The initial ultimate BOD after mixing of the Colorodo River is 15 mg/L. The DO in the river after the wastewater and river have mixed is at saturation. At 25C, the deoxygenation rate constant (kd) is 0.2 d-1 and the reaeration rate constant (kr) is 0.4 d-1. Determine the critical point (tc) and the critical DO. If the critical point in a DO sag curve is found to be 18km downstream from the discharge point of untreated wastewater, would you expect the critical point to move upstream (toward the discharge point), downstream, or remain in the same place, if the wastewater is treated.