Basalt Groundwater Research Articles

Determination of radon source in basaltic groundwater, using geochemical tracers and chemometric statistical analysis.

Geochemical tracers such as stable isotopes are widely used in groundwater studies for determining aquifer connectivity and groundwater-surface water interactions. An analysis of dissolved radon (222Rn), major ions and trace element chemistry in groundwater was conducted in the fractured-rock aquifer system of Springbrook plateau, southeast Queensland, Australia. Chemical tracers were used to explore hydrological connectivity between the basalt formation and the underlying rhyolite formation. Water samples were collected from groundwater bores installed in both rock formations, from August 2021 to November 2023. Analysis revealed higher than expected concentrations of radon present in groundwater extracted from the basaltic aquifers (>20 Bq/L). A geochemical analysis of rock samples collected from the plateau, combined with a statistical analysis of water sample chemistry, confirmed the rhyolite formation as the primary source of radon. This indicates a strong hydrological connectivity between the rhyolite and basalt formations, such that the dissolved radon gas in groundwater is easily able to migrate through the network of fractures from the rhyolite formation into the overlying basalt formation. There are indications that seasonal rainfall events may be an important factor controlling the extent of vertical groundwater movement, as shown by temporal changes in radon concentrations. Hence, the groundwater aquifers in both formations should not be considered as discrete, disconnected systems. The geochemical tracers in both water and rock samples used in this investigation, combined with a chemometric statistical analysis, proved to be useful for identifying inter-aquifer connectivity in an area with no previous groundwater investigations.

Timing and Source of Recharge to the Columbia River Basalt Groundwater System in Northeastern Oregon.

Recharge to and flow within the Columbia River Basalt Group (CRBG) groundwater flow system of northeastern Oregon were characterized using isotopic, gas, and age-tracer samples from wells completed in basalt, springs, and stream base flow. Most groundwater samples were late-Pleistocene to early-Holocene; median age of well samples was 11,100 years. The relation between mean groundwater age and completed well depth across the eastern portion of the study area was similar despite differences in precipitation, topographic position, incision, thickness of the sedimentary overburden, and CRBG geologic unit. However, the lateral continuity in groundwater age was disrupted across large regional fault zones indicating these structures are substantial impediments to groundwater flow from the high-precipitation uplands to adjacent lower-precipitation and lower-elevation portions of the study area. Recharge rates calculated from the age-depth relations were <3 mm/yr and independent of the modern precipitation gradient across the study area. The age-constrained recharge rates to the CRBG groundwater system are considerably smaller than previously published estimates and highlight the uncertainty of prevailing models used to estimate recharge to the CRBG groundwater system across the Columbia Plateau in Oregon and Washington. Age tracer and isotopic evidence indicate recharge to the CRBG groundwater system is an exceedingly slow and localized process.

Study on the Law of the Electric Folding Water Coefficient in Chayuo Middle Banner

In this paper, based on the investigation and research of groundwater types, topography and geomorphology, geological structure, stratigraphic lithology, groundwater richness and agricultural irrigation wells in the area of Chayou Middle Banner Inner Mongolia, a test area is selected and typical wells are determined. The estimating water consumption of typical wells was measured. Based on the calculation results, the distribution map of the Electricity-to-water conversion factor was drawn, and the influence of groundwater type on the Electricity-to-water conversion factor was analyzed. The results show that the type of groundwater has a significant impact on the number of electric water conversion factors, and the electric water conversion coefficients of fracture pore pressure water and groundwater in Neoproterozoic clastic rocks are relatively large; The electric water conversion coefficient of pore and fissure water pressure and groundwater in Neoproterozoic basalt ranks second; Quaternary loose rock pore water average; The bedrock fissure water is the smallest. At the same time, the influence of topography, atmospheric precipitation, and agricultural production on the Electricity-to-water conversion factor under the same type of groundwater was preliminarily investigated.

Hydrogeochemical and isotopic evidences of unique groundwater recharge patterns in the Mongolian Plateau

AbstractIn arid and semi‐arid areas, local precipitation is insufficient to fulfil the water requirements of the fragile local environment; hence, water is obtained from groundwater. The Hulun Lake Basin is located in the Mongolian Plateau, which is home to numerous lakes. In this study, we used remote sensing and isotopic tracing of naturally occurring isotopes (δ18O, δ2H, and 87Sr/86Sr) to identify and quantify the various water inputs into the basin. Based on the lake water balance calculation and precipitation and river inputs, a 5.4 × 108 m3/year groundwater recharge rate was determined. Groundwater and river water with depleted δ18O and δ2H were identified close to the faults near Hulun Lake. The groundwater recharge into Hulun Lake is aided by the faults. The δ18O and δ2H compositions of the groundwater, rivers, and lakes were consistent and more depleted than those of precipitation in the local mountains and plains. Therefore, the rivers and lakes are assumed to be primarily recharged by groundwater. The low strontium isotopes (87Sr/86Sr) in the samples suggest that the water was primarily recharged by basalt groundwater, which was identified under the Cenozoic strata instead of the sandstones, granites, and tuffs, which are the primary rocks in the study area. Moreover, the faults were widely distributed in the study area, allowing for groundwater upwelling from basalts. For the areas with volcanic rocks and faults, particularly in arid and semi‐arid areas, the basalt groundwater recharge through faults is critical for environmental sustainability. This research provides necessary information for future hydro‐ecosystem resource management in arid and semi‐arid areas.

Coastal upward discharge of deep basalt groundwater through developed faults: A case study of the Subei Basin, China

The relationship between groundwater and seawater is sensitive to groundwater exploitation, thus, not a simple result of groundwater and seawater lateral flow. The upward recharge of deep groundwater leads to a more complex relationship between groundwater and seawater in coastal regions with developed faults. The Quaternary confined groundwater level is significantly decreased in the case of groundwater overexploitation in the coastal region of the Subei Basin, where active faults are developed. The water level and hydrochemistry data for confined groundwater during periods of groundwater overexploitation was analyzed in the Subei Basin. Results show that confined groundwater is negligibly affected by seawater intrusion, while groundwater desalination is apparent during this period. High confined groundwater levels have been observed for many years in the area with intense groundwater exploitation. Additionally, the chemical and stable isotopic characteristics of confined groundwater, phreatic water, and surface water in the study area were investigated to reveal the pathways and origin of deep groundwater. The hydrogeochemical results demonstrate that the confined groundwater originates from basalt groundwater and is related to deep circulation. The active faults in the study area serve as pathways for upward recharge of basalt groundwater. Our findings provide new insights into the relationship between groundwater and seawater, and indicate that the upward recharge of deep groundwater should be considered in coastal regions with developed faults.

Influence of Freshwater Discharges on Biogeochemistry and Benthic Communities of a Coral Reef Ecosystem (La Réunion Island, Indian Ocean)

We investigated the influence of freshwater discharges on biogeochemistry and benthic communities of La Saline fringing reef, the largest coral reef system of La Reunion Island (France, Indian Ocean). Sampling was conducted in February-March 2012 along a land-ocean continuum, including rivers, groundwater, reef waters, and oceanic waters. Our results indicated the discharges of basalt groundwater (enriched in nitrates) in the southern part of the reef, and the discharges of sand groundwater and river waters (enriched in organic matter) in sites located northward. These discharges mainly impacted fore reef surface waters, while groundwater resurgences were more diffuse and not clearly detected in depth. We highlighted the relationship Si(OH) 4 /NO 3 − to identify basalt groundwater discharges. We also put forward the relationships humic-like fluorescence/NH 4 + and tryptophan-like fluorescence/PO 4 3− to identify sand groundwater discharges and wastewater pollutions, respectively. We observed the eutrophication of the southern part of the reef through higher phytoplankton biomasses, a massive presence of fleshy algal formations and a low coral coverage. The spatial homogeneity of the benthic community structures onto the entire slope contrasted with the spatial heterogeneity of chemical variables in water. This reflected the different spatial and temporal scales involved in biological and chemical processes in coral reef ecosystems.

Rapid CO2 mineralisation into calcite at the CarbFix storage site quantified using calcium isotopes

The engineered removal of atmospheric CO2 is now considered a key component of mitigating climate warming below 1.5 °C. Mineral carbonation is a potential negative emissions technique that, in the case of Iceland’s CarbFix experiment, precipitates dissolved CO2 as carbonate minerals in basaltic groundwater settings. Here we use calcium (Ca) isotopes in both pre- and post-CO2 injection waters to quantify the amount of carbonate precipitated, and hence CO2 stored. Ca isotope ratios rapidly increase with the pH and calcite saturation state, indicating calcite precipitation. Calculations suggest that up to 93% of dissolved Ca is removed into calcite during certain phases of injection. In total, our results suggest that 165 ± 8.3 t CO2 were precipitated into calcite, an overall carbon storage efficiency of 72 ± 5%. The success of this approach opens the potential for quantification of similar mineral carbonation efforts where drawdown rates cannot be estimated by other means.

Uranium Dissolution and Geochemical Modeling in Anoxic and Oxic Solutions

ABSTRACTHigh Level Waste (HLW) glasses are to be stored in deep geologic repositories around the world. Some potential repository geologies have oxidizing groundwaters while some have reducing or anoxic groundwaters. The differences in the oxidizing potential of the groundwater, expressed as groundwater Eh, which has a profound impact on the release of multivalent species such as iron and uranium from the glass. Static leach testing of monolithic glass samples (ASTM C1220) doped with uranium were performed at 90°C in an Ar glovebox under anoxic and oxic conditions. Tests were performed in both deionized water and in simulated basaltic groundwater that was pre-equilibrated at low Eh. Geochemical modeling of the measured Eh-pH conditions from the oxic and anoxic experiments using Geochemist’s Workbench software, suggested that different colloidal species control the release of uranium species under oxic and anoxic conditions.

Recharge, groundwater flow pattern and contamination processes in an arid volcanic area: Insights from isotopic and geochemical tracers (Bara aquifer system, Republic of Djibouti)

Fractured volcanic aquifers are the main water resources in the arid climate of the Republic of Djibouti. Nonetheless, these strategic reservoirs are overexploited and their comprehensive understanding is therefore a pre-requisite for a sustainable use. A geochemical and isotopic survey, including major ion chemistry, 2H, 18O, 13C, 3H, 87Sr/86Sr, 15N was performed and combined with existing 14C data to study recharge, contamination processes and groundwater flow patterns inside and between the compartments of a complex aquifer system composed by basaltic rocks and by alluvium located in Petit Bara, Grand Bara, and Mouloud areas (Southwest of Djibouti). A main feature was the common trend from a fresh Na-Cl-HCO3 water type (alluvium groundwaters) to an intermediate water type (alluvium and basalt groundwaters) and finally to a Na-Cl-SO4 water type (most mineralized basalt groundwater). Elementary and isotopic nitrate evidenced and located anthropogenic and geogenic origins of nitrate. Alluvium groundwaters had δ2H and δ18O signature of modern precipitation while basalt groundwaters were significantly depleted and enriched in δ13C due to water-rock interactions. Modern radiocarbon and tritium were evidenced in the alluvium groundwaters, while recalculated radiocarbon ages located recharge of the basalt groundwaters in the early to mid-Holocene. These features revealed a common evolutionary pattern, with a recharge from wadi-rivers to the alluvium and a downward circulation to the basalt through major faults, combined with a mixing with a more geochemically evolved groundwater. Accordingly, highly saline groundwater at the outlet of the Petit Bara plain was found to be diluted by modern recharge in the alluvium. Two major basaltic aquifer compartments were found to be connected (Grand Bara and Mouloud), revealing a global northeastward flowpath below the endorheic Grand Bara plain.

Stable Isotopes of Lithium as Indicators of Coal Seam Gas-bearing Aquifers

In this study lithium isotopes were used in combination with hydrochemistry to investigate interactions between coal-seam-gas bearing sedimentary bedrock aquifers and surrounding basalt and alluvial aquifers in a large catchment in eastern Australia. Understanding groundwater transport and aquifer connectivity is critical to managing coal seam gas (or coal bed methane) developments, because large volumes of water need to be extracted in order to release the sorbed gas; however, to date lithium isotopes have not been applied to coal seam gas groundwater management problems and no information on the δ7Li of coal or coal-seam groundwater is available. Li/Cl and Li/Na ratios in the coal-bearing and sedimentary bedrock aquifers are distinct (>0.0001) from alluvial and basalt aquifers (<0.0001). Preliminary δ7Li results for coal measure samples are typically between 7 and 11‰; many of these samples also contain methane, and can therefore be expected to be influenced by coal and the early stages methanogenesis. Interestingly the coal measure with lowest δ7Li value occurs in an area where the coal measures outcrop and direct recharge is likely, with nearby basalt groundwater having much higher δ7Li values (δ7Li>18‰). Preliminary lithium isotope results show that δ7Li may be effective in distinguishing groundwater flow paths in the coal-bearing aquifer from basalt aquifers, and from a transitional zone between the alluvium and underlying coal measures. Further lithium isotope analysis is being carried out to: a) compare the δ7Li between alluvial, basalt and coal-bearing aquifers to further investigate aquifer connectivity; b) to describe δ7Li for CSG production waters with low- and high-methane groundwater in the coal-bearing aquifer; c) to describe the δ7Li from coal and basalt leachate.

The Archaea Community Associated with Lava-Formed Gotjawal Forest Soil in Jeju, Korea

The abundance and diversity of archaeal assemblages were analyzed in soils collected from Gyorae Gotjawal forest, Jeju, Korea. Gotjawal soil refers to soil derived from a lava-formed forest, characterized by high organic matter content, fertility, and poor rocky soil. Using domain-specific primers, archaeal 16S rRNA gene sequences were PCR amplified for clone library construction, and a total of 185 archaeal clones were examined. The archaeal clones were affiliated with the phyla Thaumarchaeota (96.2%) and Euryarchaeota (3.8%). The most abundant thaumarchaeal group (90.3% of the clones) was the group I.1b clade, which includes soil ammonia-oxidizing archaea. The unique characteristics of Gotjawal soil, including basalt morphology, vegetation, and groundwater aquifer penetration, may be reflected in the archaeal community composition. Further study is necessary to understand the unique factors of Gotjawal soils that influence archaeal abundance, composition, and diversity.

Appraisal and evolution of hydrochemical processes from proximity basalt and granite areas of Deccan Volcanic Province (DVP) in India

Summary This paper deals with a systematic hydrochemical study carried out at proximity basalt and granite areas of Deccan Volcanic Province (DVP) in India to assess groundwater quality and evaluate the hydrochemical processes. A total of 40 groundwater samples were collected equally from these areas and analyzed. Results showed that the groundwaters rich in alkaline earth in the basalt and alkali rich element in the granite. The dominancy of cations was observed as Ca2+ > Mg2+ > Na+ > K+ in the basalt and Na+ > Mg2+ > K+ > Ca2+ in the granite, whereas anions as HCO 3 - > Cl - > SO 4 2 - and Cl - > HCO 3 - > SO 4 2 - , respectively. Hydrochemical processes were identified with the helps of ion exchange, carbonate weathering and dissolution, multiple ionic ratios, and silicate weathering, which shown the predominance of carbonate, dolomite, calcite and silicate (anorthite) weathering in basalt, but in granite, silicate (alkali feldspar) weathering was dominated. Factor analysis also showed that there were multiple processes acting on groundwaters, were separated from the main cluster. Salinity, Sodium Absorption Ratio (SAR), Soluble Sodium Percentage (SSP), Residual Sodium Carbonate (RSC), Kelley’s Ratio (KR) and Permeability Index (PI) in well samples showed that groundwater in basalt was more suitable for irrigation purposes. Further, a digital elevation model (DEM) was generated using Global mapper (8.0 version) software, which aided to decipher the thickness of basalt trap, and vertical transition zone of basaltic (trap) and granitic (basement) aquifer at this DVP comprising with the well depths and groundwater chemistry.

Water–Rock Interactions: An Investigation of the Relationships Between Mineralogy and Groundwater Composition and Flow in a Subtropical Basalt Aquifer

A holistic study of the composition of the basalt groundwaters of the Atherton Tablelands region in Queensland, Australia was undertaken to elucidate possible mechanisms for the evolution of these very low salinity, silica- and bicarbonate-rich groundwaters. It is proposed that aluminosilicate mineral weathering is the major contributing process to the overall composition of the basalt groundwaters. The groundwaters approach equilibrium with respect to the primary minerals with increasing pH and are mostly in equilibrium with the major secondary minerals (kaolinite and smectite), and other secondary phases such as goethite, hematite, and gibbsite, which are common accessory minerals in the Atherton basalts. The mineralogy of the basalt rocks, which has been examined using X-ray diffraction and whole rock geochemistry methods, supports the proposed model for the hydrogeochemical evolution of these groundwaters: precipitation + CO2 (atmospheric + soil) + pyroxene + feldspars + olivine yields H4SiO4, HCO3−, Mg2+, Na+, Ca2+ + kaolinite and smectite clays + amorphous or crystalline silica + accessory minerals (hematite, goethite, gibbsite, carbonates, zeolites, and pyrite). The variations in the mineralogical content of these basalts also provide insights into the controls on groundwater storage and movement in this aquifer system. The fresh and weathered vesicular basalts are considered to be important in terms of zones of groundwater occurrence, while the fractures in the massive basalt are important pathways for groundwater movement.

Multi-proxy approach ( 2H/H, 18O/ 16O, 13C/ 12C and 87Sr/ 86Sr) for the evolution of carbonate-rich groundwater in basalt dominated aquifer of Axum area, northern Ethiopia

Isotopic and chemical composition of groundwater from wells and springs, and surface water from the basalt-dominated Axum area (northern Ethiopia) provides evidence for the origin of water and dissolved species. Shallow (depth < 40 m) and deep groundwater are distinguished by both chemical and isotopic composition. Deep groundwater is significantly enriched in dissolved inorganic carbon up to 40 mmol l −1 and in concentrations of Ca 2+, Mg 2+, Na + and Si(OH) 4 compared to the shallow type. The δ 2H and δ 18O values of all solutions clearly indicate meteoric origin. Shifts from the local meteoric water line are attributed to evaporation of surface and spring water, and to strong water–rock interaction. The δ 13C DIC values of shallow groundwater between −12 and −7‰ (VPDB) display the uptake of CO 2 from local soil horizons, whereas δ 13C DIC of deep groundwater ranges from −5 to +1‰. Considering open system conditions with respect to gaseous CO 2, δ 13C DIC = +1‰ of the deep groundwater with highest PCO 2 = 10 −0.9 atm yields δ 13C CO2(gas) ≈ −5‰, which is close to the stable carbon isotopic composition of magmatic CO 2. Accordingly, stable carbon isotope ratios within the above range are referred to individual proportions of CO 2 from soil and magmatic origin. The uptake of magmatic CO 2 results in elevated cations and Si(OH) 4 concentrations. Weathering of local basalts is documented by 87Sr/ 86Sr ratios of the groundwater from 0.7038 to 0.7059. Highest values indicate Sr release from the basement rocks. Besides weathering of silicates, neoformation of solids has to be considered, which results in the formation of, e.g., kaolinite and montmorillonite. In several solutions supersaturation with respect to calcite is reached by outgassing of CO 2 from the solution leading to secondary calcite formation.

Strontium isotopes as tracers to delineate aquifer interactions and the influence of rainfall in the basalt plains of southeastern Australia

Summary To better understand the spatial distribution of groundwater salinisation in western Victoria, southeast Australia, the interactions between a surficial basalt aquifer and an underlying extensive palaeodrainage (‘deep lead’) system were studied using a multi-disciplinary approach, combining strontium isotope analyses with major ion chemistry and the interpretation of geological and hydrogeological data. The strontium isotopes proved particularly useful in delineating flow paths and hydraulic connections between the two aquifers, which have contrasting 87Sr/86Sr ratios. The freshest basalt groundwaters lie beneath volcanoes and have 87Sr/86Sr signatures close to the whole-rock strontium isotope ratios of the basalts (∼0.7045), indicating the strong influence of basalt weathering. With increasing distance from the eruption points, basalt groundwaters become progressively more saline and the strontium isotope ratios evolve towards the more radiogenic signatures of local rainfall (0.710–0.711), due to the slow addition of infiltration concentrated by evapotranspiration during its passage through the thick, clay-rich soils developed on the basalt lavas. Overall, the influence of rainwater on the strontium isotope signatures of the basalt groundwater is much greater than that of basaltic weathering, indicating that rainwater can play a greater role in determining groundwater strontium composition than is often realised. Most parts of the palaeodrainage system beneath the basalt are preferentially recharged through the volcanoes, as shown by strong downwards hydraulic gradients and groundwater 87Sr/86Sr ratios similar to the least radiogenic basalt groundwaters. However, in the northwestern part, groundwater 87Sr/86Sr ratios are closer to those of the source material of the sediments (Palaeozoic bedrock), indicating that here recharge occurs predominantly in the headwaters where the basalts are absent. In the southern and western sections of the palaeodrainage system there is an upward flux into the overlying basalts, as shown by strong upward hydraulic gradients and elevated strontium isotope signatures in basalt groundwaters. This occurs because lateral groundwater flow in the palaeodrainage system is restricted by shallow subsurface basement ridges, and ultimately discharges to the surface as salt lakes.

Water Resource Implications of 18O and 2H Distributions in a Basalt Aquifer System

AbstractOngoing decline of water levels in the confined basalt aquifers of the Pullman‐Moscow Basin of Washington and Idaho has prompted study of the timing, amount and distribution of recharge to the system. Previous radiocarbon ages indicate residence times on the order of 103 years and greater and suggest a low rate of recharge to the lower basalt aquifer since the end of Pleistocene time. By contrast, more recent hydrodynamic flow modeling studies invoke a larger Holocene recharge rate through the unconfined loess unit to the upper and lower basalt aquifers, which implies relatively short residence times (102 years). Stable isotopes were used to independently assess contrasting recharge models by comparing 18O/16O and D/H ratios of late‐Holocene shallow ground water and deep ground water. Linear regression of local precipitation ratios yields δD = 6.9 δ18O −18.5. There is no evidence of fractionation of ground water ratios by recharge processes or water‐rock interactions. Deep basalt ground water δ18O values are depleted by 0.4 to 4.9 per mil relative to shallow, recently recharged ground waters and have δ18O values statistically distinct from waters sampled from other stratigraphic units. These findings suggest that the deep waters in the basin were not precipitated under current climate conditions and that aquifer recharge rates to the deep basalt aquifer are substantially lower than have been recently estimated. This in turn suggests that a sustainable ground water exploitation scheme must reduce reliance on the deep ground water resource.

Hydrogeological framework of the Deccan basalt groundwater systems, west-central India

Deccan basalts of west-central India are hydrogeologically inhomogeneous rocks. A proper understanding of the physical framework of the basalts within which groundwater resides and moves is a key to the hydrogeology of these rocks. Two types of basalt, the vesicular amygdaloidal basalt and the compact basalt, occur as alternate layers in the volcanic pile. Although the rocks are generally inhomogeneous, structures in the basalt, such as sheet joints and vertical joints, serve as zones of groundwater flow. In the shallow subsurface, two groundwater systems are operative. Groundwater system A consists of a vesicular amygdaloidal basalt underlain by a compact basalt, whereas groundwater system B consists of a vesicular amygdaloidal basalt overlain by a compact basalt. Groundwater system A has a better developed network of openings and, as a consequence, this system has a higher transmissivity and storage coefficient than groundwater system B. Wells tapping groundwater system A have higher yields on average and irrigate more hectares of cropland than do wells tapping groundwater system B. This simple systems concept offers a practical methodology for understanding the geometry of the physical framework that contains groundwater in the Deccan basalts. The efficacy of the concept is in its widespread utility for the region. The concept may also be extrapolated to help understand the hydrogeology of deeper Deccan basalt groundwater systems.

Evidence against hydrogen-based microbial ecosystems in basalt aquifers

It has been proposed that hydrogen produced from basalt-ground-water interactions may serve as an energy source that supports the existence of microorganisms in the deep subsurface on Earth and possibly on other planets. However, experiments demonstrated that hydrogen is not produced from basalt at an environmentally relevant, alkaline pH. Small amounts of hydrogen were produced at a lower pH in laboratory incubations, but even this hydrogen production was transitory. Furthermore, geochemical considerations suggest that previously reported rates of hydrogen production cannot be sustained over geologically significant time frames. These findings indicate that hydrogen production from basalt-ground-water interactions may not support microbial metabolism in the subsurface.

Methane in Columbia River Basalt Aquifers: Isotopic and Geohydrologic Evidence for a Deep Coal-Bed Gas Source in the Columbia Basin, Washington

Methane occurs as a dissolved constituent in groundwater from confined aquifers in the Columbia River Basalt Group, Columbia basin, Washington. Isotopic compositions of methane in groundwater indicate that the methane is a mixture of biogenic (^dgr13C-CH4 to -88^pmil and ^dgr2H-CH4 to -265^pmil) and thermogenic (^dgr13C-CH4 to -35^pmil, and ^dgr2H-CH4 to -134^pmil) components. Chemical and isotopic data are consistent with entrainment of deep, coal-bed-generated methane in upwelling groundwater from below the Columbia River Basalt Group (>4 km) that mixes with near-surface groundwater. The areal distribution pattern of methane suggests that fault intersections are necessary for vert cal migration of deep methane through the basalt. This study suggests that deep subbasalt coal-bed methane in the Columbia basin has infiltrated the shallow basalt groundwater system, and isotopic analyses of methane in groundwater from structurally favorable locations can be used to identify potential exploration targets. The wide areal distribution of methane in this large, relatively unexplored frontier province suggests economic gas reserves.

Studies on leaching behaviour of sodium borosilicate glasses by neutron activation: Effects of groundwater composition, pH, surface area to volume ratio, and temperature

Static leaching experiments have been conducted to evaluate the durability of sodium borosilicate glass as the host matrix for immobilized high-level radioactive wastes. Simulated granitic groundawater, synthetic Grande Ronde basaltic groundwater and distilled deionized water have been used. The results indicated a strong influence of the leachant composition through both its pH and nature as well as concentrations of the ions present on the leach rate. The roles of silicon, boron and a few other elements on leaching have been examined. Three surface area to volume ratios (SA/V) and two temperatures were investigated. Total mass loss and normalized elemental mass loss results showed that the rate of release decreased with increased SA/V ratio in the three leachants at both temperatures. The rate of leaching at 90 °C was 5–30 times higher than that at 40 °C. Activation energies for the glass at three SA/V ratios have been calculated.