Problem 5: In groundwater systems, an anaerobic environment, benzene can be oxidized by different species of microbes that utilize sulfate (instead of Oxygen, e.g. HW 1). A very slow moving plume of groundwater contaminated with Benzene (C6H6 ) is measured to be decreasing in concentration by first order kinetics with a reaction coefficient, k = 0.0575 yr-1 . The plume was contaminated by Benzene 40 years ago and was recently measured to have a benzene concentration of 0.7 mg/L. Show how to estimate the concentration of Benzene in the plume 40 years ago?