Groundwater systems flow regimes

Chemical mass is redistributed within a groundwater flow regime as a result of three principal transport processes advection, hydrodynamic dispersion, and molecular diffusion (e.g., Bear, 1972 Freeze and Cherry, 1979). Collectively, they are referred to as mass transport. The nature of these processes and how each can be accommodated within a transport model for a multicomponent chemical system are described in the following sections. 

Specific Discharge q, Effective Mean Flow Velocity u, and Travel Time fw for Different Flow Regimes in Groundwater System S... 

On April 5, at noon, the 2,4-dinitrophenol concentration in River R at Groundwater System S (GWS, see Illustrative Example 25.1 and 25.2) suddenly increases from 0 to 50 ng L 1 and then remains constant. At what time does the concentration in the wells of the GWS reach 25 ng L-1 and 47.5 ng L 1, respectively Calculate the time for all three flow regimes. When are these concentrations reached 3 m from the river if no water is pumped from the wells (Natural Regime) ... 

Calculate the annual sinusoidal variation of the PCE concentration in the wells of Groundwater System S relative to the variation in River R. Compare this number with the relative variation of a nonsorbing chemical such as 2,4-dinitrophenol (see Illustrative Example 25.5). Determine the time lag of oscillation in the well relative to the variation in the river. Use all three flow regimes of Illustrative Example 25.1. 

This brief discussion of the flow regime of an unconfined system emphasizes its three-dimensional nature and the large variety of water fluxes, velocities, and ages that prevail in each case study. The unconfined groundwater regime differs fundamentally from the one-dimensional tube of Darcy s experiment, with its particular properties (section 14.6). 

Differences in weathering regimes between well and poorly leached parts of a groundwater flow system have been noted previously in the literature. For example, Kovda and Samoilova (1969) presented a diagram (Fig. 13) showing how kaolinite tends to accumulate in uplands and montmorillonite in lowlands as a consequence of groundwater flow. The formation of montmorillonite results from the increased availability of silica so that a reaction of the following type prevails ... 

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