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Five groundwater samples taken from different hydrogeologic settings in Connecticut were analyzed for major cation chemistry and the concentration of U and Th decay series nuclides 238U, 234Th, 226Ra, 222Rn, 2•øpb, 2•øpo, 232Th, 228Ra, 228Th, and 224Ra. The concentration of 222Rn in the waters ranged between 103 and 104 dpm 1-• and was three to four orders of magnitude greater than that of the shortlived alpha daughters 224Ra, 228Ra, and 234Th, even though the rates of supply of these four nuclides to solution are expected to be similar. We infer that sorption removes radium and thorium from these groundwaters on a time scale of 3 minutes or less. The (224Ra/228Ra)•.and (234Th/228Th) activity ratios in these waters indicate that desorption of these nuclides occurs on a time scale of a week or less and that equilibrium between solution and surface phases is established. In situ retardation factors for radium, thorium, and lead may therefore be calculated directly from the isotopic data; values range from 4,500 to 200,000. Neither sorption time scales nor retardation factors are, strongly dependent on the nuclide or on hydrogeology of the aquifer. Since our study includes nuclides with diverse chemical properties, we suggest that other uncomplexed heavy metals and transuranic elements will also behave in a manner similar to those measured here. The approach presented here should therefore find application in developing site-specific models of the transport of radioactive or stable elemental waste through water-saturated media. 1. geochemical properties, their behaviors may serve as indica-1On leave from the Physical Research Laboratory, Ahmadabad, India. tors of the in situ chemical behavior of other nuclides injected into the system. With this aim we have analyzed several groundwaters from Connecticut for virtually every long-lived (half-life > 1 day) member of the 238U and 232Thseries in order to understand the processes controlling their concentration in solution and thereby to estimate the rates of those processes. The U and Th series nuclides are uniquely suited to this study because several isotopes of the same element are continuously introduced into groundwaters and because the supply rates of many of these nuclides can be estimated with adequate accuracy. Measurements of the distribution of these natural decay series nuclides yield site-specific empirical data on the in situ sorption processes. Parameters such as distribution coefficients or retardation factors derived from these measurements may be used in models of transport of both radioactive and stable nuclides that show analogous chemical behaviors. METHODSFive groundwater samples from the major aquifer types of Connecticut were collected for this study. The sampling locations, aquifer descriptions, and water chemistries are given in Table 1. Samples GW-3 and GW-7 were both taken from municipal water supply production wells in glacial drift aquifers. The large volumes of water pumped from these wells (Table 1) suggests that recharge is induced from n...

[1] Sr and Nd concentrations and isotope compositions in sediment of the Ganga River, from Gangotri to Rajmahal, and its tributaries have been measured to determine provenance and the spatial variability in physical erosion among the Ganga subbasins. Sr and Nd in silicates range from 37 to 138 and from 10 to 36 mg/g, with 87 Sr/ 86 Sr and e Nd of 0.7474-0.8428 and À25.5 to À15.5, respectively. The results suggest that >65% of Ganga mainstream sediments are derived from the Higher Himalayan Crystallines highlighting intense physical erosion in this region. The 87 Sr/ 86 Sr values of sediments in the Gangetic plain show nearly identical trends during two seasons, with a sharp and significant decrease at Barauni downstream of Gandak confluence. This brings out the major impact of the sediment contribution from the Gandak to the Ganga mainstream. Model calculation suggests that about half of the Ganga sediment at Rajmahal is sourced from the Gandak. The erosion rates in the Himalayan subbasins of the Ganga range between 0.5 and 6 mm/a (where a is years), with the Gandak having the highest erosion rate. High relief and intense precipitation over the headwater basins of the Gandak appear to drive the rapid and focused erosion of this basin. The results of this study and those in literature suggest that the eastern syntaxis (Brahmaputra), the western syntaxis (Indus), and the Gandak have much higher physical erosion rates than the other Himalayan basins. Focused erosion in the hot spots of these river basins contributes significantly to the global riverine sediment budget and influence regional tectonics.

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