Groundwater resistance

As discussed previously, some soil environments and ground waters can be corrosive to buried metal structures. Resistivity measurements, which can be made both in the field and in the laboratory, indicate how corrosion currents will flow through soils or ground waters. High concentrations of chlorides and sulfates contribute to a reduction in resistivity and an increase in the corrosion activity of a material. In the presence of oxygen, chloride ions can be extremely corrosive to steel. Similarly, high levels of sulfates can cause a reduction in soil or groundwater resistivity and corrosion of steel and concrete. 

Coatings must be considered for aU applications of steel. Cathodic protection should be considered for steel pipe where soil or groundwater resistivity is less than 10,000 t2-cm, and where steel win be in contact with process streams. Cathodic protection of steel is strongly recommended where resistivity is less than 5000 Q-cm. For aU exposures, steel should be electrically isolated from dissimilar metals to prevent the formation of unfavorable galvanic corrosion ceUs. In areas where abrasive materials are hkely to damage coatings, cathodic protection by impressed current or galvanic anodes may be desirable. 

Electromagnetic (EM) Conductivity Measures the electrical conductivity of materials in microohms over a range of depths determined by the spacing and orientation of the transmitter and receiver coils, and the nature of the earth materials. Delineates areas of soil and groundwater contamination and the depth to bedrock or buried objects. Surveys to depths of SO to 100 ft are possible. Power lines, underground cables, transformers and other electrical sources severely distort the measurements. Low resistivities of surficial materials makes interpretation difficult. The top layers act as a shunt to the introduction of energy info lower layers. Capabilities for defining the variation of resistivity with depth are limited. In cases where the desired result is to map a contaminated plume in a sand layer beneath a surficial clayey soil in an area of cultural interference, or where chemicals have been spilled on the surface, or where clay soils are present it is probably not worth the effort to conduct the survey. 

A safety analysis (9) has shown that these cylinders should resist the reducing groundwater, which percolates through Swedish bedrock, for about 106 years. Still, the Swedish authorities have requested information about the consequences of the groundwater coming into contact with the plutonium. 

Ortiz-Bernad I, RT Anderson, HA Vrionis, DR Lovley (2004a) Resistance of solid-phase U(VI) to microbial reduction during in situ bioremediation of uranium-contaminated groundwater. Appl Environ Microbiol 70 7558-7560. 

The figure illustration shows occurrence of clogging by plotting data from an observation well (OW) and compare that to the production well (PW). In this case the production well shows a decreased specific capacity while the observation well shows a steady level versus time. The only explanation is then that the resistance for water to enter the production well is increasing. The increased resistance will lower the drawdown inside the well, while the groundwater table outside the well is kept constant. This will increase the hydraulic gradient (the driving force) between the well and the aquifer and hence maintain a constant flow rate. 

The forces resisting groundwater flow are shearing stress and normal stress due to viscosity, collision, and turbulence. 

Toxaphene partitions to the atmosphere, surface and groundwaters, soil and sediment particulates, and adipose tissue. As a result of its volatility and resistance to photolytic transformation, toxaphene has been transported over long distances in the atmosphere (USPHS 1994). Toxaphene residues have been detected in various environmental compartments hundreds of kilometers distant... 

Hexachloroethane is also relatively resistant to degradation in the aquatic environment. No hydrolysis of hexachloroethane in water was observed after 11 days at 85 C at 3 pH levels (3, 7, and 11) (Ellington et al. 1987). However, hexachloroethane may be reduced in aquatic systems in the presence of sulfide and ferrous ions (Kriegman-King and Reinhard 1991). The transformation rate of hexachloroethane to tetrachloroethylene under simulated groundwater conditions at 50 C was evaluated without ferrous or sulfide ions, with minerals (biotite and vermiculite) providing ferrous ions, and with minerals and sulfide ions. Reported half-lives for hexachloroethane were 365 days for hexachloroethane alone, 57-190 days with minerals present, and 0.45-0.65 days in the presence of both minerals and sulfide. 

Biotic and abiotic degradation of 1,2-dibromoethane in surface waters is slow relative to volatilization of the compound to the atmosphere (ERA 1987b). 1,2- Dibromoethane is resistant to hydrolysis (Jaber et al. 1984) the hydrolytic half-life of the compound has been reported to range from 2.5 years (Vogel and Reinhard 1982) to 13.2 years (HSDB 1989). As a result of its hydrolytic stability and the limited biological activity in subsurface soils, 1,2- dibromoethane leached to groundwater is expected to persist for years. 

Cresols are widely distributed natural compounds. As discussed above, they are formed as metabolites of microbial activity and are excreted in the urine of mammals (Fiege and Bayer 1987) and humans (Needham et al. 1984). Cresols from human urine are probably biodegraded at municipal sewage treatment facilities prior to release to ambient waters. However, for combined septic and storm sewage systems, cresols may be released to surface waters during periods of precipitation when influent volumes exceed treatment plant capacities. Also, in rural and suburban areas where septic tanks are used (o- and m-cresols can resist anaerobic digestion), human excrement may be a nonpoint source release of cresols to groundwater. 

Cbee-Sanford J.C., R.I. Aminov, I.J. Krapac, N. Garrigues-Jeanjean, and R.I. Mackie (2001). Occurrence and diversity of tetracycline resistance genes in lagoons and groundwater under-l)dng two swine production facilities. Applied and Environmental Microbiology 67 1494-1502. 

The Turbostripper is an air stripper technology for removal of volatile organic compounds (VOCs) from groundwater or wastewater. According to the vendor, it is a 100% nonclogging unit, based on its use of the patented Turbolill chemically resistant plastic ellipsoids. 

Any solid waste form should serve to reduce waste volume and provide short term stabilization under conditions such as fracture, fire, or water immersion which could result from a transportation mishap. In the geologic storage scenarios currently receiving the most scrutiny, the most likely path to the biosphere has been identified as aqueous transport of nuclides via groundwater. Thus an acceptable waste form would also resist dissolution under ambient repository conditions, with the obvious benefit of assuring a sufficiently low nuclide release rate into an aquifer to preclude a significant threat to health and safety. 

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