CE 326
Air Pollution Design Analysis
Objective:
To apply engineering knowledge towards critically analyzing an air pollution control
system design (Due December 6)
Your long-time local service station recently decided to install new gasoline tanks to replace the old
steel tanks installed in the 1950’s. After excavating the old tanks they found them rusted and
leaking into your town’s groundwater. Being conscious citizens, they decided to remediate the
gasoline-contaminated groundwater by pumping it out of the ground and blowing the gas off in an
air-stripping tower. Since the service station is lucky enough to be in Iowa, they can directly
discharge the vapors into the atmosphere, and currently do so from a 9 m tall, 30 cm diameter PVC
exhaust stack. The remediation effort is expected to take ten years to complete.
Your neighbors (Rahul, Nancy, Mumbe, and the Smiths) are concerned about vapors from the stack
because they are directly downwind. The Smiths are particularly concerned because they have a
two-year old daughter who plays every day in the back yard. The service station owner assures the
people of your neighborhood that there is no risk to the people of your neighborhood. Since you are
the neighborhood engineer (and because you are also downwind of the stack), they have asked you
to evaluate the service station’s design. They want to know if it’s safe.
The following is a map of your neighborhood, information you have obtained describing your local
atmospheric conditions, and the air stripping tower design parameters needed to design the airstripping tower stack:
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CE 326
Air Pollution Design Analysis
Atmospheric conditions:
Local atmospheric conditions are slightly unstable to neutral with an average wind speed of 2 m/s
and peak gusts up to 13 m/s. The yearly average temperature in your town is 20ºC and the wind
always blows in exactly the same direction, as indicated on the map. The atmospheric pressure in
your town averages 1 atm.
Pilot Scale Treatment Data (use these for your calculations):
Benzene (C6H6) peak concentration =
400 ppmv
Stack Gas Flow rate =
60000 L/min
Stack Gas Temperature =
20ºC
Using this information, the service station engineers’ assumptions for their design and a summary
of their RBSL and downwind concentrations are given on the last page.
Questions:
1. Critically evaluate the service station engineers’ assumptions for atmospheric conditions and the
risk model. Construct a table including:
(a) The assumption you think is incorrect
(b) Why it is in error
(c) Your recommendation to correct the error
(d) The effect your recommendation in part c will have on the RBSL or down wind
concentration.
2. Using your evaluation in question 1, reassess the stack design.
(a) Using your recommendations for changes in the design assumptions and using the physical
stack height of 9 m, calculate:
i. The RBSL for benzene inhalation for each individual (in µg/m3)
ii. The ground level concentrations of benzene for each individual at the locations shown
on the map (R, N, M, S and Y) (in µg/m3).
iii. Using the calculated concentration of benzene from ii, determine your own increased
cancer risk from inhaling this concentration over the course of ten years. Is this level
of risk acceptable to you? Why?
(b) Determine the maximum concentration of benzene that can be emitted from the 9-m tall
stack (g/s) at a rate of 60000L/min so that Rahul, Nancy, Mumbe, the Smiths, or you do not
get exposed above the RBSL for benzene. Report your answer in ppmv.
(c) Determine the minimum stack height (to the nearest 0.1-m) required to emit benzene at
400ppmv and 60000L/min so that Rahul, Nancy, Mumbe, the Smiths, or you do not get
exposed above the RBSL for benzene.
(d) Show a plot of the centerline ground level concentration of benzene (µg/m3) versus distance
downwind (m) for your selected stack height. Is there some location that exceeds RBSLs?
3. Evaluate the service station engineers’ design by comparing it to your calculated results in part
2. Is the service station’s design safe? Why? Do you have any special concerns that were not
addressed by the services station’s engineers? What were they? How should they be
addressed? Your evaluation should be approximately one to two pages and written as a letter to
the service station engineers (if you feel it is not safe) or your neighborhood association (if you
feel it is safe) (make up a name and address to send it to). Some ideas that may help you with
your evaluation may be:
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CE 326
Air Pollution Design Analysis
(a)
(b)
(c)
(d)
What factors are not considered that may affect a person’s risk of cancer in this situation?
What are some of the problems with the risk model that may affect your evaluation?
What can be done to reduce pollutant discharge in the air stripping operation?
Can you think of a more appropriate design for treatment of the groundwater? What would
it be? Why would you use it?
Final Report:
Format your design report in the following manner:
1) Your letter from question 3.
2) Your table of assumptions that were in error from question 1.
3) The question 2 summary sheet.
4) Your downwind concentration versus distance plot from question 2 d. If there are
locations where the ground level concentrations exceed RBSLs show where.
5) Your calculations, spreadsheet solutions, and written answers from part 2
Additional Information:
Slope factors and Reference Doses Used for Iowa Tier 1 Table Generation, taken from the Iowa
Administrative Code Environmental Protection [567] Chapter 135, Appendix A p.73, 1/15/97
Chemical
Benzene
Toluene
Ethylbenzene
Xylenes
Naphthalene
Benzo(a)pyrene
Benzo(a)anthracene
Chrysene
SFi
SFo
RfDi
RfDo
(kg-day)/mg
0.029
--------6.1
0.61
0.061
(kg-day)/mg
0.029
--------7.3
0.73
0.073
mg/(kg-day)
--0.114
0.286
2.0
0.004
-------
mg/(kg-day)
--0.2
0.1
2.0
0.004
-------
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CE 326
Air Pollution Design Analysis
Question 2 summary sheet
Names:
______________________________
Section:
_______
______________________________
Part a)
RBSL, ground level concentration, and risk calculations:
i and ii)
RBSL:
iii)
Ground Level Conc.
Rahul
_______________µg/m3
_________________µg/m3
Nancy
_______________µg/m3
_________________µg/m3
Mumbe
_______________µg/m3
_________________µg/m3
Smiths
_______________µg/m3
_________________µg/m3
You
_______________µg/m3
_________________µg/m3
Increased risk of cancer:
__________ in _______________
Is this level of risk acceptable to you? Why? (Each group member
should answer this individually. Attach a separate sheet if necessary)
Part b)
Maximum concentration of benzene for a 9-m stack emitting at a
rate of 60 000 L/min = __________________________________
Part c)
Minimum stack height required to emit benzene at 400 ppmv and
60 000 L/min =
__________________________________
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CE 326
Air Pollution Design Analysis
Air Stripping Tower Risk and Down Wind Concentration Calculations
Stack Flowrate:
Stack Exit Velocity:
Gas Temperature:
9m
0.3 m
3
1 m /s
14.15 m/s
293.15 K
Atmospheric Conditions:
Slightly Unstable to Neutral
C
Atmospheric Class:
a = 104
c = 61
d = 0.911
f= 0
10 m/s
Wind speed:
101.325
kPa
Atmospheric Pressure:
293.15 K
Atmospheric Temperature
Calculations:
Plume Rise (H):
Effective Stack Height (H):
RBSLbenzene
0.637
9.637
915.4
m
m
µg/m3
Risk Model Assumptions
Target Risk (TR):
Body Weight (BW):
Averaging Time for carcinogens (ATc):
Inhalation Rate (IRair):
Exposure Frequency (EF):
Exposure Duration (ED):
1.00E-03
80 kg
30 years
3
10 m /day
330 days/year
10 years
Properties of Benzene
Slope Factor:
Peak Concentration:
Molecular Weight:
Stack Emission Rate (Ebenzene):
0.029
400 ppm
78 g/mol
1.30 g/s
200
peak concentration = 184.2 µg/m 3
90 m down wind
180
Concentration (µg/m3)
Stack Parameters
Stack Height:
Stack Diameter:
160
140
120
100
80
60
40
20
0
0
100
200
300
400
500
Distance from the stack (m)
5
600
CE 326
Air Pollution Design Analysis
Grading Rubric for Air Pollution Design Analysis
Level of Achievement
Exemplary
Problem 1, 25%
25%
Criteria
Parts a) and b)
Identification of
incorrect
assumptions
Parts c) and d)
Critical evaluation
of service station
engineers’
assumptions
Overall
Correct table
format, spelling,
grammar, and
punctuation
Problem 2, 50%
part a), i)
Calculation of
RBSL for each
individual
Part a), ii)
Satisfactory
15% - 22%
10%
i) Six or more design or
assumption flaws listed
ii) Explanation of why
each assumption is
incorrect noted clearly
6% - 9%
i) 3-5 design or
assumption errors
indicated
ii) Explanation of why
each assumption is
incorrect noted clearly
10%
6% - 9%
i) Recommendation to
i) Recommendation to
correct the error is noted
correct the error is noted
clearly
clearly
ii) The impact on risk
ii) The impact on risk
assessment or ground level assessment or ground level
concentrations identified
concentrations indicated
but unclear
5%
3% - 4%
i) Formatted correctly as a i) Formatted correctly as a
table
table
ii) Less than one spelling, ii) Two to three spelling,
grammar, or punctuation
grammar, or punctuation
error per 100 words.
errors per 100 words.
iii) Clear and concise
iii) unclear or lengthy
explanations
50%
5%
i) Calculations are
performed correctly,
complete sample
calculations are shown.
ii) Calculations are neatly
presented and in order.
iii) All assumptions are
clearly noted
10%
30% - 44%
3% - 4%
i) Some errors in the
calculations but partial
credit can be given
because sample
calculations are shown
neatly presented and in
order OR Answers are
correct, but no sample
calculations are shown or
they are illegible.
ii) All assumptions are
clearly noted
6% - 9%
6
Unacceptable
 12%
 5%
i) <3 design or assumption
errors indicated
ii) No explanation or
unclear explanation of
why the assumptions are
in error
 5%
i) No recommendations
listed to correct the errors
ii) Impact on ground level
concentrations or risk
assessment not indicated
 2%
i) Incorrectly formatted,
hand written,
unintelligible
ii) Four or more spelling,
grammar, or punctuation
errors per 100 words
iii) unclear and lengthy
explanations
 24%
 2%
i) Calculations are
incorrect and there are no
sample calculations to
base partial credit upon.
ii) Calculations are
incorrect and illegible
iii) No assumptions are
listed
 5%
CE 326
Air Pollution Design Analysis
Calculation of
ground level
concentration of
benzene for each
individual
Part a), iii)
Risk calculations
See part a, i - iii, plus:
iv) x and y distances to
each individual clearly
noted
See part a, i - iii, plus:
iv) x and y distances to
each individual not given
 2%
See part a, i - iii, plus:
iv) No discussion of
whether the risk is
acceptable
6% - 9%
 5%
See part a, i - ii, plus:
See part a, i - iii, plus:
iv) Maximum benzene
iv) Maximum benzene
concentration reported
concentration is not based
based on some, but not all on individuals in the
the individuals
neighborhood
v) Benzene concentration
v) Benzene concentration
3
reported in ppmv or µg/m . reported in units other than
ppmv or µg/m3.
6% - 9%
 5%
See part a, i - ii, plus:
See part a, i - iii, plus:
iv) Minimum stack height iv) Minimum stack height
is based on some but not
is not based on individuals
all individuals in the
in the neighborhood
neighborhood
v) Stack height is not
v) Stack height reported to reported to the nearest 0.1
the nearest 0.1 m.
m.
10%
6% - 9%
 5%
See part a, i - iii, plus:
See part a, i - ii, plus:
See part a, i - iii, plus:
iv) Plot of the ground level iv) Plot of the ground level iv) Plot of the ground level
concentration versus
concentration versus
concentration versus
distance shown for at least distance shown for less
distance not shown or
500 m down wind
than 500 m down wind
unclear
v) Locations that exceed
v) Locations that exceed
v) Locations that exceed
the RBSL for benzene
the RBSL for benzene not the RBSL for benzene not
clearly identified
clearly identified
identified
5%
See part a, i - iii, plus:
iv) Discussion is clear and
concise (between one to
two paragraphs)
Part b)
10%
Maximum benzene See part a, i - iii, plus:
concentration that
iv) Maximum benzene
can be emitted from concentration that can be
the stack
emitted is based on all
individuals in the
neighborhood
v) Benzene concentration
reported in ppmv
Part c)
10%
Minimum stack
See part a, i - iii, plus:
height calculations iv) Minimum stack height
is based on all individuals
in the neighborhood
v) Stack height reported to
the nearest 0.1 m.
Part d)
Centerline ground
level concentration
versus distance
See part a, i - ii, plus:
iii) x and y distances to
each individual clearly
noted
3% - 4%
See part a, i - ii, plus:
iii) Discussion is clear, but
too short or long
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CE 326
Air Pollution Design Analysis
Problem 3, 25%
25%
15% - 22%
 12%
Technical issues
Critical assessment
of whether or not
the system is “safe,
/Recommendations
to the engineers
10%
i) Discussions are rational
and founded in scientific
principles
ii) Discussions are clear
and concise
iii) Discussions point to
several strengths or
weaknesses in the risk
model, the Gaussian
plume model, and
engineers’ assumptions
6% - 9%
i) Discussions are rational,
but only partially
supported scientifically
ii) Discussions are vague,
unclear, too abrupt, or too
lengthy
iii) Discussions point to
only a few strengths or
weaknesses in the risk
model, the Gaussian
plume model, and
engineers’ assumptions
Personal issues
Critical assessment
of whether or not
the system is “safe,
/Recommendations
to the engineers
10%
i) Clearly organized and
well supported argument
based on evaluation of
assumptions made by the
system’s designing
engineers, the assumptions
made in the risk equations,
and your ideas of
acceptable risk
ii) Discussion is complete,
logical, and well
supported.
iii) Respectful and
persuasive to the
neighborhood association
(to re-evaluate their
position) or design
engineers (to re-evaluate
their assumptions and
design).
5%
i) Formatted correctly as a
business letter
ii) Less than one spelling,
grammar, or punctuation
error per 100 words.
6% - 9%
i) Fairly well organized,
could be more clear and
concise, arguments are
supported by a critical
evaluation of the
assumptions made in the
system design or the risk
equation
ii) Discussion is there, but
incomplete or poorly
supported.
iii) Not persuasive to the
engineers to re-evaluate
their design or the
neighborhood association
to re-evaluate their
position
 5%
i) Discussions are not
rational nor supported
scientifically, but
supported with opinions
ii) Discussions are vague,
unclear, abrupt, or long
and drawn out.
iii) Discussions do not
point to inherent strengths
or weaknesses in the risk
model, the Gaussian
plume model, or
engineers’ assumptions
 5%
i) Poorly organized,
arguments are not
scientifically founded
ii) Discussion is illogical
and poorly supported, if
existent
iii) Attacking or rude,
makes engineers want to
increase the pollutant
emissions from the stack
or the neighbors to egg
your house
Grammar
Correct letter
format, spelling,
grammar, and
punctuation
3% - 4%
i) Formatted as a personal
letter or incorrectly
formatted as a business
letter, addressed
incorrectly
ii) Two to three spelling,
grammar, or punctuation
errors per 100 words.
8
 2%
i) Incorrectly formatted,
hand written,
unintelligible
ii) Four or more spelling,
grammar, or punctuation
errors per 100 words