What characterizes a standard absorptive drainfield?

A standard absorptive drainfield is characterized by a gravel-filled system with a biological mat. The gravel serves as a medium for wastewater to filter through, providing spaces for aerobic microorganisms to thrive. These microorganisms play a crucial role in the treatment process as they break down contaminants in the septic effluent, promoting effective filtration and absorption into the surrounding soil. The biological mat that develops on the gravel surface enhances this treatment process by providing additional surface area for microbial activity, which is essential for the purification of the effluent before it enters the groundwater.

In contrast, options like a clay-lined trench, a network of perforated pipes without media, and a solid concrete base do not align with the fundamental characteristics of a standard absorptive drainfield. A clay-lined trench would typically impede water movement rather than foster it, while a system of perforated pipes without any media does not provide adequate filtration and biological treatment. A solid concrete base may offer stability but does not serve the purpose of absorption or treatment like a gravel-filled system does. Thus, the answer accurately describes the essential elements of a functioning and effective drainfield system.