Problem 3. The initial dissolved oxygen (DO) and BOD concentrations at a reference point of a stream with an average water flow rate of 8m3/s are measured around 6 and 50mg/L, respectively. The averages values for the width (W) and depth (h) of water in stream are reported as 12m and 1m, respectively. The BOD degradation rate constant (k1) and water temperature are given as 0.26d1 and 25C. a) Calculate dissolved oxygen concentrations and oxygen vacancies ( A) by distance from the reference point (1500km ) downstream and plot data (distance vs DO and distance vs A) using excel spreadsheet. 10p b) Calculate the critical oxygen concentration (z()) and oxygen vacancy (Acr) and compare the values with those obtained from the excel graph. 5p c) Calculate the critical distance (Xcr) for the maximum oxygen vacancy and compare it to one you obtain from the excel graph. 5p d) Calculate BOD concentration at the critical distance as mg/L. 5p e) Calculate the distance (X) required to regain %90 oxygen saturation in the stream. 5p