Glossary: Site Evaluation

These definitions may help clarify some of the terms used in Worksheet A.

Basalt: A fine grained, dark colored volcanic rock (Example: Snake River Plain Basalt in southeastern Idaho).

Bedrock: Solid rock that underlies soil or other unconsolidated material.

Granite: A light colored, silica rich rock formed by the slow cooling of molten rock (Example: Idaho Batholith in central Idaho).

Limestone: A rock that is mostly composed of calcium carbonate.

Microorganisms: An organism that is microscopic in size (Example: bacteria).

Organic matter: Matter containing carbon compounds that originated from plant and animal matter.

Perched water table: A soil or non-soil material that is saturated by water, but lies above the main water table. It is formed by water that infiltrates the soil and is collected on or restricted by an impermeable layer, such as a clay lens.

Pore space: The space between individual grains of a sediment or rock.

Permeability: The quality that enables water or air to move through soil or rock. The opposite of permeable is “impermeable” (Example: Clay is relatively impermeable as compared to sand).

Soil classification: A system to provide detailed soil descriptions. The descriptions are based on soil properties such as color, texture, pH, organic content, and soil depth.

Soil drainage class: The condition of water saturation or partial saturation that existed during the development of the soils. Different classes are described by such terms as excessively drained, well drained, and poorly drained.

Soil horizon: A layer of soil that has distinct characteristics, such as color or texture. Soils are grouped as A, B, C horizons.

Soil mapping unit: A soil or combination of soils drawn on a map and where possible include unit names.

Soil series: Soils that are essentially alike in all major characteristics.

Soil texture: The relative proportions of sand, silt, and clay that make up a soil. Described in terms such as sandy loam and silty clay.

Subsoil: The B soil horizon.

Unconsolidated alluvium: Deposits of clay, silt, sand, gravel, and boulders. These sediments have been deposited by water from glaciers, rivers, lakes, etc.

Water table: The zone in the soil or subsurface that is saturated with water. It is indicated by the level at which water stands in an uncased borehole after adequate time is allowed for
adjustment.