[en] Groundwater dating with ¹⁴C_DIC is complicated by sulphate reducers such as Desulfovibrio desulfuricans which use SO^2-₄ to metabolize organic carbon, production both sulphide (H₂S and HS^-) and dissolved inorganic carbon (DIC). The process dilutes the ¹⁴C_DIC pool and modifies δ¹³C_DIC, thus precluding calculation of carbonate dissolution (q₁) by classical approaches. Two examples of high HS^- groundwaters are studied to quantify the effect of sulphate reduction on the DIC pool, and to model the accompanying ¹⁴C dilutions. Results give considerably lower estimates of age than when carbonate reactions alone are considered. Thermal groundwaters in the Yarmouk basin of northern Jordan discharge under artesian pressure from a fractured limestone aquifer with high kerogen content. Because of the modification of δ¹³C, ¹⁴C dilution by carbonate dissolution was determined by analyzing groundwaters in the recharge area. The ¹⁴C dilution from sulphate reduction was quantified by sulphide and DIC mass balance. A third dilution of ¹⁴C by incorporation of mantle CO₂ in the rift zone was identified by ¹³C mass balance calculations, showing that measured δ¹³C values were positive-shifted from calculated δ¹³C values. Corrected ages indicate Holocene recharge. This supported by their δ¹⁸O-δ²H signature, with is a qualitative indication of age. 11 refs, 5 figs, 1 tab

[en] Full text: The isotopic composition of both dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) in groundwater can now be routinely analysed by an automated total inorganic and organic carbon (TIC/TOC) instrument interfaced with a continuous flow isotope ratio mass spectrometer (CF-IRMS). The TIC/TOC analyzer uses a helium carrier gas compatible with the CF-IRMS. This allows rapid, automated analysis of concentration and ¹³C composition for these two important carbon components in groundwaters. Having developed this new method, we now add a preparation step where DOC components are separated by liquid chromatography and fraction collector, allowing the analysis of ¹³C in specific DOC compounds. This provides insights into the consumption and production of organic carbon substrates during bacterial degradation of DOC. Applications with leachate-contaminated groundwaters and methanogenic groundwaters are presented. (author)

[en] Full text: The isotopic composition of both dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) in groundwater can now be routinely analysed by an automated total inorganic and organic carbon (TIC/TOC) instrument interfaced with a continuous flow isotope ratio mass spectrometer (CF-IRMS). The TIC/TOC analyzer uses a helium carrier gas compatible with the CF-IRMS. This allows rapid, automated analysis of concentration and ¹³C composition for these two important carbon components in groundwaters. Having developed this new method, we now add a preparation step where DOC components are separated by liquid chromatography and fraction collector, allowing the analysis of δ¹³C in specific DOC compounds. This provides insights into the consumption and production of organic carbon substrates during bacterial degradation of DOC. Applications with leachate-contaminated groundwaters and methanogenic groundwaters are presented (author)

[en] Travertine precipitated from hyperalkaline paleo-groundwaters in Central Jordan appeared at first sight very suitable for dating by ESR and TL due to the presence of a g=2.0036 ESR signal and 270^oC TL peak. However, the paleodose obtained by the additive dose method was found not to agree between TL and ESR, in spite of the fact that identical sample preparation, irradiation and heat treatment procedures were followed. The possibility of using the acid-insoluble silica residue is discussed for this particular type of travertine. (author)

[en] Carbonation reactions in Portland cement grout examined in the laboratory suggest high attenuation of ¹⁴C in cementitious barriers for low- and intermediate-level radioactive waste repositories. Natural cementitious environments at two sites, Maqarin and Daba, in Jordan offer evidence that extensive carbonation can occur at field scales under both unsaturated and saturated conditions. Here, in situ spontaneous combustion of bituminous marl in the past has led to calcination and formation of calcium/silica/alumina-oxides typical of Portland cement clinker. Retrograde alteration within these metamorphic zones began with hydration and precipitation of portlandite as a rock forming mineral along with ettringite, thaumasite, and other calcium-silica-hydrate-like phases. Metamorphism was a relatively recent event at the Maqarin site. Here hyperalkaline groundwater discharge from the alteration zones with two distinct geochemical facies: (a) higher TDS Ca-K-Na-OH-SO₄ groundwaters (pH > 12.5) apparently represent the earliest discharge following hydration, and (b) lower TDS Ca-OH groundwaters (pH 12.0 to 12.4) which appear to be later-stage leachates from the alteration zone. Subsequent carbonation has precipitated secondary calcite observed in the Eastern alteration zone. In central Jordan, travertines associated with the Daba marble record a third phase of porewater discharge where silica has been remobilized during carbonation of CSH-like phases. The unique geochemical features of the Maqarin site were examined to evaluate the validity of using it as a potential natural analogue for cement grout carbonation reactions studied under laboratory conditions

[en] The study examines variations in geochemistry and isotopes in mine inflows to assess the impact of mining on deep groundwater flow in the Canadian Shield, as an analogue for a radioactive waste repository. Periodic sampling of inflow at 20 sites from 700 to 1,615 m depth showed that salinities range from 1.4 to 300 g/L, with tritium measured at all depths. Three end-members are identified: (1) Ca(Na)-CI Shield brine, (2) glacial meltwater recharged at the margin of the retreating Laurentide ice sheet at ∼10 ka, and (3) modern, tritiated meteoric water. Exponential modeling for tritium constrains surface to 1,372 m depth transit time for modern recharge to about 20 years. That glacial meltwaters have persisted in the current low-relief setting for thousands of years prior to mining suggests that hydraulic gradient, rather than fracture permeability, should be considered as a dominant constraint for advective transport modeling in safety assessment studies. (author)

[en] In many radioactive waste repository designs, cement-based materials are expected to dominate the repository and models of cement evolution predict that leaching of the cementitious material in the repository by groundwater will produce an initial stage of hyperalkaline (pH - 13.3) leachates, dominated by alkali hydroxides, followed by a longer period of portlandite and C-S-H (CaO-SiO₂-H₂) buffered (PH - 12.5) leachates. It has also been predicted that, as the hyperalkaline porewater leaches out of the near-field, significant interaction with the repository host rock and bentonite buffer and backfill may occur. This could possibly leak to deterioration of those features for which the host rock formation and bentonite were originally chosen (e.g. low groundwater flux, high radionuclide retardation capacity etc). The precise implication of cement leachate/repository host rock interaction has been studied in the laboratory and in underground research laboratories (URLs) and this work has been supported by study of natural cements in Jordan. These natural cements have been produced by the combustion of organic-rich clay biomicrites and are very close analogues of industrial cement. Following interaction with groundwaters, natural hyperalkaline leachates are produced and these move out of the cement into the surrounding host rock, subsequently interacting with and altering it. (author)

[en] This study examines variations in geochemistry and isotopes in mine inflows at the Con Mine, Yellowknife, to assess the impact of mining on deep groundwater flow in the Canadian Shield, as an analogue for a radioactive waste repository. Periodic sampling of inflow at 20 sites from 700 to 1,615 m depth showed that salinities range from 1.4 to 300 g/L, with tritium measured at all depths. Three end-members are identified: (1) Ca(Na)-Cl Shield brine, (2) glacial meltwater recharged at the margin of the retreating Laurentide ice sheet at ∼10 ka, and (3) modem, tritiated meteoric water. Exponential modeling for tritium constrains surface to 1,372 m depth transit time for modem recharge to about 20 years. That glacial meltwaters have persisted in the current low-relief setting for thousands of years prior to mining suggests that hydraulic gradient, rather than fracture permeability, should be considered as a dominant constraint for advective transport modeling in safety assessment studies. (author)

[en] The Sultanate of Oman has, in recent years, made substantial advances in its agricultural sector, with an increasing reliance on groundwater resources for irrigation. The Public Authority for Water Resources (PAWR) has developed considerable understanding of groundwater availability and quality through comprehensive exploration programmes, including a nationwide survey of enivronmental isotopes in groundwaters, surface waters, and precipitation. The aim of the isotope study was to provide estimates of mean residence times of groundwaters and define their recharge sources. This paper discusses the results of our studies of the extensive and relatively undeveloped aquifers in the southern 'Dhofar' region of Oman. Precipitation systems are discussed as potential groundwater recharge sources. Groundwaters within the interior desert or 'Najd' Region were intensively studied with additional focus on groundwaters in the Salalah Plain and Dhofar Mountains. The shallow, phreatic aquifers in the Najd were found to contain modern, tritiated waters recharged by infrequent storms. The deeper aquifers, which outcrop in the mountains to the south, contain groundwaters under flowing artesian pressure, which without exception were found to be fossil (mean residence times from 4000 to 30,000 years BP). The older age estimates were found in the northern Najd, further from the recharge area. Stable isotope data indicate that the recharge source was unlike the current monsoon which occurs today in the Dhofar Mountains. More likely, rainstorms during pluvial periods in the past were the recharge source to these aquifers. (author). 11 refs, 9 figs, 2 tabs

[en] Highlights: • Surficial uranium deposits are hosted in thick travertine and calcrete. • Tyuyamunite–strelkinite are the major components in central Jordan. • The leached water was enriched in redox sensitive U and V. • Deposition is related to unusual highly alkaline circulating water. - Abstract: Secondary uranium encrustations are hosted in thick travertine and calcrete deposits of Pleistocene–Recent age in central Jordan. The central Jordan varicolored marble and travertine are equivalent to the active metamorphic area in Maqarin, north Jordan. More than 100 samples were collected from the outcrops of the varicolored marble, travertine, calcrete, and the yellow uranium encrustations. The secondary yellow encrustations are mainly composed of uranyl vanadate complexes. Tyuyamunite Ca(UO₂)₂V₂⁵⁺O₈·3(H₂O)–strelkinite Na₂(UO₂)₂V₂O₈·6(H₂O) solid solution series are the major components and their composition reflects changes in the Ca/Na ratio in solution. Potentially, new vanadium free calcium uranate phases (restricted to the varicolored marble) were identified with CaO:UO₃ ratios different from the known mineral vorlanite (CaU⁶⁺)O₄. Carbon and oxygen isotope data from calcite in the varicolored marble are characterized by Rayleigh-type enrichment in light isotopes associated with release of ¹³C and ¹⁸O enriched CO₂ by high temperature decarbonation during combustion of the bituminous marl. Stable isotope results from uranium hosted travertine and calcrete varieties exhibit a wide range in isotopic values, between decarbonated and normal sedimentary carbonate rocks. The depleted δ¹³C and δ¹⁸O values in the travertine are related to the kinetic reaction of atmospheric CO₂ with hyperalkaline Ca(OH)₂ water. The gradual enrichment of δ¹³C and δ¹⁸O values in the calcrete towards equilibrium with the surrounding environment is related to continuous evaporation during seasonal dry periods. Uranium mineralization in central Jordan resulted from the interplay of tectonic, climatic, hydrologic, and depositional events. The large distribution of surficial uranium occurrences hosted in travertine and calcrete deposits is related to the artesian ascending groundwater that formed extensive lakes along NNW–SSE trending depressions. Fresh groundwater moved upward through the highly fractured phosphate, bituminous marl and varicolored marble to form unusual highly alkaline water (hydroxide–sulfate type) enriched with sensitive redox elements among which were U and V