You are a member of EPA enforcement team investigating the possible ongoing dumping of arsenic in Cavalier Lake. You take water samples from the middle of the lake and find that the concentration is 89.6 ppb. 10 days later you take another sample and find it is 81.9 ppb. Convinced now of the problem, you make discrete inquires at a company situated on the lake and employee confesses to you that they have been dumping 89 g/min for years but that the dumping has now stopped. If lake has a residence time of 100 days, the flowrate into the lake is 10 m3/s, the surface area of the lake is 107m2, and the rate of evaporation out from the lake is 6 cm/wk, how long ago from the second sampling time did the dumping stop?