Arizona Plumbing Practice Exam

If an existing sewer pipe is 3 feet below the benchmark and the contractor's level reads 4'-3" above the benchmark, what is the depth of the trench to be excavated, considering a 1/8 inch per foot incline?

1. 2 feet below finish grade

2. 2 feet 2 1/2 inches below finish grade

3. 3 feet 4 inches below finish grade

4. 4 feet below finish grade

The correct answer is: 2 feet 2 1/2 inches below finish grade

To determine the depth of the trench to be excavated, it's essential first to calculate the vertical distance between the existing sewer pipe and the contractor's level reading above the benchmark. The existing sewer pipe is located 3 feet below the benchmark. The contractor's level reading is 4 feet 3 inches above the benchmark, which converts to 4.25 feet. Now, if you consider the depth of the existing pipe, you combine these distances. The distance from the contractor's level down to the existing sewer pipe is: - From the benchmark, you have: - 4.25 feet (contractor's level) + 3 feet (depth of the pipe) = 7.25 feet. Next, you account for the required slope or incline of 1/8 inch per foot. To find this, you need to convert 1/8 inch to feet, which is 0.0104 feet. If we assume the trench will continue a certain horizontal distance (let's say 1 foot for simplicity), then the additional depth required for that distance would be 0.0104 feet. For a horizontal run of around 1 foot, this means we add approximately 0.0104 feet to