Question

A pristine lake is fed by 9 tributaries, two of which have become polluted with mercury from industrial waste. The total inflow is equal to the total outflow. That is, Σ i=1​ q i​ =Q out​ . The EPA MCL (maximum contaminant level) for mercury, which is considered safe to drink, is 0.002mg/L.

A) Using this standard, determine when the concentration of mercury in the lake reaches the MCL.
B) What will be the maximum level of mercury in the lake? Report your answer as a factor of the MCL. That is, if the level is 0.005 , then the factor would be 0.005/0.002=2.5. Round to the tenths place.
C) When will 99% of the maximum level be reached?
D) If the pollution from q 1​ is reduced to c 1​ =14μg/L, what value of c 2 will keep the lake at the MCL? Round to the tenth of a μg/L. Round time to the nearest day. Refer to the figure below and the table for values and units (watch units 1).

Answer 1

The question involves calculating the concentration and mass of mercury in a lake’s ecosystem, comparing it to the EPA's MCL, and adjusting pollutant levels to comply with safety standards.

Step-by-step explanation:

The student's question deals with the concentration of mercury in a lake and related environmental standards for safe water. When determining maximum contaminant levels (MCL) of pollutants such as mercury in water, both parts per million (ppm) and parts per billion (ppb) are important units for measurements.

To calculate the mercury content in a water sample, the concentration (in ppb or ppm) must be multiplied by the volume of water to find the mass of mercury present.

To determine when the concentration of mercury reaches the MCL, the amount of mercury inflow from the tributaries must be compared to the total volume of water in the lake.

For the maximum level, the steady state concentration must be calculated assuming constant inflow and outflow rates. Once the steady state concentration is reached, 99% of that value would be equivalent to 99% of the maximum level. If the concentration of mercury from one tributary is reduced, the permissible concentration from the second tributary can be calculated to maintain the water quality at the MCL.