Your consulting firm has been asked to study a stretch of the Bluish-Green River in Virginia that is badly polluted. The main point source on this stretch of the river is the Brownsville pickle plant. Below the pickle plant, D. O. levels are so low that there have been repeated fish kills. The ultimate BOD of the untreated pickle plant

wastewater is 120 mg/L. The volumetric flow rate of the plant effluent is 1.35 x 108 L/day. The D. O. concentration in the effluent is 3.0 mg/L. You may assume that there are no other significant inputs of BOD immediately below Brownsville.

Upstream of Brownsville, the Bluish-Green River has a D. O. of 7.9 mg/L and an ultimate BOD concentration of 7.2 mg/L. The river velocity is 20 km/day. The BOD decay rate is 0.25/day and the reaeration rate is 0.59/day. The upstream flow is

4.3 x 108 L/day. Temperature of the river and the effluent wastewater is 15