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Phreatic zone

Treats a variety of contaminants in both the vadose and phreatic zones. [Pg.491]

Vacuum-vaporized well (German Unterdruck-Verdampfer-Brunnen abbreviation UVB) technology for in situ treatment of the capillary fringe, phreatic zone, and vadose zone contaminated with volatile organic compounds, including NAPLs, represents to us one of the most promising in situ bioremediation technologies (U.S. [Pg.155]

One approach used to date (Plummer et al., 1976 Halley and Harris, 1979 Budd, 1984, 1988) is to assume that the rate of conversion of aragonite to calcite (dA/dt) in the phreatic freshwater zone is directly proportional to the mass of aragonite present at a given time, and that the surface area of aragonite per unit mass of aragonite present in the phreatic zone does not change with time ... [Pg.351]

In contrast, Lafon and Vacher (1975) estimated the half-life of aragonite in the vadose zone of Bermuda as about 230,000 years, and the half-life of high-magnesian calcite as only 60,000 years. Minor corrections need to be made to these estimates, because of new estimates of limestone ages for Bermuda, but the fact still remains that stabilization in the vadose freshwater zone is much slower than in the phreatic zone (Land, 1970 Steinen and Matthews, 1973 Steinen, 1974 Vacher et al 1989). [Pg.352]

In a warm and semi-arid climate thick calcretes can develop. Alteration in the vadose zone is relatively rapid but not as rapid as in the phreatic zone. Surface karst is present locally, and caves are small and rare. The mineralogical changes follow the pattern of Figure 7.25, but at a rate slower than that for a warm, subtropical climate like Bermuda. Under the extreme of a warm, wet tropical climate, extensive terra-rossa soils can develop, and dissolution features, such as caves, solution pipes and fractures, should be prevalent. Mineralogical stabilization should occur rapidly. [Pg.363]

The conduit that feeds Rock Spring is entirely in the phreatic zone. It has been explored by SCUBA diving for roughly 400 meters. The conduit carries a flux of clastic sediments. The diver reports a lift tube where the flow rises about 4 meters up a slope. Channel facies sediments collected from bottom and top of the lift tube were dried and sieved. The resulting grain size distribution (Fig. 9) reveals little difference between the bottom and the top of the tube. These sediments are being swept down the conduit by pipe flow and quite clearly follow undulations in the pipe. [Pg.16]

Figure 2.1 Settings for calcrete development. In fluvial settings pedogenic calcretes can develop on floodplains and terraces, whereas groundwater calcretes may form in channel deposits or around the capillary fringe and upper part of the phreatic zone in more permeable parts of the floodplain. In alluvial fans paired calcretes may develop on the fans, with hydromorphic calcretes near discharge zones. Figure 2.1 Settings for calcrete development. In fluvial settings pedogenic calcretes can develop on floodplains and terraces, whereas groundwater calcretes may form in channel deposits or around the capillary fringe and upper part of the phreatic zone in more permeable parts of the floodplain. In alluvial fans paired calcretes may develop on the fans, with hydromorphic calcretes near discharge zones.
Aeolianites that become submerged below the groundwater table may become cemented in the phreatic environment. In this zone, pore spaces between sand grains are completely filled with water and any cements derived from the interstitial waters are often isopachous in nature (Muller, 1971). Large solution volumes and longer residence times in the phreatic zone can result in coarser spar compared with the vadose zone. Increases in temperature, degree of supersaturation and NaCl content appear to result in larger cement crystal sizes (Badiozamani et al., 1977). [Pg.151]

Pore waters in oxic zones are characterized by a dissolved oxygen content greater than 0.5 ml/1. Oxic carbonates prevail in (i) subaerial environments, such as the vadose zone where the pores are periodically filled with gas, air and/or water (ii) immediately below the sediment-water interface in aquatic environments and (iii) in the phreatic zone below the water table where all the pores are regularly filled with water. The thickness of the oxic zone depends on the penetration, by diffusion or advection, of oxygen below the sediment surface. Oxygen diffusion into pore waters is largely controlled by the organic content and the rate of deposition. In marine and lacustrine sediments the... [Pg.2]

Unlike marine sediments, where early diagenesis typically occurs entirely within the phreatic (saturated) zone, early diagenetic alterations in terrestrial sediments occur in both vadose (unsaturated) and phreatic zones. Furthermore, in terrestrial... [Pg.27]

Phreatic carbonate is carbonate that precipitated by non-pedogenic processes in the phreatic zone. Terrestrial phreatic carbonates have been described by many workers (Mann Horwitz, 1979 Arakel ... [Pg.28]

Calcite precipitation under phreatic conditions can continue uninterrupted by an air-water interface (Morse Mackenzie, 1990). Thus, isopachous or drusy, poikilotopic and blocky spar cements are most often associated with precipitation in the phreatic zone (Jacka, 1970 Folk, 1974 Retallack, 1990 Bums Matter, 1995). Sparry cements can also form in the vadose zone as calcans or crystic nodules, but they are associated with soil zonation, highly dense micritic cements and nodules (Weider Yaalon, 1982). Because these cements are not associated with such features they are unlikely to represent calcans or crystic nodules. [Pg.45]

Phreatic cementation is very rarely associated with rhizocretions (Wright Tucker, 1991 Spotl Wright, 1992 Mora et ai, 1993). The lack of rhizocretions indicates that cementation occurred below the zone in which plants had their roots, in the phreatic zone. [Pg.45]

Ovoid and elongate concretions and type 1 tabular units appear to have formed principally in the phreatic zone, because they have poikilotopic and blocky spar cements, are associated with coarser, better sorted units, show preservation of original sedimentary structures, and are not associated with rhizocretions. In the Zia, preferential cementation of coarser, better sorted layers operates on the scale of both thin section and outcrop, something also noticed by Lynch (1996). Elongate concretions have been noted by other workers and attributed to groundwater flow in the phreatic zone (McBride et al., 1994, 1995 Mozley Davis, 1996). Orientations of these elongate concretions tend to be uniform within a single outcrop, often on the scale of several kilometres, as would be unexpected in vadose-zone cementation (Mozley Davis, 1996). [Pg.45]

Cements near the vadose end-member are associated with typical vadose features however, these features are less apparent than in type 2 tabular units, and sparry void filling cements are sometimes more abundant than micrite. As stated previously, micrite-spar cement textures could have initially formed in the vadose zone as pendant and meniscus envelopes around grains or groups of grains (Jacka, 1974 Reeves, 1976 Warren, 1983). Upon burial, these initial vadose cements would provide sites for further calcite precipitation and the unfilled voids could subsequently be filled with sparry calcite in the phreatic zone (Jacka, 1970 Funk, 1979). The vadose contribution to cementation may have been overlooked in the past because of this overprinting. [Pg.46]

Winter rainfall is isotopically lighter, so that main recharge events that penetrated into the phreatic zone may have occurred during the summer when isotopic values are heavier (Quade et al., 1989 Cerling Quade, 1993 Wang et al., 1993). [Pg.46]

Phreatic-zone cementation occurred preferentially in units that had the highest primary permeabilities (i.e. coarser-grained and better-sorted layers). Thus extensive calcite cementation has resulted in a permeability inversion, in which zones of high primary permeability are now low-permeability zones. [Pg.47]

Cementation in the phreatic zone occurred preferentially in zones of high primary permeability, whereas vadose cementation occurred principally in association with soil development. Pedogenic carbonates may have served as nucleation sites for later phreatic cementation, leading to complex zones of mixed pedogenic and phreatic cements. [Pg.48]

Carbonate cements are often among the dominant components of diagenesis and hence are of decisive importance in determining the reservoir quality of sandstone sequences. Despite this, the timing, the geochemical conditions of precipitation and dissolution, as well as the source and fate of these cements are not fully understood. In continental and near-shore sediments, cements commonly precipitate as calcretes and dolocretes in the vadose and phreatic zones, and attain a variety of mineral-ogical, textural and distribution patterns as well as elemental and isotopic compositions. These cements form lenses and layers of densely cemented... [Pg.53]


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