What type of soil can be used to backfill a gravelless pipe drainfield?

The correct response indicates that a variety of soil types, specifically Class Ib, II, or III, can be utilized to backfill a gravelless pipe drainfield. This selection is sound because these classifications of soil typically possess physical properties that are conducive to effective drainage and filtration, which are critical for the proper functioning of a drainfield system.

Class Ib, II, and III soils are generally characterized by their moderate drainage capabilities, allowing effluent to move through the soil at a rate that is neither too rapid nor too slow. This balanced drainage is essential for preventing issues such as oversaturation or blockage, which can lead to system failures.

In contrast, other options are less appropriate. Class I soil usually refers to the best soils for drainage fields but may not provide the necessary structure for gravelless systems. Granular and sandy soils, while excellent for drainage, may not retain enough moisture or nutrients for effective treatment. Clay soil, on the other hand, is known for its poor drainage properties, often leading to slow percolation and potential environmental issues. Thus, the use of Class Ib, II, or III soils aligns with the comprehensive requirements of constructing a durable and efficient gravelless pipe drainfield.