Where Does Groundwater Occur?

Where Does Groundwater Occur?

Groundwater can be found in both consolidated materials (hard rock) and unconsolidated materials (sand, gravel, or soft rock). As shown in Figure 1-2, any type of rock can serve as an aquifer if it is sufficiently porous and permeable.

Types of Aquifer Materials

Sedimentary Rocks (Most Common Aquifers)

Formed from erosion of pre-existing rocks

Include both hard and soft varieties:

Hard Sedimentary Rocks:

Limestone/Dolomite: Fractures created by earth movements allow water to form solution channels, yielding large water volumes.

Sandstone: When fractured or loosely cemented, can provide significant water (though yields vary).

Shale: Compacted clays rarely form aquifers but may yield minor water from fractures.

Soft Sedimentary Formations:

Sand, gravel, or mixtures—our most productive aquifers due to variable particle sizes and pore spaces.

Igneous Rocks (Poor Aquifers)

Formed from cooled molten material (e.g., granite).

Only hold water in weathered surface crevices.

Metamorphic Rocks (Generally Poor Aquifers)

Result from heat/pressure altering sedimentary/igneous rocks.

Rarely productive, except marble (metamorphosed limestone), which can form solution channels like limestone.