A large amount of chlorine is accidentally spilled at a wastewater treatment plant that discharges into a river. The concentration of chlorine as a function of time is measured at two locations downstream of the plant. Far downstream of the plant outlet (x1) the standard deviation of the concentration distribution 1 = 250 m and at a distance x2 = x1 + 10 km the standard deviation is, 2 = 900 m. The mean velocity of the river is, U = 0.6 m/s. A.

(a) Estimate the value of the longitudinal dispersion coefficient for this river.

(b) If the chlorine decays at a rate given by the first order reaction coefficient k = 0.001 d^-1, describe how this will affect your answer to (a)