Environmental Engineering Reference
In-Depth Information
TABLE 4.13. Measured Dye Concentrations Downstream of Release Location
Concentration (mg/L)
Concentration (mg/L)
Time (min)
At 500 m
At 1000 m
Time (min)
At 500 m
At 1000 m
0
0
0
16
0.17
0.35
1
0
0
17
0.04
0.73
2
0
0
18
0.01
1.1
3
0
0
19
0
1.9
4
0
0
20
0
2.7
5
0
0
21
0
1.9
6
0.03
0
22
0
1.1
7
0.05
0
23
0
0.67
8
0.12
0
24
0
0.41
9
0.45
0
25
0
0.21
10
0.92
0
26
0
0.07
11
2.3
0
27
0
0.03
12
3.3
0
28
0
0.01
13
2.3
0.02
29
0
0
14
1.1
0.04
30
0
0
15
0.57
0.22
Estimate the longitudinal dispersion coefficient in
the river.
contaminant in the discharge such that the water-
quality standard will be met on the boundary of
the mixing zone. (b) Determine the minimum dif-
fuser length and location of the diffuser that must
be used to discharge the maximum concentration
calculated in Part (a); and (c) Estimate the con-
centration of the contaminant 500 m downstream
of the mixing zone.
4.15. An accidental contaminant release into a river
causes a contaminant concentration of 200 mg/L
to be maintained at the spill site for a duration of
15 minutes. The contaminant has a first-order
decay coefficient of 10 d −1 , the mean flow velocity
in the river is 15 cm/s, and the longitudinal disper-
sion coefficient is 20 m 2 is Assuming that the con-
taminant is well mixed across the river, estimate
the maximum contaminant concentration 3 km
downstream of the spill. Would it be appropriate
to assume that the duration of the spill is small
relative to the travel time to the downstream
location?
4.17. If the river described in Problem 4.14 is 20 m wide
and 5 m deep, estimate the mass of dye that was
used in the tracer study. verify that the assumption
of a conservative dye is reasonable.
4.18. Henry's constant, H , is an important parameter
for estimating the volatization of voCs in streams.
Use Equation (4.55) to estimate H for chloroeth-
ane, 1,2-dichloroethane, and vinyl chloride at
20°C. Compare these values with the values of H
given in Table 4.3.
4.16. A river has an approximately trapezoidal shape
with a bottom width of 10 m and side slopes of 3:1
(H :v). The 7Q10 flow in the river is estimated as
9.5 m 3 is Manning's n is estimated as 0.023, and
tracer experiments in the river have indicated that
the Koussis and Rodríguez-Mirasol (1998) formu-
lation adequately describes longitudinal disper-
sion in the river. A factory proposes to discharge
industrial wastewater at a rate of 2.5 m 3 /s contain-
ing a contaminant that has a first-order decay con-
stant of 3 h −1 , the water-quality standard for this
contaminant is 5 mg/L, and this standard must be
met on the boundary of a mixing zone that is
located 100 m downstream of the discharge loca-
tion. A hydraulic analysis of the channel flow indi-
cates that depth-of-flow in the middle of the
channel under combined flow conditions is 1.8 m.
(a) Determine the maximum concentration of the
4.19. A river water contains ethylbenzene (C 8 H 10 ) at a
concentration of 22 mg/L. Express this concentra-
tion in mol/m 3 . The molecular weight of ethylben-
zene is 106.17 g/mol.
4.20. A river has a mean velocity of 7 cm/s, a width of
20 m, and a depth of 1.3 m. The water and air
temperatures are both 17°C, and the average wind
speed is 8 m/s.
(a) If the longitudinal dispersion coefficient in the
river is 2.5 m 2 is estimate the maximum con-
centration 10 km downstream of a location
where 12 kg of tetrachloroethene has been
spilled into the river.
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