The following two contaminants are present in a gasoline mixture: hexane and octane. If a gasoline spill has occurred in the subsurface due to an underground storage tank rupture and contaminated the groundwater, how quickly will these chemicals be detected in a monitoring well 100 m away? The arrival time of a conservative tracer (chloride ion) was observed to take only 50 days. The soil had an organic carbon fraction of 1% and a porosity of 0.45. The soil density was 1.3 g/cm3.