An article in the ASCE Journal of Energy Engineering ["Overview of Reservoir Release Improvements at 20 TVA Dams" (Vol. 125, April 1999, pp.s 1-17)] presents data on dissolved oxygen concentrations in streams below 20 dams in the Tennessee Valley Authority system. The observations are (in milligrams per liter): 5.0, 3.4, 3.9, 1.3, 0.2, 0.9, 2.7, 3.7, 3.8, 4.1, 1.0, 1.0, 0.8, 0.4, 3.8, 4.5, 5.3, 6.1, 6.9, and 6.5.

a. Is there evidence to support the assumption that the dissolved oxygen concentration is normally distributed?

b. Find a 95% CI on the mean dissolved oxygen concentration.

c. Find a 95% prediction interval on the dissolved oxygen concentration for the next stream in the system that will be tested.

d. Find an interval that will contain 95% of the values of the dissolved oxygen concentration with 99% confidence.

e. Explain the difference in the three intervals computed in parts (b), (c), and (d).