Aquifers monitoring systems

Monitoring the well for leaks and nearby aquifers for contamination must also be considered. The extent of monitoring will vary based on the applicable environmental regulations and nearby potable aquifers. Monitoring wells can be constructed to monitor shallow or deep aquifers, and the cost of a these wells is determined by the required depth and the geology of the site. Additional costs include ancillary surface equipment and alarm systems (Mickley 2006). 

Injection and monitoring systems. An injection well (A in Fig. 16.7), 500 m deep, was drilled into the lower confined limestone aquifer, and later a second well (B) was drilled 400 m west of the first one. A deep monitoring well, 400 m south of A, was drilled into the receiving aquifer. A shallow monitoring well was drilled into the upper limestone aquifer, 30 m from injection well A. Hence, changes in the chemical composition could be monitored both in the receiving and overlying aquifers. 

Fly ash and bottom ash has been declared a special waste by the U.S. Environmental Protection Agency, in concordance with the Federal Resource Conservation and Recovery Act (R.C.R.A.). This designation requires that coal ash disposal ponds be sealed to prevent downward percolation of leachate and that groundwater monitoring systems be installed at the site. Many disposal ponds constructed prior to 1976 are unlined and may allow the infiltration of leachate into the groundwater aquifer. While newer ponds may be lined, the life of the lining before it is breached is unknown. Therefore, information is needed on the chemical composition of ash leachates to evaluate the effect of this leachate on groundwater quality. 

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. 

D.A. Blum, J.A. Carr, R.K. Davis, and D.T. Pederson, Atrazine in a stream-aquifer system transport of atrazine and its environmental impact near Ashland, Nebraska Ground Water Monitor Remed. 13(2) 125, 1993. 

The rapid increase from 26 to 98% waste fluid in the deep monitoring well indicated that the nonneutralized waste dissolved the aquifer carbonates and developed a highly conductive karstic system, which was very alarming in terms of waste disposal in the aquifer. During all this time no chemicals arrived in the upper monitoring well. 

Many of the important chemical reactions controlling arsenic partitioning between solid and liquid phases in aquifers occur at particle-water interfaces. Several spectroscopic methods exist to monitor the electronic, vibrational, and other properties of atoms or molecules localized in the interfacial region. These methods provide information on valence, local coordination, protonation, and other properties that is difficult to obtain by other means. This chapter synthesizes recent infrared, x-ray photoelectron, and x-ray absorption spectroscopic studies of arsenic speciation in natural and synthetic solid phases. The local coordination of arsenic in sulfide minerals, in arsenate and arsenite precipitates, in secondary sulfates and carbonates, adsorbed on iron, manganese, and aluminium hydrous oxides, and adsorbed on aluminosilicate clay minerals is summarized. The chapter concludes with a discussion of the implications of these studies (conducted primarily in model systems) for arsenic speciation in aquifer sediments. 

Monitoring of the vadose (unsaturated) zone may, in certain areas, be another promising step towards an "early warning" system. Ground water contamination if detected early enough from this zone, could allow for remedial measures to be implemented sooner and aquifer restoration costs significantly reduced. In areas with a very shallow vadose zone (i.e., Smith River with less than 10 feet depth), there may be insufficient lead time for preventive regulatory action. 

A uniform and constant Darcy velocity of 15 myear-1 and effective porosity of 0.3 were used along the entire cross-section. The tailings fluid has relatively high chloride concentrations (0.016 mol L 1) compared with the background water has only 0.0007 molL-1. It is widely believed that Cl- acts as a conservative solute in most aquifer systems, and thus its distribution can be used to retrieve dispersivity for the aquifer. By trial and error, a longitudinal dispersivity between 10 to 15 m appears to fit the concentration differences best in monitor wells sampled in September, 1994. It... 

Compared to the monitoring of all other natural waters, the satisfactory collection and interpretation of groundwater quality data requires an essentially 4D (four-dimensional) approach, because the large volume and the complexity of many aquifer systems (or hydrogeologic typologies) result in flow paths with residence times of very variable timescale, ranging from months to millennia (and usually counted in decades or... 

In practice, adequate and cost-effective selection of monitoring wells requires some prior basic knowledge of the main characteristics of the aquifer system under consideration, including at minimum some information on ... 

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