Question

Assume that the concentration of lead (Pb⁺²) in both Lake Superior and Lake Erie is zero. Due to pollution, the concentration of lead in both cases suddenly increases to 1 mg/L. For each case, how long, in years until the concentration of lead reaches 0.5 mg/L? Treat lakes as CMFR.

Lake Erie: V = 468 (10⁹) m³ ; Q_e = 182 (10⁹) m³/yr ; HRT = 2.6 years

Lake Superior: V = 12,000 (10⁹) m³ ; Q_e = 67 (10⁹) m³/yr ; HRT = 179 years

Answer: Superior – 286 years, Erie – 4.1 years

Answer 1

Lake Erie

Given Residence time = containing volume divided by flow rate = V/Q= 468/182 = 2.6 year at concentration 1 mg/L

      Residence time at 1 mg/l = twice of 0.5 m/l residence time = - 4.1 year

Lake superior

V/Q =12000/67 = 179 YEAR at concentration of 1 mg/l

Residence time at 1 mg/l = twice of 0.5 mg/l residence time = -286 year

Residence time (year ) = 286+4.1 =291.1 (year)

we are present 2018 .substituting 291 year bring us back to 1727 .what was happening in the lake in 1727 ..