What material should cover the top of the absorption field gravel?

The correct answer is permeable material because it plays a crucial role in the functionality of an absorption field in a wastewater treatment system. The absorption field, typically part of a septic system, is designed to allow effluent to percolate into the ground where it can be naturally filtered by the soil.

Using permeable material on top of the gravel helps to maintain the flow of air and water while simultaneously preventing sediment from clogging the gravel and impeding water movement. This is essential for maintaining a functioning absorption field because proper drainage and aeration are vital for the microorganisms that break down waste.

On the other hand, materials such as tar paper, plastic, or treated paper would obstruct this necessary flow, which could lead to system failure over time. Tar paper and plastic would create a barrier, preventing effluent from reaching the soil effectively, while treated paper may not provide the necessary permeability and could also introduce undesirable chemicals into the system. Thus, using a permeable material ensures the absorption field operates effectively, facilitating the treatment of wastewater through natural processes.