is less toxic to aquatic
     organisms  and algae growth  is
     reduced.
 7.  Dry weather storm sewer flow has
     a negligible effect on algal produc-
     tion in Lake Eola.
 8.  Maximum algal growth in bioassay
     experiments generally occurred
     after 6 to  11 days  of incubation.
     When stormwater runoff is added
     to Lake Eola water, however, a
     growth lag is often experienced
     that may extend the time required
     to  reach maximum  yield to  as
     many as 18 days.
 9.  Continuous stormwater inputs
     into Lake  Eola  during the  rainy
     season greatly  enhances  algal
     growth because of  the  constant
     input  of nutrients and dilution  of
     toxic components. Inputs of storm-
     water after a long  dry spell may
     inflict serious  toxic effects  on
     aquatic life.
10.  Concentrations of copper and zinc
     in  Lake Eola  are  sufficient to
     cause incipient inhibition of algal
     production. Average stormwater
     runoff concentrations of copper,
     zinc,  and  lead  are  sufficient to
     produce complete inhibition or
     algicidal effects.
11.  Human pathogens were identified
     in the lake. Clostridium was iso-
     lated  from bottom  samples and
     Salmonella from  water samples.

Sediment
  During this study,  sediment  phos-
phorus was characterized and the mag-
nitude and effect of anaerobically re-
leased phosphorus were studied to
determine the effects on the productivity
of Lake Eola and the related eutrophica-

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tion. Based on the results of this re-
search, the following conclusions were
reached:

 1.  The major source of phosphorus
     entering Lake Eola is from storm-
     water runoff. The  major phos-
     phorus sink is the sediments. Both
     components  greatly exceed the
     quantity of phosphorus stored  in
     the water column at any time.
 2.  The input of stormwater runoff
     has severely affected the natural
     decomposition cycle in the Lake
     Eola ecosystem,  resulting in an
     accumulation of partially decom-
     posed organic matter with a con-
     stantly high oxygen demand.
 3.  Flocculent sediment particles  of
     smaller size  and density contain
     considerably more  phosphorus
     than larger and more dense parti-
     cles. In Lake Eola, flocculent, deep
     water particles  contained about
     61 percent more phosphorus than
     discrete, dense sand particles from
     the shallow areas.
 4.  A thick mat of decomposing algal
     cells covers the sand placed over
     the  sediments in the Lake Eola
     restoration project  of  1973 be-
     cause the source of phosphorus
     was not controlled.
 5.  Aerobic phosphorus release be-
     cause of turbulent agitation of the
     sediments is most likely an insig-
     nificant  phosphorus source, but
     may serve to maintain lake water
     phosphorus levels when productiv-
     ity has depleted the phosphorus in
     the water column.
 6.  The  hypolimnion of Lake Eola
     remains anaerobic from mid-May
     to mid-August, corresponding  to
     the wet season and the associated
     increase of  stormwater runoff
     during this period. This anaerobic
     condition enhances phosphorus
     release from the bottom sedi-
     ments.
 7.  Anaerobically  released phos-
     phorus, when  mixed out of the
     hypolimnion, has the potential for
     increasing water column phos-
     phorus  by 11.6 fjg P04~3-P/L,
     which amounts to 50 percent of
     the average orthophosphorus con-
     centration in the lake (23 /jg/L).

Selection of Management
Practices
  Many stormwater practices are avail-
able and tested in many geographical
regions. Unfortunately, few of  these
practices have been documented rela-
tive to their  removal efficiencies for
selected water quality measures. Diver-
sion of the first-flush of stormwater has
been documented. If the first-flush is
percolated through soil, direct surface
discharge of pollutants is eliminated. If
soil conditions and water table permit
percolation, then diversion for storage
and treatment by percolation is possible.
There appears, however, to be a need
for more documentation on other prac-
tices. The following conclusions expand
upon our existing knowledge.

  1.  Percolation is possible after storm-
     water diversion in urban  areas.
     Perforated  pipe under sidewalks
     and parking lots within municipal
     right-of-way should be examined.
  2.  Diversion of the first 0.64 cm (0.25
     in.) of every stormwater  runoff
     event will produce long-term re-
     moval efficiencies of at least 80
     percent.
  3.  Sedimentation will remove sus-
     pended  materials. The reduction
     reported herein ranged from a high
     of 52 percent for TSS to a low of 20
     percent  for lead.
  4.  Alum coagulation plus detention
     improved stormwater quality more
     than detention only. Of the water
     quality  parameters investigated,
     only the nitrogen forms and Ca
     were not reduced by alum coagula-
     tion. The reduction of TP and TSS
     after alum coagulation and deten-
     tion was in excess of 90 percent.
  5.  Standard isoconcentration lines
     and regression equations relating
     the percent removal of any of the
     water quality variables were devel-
     oped as linear or semi-log func-
     tions of  settling velocity or deten-
     tion time. The regression equations
     were developed using an  alpha
     error of less than 5 percent.  The
     regression  equations are easy to
     use.
  6.  Phosphorus release experiments
     using alum stormwater sludge,
     lakewater, and lake sediment indi-
     cated that the phosphorus re-
     moved  by  alum coagulation of
     stormwater would be retained in
     the solid form in a simulated  lake
     environment for aerobic or anoxic
     conditions with or without gentle
     mixing.

  After defining  the stormwater man-
agement practices for the watershed, a
computer program  "MANAGE" was
used as a methodology for the choice of
the least cost combination. As a general
methodology, however, more work was
needed to estimate  localized cost-
efficiencies for stormwater manage-
ment practices. Incorporating  mathe-
matical programming  methods to this
work allows one to select a combination
of practices that will remove a maximum
amount of pollutants at least cost.

Implementation  Steps
  Based on citizen concern and histori-
cal water quality data on fish and duck
kills, oxygen depletion, and algal blooms,
it was evident that the factor causing
the water quality impact  had to  be
identified. Trophic state analysis indi-
cated that the lake  was  estimated as
eutrophic. In laboratory tests,  algal
productivity was related to stormwater.
Also, the bottom sediments were shown
to contribute to the phosphorus concen-
tration in the water column.
  Based  on  the  runoff quality and
quantity data along with lake limnologi-
cal data,  an  implementation  plan  for
stormwater  management was devel-
oped. Since phosphorus is  most  likely
the limiting nutrient, it will be controlled.
The two  major sources of phosphorus
are stormwater and lake bottom mud
recycling. By reducing stormwater phos-
phorus mass inputs, littoral zone plant-
ing, and coagulant coverage of bottom
muds, it is predicted that the effects of
stratified conditions  (anaerobic) will be
minimized and algal  blooms  will  be
reduced.
  The stormwater management will be
done by diversion/percolation of parking
lot runoff and limited street runoff
approximately 24.0 hectares (60 acres)
In addition,  most  of the  areas no
managed with this method will  be
diverted for filtration before discharge t(
the lake, approximately 27.0  hectares
(66 acres).
  The full report was  submitted ir
fulfillment of Grant No. R-805580 b'
the University of Central Florida unde
sponsorship of the U.S. Environmenta
Protection Agency.

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Martin P.  Wanielista, Yousef A. Yousef,  and James S.  Taylor are with the
  University of Central Florida, Orlando, FL 32816.
Richard P. Traver is the EPA Project Officer (see below).
The complete report, entitled "Stormwater Management to Improve Lake Water
  Quality," (Order No. PB 82-227 711; Cost: $21.00, subject to change) will be
  available only from:
        National Technical Information Service
        5285 Port Royal Road
        Springfield, VA22161
        Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
        Oil and Hazardous Materials Spills Branch
        Municipal Environmental Research Laboratory-Cincinnati
        U.S. Environmental Protection Agency
        Edison, NJ 08837
                                                                            •&U. S. GOVERNMENT PRINTING OFFICE: 1982/559-092/0459

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Agency                          Cincinnati OH 45268                                          Protection
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