CE 577 16 December 1993
Open book, open notes.
Answer all questions. Please state any additional assumptions you made, and show all work.
I. (50%) The Haw River receives discharges from two paper mills as shown below. Determine the concentration of dissolved oxygen in the river at milepoint 15, where it flows into Jordan Reservoir.
Source |
River Mile |
Flow (cfs) |
BOD5 (mg/L) |
D.O. (mg/L) |
kb (day-1) |
NH3-N (mg/L) |
---|---|---|---|---|---|---|
Upstream Flow |
0 |
35 |
2.5 |
7.2 |
0.3 |
0.1 |
Plant #1 |
0 |
5 |
62 |
2 |
0.2 |
5.5 |
Plant #2 |
5 |
3 |
44 |
3.5 |
0.2 |
2.5 |
Additional Information:
U = 0.20 ft/sec = 3.27 miles/day T = 30oC
DOsat or Cs = 7.56 mg/L (at 30oC) H = 5 ft
CBOD deoxygenation rate (kd) = 0.23 day (at 20oC) for kd, theta=1.047
NBOD deoxygenation rate (kN) = 0.26 day (at 30oC) for kN, theta=1.06
CBOD settling rate (ks) = 0.080 day-1 (at 30oC) for reareation, theta=1.024
II. (40%) Lake Thomann was in an undeveloped watershed until January 1, 1988 when the new Cataclysmic Chemical Company (CCC) plant went on line. From this day until the present it has been discharging its partially treated wastewater into Lake Thomann at a steady rate. This wastewater has a high concentration of 1,2-Dichlorobenzene (DCB). If the ambient water quality standard for this compound is 10 ug/L, how long will it take to reach this level in Lake Thomann? Assume the lake is at a temperature of 25 C. You may wish to neglect diffusion across the sediment:water column interface. (universal gas constant, R=8.206x10-5 atm m3/deg K mole).
CCC Wastewater Characteristics
Flow |
3500 m3/day |
---|---|
DCB Conc. |
500 ug/L |
Properties of 1,2-Dichlorobenzene
Property |
Value |
---|---|
Molecular Weight |
147.0 |
Melting Point |
-17.0 C |
Boiling Point |
180 C |
Vapor Pressure @25 C |
1.5 torr |
Solubility in Water @25 C |
145 mg/L |
log(Kow) |
3.38 |
Diffusivity in Water |
6.2x10-6 cm2/sec |
Henry's Law Const @25 C |
0.00194 atm m3/mole |
Biodegradation Rate |
~0 |
Hydrolysis Rate |
~0 |
Photolysis Rate |
very small |
Characteristics of Lake Thomann
Characteristic |
Value |
---|---|
Volume |
4,500,000 m3 |
Outflow |
50 m3/day |
Mean Depth |
2 meters |
Mean Wind Speed |
2.5 m/sec |
Solids Settling Rate |
0.2 m/d |
Solids Resuspension Rate |
0.00001 m/d |
Solids Burial Rate |
0.000027 m/d |
Water Column Suspended Solids |
2.2 mg/L |
Mixed Sediments Suspended Solids |
12,000 mg/L |
Thickness of Mixed Sediments |
0.2 meters |
Fraction of Organic Carbon in Solids |
0.2 |
Density of Suspended Solids |
1.55 g/mL |
III. (10%) Answer Either Problem III.A. or the multiple choice questions in section III.B.
III.A. A pollutant is present at a concentration of 144.3 ug/L at milepoint 0 in the Mueller River in Germany. By milepoint 3.6, the concentration has dropped to 24.5 ug/L. The mean flow velocity is 0.22 miles per day. The flow rate is 22 cfs at milepoint 0 and 83 cfs at milepoint 3.6. Calculate the 1st order loss rate for this pollutant at the ambient temperature.
a. Occurs more quickly at high temperature
b. Occurs more slowly at high temperature
c. Is not itself affected by temperature, but it can alter the water temperature
d. is the name for a change in the earth's atmosphere
a. always occurs at the point of dischage of a wastewater
b. is a cause of aquatic toxicity
c. is commonly inhibited in the BOD test
d. results in the formation of nitrogen gas
e. leads to a reduction in BOD
a. are easily biodegraded
b. never adsorb
c. are not normally present in the environment
d. are not subject to photolysis
e. are deposited mostly from atmospheric sources
a. in lake models for BOD
b. in river models for conventional pollutants
c. in estuary models
d. in toxics models for substances that persist in the sediments
a. one where the rate is proportional to the concentration of end products
b. one where the rate is proportional to the product of two concentrations of reactants
c. is one that occurs more quickly than a first order process
d. one that only starts after the preceeding first order process is complete
e. never encountered in the natural environment.