1a) An aqueous solution containing 35 kg of endosuflan insecticide is accidentally released into a small stream. The stream dimensions are 17.5 meters wide and 1.15 meters deep. The stream velocity is 1.1 m/s. The stream channel drops 24m over a distance of 10 km. Endosuflan decays by a first-order reaction with a half-life of 15 days. Assuming the solution mixes immediately with the stream water, determine the concentration at a distance of 4.00x10^3 meters and a time of 1 hour.
1b) At what distance does the peak concentration occur at 7.5 hours after the pollutant release?
1c) Assuming a drinking water standard of 0.005 mg/L, estimate,when the water at a distance of 25km will be below this concentration.