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Contaminated and Hazardous Waste Site Management

Glossary G


Gaining Stream: A stream or part of a stream where the flow is solely or partly contributed to by the inflow of groundwater. Also called Effluent Stream.

Galvanic: Describes geophysical techniques that require direct contact with the ground in order to pass current. The alternative is to induce currents in the earth.

Gas Chromatography (GC): A method for separating, identifying and measuring concentrations of organic compounds. Compounds pass through a chromatographic column and the different rates of travel through it form the basis for their separation and identification. Detection limits are usually 1 to 10 micrograms per litre.

Gas Chromatography/Mass Spectroscopy (GC/MS): A method for separating, identifying, and quantifying organic compounds. The compounds are separated in the GC, but their identification is based on both their retention time in the GC column and their mass spectral pattern. Quantification is achieved by measuring peak heights in the mass spectra. Detection limits are usually 5 to 10 micrograms per litre.

Gas Drive Pump: The pump mechanism depends on lifting a column of water from within the pump body and attached tubing by using pressurized gas.

Geomagnetic Field: The Earth's magnetic field.

Geomorphology: Geomorphology is the science dealing with the origin and evolution of land forms.

Geophones: Receivers used to record the seismic energy arriving from a source, in seismic geophysical methods.

Geophysical Mapping: Locating geophysical anomalies in space (as opposed to time, which is geophysical monitoring).

Geophysical Monitoring: Observing the change in a geophysical measurement with time.

Glacio-Fluvial Deposits: Deposits related to the joint action of glaciers and meltwater streams.

Gradient: The rate of change in value of a physical or chemical parameter per unit change in position. For example, hydraulic gradient is equal to the difference in head measured at two points (usually wells) divided by the distance separating the two points. The dimensions of head and distance are both lengths, therefore the gradient is expressed as a dimensionless ratio (L/L).

Grain size: General dimensions of sediment or rock particles. The grain size distribution describes the occurrence of sediment grains of different sizes and can be related to the hydraulic conductivity of the granular material.

Graphite Furnace Atomic Absorption (GFAA): Atomic absorption which utilizes a graphite cell for excitation.

Ground Penetrating Radar (GPR): A geophysical method in which bursts of electromagnetic energy are transmitted downwards from the surface, to be reflected and refracted by velocity contrasts within the subsurface. Also known as "Ground Probing Radar".

Groundwater: Underground water that fills pores in soils or openings in rocks to the point of saturation. In aquifers, groundwater occurs in sufficient quantities for use as drinking and irrigation water and other purposes.

Groundwater Catchment Area: An area contributing natural replenshment (recharge) of the groundwater regime. It may include localized discharge areas.

Groundwater Divide: The rather vague division between groundwater basins. When the divide meets the land surface, water on one side of the divide will flow into one groundwater system, while water recharging on the other side of the divide will flow into another groundwater system or basin. Somewhat analogous to surface water basins and divides.

Groundwater Flow: Movement of water through openings in sediment and rock of the saturated zone.

Groundwater Mining: Permanent depletion of groundwater reserves.

Groundwater Quality Assessment: The process of analyzing the chemical characteristics of groundwater to determine whether any hazardous materials exist.

Groundwater Table: That surface below which rock, gravel, sand or other material is saturated. It is the surface of a body of unconfined groundwater at which the pressure is atmospheric.

Groundwater Zone: All the rocks in the saturated zone, including those containing perched groundwater.

Grout: A watery mixture of cement (and commonly bentonite) without aggregate that is used to seal the annular space around well casings to prevent infiltration of water or short-circuiting of vapor flow.

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