Environmental Studies Chapter 2 Homework The Travel Time Between The Two Points

28. From Fig. 2.37, the Earth’s surface receives wavelengths of 0.3 mm

(300 nm) and above. Thus, only aniline will absorb sunlight and

potentially degrade by direct photodegradation; the anilinium ion

will not. A water treatment scheme using sunlight should therefore

favor the aniline form. From the acid-base reaction provided:

29. a. To calculate the maximum concentrations of Na

þ

and metham

downstream of the spill, the velocity of the Sacramento River must

be estimated from data on its discharge rate and average geometry:

Then, travel times to Dunsmuir and Shasta Lake can be

estimated:

e39CHAPTER 2 SOLUTIONS

At the town of Dunsmuir, the maximum concentration of Na

þ

will be:

At the point where the Sacramento River reaches Shasta Lake,

the maximum concentration of Na

þ

will be:

Metham concentration

Metham degrades by both acid and neutral hydrolysis

and by photolysis. To use Eq. (2.12), a combined, first-order

decay rate must first be estimated for these degradation

processes:

e40 SOLUTIONS MANUAL ONLINE

Using Eq. (2.12) and the results of the mass calculation performed

above (initial [Na

þ

]/m

2

equals initial [metham]/m

2

):

b. The effect of longitudinal dispersion can be seen from the

attenuation of the Na

þ

peak concentration between Dunsmuir and

Shasta Lake:

For hydrolysis of metham, the first-order decay rate is:

Peak attenuation due to hydrolysis alone can then be estimated

as:

e41CHAPTER 2 SOLUTIONS

Dunsmuir to Shasta Lake.

c. Using Eq. (1.21), the half-life for hydrolysis is:

d. The total load of metham depends on the total mass of metham in

the river, which is affected only by degradation reactions, not by

0:92 0:18 ¼0:16

Note that this is equivalent to summing the decay constants for

the two processes:

e42 SOLUTIONS MANUAL ONLINE

Shasta Lake.

One might ask whether metham at the tailing edge of the plume

has significantly more time to degrade than metham at the leading

edge of the plume. To determine this, consider how much the

metham plume has spread by the time it arrives at Shasta Lake.

From Eq. (2.7):

30. a. Using the Deffeyes diagram in Fig. 2.20, follow a vertical line from

C

of 410

4

mol/liter to where it intersects with a horizontal line

e43CHAPTER 2 SOLUTIONS

31. a. To estimate the reaeration coefficient, assume that the surface

renewal model is applicable to gas exchange in the stream. Then

the gas exchange coefficient for oxygen can be estimated from the

relationships:

b. Given the dimensionless Henry’s law constant of 0.02, resistance to

gas exchange in the stagnant air layer immediately above the water

c. First estimate the overall pseudo-first-order rate constant k

T

at the

stream pH of 8.5:

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d. If volatilization is also considered as a loss mechanism, the overall

loss rate can be estimated as:

32. a. First estimate the river’s velocity using the Che

´zy-Manning

equation. For SI units, use Eq. (2.2b).

Using Eq. (2.4):

c. 95% of the chemical mass is contained within the portion of the

river lying within two standard deviations upstream and two

d. To estimate the reaeration coefficient, first estimate the rate at

which propane is being lost due to gas exchange with the

e45CHAPTER 2 SOLUTIONS

Assuming the surface renewal model is applicable, the

reaeration coefficient can be estimated as:

e. Equation (2.14) can be used to estimate the length of the transverse

mixing zone. To estimate the transverse dispersion coefficient,

assume that the uniform small river is a straight channel, and

therefore Eq. (2.16a) applies:

33. a. Under these conditions, the TCE is a pure phase liquid. First

estimate the TCE concentration just above the surface of the

e46 SOLUTIONS MANUAL ONLINE

Using Eq. (2.36) (or, alternatively, Eq. 2.35) to estimate the gas

exchange coefficient for air-side control:

b. Once the rain covers the TCE, the volatilization of TCE will be

controlled by the water side. Equation (2.34) can be used to

estimate the gas exchange coefficient:

34. a. First estimate the toluene concentration in the stream at the location

of the seep:

Use the stream depth to convert to a first-order loss coefficient:

e47CHAPTER 2 SOLUTIONS

Then use Eq. (1.20) to estimate the concentration of toluene at

point B:

b. Now consider that the chemical seeping from the ground is the

methyl ester of dichloroacetic acid. Neglecting volatilization and

acid-catalyzed hydrolysis, a pseudo-first-order loss rate can be

estimated based on neutral and base-catalyzed hydrolysis rates

and the stream pH:

35. a. First estimate the travel time to the municipal waterworks, using

Eq. (2.3a):

Then use Eq. (2.12) to estimate the maximum concentration

expected at the waterworks:

b. At the time of the peak organism concentration at the intake pipe,

the standard deviation of the cloud of organisms can be estimated

from Eq. (2.7):

c. If the organisms have a 10-hr half-life in the river, the maximum

concentration will be slightly decreased. First use Eq. (1.21) to

convert the half-life to a first-order decay rate:

e48 SOLUTIONS MANUAL ONLINE

m3

36.

a. At a peof 7 and a pH of 4.5:

b. Under sulfidic conditions, peis on the order of 4 (Fig. 2.28).

Therefore:

Pu

is the dominant plutonium species.

c. From Fig. 2.28, aerated water has a peon the order of 14. Therefore:

37. a. Given the Alk of 0.2 meq/liter and the pH of 7, use the Deffeyes

b. To estimate the pH of the wastewater after the organic matter has

been fully mineralized, the new C

T

and the new Alk must first be

e49CHAPTER 2 SOLUTIONS

b. When 510

5

mol HCl is added to the one liter sample, the

alkalinity decreases (see Eq. 2.41):

39. a. The benzene flux to the atmosphere will be controlled by the water

side. Assuming the thin film model applies to the pond, the gas

exchange coefficient for benzene can be estimated using Eq. (2.32):

b. Assuming volatilization is the only loss process for benzene in the

pond, Eq. (1.20) can be used to estimate the benzene concentration

e50 SOLUTIONS MANUAL ONLINE

Dividing both sides by volume and recognizing that (mass

benzene

/

volume) equals C

benzene

and (area/volume) equals (1/depth):

40. a. H2CO3

½þHCO3

½þCO32



¼0:001 mol=liter

From Eqs. (2.43) and (2.44):

b. Use Eq. (2.42) to determine if the lake is in equilibrium with the

atmosphere:

e51CHAPTER 2 SOLUTIONS

c. The reaction for calcium carbonate can be written as:

41. Assuming there has been no disturbance, the deepest sediments are

the oldest. PCB deposition began when the sediment now located at a

25 cm depth was first deposited.

42. a. If methane production is to begin immediately after the bioreactor

is filled, there must not be any other more energetically favorable

b. The first bubbles will consist of approximately 0.8 atm N

2

and

0.2 atm CH

4

, assuming total pressure of 1 atm in the bioreactor.

Use Eq. (1.25) to convert the partial pressure of CH

4

to a gas phase

concentration:

e52 SOLUTIONS MANUAL ONLINE