Aquifer definition

Water and hydrocarbons occurring together, in shallow aquifer systems, may be considered immiscible for flow calculation purposes however, each is somewhat soluble in the other. Since groundwater cleanup is the purpose behind restorations, it receives greater attention. Definition of water quality based on samples retrieved from monitoring wells relies heavily upon the concentration of individual chemical components found dissolved in those samples. An understanding of the processes that cause concentration gradients is important for the proper interpretation of analytical results. 

Impact of Vadose Zone. The vadose zone is defined as that zone above the water table and below the soil media which is unsaturated. For purposes of this document, this strict definition can be applied to all water table aquifers. However, when evaluating a confined aquifer, the "impact" of the vadose zone is expanded to include both the vadose zone and anysaturated zones which overlie the aquifer. The significantly restrictive zone above the aquifer which forms the confining layer is used as the type of medium which has the most significant impact. 

If a separate consideration of an ensemble of single streamtubes should be required due to large-scale physico-chemical heterogeneities, the model discretisation must be chosen in accordance with the residence times of a conservative tracer in the homogeneous sub-regions (zones) of the aquifer domain considered (Fig. 7.6). In this case, a definite value of the total travel time rQ, , k) of a conservative tracer along each... 

A two-step field test was used to examine the mobility of 4-nitroluene. A solution containing both 4-nittotoluene and KCl was injected into a sandy aquifer and monitored at an exU action well. A solution containing CaCl2 was subsequenUy injected into the aquifer, and mobility of the NAC was found to increase. In the presence of KCl, NAC mobility was attenuated by K-exchanged minerals present. Upon introduction of CaCb, ion exchange of ions by Ca + ions was proposed to account for the increased mobility of the NAC. This smdy provided field-scale evidence that exchangeable cations play a definite role in NAC mobility in soils and subsurface environments. 

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