Velocity of ground-waters

Sugisaki, R., Measurement of effective flow velocity of ground water by means of dissolved qases, American J. Sci.. 259. 144-153 (1961). 

In the area surrounding the study site and away from streams, Hayes (22) estimated that the transmissivity of the Upper Floridan aquifer ranged from about 4,000 to 6,000 ft /d. The effective hydraulic conductivity of the aquifer in this area was estimated to be about 100 ft/d, and the effective porosity was estimated to be about 20 percent (22). Hayes (22) reported that the hydraulic gradient in the northern part of the Dougherty Plain was about 2 ft/mi, and so the average velocity of ground-water flow in the vicinity of the study site is about 0.2 ft/d. 

Average velocity of ground water in porous media (rocks) is expressed as... 

H- He ages have been used to determine ground-water flow velocities in different situations. Vertical H- He profiles allowed determination of ground-water recharge rates (e.g., Schlosser et al. 1988 Solomon and Sudicky 1991 Solomon et al. 1993). Horizontal... 

The main source of fluoride in ground water is fluoride-bearing rocks such as fluorospar, fluorite, eiyolite, fluorapatite and hydroxylapatite [12]. The flouride content in ground water is a function of several faetors including hydrogeological environment, solubility of fluoride minerals in water, velocity of flowing water, pH, temperature as well as coneentrations of other species such as calcium and bicarbonate ions in water [13,14]. 

Hydrodynamic dispersion causes a contaminant plume to spread out from the main direction of ground water flow. Dispersion dilutes the concentrations of the contaminant, and introduces the contaminant into relatively pristine portions of the aquifer where it mixes with more electron acceptors cross gradient to the direction of ground-water flow. As a result of dispersion, the solute front travels at a rate that is faster than would be predicted based solely on the average linear velocity of the ground water. Figure 22.1 illustrates the effects of hydrodynamic dispersion on an advancing solute front. Mechanical dispersion is commonly represented by the relationship ... 

So we deduce that only one DMB molecule out of 11 will be in the moving ground-water at any instant (Fig. 9.6). This result has implications for the fate of the DMB in that subsurface environment. If DMB sorptive exchange between the aquifer solids and the water is fast relative to the groundwater flow and if sorption is reversible, we can conclude that the whole population of DMB molecules moves at one-eleventh the rate of the water. The phenomenon of diminished chemical transport speed relative to the water seepage velocity is referred to as retardation. It is commonly discussed using the retardation factor, Rfi, which is simply equal to the reciprocal of the fraction of molecules capable of moving with the flow at any instant, ff (see Chapter 25). 

Dispersivity is a property of the porous medium that has been shown to be proportional to the scale of the system under consideration [4]. Thus, the dispersivity of a porous medium in a laboratory column will be considerably smaller than the dispersivity of an aquifer through which contaminated ground-water is flowing over distances of hundreds of meters. Presumably, this scale-effect is due to the increased spreading caused by variations in velocities due to larger scale heterogeneities [2]. 

The intimate mixing of oxidizer and fuel in emulsions give these explosives much higher detonation velocities when compared to ANFO. For example, in 150 mm diameter PVC ANFO has a velocity of about 4000 m/sec, and a sensitized emulsion would have a velocity closer to 6000 m/sec at a density of 1.20-1.25 g/cc. Also, the layer of oil surrounding each oxidizer solution droplet protects the emulsion from extraneous water intrusion and subsequent deterioration of the explosive. Many studies have shown that when mining operations use emulsion explosives rather than ANFO, which has basically no water resistance, the amount of nitrate salts in mine ground water is reduced considerably. This can be a very important factor in today s environmentally conscious mining and explosives industry. 

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