What soil types should be used for backfilling above the barrier and gravel?

The option that indicates the correct types of soil for backfilling above the barrier and gravel is grounded in the specific classifications recognized for soil used in on-site sewage facilities. The designation of soil types 1b, 11, or 11 soil refers to classifications that possess characteristics suitable for effective drainage and support of the system while minimizing issues such as soil saturation and compaction.

When backfilling above the barrier and gravel, it is essential to use soils that yield good structural integrity and facilitate proper water movement. Soils identified as 1b, 11, or 11 soil are generally well-drained and prevent excessive moisture retention, which is critical in maintaining the functionality of the sewage system.

In contrast, the other choices include soil types that may not provide the necessary drainage characteristics or structural support for backfilling. For example, some of the other soil types can retain too much moisture or decompose over time, leading to potential system failures or complications. Thus, the identification of 1b, 11, or 11 soil types ensures adherence to best practices for ensuring the long-term performance of on-site sewage facilities.