What is a sand lens?

• A. A rocky barrier preventing water movement
• B. A convex layer of sand containing fresh groundwater
• C. A dense layer of clay
• D. A geological fault line

Answer: (B)

A sand lens refers to a localized, generally horizontal deposit of sand that can contain fresh groundwater. This formation typically occurs within subsurface materials, often sandwiched between layers of less permeable materials such as clay or silt. The term "lens" reflects the shape of the deposit, which is convex and can be thick in the center, tapering off at the edges.

In a sand lens, the sand particles allow for relatively high permeability, enabling water to flow through it. The presence of fresh groundwater in a sand lens can be significant for aquifers, as it may serve as a source of potable water for wells and ecosystems. Understanding the characteristics of a sand lens is essential in environmental health and hydrology, especially for groundwater management and ensuring the safety of drinking water supplies.