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Sampling Frequency: The interval between the collection of successive samples.

Saturated Zone: The area below the water table where all open spaces are filled with water under pressure equal to or greater than that of the atmosphere.

Saturation: The condition of a liquid when it has taken into solution the maximum possible quantity of a given substance at a given temperature and pressure.

Semi-Confined Aquifer: An aquifer partially confined by soil layers of low permeability through which recharge and discharge can still occur.

Semivolatile Organic Compounds: Organic compounds that volatilize slowly at standard temperature (20 degrees C and 1 atm pressure).

Silt: Sedimentary materials composed of fine or intermediate-sized mineral particles.

Soil Gas: Gaseous elements and compounds in the small spaces between particles of the earth and soil. Such gases can be moved or driven out under pressure.

Soil matrix:  An assemblage of mineral particles of various sizes, shapes, and chemical characteristics, together with organic materials, in various stages of decomposition and living soil populations.

Soil Moisture: The water contained in the pore space of the unsaturated zone.

Solubility: The amount of mass of a compound that will dissolve in a unit volume of solution. Aqueous Solubility is the maximum concentration of a chemical that will dissolve in pure water at a reference temperature.

Source Area: The location of liquid hydrocarbons or the zone of highest soil or groundwater concentrations, or both, of the chemical of concern.

Source-Water Protection Area:  The area delineated and protected by a regulatory body (e.g. Conservation Authority) for a public water supply.

Sparge or Sparging: Injection of air below the water table to strip dissolved volatile organic compounds and/or oxygenate ground water to facilitate aerobic biodegradation of organic compounds.

Specific Yield: The amount of water a unit volume of saturated permeable rock will yield when drained by gravity.

Static Water Level: 1. Elevation or level of the water table in a well when the pump is not operating. 2. The level or elevation to which water would rise in a tube connected to an artesian aquifer or basin in a conduit under pressure.

Stratification: Separating into layers.

Subsurface:  The geologic zone below the surface of the earth. Rock and soil materials lying near, but not exposed at, the Earth's surface.

Sump: A pit or tank that catches liquid runoff for drainage or disposal.

Surface Runoff: Precipitation, snow melt, or irrigation water in excess of what can infiltrate the soil surface and be stored in small surface depressions; a major transporter of non-point source pollutants to rivers, streams, and lakes..

Surface Water:  Includes water bodies (lakes, wetlands, ponds, etc.), water courses (rivers and streams), infiltration trenches and temporary ponds.

Surfactant: A detergent compound that promotes lathering.

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