CEE 577 |
8 April 2002 |
Closed
book, 1 sheet of notes allowed.
Answer
both questions. Please state any
additional assumptions you made, and show all work.
I.
(50%)
Bovine Brook emerges from pristine headwaters and runs through an agricultural region
before it reaches the city of Poultryville.
The BOD of the headwaters is 4 mg/L, and the dissolved oxygen is 8.8
mg/L (saturation is 10.1 mg/L for 15oC). Starting at mile point zero, there is a significant non-point
agricultural runoff of BOD amounting to 40 kg/mile/day. At mile point 4.0, the stream is met by the
Poultryville WWTP outfall. Here a WW
flow of 1 cfs is discharged with a CBOD of 150 mg/L, an ammonia-N concentration
of 24 mg-N/L and a DO of 6 mg/L.
Immediately past this outfall is 4 more miles of agricultural land. This is better managed than the upstream
land, so that the runoff BOD averages 15 kg/mile/day. Calculate the dissolved oxygen concentration 4 miles
downstream of the Poultryville WWTP outfall (T=15oC). Assume the flow is constant at 40 cfs from
the headwaters to the end of the non-point agricultural runoff. You may also assume an SOD downstream of the
WWTP outfall of 2.0 g/m2/d.
Additional Information:
U = 0.150 ft/sec = 2.45 miles/day T
= 15oC
DOsat or Cs = 10.1 mg/L (at 15oC) H
= 4 ft = 1.22 m
BOD deoxygenation rate (kN = kd)
= 0.8 day-1 (at 15oC) for kN and kd,
=1.047
CBOD settling rate (ks) = 0.080 day-1 (at 15oC) for reareation, =1.024
Calculate ka and adjust for temperature:
ka = 0.555 d-1
Divide stream into two reaches of 4 miles in length. The travel time for each is:
t = 1.63 d
The non-point CBOD load is:
Overall deficit = terms incorporating (CBOD point deficit + point BOD + distributed deficit + distributed BOD)
The non-point CBOD load is:
Overall deficit = terms incorporating (CBOD point deficit + point BOD + distributed deficit + distributed BOD)
Segment #1 |
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General Parameters |
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U = |
0.15 |
ft/s
= |
2.454545 |
mi/day = |
0.045721 |
m/s |
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T = |
15 |
deg-C |
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Cs = |
10.1 |
mg/L |
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Options for ka |
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H = |
4 |
ft
= |
1.219215 |
m |
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0.6825 |
/d @ |
20 |
deg-C |
EPA SMWLA |
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kd = |
0.8 |
/d @ |
15 |
deg-C |
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0.6245 |
/d @ |
20 |
deg-C |
O'Connor-Dobbins |
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ks = |
0.08 |
/d @ |
15 |
deg-C |
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kN
= |
0.8 |
/d @ |
20 |
deg-C |
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SOD = |
0 |
g/m2/d @ |
20 |
deg-C |
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x = |
4 |
miles = |
21120 |
ft |
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slope = |
3.5 |
ft/mi |
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Upstream Water |
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Qu = |
40 |
cfs |
Selected Reaeration Coefficient |
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Lou = |
4 |
mg/L |
ka
= |
0.6245 |
/d @ |
20.0000 |
deg-C |
O'Connor-Dobbins |
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Lnou = |
0 |
mg/L |
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Cu = |
8.8 |
mg/L |
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Point Source |
Carbonaceous |
Nitrogeneous |
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Qw = |
0 |
0 |
cfs |
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Low = |
30 |
1.33 |
mg/L |
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Cw = |
7.5 |
7.5 |
mg/L |
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Non-Point Source (Lrd) |
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runoff= |
40 |
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kg/mi/d |
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runoff= |
1.003220979 |
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mg/L/d |
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runoff= |
1.003220979 |
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mg/L/d |
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Parameter Calculations |
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Tdesign = |
15 |
15 |
deg-C |
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deox rate = |
0.8 |
0.635853 |
/d @ |
15 |
deg-C |
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tot. loss rate= |
0.88 |
0.635853 |
/d @ |
15 |
deg-C |
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ka = |
0.554683912 |
0.554684 |
/d
@ |
15 |
deg-C |
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sb' = |
0 |
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mg/L/d @ |
15 |
deg-C |
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Initial Values (from mass balance) |
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Lo = |
4 |
0 |
mg/L |
0 |
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Co = |
8.8 |
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mg/L |
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Do = |
1.3 |
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mg/L |
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x/U = |
1.62962963 |
d |
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Dissolved Oxygen Deficit Terms ‚ |
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Net |
CBOD Terms ‚ |
Net |
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Desired x |
time |
--------- |
--------- |
--------- |
--------- |
--------- |
--------- |
Diss |
--------- |
--------- |
CBOD |
(miles) |
(d) |
Init-D |
C-PS |
N-PS |
SOD |
C-NPS-1 |
C-
NPS-2 |
Oxygen |
PS |
NPS-1 |
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--------- |
--------- |
--------- |
--------- |
--------- |
--------- |
--------- |
--------- |
--------- |
--------- |
--------- |
--------- |
0 |
0 |
1.30 |
0.00 |
0.00 |
0 |
0.00 |
0.00 |
8.80 |
4.00 |
0.00 |
4.00 |
4 |
1.62963 |
0.5265 |
1.6392 |
0.0000 |
0.0000 |
0.9783 |
-0.4672 |
7.4232 |
0.9533 |
0.8683 |
1.8217 |
Segment #2 |
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General Parameters |
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U = |
0.15 |
ft/s
= |
2.454545 |
mi/day |
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T = |
15 |
deg-C |
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Cs = |
10.1 |
mg/L |
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Options for ka |
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H = |
4 |
ft
= |
1.219215 |
m |
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0.6825 |
/d @ |
20 |
deg-C |
EPA SMWLA |
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kd = |
0.8 |
/d @ |
15 |
deg-C |
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0.6245 |
/d @ |
20 |
deg-C |
O'Connor-Dobbins |
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ks = |
0.08 |
/d @ |
15 |
deg-C |
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kN
= |
0.8 |
/d @ |
20 |
deg-C |
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SOD = |
2 |
g/m2/d @ |
15 |
deg-C |
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x = |
2 |
miles = |
10560 |
ft |
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slope = |
3.5 |
ft/mi |
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Upstream Water |
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Qu = |
40 |
cfs |
Selected Reaeration Coefficient |
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Lou = |
1.822 |
mg/L |
ka
= |
0.6245 |
/d @ |
20 |
deg-C |
O'Connor-Dobbins |
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Lnou = |
0.000 |
mg/L |
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Cu = |
7.4232
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mg/L |
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Point Source |
Carbonaceous |
Nitrogeneous |
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Qw = |
1 |
1 |
cfs |
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Low = |
150 |
109.68 |
mg/L |
24 |
mg-N/L |
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Cw = |
6 |
6 |
mg/L |
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Non-Point Source (Lrd or Sd) |
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runoff= |
15 |
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kg/mi/d |
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runoff= |
0.367032065 |
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mg/L/d |
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runoff= |
0.367032065 |
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mg/L/d |
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Parameter Calculations |
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Tdesign = |
15 |
15 |
deg-C |
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deox rate = |
0.8 |
0.8 |
/d @ |
15 |
deg-C |
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tot. loss rate= |
0.88 |
0.8 |
/d @ |
15 |
deg-C |
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ka = |
0.554683912 |
0.554684 |
/d
@ |
15 |
deg-C |
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sb' = |
1.6404 |
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mg/L/d @ |
15 |
deg-C |
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Lo = |
5.435764835 |
2.675122 |
mg/L |
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Co = |
7.388481053 |
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mg/L |
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Do = |
2.711518947 |
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mg/L |
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x/U = |
0.814814815 |
d |
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Dissolved Oxygen Deficit Terms ‚ |
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Net |
CBOD Terms ‚ |
Net |
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Desired x |
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--------- |
--------- |
--------- |
--------- |
--------- |
--------- |
Diss |
--------- |
--------- |
CBOD |
(miles) |
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Init-D |
C-PS |
N-PS |
SOD |
C-NPS-1 |
C-
NPS-2 |
Oxygen |
PS |
NPS-1 |
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--------- |
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--------- |
--------- |
--------- |
--------- |
--------- |
--------- |
--------- |
--------- |
--------- |
--------- |
0 |
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2.71 |
0.00 |
0.00 |
0.000 |
0.00 |
0.00 |
7.388 |
5.44 |
0.00 |
5.44 |
4 |
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1.10 |
2.23 |
1.16 |
1.760 |
0.36 |
-0.17 |
3.663 |
1.30 |
0.32 |
1.61 |
II.
(50%)
Silver lake is an urban surface water that has received inputs of nickel
for many years. Efforts to clean up the
lake have resulted in the termination of all nickel loads. Lake levels have dropped due to decay
(0.00005 d-1) and hydraulic flushing. Unfortunately, Senator Porkbarrel has succeeded in getting his
brother's chrome fender business exempted from the nickel ban. The amount on nickel discharged is directly
related to the amount of product produced.
Due to changes in the automotive industry, production has dropped off
since the business began (see table below).
During this time nickel waste has been constant at 3.3 Kg Ni per ton of
product. The output data below were
collected for a few selected years. On
January 1, 1985, the lake concentration of nickel was 0.13 mg/L. The lake has a volume of 12.5 million cubic
meters, a surface area of 3 million square meters, and an outflow of 8000 cubic
meters per day. Ignore any temperature
effects.
Year |
Output (tons/yr) |
1965 |
580 |
1975 |
510 |
1985 |
440 |
1995 |
370 |
Loading from 1985
Step
load:
with
linear decrease:
III. (50%) On a separate sheet of paper,
answer any five (5) of the following questions.
A.
Describe
the difference between mechanistic and empirical modeling
B.
Is
a first order reaction always faster than a zero order reaction? Explain.
C.
Describe
the differences between point and non-point loading and give examples.
D.
Explain
the relationship between Secchi-disk depth and lake trophic state. Why is there such a relationship?
E.
Describe
3 different methods for determining stream velocity.
F.
Explain
what the light and dark bottle method measures and how it works
G.
Describe
the factors that determine re-aeration in rivers, and contrast this with the
factors that determine re-aeration in lakes.
In your description, relate micro-scale processes (molecules) to
macro-scale (bulk water or air)