Soil Formation Classification: Understanding Aquitard Properties

The question asks us to identify the type of soil formation that allows only seepage, is partly permeable, and yields very little water. Let's break down the different terms related to soil permeability and water yield.

Defining Hydrogeological Terms

In hydrogeology, formations are classified based on their ability to store and transmit groundwater. The key terms are:

• Aquifer: This is a saturated underground layer of rock or soil that holds and transmits groundwater easily. Aquifers are permeable and can yield significant amounts of water to wells or springs. Think of them as major underground reservoirs.
• Aquitard: This is a layer of soil or rock that is saturated but transmits groundwater much more slowly than an aquifer. It is considered partly permeable. While it doesn't yield large quantities of water, it does allow a slow movement of water, known as seepage, and can give an insignificant yield. This definition closely matches the description in the question.
• Aquiclude: This is a layer that is essentially impermeable, meaning it does not allow significant amounts of groundwater to pass through it. It might hold water, but it cannot transmit it effectively.
• Aquifuge: Similar to an aquiclude, this is a geologic formation that contains groundwater but does not transmit it because it is not permeable. It acts as a barrier to groundwater flow.

Analyzing the Question's Criteria

The question provides specific characteristics:

• Permeability: The formation is described as partly permeable. This rules out Aquicludes and Aquifuges, which are impermeable.
• Water Movement: Only seepage is possible. This indicates a slow transmission of water.
• Water Yield: It is capable of giving an insignificant yield. This means it cannot supply water in large quantities.

Comparing these criteria to the definitions:

• Aquifers are highly permeable and yield significant amounts.
• Aquitards are partly permeable, allow seepage, and yield insignificantly.
• Aquicludes and Aquifuges are impermeable and do not transmit water.

Therefore, the soil formation described fits the definition of an Aquitard perfectly.