The Bacteriological Aspects of Stormwater PollutionAuthor(s): E. E. Geldreich, L. C. Best, B. A. Kenner, D. J. Van DonselSource: Journal (Water Pollution Control Federation), Vol. 40, No. 11, Part I (Nov., 1968), pp.1861-1872Published by: Water Environment FederationStable URL: http://www.jstor.org/stable/25036149Accessed: 01/07/2010 11:50
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THE BACTERIOLOGICAL ASPECTS OF STORMWATER POLLUTION
E. E. Geldreich, L C. Best, B. A. Kenner, and D. J. Van Donsel
There has been a growing concern
in recent years with the pollution con
tributed to streams from stormwater
drainage. Earlier bacteriological an
alysis of separate and combined sewer
systems measured only the total coli form population present in this pol lutional source (1) (2) (3) (4). Re cent studies on the origins of fecal coliforms and fecal streptococci have
generated renewed interest in these
groups as better indicators of pollu tion by warm-blooded animals than
the total coliform group traditionally used in stream pollution investigations
(5). Using additional bacteriological pro
cedures, Weibel et al. (6) determined that 90 percent of all stormwater sam
ples from a separately sewered urban area had counts of total coliform, fecal coliforms, and fecal streptococci exceeding 2,900, 500, and 4,900/100
ml, respectively. Burm and Vaughn
(7), in a bacteriological comparison study of combined and separate sewer
discharges also used these three bac
teriological parameters. They found
the total coliform densities in the sep arate storm sewers to be approxi
mately one-tenth of those in combined sewers where median monthly values
were as high as 37,000,000 coliform
E. E. Geldreich and D. J. Van Donsel are
Research Microbiologists, National Water
Supply Research Laboratory, U. S. Public
Health Service, Cincinnati, Ohio. L. C. Best
is Microbiologist, Technical and Advisory
Investigations Activities, FWPCA, Depart ment of the Interior, Cincinnati, Ohio. B.
A. Kenner is 'Research Microbiologist, Waste
Identification and Analysis, Cincinnati Water
Research Laboratory, FWPCA, Department
of the Interior y Cincinnati, Ohio.
organisms per 100 ml. Fecal coli form densities were approximately 20
percent of the total coliform in com
bined sewage. Analysis of their data indicated the fecal coliform content of separate systems to be 7.6 percent of the total coliform population. They also reported that discharges from the combined sewer system have fecal
streptococcus densities about twice as
great as those from the separate storm
system (508,000 vs. 208,000/100 ml).
Although there now is available ex
cellent quantitative data to demon strate the magnitude of stormwater bacterial pollution densities, the sur
vival and persistence of these orga nisms in stormwater as related to sea
sonal temperatures and nutrients avail
able, the probable sources of the fecal and nonfecal pollution, and the fur ther evaluation of the potential health hazard by quantitative pathogen de tection have not been reported. These areas were selected for the develop
ment of this research project.
Methods
Stormwater w7as collected at selected locations along suburban street gut ters and from a storm sewTer outfall
that drained a small portion of a
wooded hillside bordering a city park. Standard manual sampling procedures
were used. At two other locations where drainage from a suburban busi ness district and agricultural land was studied, sampling was pro
grammed by automatic equipment pre
viously described by Weibel et al.
(6). All samples were examined for total
1861
1862 JOURNAL WPCF November 1968
coliforms, fecal coliforms, and fecal
streptococci by the membrane filter
(MF) technique with the use of M
Endo MF (8), M-FC (9), and KF
Streptococcus (10) media, respectively. For quantitative recovery of Salmo nella in stormwater, a 48-hr selective
growth procedure involving 41 ?C in
cubation and the MF technique was
used. Following sample filtration, the MF was first cultured for 18 to 24 hr on double-strength selenite bril
liant green sulfa medium for pre
liminary selective enrichment, then
transferred for final incubation and
differentiation on double-strength
xylose lysine brilliant green medium
(11). All suspected Salmonella colo nies were checked further for cultural
purity, for biochemical reactions to
selected tubed media to identify Salmonella, and finally, by serologi cal procedures, to verify Salmonella
species.
As background data to the study of bacteria present in stormwater run
off, samples of rainfall were taken from a location atop an eight-floor
building in a residential and light in
dustrial area. These samples were
collected in sterile stainless steel pans
placed in position at the start of rain
fall occurring during normal working hours. Volumes analyzed varied from 100 to 500 ml per test depending entirely on the amount of rainfall col
lected in a given storm.
Survival studies of pollution indi
cator strains and Salmonella typhi murium were made with the storm
water and rainwater samples collected in the four seasonal periods. Such
samples were sterilized by MF filtra
tion and split into four equal portions. Individual portions were inoculated
with different strains of organisms consisting of a coliform (-h + IMViC type), a fecal coliform
( + + -- IMViC type), a Strepto
coccus faecalis var. liquifaciens strain, and a S. typhimurium culture. Incu
bation temperature of 10? and 20? C, which represented the ones nearest to
the original water temperature re
corded at time of sample collection were used. All inoculated water sam
ples were examined at 1-, 2-, 3-, 7-,
and 14-day periods for the bacterial
density remaining. In the investigation of the fecal
material from cats, dogs, and various
rodents, procedures previously em
ployed (12) were used for quanti tative measurement of the pollution indicators present. In addition, pure culture studies were conducted on the various coliform and fecal strepto coccus strains isolated to determine the
percentage distribution of types.
Results and Discussion
Seasonal Variations in Stormwater Pollution
Stormwater examined from city streets, a suburban business district storm drain, and a wooded hillside
adjacent to a city park all had a
bacteriological composition similar to
stormwater runoff collected from cul tivated farm fields. In a study of
median values, seasonal differences in the bacterial densities for total coli
forms, fecal coliforms, and fecal
streptococci were noted for the data from the four stormwater sources
(Table I). Total coliform peak densi ties for urban locations (wooded hill
side, street gutters, and suburban busi ness district) occurred in autumn.
This also was noted for fecal coliform
and fecal streptococcus densities in
urban street gutters and business dis trict stormwater runoff. These latter
two indicator systems, however, reached an earlier peak (summer pe
riod) for stormwater runoff collected from the wooded hillside.
In drainage from rural stormwater
runoff, the possible existence of sum mer and winter peaks in bacterial indicator densities was demonstrated.
These peaks may be related, in part, to more lateral drainage during the summer growing season and the win ter period of frozen ground condi
Vol. 40, No. 11, Part 1 STORMWATER POLLUTION 1863
TABLE I.?Seasonal Variations (Median Values) for Bacterial Discharges in
Stormwater and Rainwater from Suburban Areas, Cincinnati, Ohio, and in
Agricultural Land Drainage, Coshocton, Ohio
Date Total Samples
Season Total Coliform
Fecal Coliform
Fecal Strep
tococcus
Ratio FC/FS
Feb. 62 to
Dec. 64
Jan. 62 to
Jan. 64
Apr. 62 to
Jul. 66
Jan. 63 to
Aug. 64
Jun.65 to
Feb. 67
278
177
294
94
49
Spring Summer
Autumn
Winter
Spring Summer
Autumn
Winter
Spring Summer
Autumn
Winter
Spring Summer
Autumn
Winter
Spring Summer
Autumn
Winter
2,400 79,000
180,000 260
1,400
90,000 290,000
1,600
22,000 172,000 190,000 46,000
4,400 29,000 18,000 58,000
<1.0
<1.0
<0.4
<0.8
190 1,900
430 20
230 6,400
47,000 50
2,500 13,000 40,000
4,300
55 2,700
210 9,000
<0.3
<0.7
<0.4
<0.5
940 27,000 13,000
950
3,100 150,000 140,000
2,200
13,000 51,000 56,000 28,000
3,600 58,000
2,100 790,000
<1.0
<1.0
<0.4
<0.5
0.20
0.70
0.03
0.02
0.07
0.04
0.34
0.02
0.19
0.26
0.71
0.15
0.02
0.05
0.10
0.01
tions. In the spring and autumn,
however, land cultivation results in
greater downward migration of wa
ter, with its associated bacteria, into the soil and groundwater table.
Fecal streptococcus densities were
consistently higher than fecal coliform levels in all four different sources of stormwater runoff. The highest me
dian value for fecal streptococci
(790,000/100 ml) occurred in the rural runoff during winter. A me
dian value of 47,000/100 ml repre sented the highest fecal coliform
density and this occurred in storm
water discharges from street gutters
during autumn. Fecal coliform to
fecal streptococci ratios were less than 0.71 in the four separate storm sewer
systems.
The fecal coliform segment of the
total coliform population in all 843
stormwater samples averaged 8.6 per
cent; a 21.1-percent maximum value was reached for those samples col
lected in autumn from the suburban
business district. Fecal coliform per
centages for all other seasons from
that source and the other stormwater sources were less than 16.5 percent,
with rural spring and autumn sam
ples containing only 1.3 and 1.2 per cent fecal coliforms. The autumn
samples from the wooded hillside con
1864 JOURNAL WPCF November 1968
tained the least amount of fecal coli
forms, only 0.2 percent of the 180,000 total coliforms per 100 ml.
Rainwater Contamination
Infrequently rain or snow falling to the earth is contaminated with traces of matter and occasional bac
teria acquired via air-borne particu lates. Pollution indicator counts for
rainfall were generally less than 1 per 100 ml as demonstrated by the median
values in Table I. There were 7 indi
vidual storms during the two summers,
however, that had total coliform densi
ties between 1 and 92/100 ml. One of these rain samples had 1 fecal
coliform per 100 ml and two samples contained 1 and 2 fecal streptococci per 100 ml, respectively. These orga nisms may have been associated with
soil particles or insect or vegetation
fragments found on microscopic ex
amination of debris trapped by the
membrane filtration method used in
the bacteriological examination of
these rainwater samples.
To demonstrate further the low bac
terial nutrient levels characteristic of
rainwater, the distilled water suitabil
ity test (13) was used to compare the
relative magnitude of nutrients avail
able in rainwater with those available
in triple-distilled water. These data
presented in Table II, representing an
average of 34 individual determina tions for the four seasons, were com
pared with a similar examination of 15 triple-distilled water samples. Ke sults indicate a detectable increase of the nitrogen content in rainwater dur
ing the spring and summer months.
The detectable carbon content de
rived from possible organic contami nation was minimal during all sea sons. As a reference point, significant bacterial nutrients in distilled water that will support growth would have a nutrient ratio above 3.0, as detected
by the distilled-water suitability test. The highest nutrient ratio for rain water examined in this study was 2.6 ; this occurred during the spring
months and was associated with the increased incidence of combined dust and rain showers.
Soil Contribution
Because rain falling to the earth contains insignificant bacterial con
tamination, the major contamination of this basic water source then must occur on contact with the polluted land environment. Soil in areas re
mote from man and his culture re
ceives insignificant levels of occasional contamination from wild animals and,
therefore, generally does not contain
TABLE IL?Relative Magnitude of Bacterial Nutrients in Rainwater
Compared with Similar Values for Triple-Distilled Water
Rainwater
Number of Samples
Sample pH
Nutrient Ratios
Relative Values
Nitrogen
7
10
9
Median
4.5
5.6
5.6
5.6
2.6
1.6
1.1
1.6
5.3 1.7
0.93
0.83
0.59
0.49
0.71
Triple-Distilled Water
15 6.8 0.8 0.21
Vol. 40, No. 11, Part 1 STORMWATER POLLUTION 1865
TABLE III.?Occurrence of Nonfecal Coliform IMViC Types in Soils, Stormwater, and Streams
Soil Samples
Total Strains
Percent Occurrence
Urban Stormwater
Total Strains
Percent Occurrence
Untreated Surface Water
Total Strains
390 75
7 1,109
80 181 157 61
4 1
53 6 0 0
0.4
18.3
3.5
0.3
52.0
3.8
8.5
7.4
2.9
0.2
0.1
2.5
0.3
10
106 7 0
156 45
203 26 34
2 2 2 0 0 0
1.7
17.9
1.2
26.3
7.6
34.2
4.4
5.7
0.3
0.3
0.3
86
1,507 136
18 971 373 469 443 229
6 49 23 0 0 0
2,132 593 4,310
Order of
Frequency
- +
- +
--+ + - + + +
-+ + + - +
- +
- + +
-- + +
- +
- +
-+ + +
any fecal coliforms (14). In con
trast, soil in areas populated by man, either on farms or in cities, receives
varying levels of warm-blooded-ani mal pollution from humans, pets, farm
animals, and rodents. As a result, soil contributes fluctuating densities of fecal contamination to drainage wa
ter, the amount being related to the
intensity and frequency of soil pollu tion. Survival of pollution indicators and any associated intestinal patho gens in soil and their possible transfer to stormwater is related to many fac tors (15). Some of these factors in clude sunlight exposure of the soil, temperature, frequency of rainfall, soil moisture, soil pH, organic matter,
frequency of recontamination of a soil
site, and the presence of competing or
antagonistic organisms in the soil en
vironment.
Analysis of the data presented in Table I indicates that fecal pollution accounts for an average of 8.6 percent of the median total coliform bacteria
present in stormwater examined.
Logically, the remaining non-fecal coliforms are assumed to be con
tributed to stormwater and the re
ceiving stream from the soil environ ment. To test this hypothesis, all
non-fecal coliform IMViC types from 251 soils widely distributed geographi cally (14) were compared with simi lar coliforms from untreated surface
water supplies for 14 major cities
(16) and from urban stormwater run
off collected from the same locations
reported in Table I. The results of this comparison, presented in Table
III, demonstrate the distribution simi
larity for non-fecal coliform types found in soil, stormwater runoff, and untreated surface water supplies. The three most common IMViC types in soil (- + -+,-++, and - + + + )
were also the most common in storm water and untreated surface waters. These three coliform IMViC types accounted for 78.8 percent soil strains, 78.4 percent stormwater strains, and 68.4 percent untreated surface water strains.
1866 JOURNAL WPCF November 1968
Bacterial Survival in Stormwater
Stormwater occurs at irregular pe
riods, and the resulting volume may exceed the normal loading capacity of
the usual treatment facility. If storm
water from separate systems is to be
treated before discharge into a re
ceiving stream, large holding reser
voirs will be necessary. During this
holding period, which might last a
few hours or a few days, the status
of the bacterial population becomes a
primary concern. For this reason, bac
terial survival studies w7ere performed on samples collected over a two-year
period in an effort to establish guide lines on stormwater natural self-puri
fication rates. Analysis of data col lected on 52 samples indicated no
significant differences related to pos sible effects from widely varying con
centrations of chemical contaminants
in stormwater runoff. There was, how
ever, a positive correlation for water
temperature and bacterial survival.
The survival data presented in Fig
'SjK^i?i?i?i?i?i?i?i?i?i?i i rq
50 f|\ ^? J
*\ \. if
? ?h ^V . "
'-*.?3 0.8 |?
X. -^ m?*Q
0 5L ?- FECAL COLIFORM >v
0.4L y-x AEROBACTER AEROGENES ^S. -H
? -* STREPTOCOCCUS FAECAL IS ^V^ I
I O.o SALMONELLA TYPHIMURIUM
]^
o,l_L_J_I_I_I_I_I_I_I_I_I_I_I_I 1 2 3 4 5 6 7 8 9 10 M 12 13 M
LENGTH OF TIME, days
FIGURE 1.?Persistence of selected enteric bacteria in stormwater stored
at 20?C
Vol. 40, No. 11, Part 1 STORMWATER POLLUTION 1867
ures 1 and 2 were divided into those
studies made on winter stormwaters
with temperatures ranging from 0? to
12 ?C and for spring, summer, and autumn samples with recorded tem
peratures ranging from 18? to 25?C. For these experiments 10? and 20 ?C incubation temperatures were chosen to represent the average winter and summer stormwater temperatures, re
spectively. The resulting data indi
cate organism persistence remained at
higher levels for winter studies
(10?C) during the 14 days of storage as compared with data from the sum
mer (20?C) studies. S. faecalis per sisted longer at both temperatures and at higher levels than either the Aero bacter aerogenes, fecal coliform, or S.
typhimurium strains used. S. typhi murium persistence at 10 ?C was
slightly higher than that of A. aero
genes but less than that of the fecal
coliform for the first 11 days of stor
age. These data indicate a closer
die-away pattern between fecal eoli
0.7 0.6
-* FECAL COLIFORM
*-X AEROBACTER AEROGENES - STREPTOCOCCUS FAECALIS
o.O SALMONELLA TYPHIMURIUM
J_L J__J_L 6 7 8 9
LENGTH OF TIME, days
10 11 12 13
FIGURE 2.?Persistence of selected enteric bacteria in stormwater stored
at 10? C.
1868 JOURNAL WPCF November 1968
forms and S. typhimurium than be tween fecal streptococci and the
Salmonella strain.
Cats, Dogs, and Rodent Contribution
The fecal coliform to fecal strepto coccus ratios for stormwater were al
ways below 0.7, indicating that pollu tion by warm-blooded animals other than man was probably responsible (17). In the urban community such
animals would likely be animal pets, particularly cats and dogs, plus a sub stantial rodent population. Data col lected on the percentile distribution of
five-tube Most Probable Number
(MPN) values for total coliform, fecal
coliform, and fecal streptococcus pro cedures used to examine rat, chip
munk, rabbit, cat, and dog feces are
summarized in Table IV. These data are based on the bacterial densities found in feces per gram of wet weight for individual values at the 25, 50, and 75 percent quartile points. The
relatively low coliform densities re
ported here for both rabbits and chip munks was observed similarly by Drake et al. (18) in their study of the incidence of coliforms in the feces of common wild animals. With the use of the 50-percent quartile points or median values, a fecal coliform to fecal streptococcus ratio was calcu
lated for each species. These ratio values ranged from a low of 0.0004 for rabbit feces to 0.29 for cat fecal ma
terial. Such ratios are, in general, smaller than those reported for farm animals (19). By contrast, the fecal coliform to fecal streptococcus ratio for man is 4.4 and above 4.0 for various domestic sewages.
The biochemical reactions of 2,635 coliform strains isolated from feces of rats, chipmunks, rabbits, cats, dogs, and a raccoon are reported in Table V. Pour coliform IMViC types ( + +-, ?
H-,-r-+, and + + + -) rep
resenting 98.7 percent of this animal coliform population plus three "oc casional" types were recovered. No
single type in the "occasional'' group constituted more than one percent of the coliform content. There was a
high correlation (95.3 percent) be tween the fecal coliform test and the fecal origin of these 2,635 strains iso lated from 57 different animals.
These data again demonstrate that the fecal coliform test is not specific for
any one coliform type or group of IMViC types, but instead has an ex
cellent positive correlation for coli forms derived from the intestinal tract of warm-blooded animals.
Possible similarities of fecal strepto coccus type distribution in feces of rodents and pets and in stormwater
samples are compared in Table VI. Both in the feces of these animals and in the various storm waters, the entero coccus segment of the fecal strepto coccus group predominates. There
TABLE IV.?Percentile Distribution by Quartile of MPN Values per Gram for Rodent, Cat, and Dog Fecal Material
Animal Feces
Number of Samples
Rat Chipmunk Rabbit Cat
19
Total Coliform 25% Level 50% Level 75% Level
Fecal Coliform 25% Level 50% Level 75% Level
Fecal Streptococcus 25% Level 50% Level 75% Level
FC/FS RATIO
13,000 330,000
14,000,000
13,000 330,000
14,000,000
490,000 7,700,000
11,500,000
80 148,000
130,000,000
80 148,000
130,000,000
94,000 6,000,000
410,000,000
90 4,100
2 20
2,000
2,700 47,000
270,000
630,000 7,900,000
92,000,000
630,000 7,900,000
92,000,000
220,000 27,000,000
2,760,000,000
0.04 0.03 0.0004 0.29
Vol. 40, No. 11, Part 1 STORMWATER POLLUTION 1869
TABLE V.?Occurrence of Coliform Types in Animal Fecal Samples
Animal No. of Strains Examined
Total Fecal Coli form
Strains
+ + -- -
+ -- --
+ + + + + -
+ + -
+ -
+ -
+
Rodentia
Rat
Chipmunk Lagomorpha
Rabbit Carn?vora
Cat Dog Raccoon
317 100
251
600 1,317
50
316 50
201
600 1,295
50
282 0
196
586 1,253
49
0 50
7 41
0
30 0
49
0 8 1
0 50
6 11 0
Total strains 2,635 Percent fecal coliforms
Percent strain occurrence 95.3%
89.8 3.7 3.3 1.9 1.0 0.2 0.1
were no significant differences in the fecal streptococcus distribution among either the three stormwater sources or
for any stormwater source for differ ent seasons of the year.
The atypical fecal streptococcus grouping consists of a S. faecalis strain that can hydrolyze starch and S. faecalis var. liquefaciens that is
capable of peptonization of milk. Both types are of limited sanitary significance since they are the pre dominant feoal streptococcus group isolated from vegetation, insects, or
soil (19). The only discrepancy in the fecal
streptococcus type distribution in
rodents, pets, and stormwater was to be found in the percentage of the S. bovis and S. equinas group. In this
case, S. bovis and S. equinus were at
a significant level in rodents (17.1
percent) and dogs (32.0 percent). Little or none of these two members of the fecal streptococci was found in the 3,079 stormwater strains exam
ined. Laboratory data on the survival of S. bovis and S. equinus indicate these two fecal streptococcus strains are the most sensitive pollution indi
cators, with rapid die-away once they have been removed from the warm
blooded animal intestinal tract. For
example, S. bovis and S. equinus sur
vivais in various stormwater samples were always less than 30 percent in 24 hr with less than 1 percent viable after 1-day storage. Thus, recovery of these fecal streptococcus strains in stormwater reflects very recent soil
contamination with prompt transfer to the water environment through con
current stormwater runoff.
Salmonella in Stormwater
With demonstration of significant fecal pollution in stormwater, there is
always an opportunity for the chance occurrence of Salmonella in this source
of water pollution. With the use of
experimental media previously de scribed for the quantitative recovery of Salmonella, positive results were
obtained for a stormwater sample from the business district separate storm sewer system (20). This storm
water sample contained 4,500 S.
thompson per 100 ml. The bacterial
pollution indicator densities were
3,800,000 total coliforms, 450,000 fecal
coliforms, and 370,000 fecal strepto cocci per 100 ml. These limited data indicate that one Salmonella was de tected for every 100 fecal coliforms in the stormwater sample analyzed.
Although Salmonella could not be found in other stormwater samples examined by current experimental pro
1870 JOURNAL WPCF November 1968
TABLE VI.?Fecal Streptococcus Distribution in Rodents, Cats, and
Dogs and Three Types of Stormwater
Source No. of Strains Examined
Percentage Distribution of Fecal Streptococci
Season Enterococcus *S. bovis S. equinus
Animals
Rodents
Cats
Dogs
539 268 585
47.3
89.9
44.0
Total 1,392 Average 54.2
17.1
1.5
32.0
20.3
Stormwater
Residential streets 745 180 40
193
Spring Summer
Autumn
Winter
81.6
66.6
85.0
85.0
Total 1,158
Average 80.0
Business district 417 439 296 324
Spring Summer
Autumn
Winter
82.3
71.1
75.7
86.1
Total 1,476
Average 78.5
Rural 227 90 96 32
Spring Summer
Autumn
Winter
90.8
86.7
77.1
96.9
Total 445 Average 87.4
0.4
0.0
0.0
1.6
0.5
1.7
0.0
1.7
3.4
1.6
0.9
0.0
0.0
0.0
0.5
cedures, its presence in this one in
stance is significant. Agricultural animals are frequent
sources of Salmonella. Miner et al.
(21) reported isolation of Salmonella in the litter and runoff from two
cattle feedlots holding apparently nor
mal animals. Entry of such material into stormwater runoff may be a sig
nificant source of pathogens in rural areas.
Summary and Conclusions
Stormwater examined from city streets, a suburban business district storm drain, and a wooded hillside
adjacent to a city park all had a bac
teriological composition similar to
stormwater runoff collected from cul
tivated farm fields. Seasonal differ ences in the bacterial densities for total coliforms, fecal coliforms, and fecal streptococci were noted in a
study of median values. The fecal coliform segment of the total coliform
population for all stormwater samples averaged 8.6 percent. For stormwater
samples collected in autumn from the suburban business district, however, 21.1 percent fecal coliforms were ob served.
Data collected on 49 rainwater sam
ples indicated pollution indicator counts generally were less than 1/100
ml, but individual storms occasionally
may contain a few coliforms. The
Vol. 40, No. 11, Part 1 STORMWATER POLLUTION 1871
origin of these positive samples was
associated with material acquired in
dust storms or from insect and vegeta tion fragments. The major contamina tion of rainwater occurs from contact
with the polluted land environment. Data showed the similarity of the non fecal coliform distribution patterns for strains examined in soil, stormwater
runoff, and untreated surface waters.
Differences in the fecal coliform con tent for a particular soil, stormwater, or untreated surface water were re
lated to varying levels of fecal con
tamination present.
In the urban community fecal con tamination in separate stormwater sys tems is derived initially from the fecal
material deposited on soil by cats, dogs, and rodents. Both in the storm water and in fecal material from the
animals, the enterococcus segment of the fecal streptococcus group showed similar percentage patterns and the ratios of fecal coliforms to fecal
streptococci were generally less than 0.7. By contrast, the fecal coliform to fecal streptococcus ratio for man is 4.4 and above 4.0 for various domestic
sewages.
Studies of bacterial survival in stormwater indicated organisms per sisted at higher levels for winter stud ies (10?C) than they did in the sum
mer (20? C) studies. Comparison survival studies for S. typhimurium,
A. aerogenes, S. faecalis, and a fecal coliform strain demonstrated that the
die-away pattern of S. typhimurium resembled that of the fecal coliform strain more closely than it did for that of fecal streptococcus strain, S.
faecalis. S. thompson was isolated in one
storm sample at a level of 4,500/100 ml. The bacterial pollution indicator densities for this sample from the business district separate storm sewer
system were 3,800,000 total coliforms, 450,000 fecal coliforms, and 370,000 fecal streptococci per 100 ml.
Stormwater can be a major source
of intermittent pollution to bathing beaches and to water supply reservoirs
opened to limited public recreational uses. Eegulations to prohibit cats and
dogs on public beach areas and an
adequate garbage control plan to dis
courage increased rodent habitation will be of benefit. Diverting storm drains and land drainage away from beaches and reservoirs are also im
portant engineering considerations.
Finally, in areas where such storm
drainage cannot be diverted economi
cally to prevent deterioration of water
quality, treatment methods must be
developed to handle the large volumes of irregular discharges that character ize stormwater.
Acknowledgments
The authors wish to express their
appreciation to Messrs. G. G. Robeck, S. R. Weibel, R. J. Anderson, and R. B. Weidner, Engineering Research
Section, for their engineering assist ance in locating separate stormwater
systems in suburban, agricultural, and industrial areas. Special recognition also is given to Mr. Martin P. Milet of Williamsdale Kennels for a source of fecal samples from healthy cats and
dogs fed a normal diet free from antibiotic additives.
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1872 JOURNAL WPCF November 1968
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