Aquifers contamination mechanism

Aerobic treatment of aquifer oxygen is usually supphed by one of three methods direct air sparging of air or oxygen into wells screened below the contaminated zone, saturation of water with air or oxygen prior to reinjection, or addition of an oxidant (typically a peroxide compound) directly into an injection well or injection water. Regardless of the mechanism of introduction, the important factor is that the oxidant is distributed throughout the contaminated zone at a concentration and rate such that it can be utilized by the microorganisms. 

Electrokinetics has been used to mobilize metals and dissolved contaminants to in situ treatment or recovery zones. Electrokinetic transport uses these mechanisms to move bacteria through the subsurface to the contaminated media. The technology can be used to treat organic contaminants that adsorb to aquifer soils including halogenated hydrocarbons and non-aqueous-phase liquids (NAPLs). 

The half-life with respect to chemical transformation of CH3I in seawater at 20°C was determined to be 20 days, as compared to about 200 days in freshwater (reaction with H20 yielding CH3OH). In a case of a groundwater contamination with several alkyl bromides, Schwarzenbach et al. (1985) reported the formation of dialkyl sulfides under sulfate-reducing conditions in an aquifer. They postulated that in an initial reaction, primary alkyl bromides reacted with HS" by an SN2 mechanism to yield the corresponding mercaptans (thiols) ... 

See, for example, M. L. Brusseau and P.S.C. Rao. Sorption nonideality during organic contaminant transport in porous media, Crit. Rev. Environ. Control 19 33 (1989) and W. W. Wood, T. F. Kraemer, and P. P. Hearn, Jr., Intragranular diffusion An important mechanism influencing solute transport in clastic aquifers Science 247 1569... 

To mitigate radioactive contamination, it is important to understand the processes and mechanisms of interactions between radionuclides and the solid material of aquifers. Cationic radionuclides may be sorbed by processes such as ion exchange or surface complex formation, thus retarding their transport by groundwater. 

From 10 to 104 mg kg-1 TCE sorb to low-organic-matter minerals (Estes et al., 1988 Farrell Reinhard, 1994a,b), so all contaminated aquifer materials are potential long-term sinks and longer-term sources of TCE, but little or nothing is known about the mechanisms of adsorption. Clay minerals often comprise the bulk of the surface area in low-organic-matter aquifer materials, so the interactions of TCE and clays are of special interest. 

Adsorption/Desorption While some contaminants move freely down the flow path at a velocity close to that of the groundwater itself, some tend to enter into complex adsorptioti/desorpfion reactions on the surfaces of soil and rock minerals. This often greatly retards their transport and increases their persistence into the aquifer system. Many organic compounds and heavy metals are prone to adsorpfion/desorpfion mechanisms. 

The chemical sciences offer insight into the molecular mechanisms of biogeochemical processes, links between nano-, laboratory, and field scales through modeling and simulation, sensors for the detection and quantification of chemical constituents of groundwater, and chemical reagents and chemistry-based technologies for in situ remediation of contaminated aquifers. 

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