CE 221 Introduction to Environmental Engineering
Exam I
September 25, 2002
7:00 - 9:00 pm
Room 200 AEC
Problem Solving
Problem 1 25 Points
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Problem 2 15 Points
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--------------------------------------------------------------------------------------------------------------------Sub Total (40 Points)
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Short Answers
Wetlands (9 Points)
S A #1
S A #2
S A #3
3 Points
3 Points
3 Points
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Defining Regulations (11 Points)
S A #4
3 Points
S A #5
3 Points
S A #6
3 Points
S A #7
2 Points
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Hydrologic Cycle (8 Points)
S A #8
2 Points
S A #9
3 Points
S A #10
3 Points
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Other (12 Points)
S A #11
S A #12
S A #13
S A #14
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4 Points
2 Points
3 Points
3 Points
--------------------------------------------------------------------------------------------------------------------Sub Total (40 Points)
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______________________________________________________________________________
Total (80) Points
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Final Score %age
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Initial __________
Name ________________________
CE 221 Introduction to Environmental Engineering
Exam I
September 25, 2002
Be sure to print your name at the top of this page and initial this page and all
subsequent pages. All work is to be done neatly using a dark pencil or pen. Answers
are to be underlined or boxed.
Problem 1 (25 Points)
Consider a 10.0 x 106 m3 lake fed by a polluted stream having a flow rate of 5.0 m 3/s
and pollution concentration equal to 10 mg/l (figure below). There is also a sewage
outfall that discharges 0.5 m3/s of wastewater having a pollutant concentration of 100
mg/L. The stream and sewage wastes have a reaction rate coefficient of 0.20 day-1.
Figure 1 - Polluted Lake
A. Assuming the pollution is completely mixed in the lake, and assuming no
evaporation or other water losses or gains, find the steady-state concentration and
the hydraulic detention time. Express your steady concentration in mg/L and your
detention time in days. (4 Points)
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B. Suppose the condition of the lake is deemed unacceptable. To solve the problem it
is decided to divert the sewage outfall around the lake, therefore the outfall flow is
completely eliminated from the stream as well as the pollution associated with the
outfall flow. The incoming stream maintains a flow of 5.0 m 3/sec and pollutant
concentration of 10 mg/L. Assuming complete mixing conditions, find the
concentration of pollution in the lake one week after the outfall diversion. (8 Points)
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C. Find the new steady-state concentration in the lake after the outfall diversion. (3
Points)
D. Assume the outfall from the sewage outfall is fed back into the stream at the point
where the water leaves the lake. The flow of the outfall (0.5 m3/sec) and the
concentration of pollutant (100 mg/L) in the outfall remains the same. Assume the
concentration of the pollutant leaving the lake is 2 mg/L and that there is complete
mixing of the two. What is the concentration of the pollutant 4 days downstream of
the lake/outfall mixing point assuming the reaction rate constant remains the same
(K = 0.20 day-1)? (5 Points)
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E. Assuming the stream channel leaving the lake has an average water level height of
0.75 meters and an average bed width of 3 meters, what is the distance a drop of water
travels, in meters, 4 days downstream from the exit of the pond (the point where the
outfall and pond water mix)? (5 Points)
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Problem 2 (15 Points)
A lake has pH of 7.5. A two-liter sample of the lake water is evaporated. The solids are
remaining are sent to a laboratory for analysis. The results from the laboratory revel a
mass of 440 mg of Ca(HCO3)2. From the information provided calculate the total
theoretical alkalinity of the lake water. Express your answer in mg/L as CaCO3. Show
all work and address all assumptions. (15 Points)
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Short Answer Section
Brief means one or two sentences please!
Wetlands (9 Points)
1. How does the EPA/Army Corps definition of wetland differ from the US Fish and
Wildlife Service (FWS) definition? (3 Points)
2. Wetlands act as natural wastewater treatment plants. What are three treatment
processes that wetlands provide in the way of water treatment? (3 Points)
3. Discuss three ways that wetlands, or modifications of wetlands, can be used as
engineering solutions to address contaminated runoff? (3 Points)
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Defining Regulations (11 Points)
4. Who is Lois Gibbs and how did she change the course of history? (3 Points)
5. What is “risk-based clean-up actions”? (3 Points)
6. Briefly discuss the SDWA and it’s evolution. (3 Points)
7. How does the CWA differ from the SDWA? (2 Points)
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Hydrologic Cycle (8 Points)
8. Is it possible that you could drink the same drop of water that Abraham Lincoln
drank? Provide details to your answer. (2 Points)
9. Name six of steps of the hydrologic cycle. (3 Points)
10. Express the hydraulic cycle mathematically. How might go about collecting
information needed to address your mathematical model? (3 Points)
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Other (12 Points)
11. How does a reaction that takes place in a stream differ from a reaction that takes
place in a “CSTR”? And how does a reaction that takes place in a CSTR differ from
a reaction that takes place in a batch system? Use mathematical relationships to
support your answer. (4 Points)
12. Which system, in Question 11, is the most effective and why? (2 Points)
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13. What is the pOH of pure water and why? Support your answer with mathematical
relationships. (3 Points)
14. What reaction is an oxidation reaction always accompanied by? Explain what is
involved in these reactions. Provide examples. (3 Points)
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Formula Sheet Test 1
1) Density of water = 1000 kg/m3 = 62.43 #/ft3
2) 7.48 gal/ft3
3) 8.34 #/gal
4) 1000 L/m3
5) 8.345
#L
mg  Mgal
6) at STP 22.414 L/mole
7)
dC
  KC
dt
8) Ct  C0e Kt
9) V
dC
 S  QC  KCV
dt

10) C(t )  C   (C 0  C  ) exp  K  Q
V
t 
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