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A 4 MGD WWTP discharges a secondary treated effluent into a receiving stream. The wastewater has the following characteristics:

BOD5= 20 mg/L

DO = 2.0 mg/L

Water Temperature = 24C

The receiving upstream from the point of discharge has the following characteristics:

Flowrate = 18 cfs

BOD5= 4 mg/L

DO= 6 mg/L

Water Temperature = 27C

Cross-sectional Area = 36 sqft

a. 3.2

b. 5.2

c. 7.2

d. 8.4

The reaeration rate is estimated to be 0.4 1/day. (Base e at 20C), and the temperature correction coefficient is 1.024. the deoxygenation rate

constant is estimated to be 0.23 1/day. (Base e at 20C) and the temperature correction coefficient is 1.047. reaeration and deoxygenation are

the only major factors affecting the dissolved oxygen concentration in the stream after mixing with wastewater effluent. Assume the time of

travel in the stream to reach the maximum dissolved oxygen deficit is 3 days. The dissolved oxygen deficit (mg/L) at this location downstream

from the point of discharge is most nearly: