3) A "sentinel" monitoring well is located 50 m downgradient from a known contaminant source. The contaminant is conservative. If the dispersion coefficient is 4.2 m2/d, the average linear groundwater velocity is 0.025 m/day, the initial concentration is 100 mg/L, determine the following: a. The plug flow time to travel 50 m downgradient . b. The concentration 50 m downgradient after 215 days (assuming only advection and hydrodynamic dispersion). c. The time when C/C0 reaches 50% at the sentinel monitoring well (assuming only advection and hydrodynamic dispersion). d. The concentration 50m downgradient after 215 days if you have a retardation factor of 2.25 e. The time when C/CO reaches 50% at the sentinel monitoring well if you have a retardation factor of 2.25