An industrial plant emits SO2 into the atmosphere on a steady basis. Rainfall records indicate that the annual precipitation is 75 cm/year, at a pH of 4.4. A nearby lake has the following characteristics: surface area = 8 km2, average depth = 10 m, pH = 5.8, alkalinity = 25 mg/L as CaCO3. The area from which runoff drains directly to the lake is 25 km2. Assume that only 20% of the rain falling on the land reaches the lake. Assume also that on a yearly basis the lake is completely mixed, and that the small river flowing into and out of the lake can be neglected as far as acidification is concerned. How many years will it be before the lake will reach a pH of 5.0?