Terms used in this report are listed below. Aquifer A unit of saturated unconsolidated sediments, such as sand or gravel, or consolidated rocks that will yield water in significant quantities to wells and springs and allow the water to move from one location to another. Capillary fringe A zone of sediments that overlies the water table in which some or all of the spaces between sediment particles are filled with water and held against the pull of gravity by suction. Capillary suction A force that draws water into the small spaces between sediment particles and holds it against the pull of gravity similar to the process by which a spill is picked up with a paper towel. Confining unit A layer of geologic material, such as clay, that slows the vertical movement of water in an aquifer or between two aquifers. A confining unit is sometimes referred to as an aquitard. Dense nonaqueous-phase liquids (DNAPLs) A liquid chemical, such as TCE, that is heavier than water and does not readily mix with or dissolve in water. Drawdown cone A depression in the water table created by the removal of water from the aquifer by pumping from a well; also may be referred to as a cone of depression. Dual-phase extraction (DPE) A groundwater cleanup system in which ground water is extracted from the aquifer for treatment at the same time as soil vapor is removed from the unsaturated zone. Geographic-information system (GIS) A computerized information storage-and-retrieval system for data that have a geographic component. Gravel pack Well-sorted, coarse-grained sediment that is installed in the annular space surrounding a well screen. Heterogeneity Not the same everywhere; having nonuniform properties. pH A measure of the acidity of water. A neutral water has a pH of 7.0, an alkaline water has a pH of more than 7.0, and an acidic water has a pH of less than 7.0. Perched ground water Water found in pockets of saturated sediments underlain by unsaturated sediments. Permeability A measure of the ability of rocks or sediments to transmit water or other fluids. Porosity The property of rocks and sediments of having openings or void spaces between the solid particles; usually expressed quantitatively as a ratio or percentage. Preferential flow Movement of water and dissolved chemicals along distinct pathways rather than as uniform flow. Flow may follow interconnected cracks or zones having high permeability. Preferential flow is also referred to as bypass flow. Pump and treat A groundwater cleanup technique in which water is removed from an aquifer using extraction wells. The water is treated to remove contaminants and then recharged to the aquifer or used for water-supply purposes. Rebound An increase in contaminant concentrations in ground water after a period of decreasing or constant concentrations and after an extraction well is shut off. Recharge area A place where water enters the ground and percolates down to the aquifer. Screened interval The length of well casing that is perforated or slotted to receive water from the aquifer. Soil-vap...

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