The San Vicente reservoir north of San Diego currently has a residence time for water of approximately 14 days. The present volume of the reservoir is 111,000,000 m3, but the San Diego County Water Authority hopes to increase the volume of the reservoir to 298,502,604 m3 by the year 2017 in order to have a larger emergency reserve of water.
A. Assuming that minimal water is lost due to evaporation and the total volume remains constant, what is the current rate at which water enters and leaves the San Vicente reservoir?
B. The Environmental Protection Agency (EPA) limit for nitrates in potable water is 45.0 mg/L. If tomorrow, pollution sources upstream of the reservoir were to create an input concentration of NO3 equal to 61.6 mg/L, how long would it take for the water to no longer be considered potable? You may assume that the reservoir initially had only 3.0 mg/L of nitrates and that the reservoir volume is constant.
C. Find an equation for nitrate concentration as a function of time and graph. Make sure to label the initial concentration, the EPA nitrate limits, the steady-state concentration, your answer to B, and the residence time. If the current rate at which water enters and leaves remains the same in 2017, what will the new residence time of water in the reservoir be? Given the new residence time, re-compute your answer to (B).