Environmental Engineering Reference
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and a mean depth of 2.5 m. Estimate the distance
required for 50% of the nitrogen to be removed
by denitrification, and the rate of removal of
nitrate at a location where the nitrate concentra-
tion is 10 mg/L.
Table 4.14. There were 28,047 measurements
during this approximately 77-year period. The
John Day River has been found to be impaired
relative to a
E. coli
standard of 126 CFU/100 mL.
Determine the LDC for
E. coli
. If most of the
water-quality violations occurred under moist
conditions with 60-90% flow-rate exceedances,
estimate an allowable midrange
E. coli
load under
moist conditions.
4.44.
After mixing with a wastewater discharge, a fresh-
water river has a suspended solids concentration
of 100 mg/L and a temperature of 25°C. The sus-
pended solids have an average settling velocity of
0.4 m/d and the indicator bacteria have a distribu-
tion coefficient of 1.0 m
3
/g. The average light
energy on the water surface is 500 Ly/d, the depth
of the stream is 2.5 m, and the average flow veloc-
ity is 1 cm/s. Estimate the distance required for
50% attenuation of the indicator bacteria.
4.46.
The
E. coli
LDC where a stream is impaired rela-
tive to the bacteria water-quality standard is as
shown in Table 4.15. Point source discharges from
wastewater treatment plants within in the stream
add up to 0.17 m
3
/s, and these discharges are
required by regulations to meet the
E. coli
water-
quality standard of 126 CFU/100 mL. Assuming
an MoS equal to 10% of the TMDL, determine
the LA for nonpoint sources of
E. coli
.
4.45.
Ranked daily flow measurements at a section of
the John Day River in oregon are as shown in
TABLE 4.14. Flow Measurements at an Impaired Section of the John Day River
Rank
Flow (m
3
/s)
Rank
Flow (m
3
/s)
Rank
(m
3
/s)
1
1031
9817
47
19,634
11
701
264
10,518
42
20,335
10
1402
209
11,219
37
21,036
9
2104
175
11,920
33
21,737
8
2805
153
12,622
29
22,438
7
3506
134
13,323
25
23,140
7
4207
119
14,024
22
23,841
6
4908
106
14,725
19
24,542
5
5610
92
15,426
17
25,243
4
6311
85
16,128
16
25,944
3
7012
76
16,829
15
26,646
3
7713
68
17,530
14
27,347
2
8414
60
18,231
13
28,047
0
9116
54
18,932
12
TABLE 4.15. Load Duration Curve for
E. coli
Exceedance (%)
Load (×10
10
CFU/d)
Load (×10
10
CFU/d)
Load (×10
10
CFU/d)
Exceedance (%)
Exceedance (%)
0.0
1,090
35.0
49.9
70.0
11.6
2.5
278
37.5
44.6
72.5
10.6
5.0
220
40.0
39.2
75.0
9.75
7.5
185
42.5
34.7
77.5
8.73
10.0
161
45.0
30.2
80.0
7.81
12.5
141
47.5
26.3
82.5
6.88
15.0
125
50.0
23.3
85.0
5.95
17.5
112
52.5
20.5
87.5
4.96
20.0
101
55.0
18.4
90.0
4.13
22.5
90.0
57.5
16.7
92.5
3.41
25.0
80.5
60.0
15.4
95.0
2.69
27.5
71.8
62.5
14.3
97.5
1.88
30.0
63.7
65.0
13.2
100
0.18
32.5
56.5
67.5
12.4
-
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