Each soil boring shall extend at least how many inches below the surface?

The correct answer indicates that each soil boring must extend at least 60 inches below the surface. This requirement is essential for accurately assessing soil conditions, which are critical to the design and installation of private sewage systems. By reaching this depth, contractors can better evaluate the soil's characteristics, such as its texture, composition, and groundwater levels. This information is vital to ensure that the sewage system functions correctly, reduces the risk of system failure, and protects public health and the environment. The depth of 60 inches strikes a balance between obtaining sufficient data without unnecessary expenditure of resources, as shallower borings may not reveal significant issues that could affect system performance. This guideline aligns with best practices in site evaluation for private sewage systems across various regions, including Illinois.