DEFINITION
of terms as used by the earthDr
Background Monitoring Well (bMW): monitoring wells used to determine background ground-water quality.
Capillary Fringe: that zone of soil immediately above the water table (see Capillary Fringe) that acts like a sponge sucking water up from the underlying water table and retaining this water somewhat tenaciously. Soil pores act like capillary tubes. The smaller the soil pore, the greater is the rise of water within the soil pore. The pores within a soil matrix are typically composed of numerous pore sizes. At the base of the capillary fringe most if not all of the soil pores are completely filled with water. At the top of the capillary fringe, only the smallest soil pores are filled with water. Therefore, the water content of the capillary fringe decreases with increasing distance above the water table. The size of the diameter of the soil pore defines the capillary rise of the water column. It is possible that soils can be completely saturated with water, yet the water table is some number of feet below this point of complete saturation. The water table is defined by that point in the soil column where water is free to move; therefore, it is not tenaciously bound within the soil pores. The water table is physically determined by the level to which ground water flows into a porous pipe which has a diameter large enough so that capillary forces from this pipe cannot complicate the determination of the top of the water table.
In those soils where the vertical thickness of the capillary fringe at least equals the depth to the water table, then the capillary fringe can behave as a wick, wicking the waters originating from the water table to soil surface where it can be evaporated to the atmosphere.
Capture Zone: the ground water flowpaths which contribute water to the recovery system.
Capture Zone Monitoring Well (czMW): monitoring wells and piezometers used to determine if capture is effective based upon comparisons of ground-water quality and/or hydraulic levels.
Dispersion: is mechanical mixing of ground water and its dissolved constituents; and, diffusion of dissolved constituents.
Dissolved Product Contaminated Soil (solusols): those soils contaminated through contact with product dissolved in water. Dissolved product being formed by contact of a liquid state to a liquid state or gaseous state to a liquid state.
Floating Product: that portion of separate phase present at and above the water table as a free product.
Free Product: that portion of separate phase capable of gravity drainage and/or pressure driven flow through the subsurface.
Free Product Contaminated Soils (produsols): those soils contaminated through contact with separate phase.
Hydraulic Control: the establishment of a ground-water gradient, by pumping of the ground water, to induce contaminated ground water and/or free product to flow into the recovery system. Ideally, hydraulic control should result in at least one of the following conditions:
Hydraulic Influence: those ground water flowpaths which contribute water to the recovery system as well as those flowpaths affected, but not captured, by the recovery system. It is represented by a decline in hydraulic head in response to pumping. Hydraulic influence does not ensure hydraulic control.
Leachate: separate-phase product dissolved in water above the water table that is moving through the soil. Below the water table it is referred to as a plume of contaminated ground water or a plume.
Plume: separate-phase product dissolved in ground water that is moving through the subsurface by advective forces and dispersion.
Plumelet: a slug of contaminated ground water that originated by hydraulically splitting the plume into two portions.
Product Wetting: the act of soil becoming contaminated by separate phase product as it migrates through the soil. As product spreads, either horizontally or vertically, the soil pores become saturated. Product will tend to migrate through the larger pores before it will migrate through the smaller soil pores. There are numerous interconnections between the soil pores. Smaller pores (micropores) tend to branch into slightly larger pores (mesopores) and then, into the largest soil pores (macropores). These interconnections are analogous to the branching of a dendritic stream. As the product migrates through the largest pores, the product encounters many of these interconnections with the smaller pores. The product may be able to flow into these smaller pores provided that the pore isn't blocked by water. Water is held more tenaciously by the smaller pores than by the larger pores. The product may be able to displace this water provided that the water is not held too tenaciously by the soil pore. Product wetting is oldest closer to the spill and younger farther from the spill.
Produsols: separate phase contaminated soil. It can include either product entrained in the soil pores or product entrained in the soil pores and free product.
Residual Saturation: that portion of separate phase remaining in the soil after gravity drainage of free product. It is synonymuos with entrained product, and is frequently used interchangeably with free product contaminated soil.
RIVD: an acronym for recharge-induced-vertical-displacement. As ground water flows horizontally, recharge events superimpose recharge waters above the existing water table surface. As a plume moves horizontally, recharge events can superimpose clean recharge water above the plume, which vertically displaces the plume downward. See superposition.
Separate Phase: a non-aqueous phase liquid.
Solusols: dissolved product contaminated soil. This includes both the dissolved product in the soil solution and in the ground water and that adsorbed or absorbed (collectively - sorbed to the soil particles. Solusols can form from one of two genetic processes. Contaminant vapors in the soil atmosphere can dissolve into the soil solution or separate phase dissolves into the soil solution or into the ground water.
Source: free product and free product contaminated soil resulting from releases from underground storage tank systems and other spills or regulated units.
Source Control: the prevention of further contaminant transport away from the source-recharge area. It can include product recovery, soil remediation (including soil removal), and/or hydraulic control of the source-recharge area.
Source-Recharge Area: in plan view, that area of the water table where leachate and/or free product recharge the phreatic surface and includes that area of the capillary fringe or the saturated zone containing separate phase. It includes all areas where contaminant mass loading of the water table occurs. This area can be more extensive than the area of the source.
Source-Recharge Area Monitoring Well (sraMW): those monitoring wells used to define the extent of the source-recharge area.
Splitting the Plume: splitting the plume into two portions by pumping ground water so as to influence all ground-water flowpaths of the plume to be captured by the pumping well(s). The purpose of plume splitting is often to encourage clean ground to flush contaminated ground water from beneath a structure or prevent the continued migration of contaminants from the source recharge area.
Stagnation Point: the extreme downgradient extent of capture.
Vapor Phase Contaminated Soil (Vaposols): those soils contaminated through contact with vapor phase product.
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