7. Arsenic in geomedia contaminates an aquifer by naturally occurring geological processes. The aquifer has a bulk density of 1.58g/cm3 and a particle density of 2.63g/cm3. The distribution coefficient, Kd value is 0.0270L/kg. The initial concentration at the source is 21.0g/L. The groundwater velocity is 1.00102m/yr and the dispersion coefficient is 0.100m2/ day. Assume a half-life of 6.00104 years. Estimate the concentration at 10.0m distance from the source 0.0800,0.120,0.150,0.160, and 1.000 years after the process begins. Also, estimate the time needed for the arsenic concentration to exceed 0.0100g/L at 20.0m from the source (use the Excel file to make this estimate). (15 points)