During a water test of a DWV system, the inspector notes that a 3-inch diameter vertical stack is 28 feet in length from the lowest to the highest point of the test. What is the minimum required test pressure at the lowest point of this system?

• A pressure equivalent to a 10-foot head of water.
• 15 psi.
• A pressure equivalent to a 28-foot head of water.
• 5 psi.