Which soil textural classes are always unsuitable for standard absorptive OSSF?

The correct choice indicates that Class IA and IV soil textural classes are always unsuitable for standard absorptive On-Site Sewage Facilities (OSSF). Class IA soils are typically very fine soils, like clays, which have low permeability. This characteristic makes it difficult for water to percolate through the soil effectively, leading to potential issues with drainage and water contamination. Such soil textures do not allow for adequate absorption of wastewater, which is a critical requirement for the proper functioning of absorptive OSSF systems.

Class IV soils, on the other hand, generally refer to very coarse or sandy soils that also struggle to adequately treat wastewater. These soils can drain too quickly, failing to retain water long enough for the necessary microbial processes that treat and purify the effluent. Consequently, the rapid drainage can lead to surface runoff and potential environmental hazard.

In contrast, the other options reference various combinations of classes that can have properties allowing some level of absorptive function, even if not optimal. Therefore, focusing on Class IA and Class IV emphasizes the properties of these specific textural classes that preclude their utility in standard absorptive OSSF applications.