Poorly treated municipal wastewater is dis- charged to a stream. The river flow rate upstream of the discharge point is Qu = 8.7 m3/s. The discharge occursataflowofQd=0.9m3/sandhasaBODcon- centration of 50.0 mg/L. Assume the upstream BOD concentration is negligible. (a) What is the BOD concentration just downstream of the discharge point? (b) If the stream has a cross-sectional area of 10 m2, "what is the BOD concentration 50 km downstream? (BOD is removed with a first-order decay rate con- stant equal to 0.20/day.)