A discharge from a potential wastewater treatment plant may affect the dissolved oxygen level in a stream. The waste characteristics are expected to be: Flow = 0.56 m°/ Ultimate BOD

= 6.5 mg/L DO = 2.0 mg/L Temperature = 25°C The water in the stream, upstream from the planned discharge,has the following characteristics: Flow = 1.9 m²/s%3D Ultimate BOD=2 mg/L DO = 9.1 mg/L Temperature = 15•C The state DO standard is 4 mg/L. Use: Deoxygenation constant = 0.2 day Reoxygenation constant = 0.40 day a. Will the construction of this plant cause the DO to drop below the state standard? b. If during a hot summer day, the flow in the stream drops to 0.2 m/s and the temperature in the stream increases to 30•C, will the state standard be met? c. In the wintertime the stream is ice covered, so that there cannot be any reaeration(k2 = 0). If the temperature of the water in the stream is 4•C, and all other characteristics are the same (as in a. above), will the state standard be met? d. Suppose your calculation showed that in part c. above the dissolved oxygen dropped to zero during the winter, under the ice. Is this bad? After all, who cares?