Deep Groundwater Flow System Research Articles

Flow systems of the Earth’s viscous subsurface: A complement to groundwater flow systems

Assessment of the long term possibilities and risks related to geological storage requires insight in the deep groundwater flow systems. The objective of this paper is to show the relevance of the deep creep flow of the earth’s viscous upper mantle and crust as a complement to the groundwater flow. The paper presents an approach based on Fourier decomposition of the topography. The creep flow equations are solved analytically, which results in simple indices like penetration depth and relaxation time characterizing the gravity-driven creep flow. Thanks to the very high effective viscosity of the Earth’s subsurface a Darcy-like equation is obtained in which the ‘creep conductivity’ is Fourier mode dependent, which allows for simple comparison with the hydraulic conductivity for groundwater flow. Order of magnitude calculations indicate that for horizontal length scales of 100–1000 km the subsurface creep velocities are 0.3–30 mm/year, respectively, which shows that creep velocities in the deep subsurface are significant with respect to deep groundwater velocities.

Geochemical Evolution and Groundwater Flow System in Batujajar Groundwater Basin Area, West Java, Indonesia

DOI:10.17014/ijog.7.1.87-104Batujajar and its surrounding areas, situated in the west of the Bandung Basin, are geologically composed of various Tertiary rock formations with complex fold and fault systems. Springs and drilled wells in sandstone aquifers, tuffaceous sand, and tuffaceous breccias mark the development of their aquifer systems. This study aimed to determine the characteristics of the hydrogeochemistry by analyzing major ions and stable isotopes (18O and 2H) of thirty-four hydrogeological objects. The groundwater flow pattern in this area is controlled by northwest-southeast lineament, as indicated by the emergence of springs along the transition zone between areas with high and low lineament density. In order of dominance, the groundwater facies are as follows:Ca-Mg-HCO3>Ca-HCO3>Ca-Na-Mg-HCO3>Na-Ca-HCO3. Hydrochemical evolutions were detected from the change of cations from Ca2+ to Mg2+ and then Na+, and this is believed to be the product of cation exchange and dissolution of silicate minerals. However, evolutions toward anion changes were not apparent yet, meaning that HCO3- ions still prevail, or in other words the groundwater flow system is local. Nevertheless, the geological and hydrogeochemical analyses, along with the relative compositions of stable isotopes, revealed that the groundwater had three systems, namely shallow, intermediate, and deep groundwater flows; all of which were segmented in three subgroundwater basins (Sub-GWB). Aquifer systems with shallow to intermediate groundwater flow were found in Sub-GWB-A, Sub-GWB-B, and Sub-GWB-C, while the other ones with deep groundwater flow system were identified in Sub-GWB-B and Sub-GWB-C.Fracture system has an important role as a connector between recharge system in hilly areas and discharge system in plain areas.

Hydrochemical impact of the hydraulic tunnel on groundwater in the complex aquifer system in Pirot, Serbia

This hydrogeochemical research was conducted to improve the understanding of (1) groundwater flow and its hydrochemical evolution in a complex karst-fissured aquifer system, and (2) the interaction between groundwater and water transported via hydraulic tunnel of the hydropower plant (Pirot, Serbia). The tunnel traverses the main fault zones between two regionally important tectonic units, Getic and Danubian, allowing deep groundwater circulation and higher infiltration of groundwater into the tunnels. Water samples were collected at the surface and within the tunnels in four different sampling campaigns, depending on the tunnel operational regime in 2016, and measurements of physicochemical parameters (pH, ORP, EC, T) and groundwater sampling for chemical analysis (Ca, Mg, Na, K, Sr, Li, HCO3, SO4, Cl, NO3, H2S) were conducted. This was a unique opportunity to investigate hydrochemical processes based on groundwater leakage along the tunnel profile line. The main problem is compounded by the fact that it is a hydraulic tunnel that transports water under pressure, thereby interacting with the hydrogeological environment. Changes in the tunnel operational mode cause hydraulic changes in the hydrogeological environment, which is a key part of this research. The presence of different hydrochemical facies appearing in the tunnel (from Na–Cl through Na-HCO3 to Ca(Mg)–HCO3 water types) pointed to the complexity of the hydrogeological system in the shallow, and deep groundwater flow systems developed in karst and fissured aquifer. Heterogeneity of bedrock had an important influence on the hydrochemical conditions accompanied by processes revealed through hydrochemical and multivariate statistical analysis: hierarchical cluster analysis (HCA) and principal component analysis (PCA). The main processes are defined as (1) dissolution processes in hypogenic conditions of the karst hydrogeological system, associated with high mineralization of groundwater, (2) cation exchange process, (3) the dissolution of different types of carbonate bedrock. A combined approach of multivariate statistical analysis and standard hydrochemical methods enabled the separation of groundwater with the highest compositional changes as points of the strongest artificial influence in the narrow tunnel zone.

Large scale quantification of aquifer storage and volumes from the Peninsula and Skurweberg Formations in the southwestern Cape

The Western Cape Province of South Africa is a relatively water-scarce area as a result of the Mediterranean climate experienced. Due to the increased usage of groundwater, and the requirement to know how much water is available for use, it is imperative as a 1 st step to establish an initial estimate of groundwater in storage. The storage capacity, namely, the total available storage of the different aquifers, and the storage yield of the fractured quartzitic Peninsula and Skurweberg Formation aquifers of the Table Mountain Group (TMG), are calculated with a spreadsheet and Geographic Information System (GIS) model. This model is based on the aquifer geometry and estimated values (based on measured data) for porosity and specific storage (calculated using the classic Jacob relation). The aquifer geometry is calculated from 1:50 000 and 1:250 000 geological contacts, faults and major fractures, with dips and aquifer formation thickness calculated through structural geology 1 st principles using a Digital Elevation Model (DEM). Balanced geological cross-sections constructed through the model areas provide an important check for the aquifer top and bottom surface depth values produced by the GIS model. The storage modelling undertaken here forms part of the City of Cape Town TMG Aquifer Feasibility Study and Pilot Project, with modelling focusing on the 3 main groundwater target areas at Theewaterskloof (Nuweberg), Wemmershoek and Kogelberg-Steenbras. In the storage models, the Peninsula and Skurweberg Formation aquifers have confined pore volumes ranging from approximately 29 bn. to 173 bn. m 3 and 4 bn. to 26 bn. m 3, respectively (based on using different porosity values ranging from 2.5% to 15%). Using an average head decline of 1 m across the confined aquifer areas across all 3 groundwater exploration areas, and confined pore volumes based on a porosity of 5%, 6.9 Mm 3 and 1.1 Mm 3 of groundwater, from the Peninsula and Skurweberg Formation aquifers, respectively, is available. The aquifer storage model intentionally makes use of low, geologically reasonable values for porosity and aquifer compressibility, so as to provide minimum large-scale 1 st estimates of potential yields; however, when new data become available these initial porosity and compressibility assumptions will probably be revised upward. The storage yield approach is also very conservative, as it does not take into account the annual replenishment of the aquifer, and constitutes the yield potential during drought conditions (zero recharge) from the confined portion of the aquifer only. The yield model therefore provides a quantitative perspective on the common public and decision-maker perception that groundwater abstraction from the deep confined Peninsula Formation aquifer will significantly dewater the system, with (often unspecified) adverse ecological conse quences. Even where the regionally-averaged decline in hydraulic head approaches 20 m, the volume released by aquifer compression generally remains in the order of 0.24% of the total volume in slow circulation within the deep groundwater flow system. A vastly greater volume of groundwater is essentially non-extractable by any practical and/or economical means.

Hydrogeochemical and Isotopic Constraints on the Pattern of a Deep Circulation Groundwater Flow System

Characterization of a deep circulation groundwater flow system is a big challenge, because the flow field and aqueous chemistry of deep circulation groundwater is significantly influenced by the geothermal reservoir. In this field study, we employed a geochemical approach to recognize a deep circulation groundwater pattern by combined the geochemistry analysis with isotopic measurements. The water samples were collected from the outlet of the Reshui River Basin which has a hot spring with a temperature of 88 °C. Experimental results reveal a fault-controlled deep circulation geothermal groundwater flow system. The weathering crust of the granitic mountains on the south of the basin collects precipitation infiltration, which is the recharge area of the deep circulation groundwater system. Water infiltrates from the land surface to a depth of about 3.8–4.3 km where the groundwater is heated up to around 170 °C in the geothermal reservoir. A regional active normal fault acts as a pathway of groundwater. The geothermal groundwater is then obstructed by a thrust fault and recharged by the hot spring, which is forced by the water pressure of convection derived from the 800 m altitude difference between the recharge and the discharge areas. Some part of groundwater flow within a geothermal reservoir is mixed with cold shallow groundwater. The isotopic fraction is positively correlated with the seasonal water table depth of shallow groundwater. Basic mineral dissolutions at thermoneutral conditions, hydrolysis with the aid of carbonic acid produced by the reaction of carbon dioxide with the water, and hydrothermal alteration in the geothermal reservoir add some extra chemical components into the geothermal water. The alkaline deep circulation groundwater is chemically featured by high contents of sodium, sulfate, chloride, fluorine, silicate, and some trace elements, such as lithium, strontium, cesium, and rubidium. Our results suggest that groundwater deep circulation convection exists in mountain regions where water-conducting fault and water-blocking fault combined properly. A significant elevation difference of topography is the other key.

Using environmental isotopes along with major hydro-geochemical compositions to assess deep groundwater formation and evolution in eastern coastal China

Hydrochemical analysis and environmental isotopic tracing are successfully applied to study groundwater evolution processes. Located in eastern China, the Jiangsu Coastal Plain is characterized by an extensively exploited deep groundwater system, and groundwater salinization has become the primary water environmental problem. This paper provides a case study on the use of a hydrochemical and environmental isotopic approach to assess possible mixing and evolution processes at Yoco Port, Jiangsu Province, China. Hydrochemical and isotopic patterns of deep groundwater allow one to distinguish different origins in deep water systems. HCO3– is the dominant anion in the freshwater samples, whereas Na+ and Cl− are the dominant major ions in the saline samples. According to δ18O, δ2H and 14C dating, the fresh water is derived from precipitation under a colder climate during the Glacial Maximum (Dali Glacial), while the saline groundwater is influenced by glacial-interglacial cycles during the Holocene Hypsithermal. The δ18O, δ2H and 3H data confirm that deep groundwater in some boreholes is mixed with overlying saline water. The deep groundwater reservoir can be divided into a saline water sector and a fresh water sector, and each show distinct hydrochemical and isotopic compositions. The saline groundwater found in the deep aquifer cannot be associated with present seawater intrusion. Since the Last Glacial Maximum in the Late Pleistocene, the deep groundwater flow system has evolved to its current status with the decrease in ice cover and the rising of sea level. However, the hydraulic connection is strengthened by continuous overexploitation, and deep groundwater is mixed with shallow groundwater at some points.

The geochemistry of Don Juan Pond: Evidence for a deep groundwater flow system in Wright Valley, Antarctica

Don Juan Pond (DJP), Antarctica, is one of the most unusual surface waters on Earth because of its CaCl2-rich composition. To investigate the evolution of pond waters during closed-basin evaporation and to understand the source of brines responsible for the chemistry of DJP, we apply a newly developed low-temperature aqueous model in the Na–K–Ca–Mg–Cl system to DJP. By modeling the closed-basin evaporation of DJP and comparing ionic ratios between DJP surface water, deep groundwater, shallow groundwater, and other surface chemistries in Wright Valley, we find that DJP is best explained by upwelling deep groundwater, as opposed to recent hypotheses proposing shallow groundwater sources. The early closed-basin evolution of brines in our model accurately predicts observed chemistries in DJP; however, late-stage closed-basin evaporation produces Mg–K-rich brines and salts that do not match the CaCl2-rich brine in DJP. Based on groundwater inflow rates to DJP, we estimate that even the most concentrated brines in DJP have undergone closed-basin evaporation for less than a year. To explain the observed lack of Mg2+ and K+ accumulation in DJP over time, and the surprisingly young age for the brines, we deduce that DJP is a localized upwelling from a regional groundwater flow-through system in which evaporated DJP brines are recycled back into the subsurface over yearly timescales. The existence of a regional groundwater flow system beneath DJP has implications for water and solute budgets in cold desert ecosystems, and may provide clues for the formation of groundwater and aqueous flows on Mars.

Hydrochemical characteristics and geothermometry applications of thermal groundwater in northern Jinan, Shandong, China

Carbonate rock thermal reservoirs are important geothermal resources but lack systematical study on a regional scale. This paper integrated hydrochemical and isotopic data to outline thermal water resources in carbonate rock aquifers as part of deep regional groundwater flow system. Hydrochemical characteristics of thermal groundwater in northern Jinan geothermal field, where Ordovician carbonate rocks are the main thermal reservoir, were examined and characterized by SO4–Ca, SO4–Ca·Na, SO4·Cl–Ca·Na and Cl·SO4–Na·Ca types. Hydrochemical evolution was revealed by analyzing correlation between different chemical constituents and their relative changes in various waters. Isotopic data allowed the origin of thermal water to be determined and presented different recharge elevations. Thermal groundwater was originated from precipitation in the northern piedmont of Tai Mountain with elevation of 708–1493m.a.s.l.. Reservoir temperature was estimated by chemical geothermometry and validated by fluid–mineral equilibria calculations. The feasibility of different geothermometers was verified, indicating that quartz geothermometers were more suitable for the geothermal system and yielded reservoir temperatures of 60–80°C. Finally, a conceptual hydrogeological model of the geothermal field was proposed: thermal groundwater was derived from regional flow system with high recharge areas, deep circulation depth and slow flow velocities, confirmed by its depleted stable isotopic contents, high chloride and TDS concentrations and long residence time. The improved understanding of this geothermal system is fundamental for the better management of this karst geothermal resource.

Use of geothermal methods in outlining deep groundwater flow systems in Paleozoic interior basins of Brazil

Results of regional-scale geothermal studies are presented, providing new insights into the characteristics of deep groundwater flow systems in the Paleozoic sedimentary basins in the Amazon, Parana and Parnaiba regions of Brazil. The study makes use mainly of bottom-hole temperature data sets for oil wells, the depths of which vary from 1,000 to 4,000 m. The techniques employed in data analysis have allowed identification of non-linear features in vertical distributions of temperature, produced by deep groundwater flows in the study area. According to the results obtained, vertical velocities of subsurface flows are found to fall in the range 10−10 to 10−9 m/s, while the horizontal velocities are significantly higher, of the order 10−8 m/s. Identification of large-scale down flows has allowed inferences as to the existence of lateral movements of groundwater. The basins in the Amazon region are found to be characterized by widespread down flow of groundwater, implying the existence of distributed recharge systems operating on regional scales. There is a systematic decrease in horizontal velocities along the direction from west to east. This feature is considered indicative of gravity driven flows induced by episodes of uplift, since Miocene times, in the Andean region.

Interaction between shallow and deep aquifers in the Tivoli Plain (Central Italy) enhanced by groundwater extraction: A multi-isotope approach and geochemical modeling

Abstract In the Tivoli Plain (Rome, Central Italy) the interaction between shallow and deep groundwater flow systems enhanced by groundwater extraction has been investigated using isotopic and chemical tracers. A conceptual model of the groundwater flowpaths has been developed and verified by geochemical modeling. A combined hydrogeochemical and isotopic investigation using ion relationships such as DIC/Cl − , Ca/(Ca + Mg)/SO 4 /(SO 4 + HCO 3 ), and environmental isotopes ( δ 18 O, δ 2 H, 87 Sr/ 86 Sr, δ 34 S and δ 13 C) was carried out in order to determine the sources of recharge of the aquifer, the origin of solutes and the mixing processes in groundwater of Tivoli Plain. Multivariate statistical methods such as principal component analysis and Cluster analyses have confirmed the existence of different geochemical facies and the role of mixing in the chemical composition of the groundwater. Results indicate that the hydrochemistry of groundwater is characterized by mixing between end-members coming directly from carbonate recharge areas and to groundwater circulating in a deeply buried Meso-Cenozoic carbonate sequence. The travertine aquifer is fed by both flow systems, but a local contribution by direct input in the Plain has also been recognized. The stable isotope data ( 18 O, 2 H, 13 C and 34 S) supports the flow system conceptual model inferred from the geochemical data and represents key data to quantify the geochemical mixing in the different groundwaters of the Plain. The results of numerical modeling (PHREEQC) are consistent with the flowpaths derived from the hydrogeochemical conceptual model. The inverse models performed generated the main geochemical processes occurring in the groundwater flow system, which also included mixing. Geochemical and isotope modeling demonstrate an increasing influence of groundwater from the deeply buried aquifer in the travertine aquifer, enhanced by lowering of the travertine aquifer water table due to quarry pumping.

Mixing of magmatic CO 2 into volcano groundwater flow at Aso volcano assessed combining carbon and water stable isotopes

To understand deep groundwater flow systems and their interaction with CO 2 emanated from magma at depth in a volcanic edifice, deep groundwater samples were collected from hot spring wells in the Aso volcanic area for hydrogen, oxygen and carbon isotope analyses and measurements of the stable carbon isotope ratios and concentrations of dissolved inorganic carbon (DIC). Relations between the stable carbon isotope ratio (δ 13C DIC) and DIC concentrations of the sampled waters show that magma-derived CO 2 mixed into the deep groundwater. Furthermore, groundwaters of deeper areas, except samples from fumarolic areas, show higher δ 13C DIC values. The waters' stable hydrogen and oxygen isotope ratios (δD and δ 18O) reflect the meteoric-water origin of that region's deep groundwater. A negative correlation was found between the altitude of the well bottom and the altitude of groundwater recharge as calculated using the equation of the recharge-water line and δD value. This applies especially in the Aso-dani area, where deeper groundwater correlates with higher recharge. Groundwater recharged at high altitude has higher δ 13C DIC of than groundwater recharged at low altitude, strongly suggesting that magmatic CO 2 is present to a much greater degree in deeper groundwater. These results indicate that magmatic CO 2 mixes into deeper groundwater flowing nearer the magma conduit or chamber.

Interaction between deep and shallow groundwater systems in areas affected by Quaternary tectonics (Central Italy): a geochemical and isotope approach

Hydro- and isotope geochemistry are used to refine groundwater conceptual models in two areas of central Italy (Acque Albule Basin and Velino River Valley) affected by extensional Quaternary tectonics, where deep and shallow groundwater flow systems are interacting. The role of geology, of recent deposits filling the plains and of main tectonic features controlling groundwater flowpaths and deep-seated fluids emergences are investigated and discussed. Environmental isotopes (2H and 18O) confirm recharge in the surrounding carbonate aquifers, and meteoric origin of both shallow and deep groundwater. Major ion chemistry indicates a mixing between shallow Ca-HCO3 groundwater from carbonate aquifers and deep Ca-HCO3-SO4 groundwater, characterised by higher salinity and temperature and high concentration in sulphates. Isotopic composition of dissolved sulphates (δ 34S and δ 18O) and dissolved inorganic carbon (δ 13C), henceforth indicated as DIC, are used to verify the presence of different sources of groundwater, and to validate the mixing model suggested by the major ion analyses. Sulphate isotope composition suggests a marine origin for the groundwater characterised by elevated sulphate concentration, whose source is present in the deep buried sequences. Carbon isotope composition confirms the role of a DIC source associated to CO2 degassing of a deep reservoir. Groundwater conceptual models are improved underlining the importance of Plio-Pleistocene sequences filling the tectonic depression. In the Acque Albule area, the travertine plateau represents a mixing stratified aquifer, where deep groundwater contribution is spread into the shallow aquifer. The alluvial–clastic–lacustrine leaky aquifer of Velino Valley enables a complete mixing of shallow and deep groundwater allowing spot-located discharge of deep groundwater along tectonic patterns and facilitating sulphate reduction in the lacustrine sediments, explaining locally the presence of H2S.

GROUNDWATER FLOW SYSTEM OF BANDUNG BASIN BASED ON HYDRAULIC HEAD, SUBSURFACE TEMPERATURE, AND STABLE ISOTOPES

To recognize the groundwater flow system in the Bandung Basin, two main methods of regional groundwater flow delineation were employed: hydraulic heads and tracers. Two different environmental tracers, i.e. subsurface temperature and stable isotope were applied. The measured temperatures and stable isotope compositions from 19 observation wells lead to the recognition of three types of flow systems within the Bandung Basin i.e., shallow, intermediate and deep groundwater flow system. The recharge area is located in the hills and upland which form the periphery of the plain. The summit area of the southern mountainous complex might have represented the highest recharge area No indication was found for water being recharged at higher elevation in the northern part of the basin which means the recharged water in the Mount Tangkuban Parahu area did not reach the Bandung Plain. This study clearly demonstrates the usefulness of these environmental tracers and hydraulic head measurement in identification of the groundwater flow system of a certain area.

Evaluation of the sustainability of deep groundwater as an arsenic-safe resource in the Bengal Basin.

Tens of millions of people in the Bengal Basin region of Bangladesh and India drink groundwater containing unsafe concentrations of arsenic. This high-arsenic groundwater is produced from shallow (<100 m) depths by domestic and irrigation wells in the Bengal Basin aquifer system. The government of Bangladesh has begun to install wells to depths of >150 m where groundwater arsenic concentrations are nearly uniformly low, and many more wells are needed, however, the sustainability of deep, arsenic-safe groundwater has not been previously assessed. Deeper pumping could induce downward migration of dissolved arsenic, permanently destroying the deep resource. Here, it is shown, through quantitative, large-scale hydrogeologic analysis and simulation of the entire basin, that the deeper part of the aquifer system may provide a sustainable source of arsenic-safe water if its utilization is limited to domestic supply. Simulations provide two explanations for this result: deep domestic pumping only slightly perturbs the deep groundwater flow system, and substantial shallow pumping for irrigation forms a hydraulic barrier that protects deeper resources from shallow arsenic sources. Additional analysis indicates that this simple management approach could provide arsenic-safe drinking water to >90% of the arsenic-impacted region over a 1,000-year timescale. This insight may assist water-resources managers in alleviating one of the world's largest groundwater contamination problems.

Environmental Isotopes as Indicators for Ground Water Recharge to Fractured Granite

To assess the contribution of accumulated winter precipitation and glacial meltwater to the recharge of deep ground water flow systems in fracture crystalline rocks, measurements of environmental isotope ratios, hydrochemical composition, and in situ parameters of ground water were performed in a deep tunnel. The measurements demonstrate the significance of these ground water recharge components for deep ground water flow systems in fractured granites of a high alpine catchment in the Central Alps, Switzerland. Hydrochemical and in situ parameters, as well as delta(18)O in ground water samples collected in the tunnel, show only small temporal variations. The precipitation record of delta(18)O shows seasonal variations of approximately 14% and a decrease of 0.23% +/- 0.03% per 100 m elevation gain. delta(2)H and delta(18)O in precipitation are well correlated and plot close to the meteoric water line, as well as delta(2)H and delta(18)O in ground water samples, reflecting the meteoric origin of the latter. The depletion of 18O in ground water compared to 18O content in precipitation during the ground water recharge period indicates significant contributions from accumulated depleted winter precipitation to ground water recharge. The hydrochemical composition of the encountered ground water, Na-Ca-HCO3-SO4(-F), reflects an evolution of the ground water along the flowpath through the granite body. Observed tritium concentrations in ground water range from 2.6 to 16.6 TU, with the lowest values associated with a local negative temperature anomaly and anomalous depleted 18O in ground water. This demonstrates the effect of local ground water recharge from meltwater of submodern glacial ice. Such localized recharge from glaciated areas occurs along preferential flowpaths within the granite body that are mainly controlled by observed hydraulic active shear fractures and cataclastic faults.

Microbial and chemical characterization of a groundwater flow system in an intermontane basin of southern New Mexico, USA

Groundwater of the southern Jornada del Muerto Basin, an intermontane basin structure associated with the Rio Grande rift located in south-central New Mexico, USA, was analyzed chemically and microbially. A microbial phospholipid fatty acids (PLFA) analysis revealed a sparse microbial population consisting of relatively simple microorganisms with no major population changes along the flow system. A nucleic acid (DNA) analysis of the groundwater resulted in the identification of ten eubacterial and one archeal species. Chemical analyses revealed that sulfate along with calcium, magnesium, iron, and manganese is removed by about an order of magnitude in concentration from the recharge area to the discharge area. The removal of iron, manganese, magnesium, and to some extent calcium can be explained by oxidation reactions and the precipitation of dolomite. Sulfate and additional calcium are most likely removed by the precipitation of gypsum. Thiobacillus spp. are oxidizing metal sulfides that occur as subsurface sulfide mineral deposits to sulfuric acid, which subsequently reacts with calcium carbonate and water to precipitate gypsum. The presence of these sulfide deposits exposed to oxygenated water in the deep groundwater flow system significantly alters its chemical and bacteriological composition.

Origin of methane in the Elk Valley coalfield, southeastern British Columbia, Canada

Coalbead methane is part of the non-conventional gas reservoirs and makes a significant contribution to gas production in some parts of the world. Initially, it was assumed that coalbed methane was of thermogenic origin, but most recent studies based on isotope and chemical data and taking into account the hydrogeology of the basin have demonstrated that secondary biogenic gases are formed in many coal-bearing basins. This study, using a similar approach, evaluated the origin of the gas in the Elk Valley coalfield located in British Columbia, Canada. Isotope data in methane samples collected from testhole wells and piezometers show a range that varies from −51.8‰ to −65.4‰ and −303‰ to −415‰ for δ 13C and δ 2H, respectively. The δ 2H data, which are among the most depleted data reported for coalbed methane, have to be related to the very depleted δ 2H values of the groundwater (−148‰ to −163‰). Isotope and chemical data collected from DIC show a trend of increasing δ 13C values (−11.9‰ to +34.9‰) associated with an increase in DIC concentration (216 to 1650 mg/l). The most 13C depleted DIC and low DIC waters are found in the shallow groundwater flow system representing conditions close to recharge areas, while the most 13C enriched DIC and high concentration DIC waters are found in the discharge areas associated with a deep groundwater flow system. The DIC pattern, which is typical for methanogenic aquifers, and the isotope data obtained in methane samples clearly indicate that the gas found in the Elk Valley coalfield is mainly biogenic in origin. This study reaffirms that an approach that combines an evaluation of the groundwater flow system, the isotopic characterization and concentration pattern of the main carbon pools (CH 4 and DIC), and the isotopic characterization of the groundwater is needed to fully evaluate the origin of gases in coal basins.

Manufacture of silicon carbide reinforced steels by spray forming

Hydrochemical analysis and environmental isotopic tracing are successfully applied to study groundwater evolution processes. Located in eastern China, the Jiangsu Coastal Plain is characterized by an extensively exploited deep groundwater system, and groundwater salinization has become the primary water environmental problem. This paper provides a case study on the use of a hydrochemical and environmental isotopic approach to assess possible mixing and evolution processes at Yoco Port, Jiangsu Province, China. Hydrochemical and isotopic patterns of deep groundwater allow one to distinguish different origins in deep water systems. HCO3– is the dominant anion in the freshwater samples, whereas Na+ and Cl− are the dominant major ions in the saline samples. According to δ18O, δ2H and 14C dating, the fresh water is derived from precipitation under a colder climate during the Glacial Maximum (Dali Glacial), while the saline groundwater is influenced by glacial-interglacial cycles during the Holocene Hypsithermal. The δ18O, δ2H and 3H data confirm that deep groundwater in some boreholes is mixed with overlying saline water. The deep groundwater reservoir can be divided into a saline water sector and a fresh water sector, and each show distinct hydrochemical and isotopic compositions. The saline groundwater found in the deep aquifer cannot be associated with present seawater intrusion. Since the Last Glacial Maximum in the Late Pleistocene, the deep groundwater flow system has evolved to its current status with the decrease in ice cover and the rising of sea level. However, the hydraulic connection is strengthened by continuous overexploitation, and deep groundwater is mixed with shallow groundwater at some points.

Fracture detection and groundwater flow characterization using He and Rn in soil gases, Manitoba, Canada

Surveys of the distribution and migration of He and Rn were carried out in the well-characterized granitic terrane of the AECL Underground Research Laboratory (URL), Manitoba as part of a joint AECL Research, United Kingdom Department of the Environment, and United States Department of Energy research initiative. The investigations were designed to determine whether concentrations of He and Rn in soil gases could be used to identify locations of groundwater recharge and discharge from bedrock fractures. The results obtained indicate that subsurface transport of He and possibly Rn in this setting appears to be controlled largely by the groundwater flow system in the bedrock. Release of dissolved gases near the ground surface causes soil gas anomalies, which reflect discharge from the deeper flow system. In the recharge area of the deep groundwater flow system at the URL site, He abundances are close to the atmospheric level, but the discharge area of the deep flow system is characterized by significant He anomalies (up to 0.5 ppm above atmosphere levels). For Rn, the recharge area has broadly distributed high concentrations, probably caused by local Rn production in U-rich overburden, while the discharge area has only localized concentrations of Rn, which are not at the same location as the He anomalies. The general nature of the groundwater flow regime in both areas is reflected in the presence and distribution of the soil gas anomalies. In addition, major fractures in bedrock, which act as preferential groundwater flow paths, have been located from soil gas anomalies, even when obscured by overburden of variable thickness and character. The distribution of He in soil gas appears to be most representative of groundwater recharge and discharge conditions in the granitic rock, while Rn may be useful for locating specific channels where more rapid groundwater discharge is occurring from deep fracture zones.

The geochemistry, age, and origin of groundwater in a mafic pluton, East Bull Lake, Ontario, Canada

The geochemistry of groundwater in the East Bull Lake gabbro-anorthosite pluton near Elliot Lake, Ontario, Canada, has been investigated. Three chemical types of groundwater are present to depths of about 650 m, and are controlled by the nature of the groundwater flow systems and the water/rock interactions in the fractures. Ca HCO 3 water is present in the recharge area of the local flow system and evolves rapidly along the direction of groundwater flow to a high-pH, Na HCO 3 water primarily by cation exchange reactions. Saline Na Cl water is present below a depth of about 350 m. On the basis of its chemistry and hydraulic head measurements, the Na Cl water is believed to be part of a deep regional groundwater flow system. Carbon-14 measurements of the Na HCO 3 water suggest that this water was recharged shortly after the last Pleistocene deglaciation. This is supported by δ 18O values that are as much as 6%. lighter than shallow modern groundwater. Despite the high Mg content of the enclosing rocks, Mg 2+ concentrations in the groundwater of this unit are <1.0 mg L −1, and may be controlled by present-day serpentinization or formation of talc. Laumontite is thermodynamically stable in the Na HCO 3 and Na Cl waters and hence could still be forming under the present low-temperature conditions (<25°C). The stable isotope composition of the Na Cl water suggests that this water type is not a geochemically evolved product of the overlying waters, although present-day albitization of the anorthosite could be responsible for the increased Ca Na ratio in the Na Cl water compared to the other water types. The salinity of this water appears to have been derived outside the pluton, possibly as an ancient infiltration into crystalline basement rocks of saline formation waters present in Paleozoic sedimentary rocks, which formerly overlay the pluton, or from nearby Proterozoic formations. This hypothesis is supported by Br Cl ratios that are similar to sea water and many present-day formation waters, and the isotopic composition of the dissolved sulphate. The He “age” of the saline water is of the order of 10 8 years. Therefore both the saline water and many of its solutes appear to have ancient origins.