Contaminated and Hazardous Waste Site Management

Glossary U

Uncertainty: The estimated quantity by which an observed or calculated value may depart from the true value.

Unconfined: Conditions in which the upper surface of the zone of saturation forms a water table under atmospheric pressure.

Unconfined Aquifer: An aquifer in which there are no confining beds between the capillary fringe and land surface, and where the top of the saturated zone (the water table) is at atmospheric pressure.

Unconsolidated Deposits: Deposits overlying bedrock and consisting of soil, silt, sand, gravel and other material which have either been formed in place or have been transported in from elsewhere.

Unconsolidated Material: Naturally occurring geologic material that has not been lithified into cohesive rock.

Unsaturated Zone: The zone between the land surface and the water table. It includes the root zone intermediate zone, and capillary fringe. The pore spaces contain water, as well as air and other gases at less than atmospheric pressure. Saturated bodies, such as perched groundwater, may exist in the unsaturated zone, and water pressure within these may be greater than atmospheric. Also known as "vadose zone."

Upconing: Upward movement of salty or brackish groundwater into wells and into aquifers previously occupied by fresh or less mineralized groundwater.

Upgradient: An upward hydrologic slope; that defines areas that are higher than contaminated areas and, therefore, are not prone to contamination by the movement of polluted groundwater.

Utility Corridor/Trenches: A subsurface trench in which pipes, electrical lines, etc. are placed. It is usually filled with coarse material and so may be much more permeable than the surrounding material.