To size a continuous flow treatment lagoon for wastewater generated from a small town in Alberta you would need retention time of the wastewater in the lagoon. An experiment is conducted by keeping the wastewater sample in a mixed vessel to investigate the reaction kinetics (rate-law). The data are reproduced in the table given below. Untreated wastewater from the town contains 50 mg/L of the contaminant. The treatment lagoon to be installed or designed should remove 90% contaminant to comply with a provincial regulation for a safe discharge of the wastewater in a nearby stream. Determine the hydraulic retention time (θ) of the lagoon. Time (hour) Concentration (mg/L) 0 60 0.5 44 1.0 33 1.5 24 2.0 18 2.5 13