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Finishing the Calculation

If you entered the numbers correctly in the simulator on the previous page, you should have finished with a final concentration of about 5.97 mg/liter. Of course, what we want to know is how many milligrams of the gasoline escaped during the time in question, so we have a few more calculations to do before we're done.

First we need to get the amount of gasoline (in milligrams) still in the reservoir. To do this, multiply the concentration by the total volume of the reservoir in liters, which we found was (898,800)(3.79) or 3,406,452 liters. So the amount of gasoline in milligrams which is still in the reservoir at is (5.97 mg/l) (3,406,452 l), or approximately 20,340,000 mg. The initial amount was 10 gallons, or 37.9 liters, and as gasoline has a density of about 800,000 mg/l, we then had originally about 30,320,000 mg spilled. Thus we have lost a total of about 10,000,000 mg into the stream, so it looks like cleanup will have to proceed.

You should now be familiar with how to use the lake simulators in this module. In general when you are using this module to solve a problem, you will need to:

  1. Determine what kind of input function to use;
  2. Determine the reaction rate;
  3. Calculate the volume, flow rate, and any other information needed by the simulator, being careful to make sure the units agree with each other;
  4. Use the information from the simulator to finish the problem.
Most problems will come from either units which don't agree (for example, using gallons and liters in the same problem), or from forgetting what needs to be done with the simulator's answer once it is generated. (In this problem for example, we needed to do some work to get from the final concentration in the reservoir to the amount of gasoline in milligrams which escaped the reservoir.)

John Hoggard <hoggard@math.vt.edu>
Last modified: Mon Aug 11 12:10:51 EDT 1997