Ground water point source origins

Organic chemicals dissolved in groundwater originate from a release source, which may be point source (defined leak) or it may emanate from an area source, such as a mass of contaminated soil. Once dissolved, the chemicals disperse into the ground-water by molecular diffusion and advection (combined as dispersion), both of which are influenced by equilibrium distribution relationships with the aquifer materials. 

Contamination of ground water with pesticides can occur in two distinctly different situations, those originating from widespread agricultural use and those attributed to a specific point source loss. Each of these situations requires a different approach to ground-water monitoring. 

For SiC>2, we have only considered sources for silica suspensions which were non-porous, such as Ludox (39), pyrogenic silica (40), heat-treated BDH silica (22), or ground quartz (41). The data from these sources at 0.1M concentration has been collected in Figure 7. The data of the various researchers is quite consistent, in spite of the differences in origin of the suspensions, and the different electrolytes used. The slope of the points above pH 7 shows that the adsorption capacitance for cations is very large for both sodium and potassium ions, around 200 pF/cm2. Such a capacitance corresponds to a distance of 0.25.X, when using the dielectric constant of immobilized water molecules. The equilibrium constant for adsorption is low, however, since both KNa+ and Kk+ lie between 0.1 and 0.01 dms/mol. A possible interpretation of these results is as follows there is little specific attraction between SiC>2 and alkali cations,... 

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