Determine the minimum DO concentration in a river downstream of a municipal treatment facility discharging at a flow rate of 5 MGD. The plant achieves secondary treatment standards (BOD5 = 30 mg/L). The wastewater temperature is 25 °C and the wastewater DO is 4 mg/L. The characteristics of the river upstream from the point of discharge are Q = 20 cfs, T =20 °C, BODu = 3 mg/L, and DO = 7 mg/L. The deoxygenation coefficient for the wastewater effluent kd is 0.17 days‐1 at 20 °C; the reaeration coefficient for the river ka is 0.40 days‐1 at 20 °C.