What typically fills the voids in saturated soil or rock?

In saturated soil or rock, the voids are primarily filled with groundwater. This occurs when the soil or rock has absorbed water to the point where all the spaces or pores in the material are filled. Groundwater is the term used to describe water that exists below the Earth's surface, stored in aquifers and soil layers. The saturation level indicates that the soil cannot hold any more water in its voids, as they are completely filled with groundwater.

Sand and gravel, while they can hold water, primarily refer to types of materials that make up the soil or rock but don’t specifically indicate what fills the voids in saturated conditions. Air and gases are typically present in unsaturated conditions where soil voids contain both water and air. Organic matter contributes to soil composition and can affect water retention, but it does not fill voids in saturated soil or rock to the same extent as groundwater does. Therefore, groundwater is the most accurate choice reflecting the condition of saturation in soil and rock.