In a gravel trench, what is the minimum and maximum depth?

The correct depth range for a gravel trench in septic system installations is indeed between 18 inches and 36 inches. This range provides an optimal balance that allows for proper filtration and treatment of wastewater, ensuring that effluent can effectively percolate through the gravel and into the surrounding soil. The specified depth allows for adequate insulation from surface activities while also ensuring that there is enough space for the gravel to function as a filter media.

Using a depth that is too shallow might not adequately treat the effluent, while going too deep could lead to complications such as reduced soil absorption capability or increased likelihood of system failure. Adhering to these depth specifications is crucial for the longevity and effectiveness of the septic system, thus reinforcing why this particular range is deemed the standard in Illinois septic system practice.