What does specific retention measure in soil?

Specific retention is a crucial soil property that measures the amount of water retained in the soil after gravity drainage occurs. It represents the volume of water that remains in the pore spaces of the soil once the excess water has drained away due to gravity. This measurement is particularly important in the context of on-site sewage facilities, as the retained water influences the treatment and absorption processes within the soil.

In practice, specific retention provides insights on how much water can be stored in the soil and utilized by plants or filtered through for further treatment. This understanding is vital for designing effective OSSF systems, ensuring that the soil can adequately handle the wastewater and that the water remains available to facilitate necessary biological processes.

The other options, while related to soil characteristics, do not directly address the concept of specific retention. For instance, air content refers to the volume of air in soil pores, water transmission pertains to how water moves through the soil, and overall density relates to the weight of soil particles. Each of these properties is important in its own right but does not specifically measure the retained water after drainage, which is the essence of specific retention.