A railroad tank car has derailed and ruptured. It discharges 380 m^3 of pesticide into the drain. As shown in the figure, the drain flows into the Lake which has a liquid volume of 40,000 m^3. The water in the creek has a flow rate of 0.10 m3/s, a velocity of 0.10 m/s, and the distance from the spill site to the pond is 20 km. Assume that the spill is short enough to treat the injection of the pesticide as a pulse, and that the pond behaves as a flow balanced CSTR. The pesticide decays via a pseudo first order rate constant of 2 day^(-1). Estimate the time it will take to flush 99 percent of the pesticide from the pond.