Residence time, of groundwater

The major findings of this exercise indicate that, in spite of the long residence times of groundwaters in the Cigar Lake ore deposit system (over 10 000 years), the Al-Si system appears to be kinetically controlled and the... 

Table X lists a few of the haloaliphatic substrates which were found to satisfy Expression 7 for some of the sulfur nucleophiles encountered (or closely related to those found) in natural waters. The results in the table indicate that among the substrates listed in Tables IV through IX, it is principally the brominated compounds for which the reactions with sulfur nucleophiles are likely to compete effectively with hydrolysis. However, due to the long residence times of groundwaters in hydrogeologic systems, reactions which are not as rapid as hydrolysis may also be significant.

HejAsw is ASW-He (this concentration is a function of temperature and pressure, although its variation is generally small compared to the radiogenic " He content), P4 is the accumulation rate of " He from in situ production and t is the residence time of groundwater (the exponential function of radioactive decay has been linearized because the residence time of groundwaters are always small compared to the decay constants of U and Th). 

Figure 8.10 Calculated average residence times of groundwater in the Ucker watershed (2400 km ).

The isotopic compositions of four lakes (see Figure 3 for lake locations, in northern Wisconsin that are within 10 km of each other and that have hydraulic-residence times of about 10 years are plotted in Figure 4. The four lakes (Crystal, Pallette, Big Musky, and Sparkling) are groundwater flow-through lakes and have no surface inflows or outflows. Thus they have the same hydrological-budget components (they receive water from precip-... 

The Livermore study used a 1.8 L upflow reactor, packed with a 1% w/w Pd/alumina catalyst, nominally 0.32 cm in diameter. (McNab and Ruiz 1998) The water supply consisted of groundwater from a well at the Livermore site and contained PCE (5-7 jig/L), TCE (500-600 tig/L), 1,1-DCE (15-25 pg/L), CT (8-15 fig/L), CF (4-10 gg/L), and 1,2-DCA (4-10 jrg/L). The water was first passed through an electrolyzer, which served as a source of hydrogen. With an average residence time of 2.3 minutes, the column showed >95% removal of chlorinated ethylenes (PCE, TCE and 1,1,-DCE) and CT. The apparent first order rate constants for all four compounds were approximately 72/hour. Chloroform was removed at a much slower rate (<32/hour) and 1,2-DCA removal was not significant. These results are also consistent with the batch studies of Lowry which showed rapid reaction of... 

The rainwater of Bermuda is in near equilibrium with atmospheric Pc02 = 10-3.5 atm., and contains small amounts of sea salt (0.07 wt. % seawater). The rainfall of 147 cm y1 is seasonally distributed. The rain enters the saturated zone by two main paths direct rainfall on marshes and ponds, and percolation downward from the vadose zone as vadose seepage and flow through rocks during times of soil water excess (Vacher, 1978). Total annual recharge of the saturated zone is about 40 cm y-1 (Vacher and Ayers, 1980). The residence time of the groundwater has been calculated as 6.5 years, and the average age of the sampled water as 4 years (Vacher et al., 1989). Such estimates are necessary for calculations of carbonate mineral stabilization rates, as shown in a later section. 

Figure 1.5(c) however, dissolved gas tracer data from 35 m (Figure 1.5(e)) may have been impacted by volatilization since this monitoring well is situated near a groundwater discharge point at the end of the sampling transect (Figure 1.2). Nevertheless, results from 31m clearly show that solute diffusion into the bedrock matrix is a significant process contributing to contaminant storage in this subsurface media, and that the diffusion process becomes increasingly important as the residence time of the solute increases in the system.

Eouvat D., Michelot J.-E., and Aranyossy J. F. (1999) Origin and residence time of salinity in the Aspo groundwater system. Appl. Geochem. 14, 917-925. 

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