Arizona Plumbing Practice Exam

What is the minimum depth of filter material under the drain lines of a disposal field?

1. 6 inches

2. 12 inches

3. 18 inches

4. 24 inches

The correct answer is: 12 inches

The minimum depth of filter material under the drain lines of a disposal field is crucial for ensuring proper wastewater treatment and preventing issues such as clogging and system failure. A depth of 12 inches provides an adequate barrier that allows for effective filtration while supporting the overall function of the drain field. This depth helps to facilitate the movement of effluent from the drain lines into the surrounding soil, allowing bacteria to break down harmful pathogens and nutrients. It also ensures that there is enough material to protect the drainage system from surface impacts and provides a buffer to accommodate soil settlement over time. In contrast, thinner layers may not provide sufficient filtration, potentially leading to more rapid clogging and decreased system efficiency, while deeper layers might be unnecessary and could complicate the system without added benefits. Thus, establishing a minimum of 12 inches aids in both the functionality of the disposal field and the long-term maintenance of the sewage treatment process.