Understanding Depth Calculations for Arizona Plumbing Exams

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?

• A. 2 feet below finish grade
• B. 2 feet 2 1/2 inches below finish grade
• C. 3 feet 4 inches below finish grade
• D. 4 feet below finish grade

Answer: (B)

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

When it comes to plumbing, one of the essentials you need to nail down is depth calculations—especially for trench excavation. Think about it: when dealing with sewer pipes, you want to ensure everything's in the right spot, right? Just like baking a cake, you don’t want too much or too little flour; you need balance!

Let's jump right in. You’re faced with a scenario: an existing sewer pipe sits 3 feet below the benchmark, and the contractor's level reads 4 feet 3 inches above that benchmark. What does this mean for your trench depth? It sounds complicated, but don't worry! We’ll break it down step by step.

First up, you need to decipher what the numbers actually represent. The existing sewer pipe being 3 feet below the benchmark means we need to account for that distance. Then, take the contractor's level, which reads 4 feet 3 inches (or 4.25 feet) above the benchmark. If we add these two figures together, you end up with 7.25 feet—this is the total vertical distance from the contractor's level down to the existing sewer pipe.

Fine and dandy, right? But here’s where it gets a bit trickier: the slope or incline. In our case, we’re talking about a 1/8 inch per foot incline—fairly standard but essential to know. To convert that into feet, you're looking at roughly 0.0104 feet per foot. Imagine your trench running along horizontally for a foot; you’ll need to add that 0.0104 feet to your initial depth calculation. If you didn’t understand it the first time, don’t sweat it—plumbing is all about repeating concepts until they sink in!

Now, let’s reassert: the combined depth from the benchmark down to the sewer pipe gives you 7.25 feet. But this isn’t the final depth of the trench! You need to consider that incline—so your trench should extend down to about 7.2604 feet. Confused yet? Don't be! It simply means that by taking into account both the depth of the pipe and the slope, you ultimately land at the trench depth of around 2 feet 2.5 inches below finish grade. That’s your final answer, option B!

You know what else is interesting? Depth calculations are not just confined to trenching for sewer pipes; they play a crucial role in many facets of plumbing. Whether you're digging for drainage systems, laying down foundation pipes, or connecting water systems, depth accuracy can make or break a project. It's all about understanding how the math plays out in real-life applications.

So, as you get ready for the Arizona Plumbing Exam, keep practicing these calculations. They’re vital not just for acing the test, but for your future career as a skilled plumber. Remember, every correct depth ensures a smooth-flowing, error-free plumbing system. You’ve got this!