Weathering depth

Within the same geographical area (e.g. water depth, weather conditions, distance to shore, reservoir setting) this is a useful tool for comparing projects of different sizes. If the indicators vary significantly then the reasons should be sought. 

HP — Hole problems HR — Hours on bit PP — Pump pressure PR — Penetration rate RIG — Rig repairs TD — Total depth/casing depth TQ — Torque TW — Twist off WC — Weather conditions... 

Plutonium is transported by the groundwater in fractures in the rock (usually <1 mm wide). A typical groundwater velocity (vw) at >100 m depth in Swedish bedrock is 0.1 tn/y. The fractures are filled with crushed, weathered, clayish minerals, which have a high capacity to sorb the plutonium. Assuming instantaneous and reversible reactions, the sorption will cause the plutonium to move considerably slower (with velocity vn) than the groundwater. The ratio between these two velocities is referred to as the retention factor (RF), defined by... 

A different approach for recovering weathering time information from U-Th series nuclides is to interpret depth variations of radioactive disequilibria in weathering profiles by simple but realistic modelling of U-Th series nuclides during formation and evolution... 

Figure 11. Distribution with depth of U/Th normahzed to the bedroek in two lateritic profiles of the Kaya toposeqnenee, about 300m apart (Burkina Faso) (Deqnineey et al. 2002 submitted). One profile is located downhill (Kaya 5) and the other one at the top of a residual hill (Kaya 1). The laterite consists of an uppermost fermginous hardtop, an intermediate pink clay nnit and a lowest pistachio unit. For Kaya 5 profile, U/Th distribntion shows a relative enrichment of U in the nppermost horizon and depletion in the lower part of the profile. This kind of distribution is quite conunon in weathering profiles bnt is not systematic as illnstrated by the Kaya 1 profile. In the latter, a relative depletion of U is observed in the npper part and a U-enriched level in the intermediate horizon. This lateral difference in U distribution is explained by vertical redistribntion of U from the ferruginons top to the nnderlying horizons, whose intensity is controlled by the evolntion of the iron oxides from the nppermost horizons (Dequincey et al. snbmitted).

Assuming that ( " U/ U) fractionation variations, Boulad et al. (1977) proposed (230Th/238u) variations with depth in a laterite from Cameroon. These authors assumed the occurrence of two main U-Th fractionation fronts one at the base of the weathering profile with U loss, and one in the upper part of the profile where U is released and redeposited deeper in the profile (Fig. 15). By fitting theoretical curves to the data, they estimated weathering rates ranging from 50 to 70 mm/ka. An estimate of 50 mm/ka was also obtained with a similar approach by Mathieu et al. (1995) for a Brazilian laterite. 

Baudoin etal. [168,169] first presented qualitative depth profiles of lacquer and polymer coatings by means of r.f. GD-OES. Quantitative depth profiles were successively obtained by Payling et al. [170] on prepainted metal coated steel. Samples comprised a (rutile) pigmented silicone-modified polyester topcoat over a polymer primer, on top of an aluminium-zinc-silicon alloy coated steel substrate. With GD-OES in r.f. mode, it was possible to determine the depth profile through the polymer topcoat, polymer primer coat, metal alloy coating, and alloy layer binding to the steel substrate with a total depth of 50 im, all in about 60 min on the one sample. GD-OES depth profiles of unexposed and weathered silicone-modified polyesters were also reported [171]. Radiofrequency GD-OES has further been used to... 

This general area has been reviewed in depth by Briggs (1990), who gives an extended bibliography of the application of XPS to a number of aspects, including plasma treatment, photooxidation and weathering, biomedical polymers and polymer-metal interactions. 

The mechanical rototilling method involves turning over soils to a depth of about 0.30 m (1 ft) below the surface to increase the rate of volatilization. Following treatment, the topsoil is moved to a nearby pile and rototilling is performed on the next 0.30 m (1 ft) of soil. The effectiveness of this mechanical rototilling method is highly dependent on weather conditions. High-speed rototillers and soil shredders can enhance the rate of volatilization. 

Performance data Two moisture monitoring systems were installed, one at Disposal Area A and one at Disposal Area AB plus in May and November 1999, respectively. Each monitoring system has two stacks of time domain reflectometry probes that measure soil moisture at 24-in. intervals to a maximum depth of 78 in., and a station for collecting weather data. Based on nearly 3 years of data, there is generally <5% change in the relative volumetric... 

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