You were hired to investigate pollution in a local stream. The streambed is scoured bedrock of volcanic origin and is slightly porous. Thus far your investigation has revealed: 1) the concentration of pollution in the water is 10mg/m3, 2) K*=1, and 3) DAB = 2x10-10 m2/s. You sent a core sample of the bedrock to the lab and discovered that the concentration in the stone was 1.6 mg/m3 at 50cm below the water-stone contact point. How long has this stream been polluted?