Hydrogeochemical Conceptual Model Research Articles

Multidisciplinary hydrogeochemical and isotopic assessment of the Pordenone Plain (Northeastern Italy) for water resources sustainability

This study aims to comprehensively characterize the hydro-geochemical and isotopic features of the complex groundwater system in the Pordenone Plain (northeastern Italy). The area is an important industrial and agricultural area exposed to severe anthropogenic pressure and climate change, which put its water resources at risk in terms of quantity and quality, making it of high scientific and social interest. The hydrogeological setting of the Pordenone Plain has been previously simplified as a phreatic continuous aquifer in the High Plain that changes into a multilayered aquifer system towards the Low Plain. However, this study reveals significant lithological and structural heterogeneities in the High Plain that exert a strong influence on its subsurface hydrodynamics. All waters exhibit a Ca(Mg)–HCO3 composition with relatively high Na–K values in the aquifers of the Low Plain likely related to cation exchange processes. Water stable isotopes (δ2H–H2O and δ18O–H2O) indicate that the deep aquifers in the Low Plain are confined by impermeable geological formations, such as clays and siltstones, which entirely restrict water mixing with shallower aquifers. Concurrently, tritium analysis provides evidence of slow recharge and flow rate. Three primary groundwater flows have been identified within the plain, as follows: 1) a surface flow that affects the unconfined or semi-confined aquifers of the High Plain hosted in gravelly sediments; 2) an intermediate flow fed by the pedemontane zone, which includes unconfined deep aquifers of the High Plain, semi-confined/shallow aquifers (at a depth of 40–50 m) located near the resurgence belt area and karst springs located in eastern pedemontane of the Cansiglio Plateau; 3) a deep flow fed by the mountainous zone that affects the deep confined aquifers of the Low Plain. A reliable hydrogeochemical conceptual model has been developed to explain the compositional variability of the studied waters, providing valuable insights for the sustainable management of groundwater resources in the Pordenone Plain.

Co-occurrence of arsenic and fluoride in groundwater of Guide basin in China: Genesis, mobility and enrichment mechanism

Endemic arsenic poisoning and fluorosis caused by primary high arsenic (As) and high fluoride (F−) groundwater have become one of the most serious environmental geological problems faced by the international society. High As and high F− groundwater exists in Neogene confined aquifers in Guide basin, with concentrations of 355 μg/L and 5.67 mg/L, respectively, and showing a co-occurrence phenomenon of As and F− in the groundwater. This poses a double threat to the health of tens of thousands of local residents. In this study, based on the systematic collection of groundwater and borehole sediment samples, analysis of hydrochemistry and isotope indexes, combined with laboratory tests, purpose of this study is to reveal the migration rule and co-enrichment mechanism of As and F− in aquifers, and finally establish a hydrogeochemical conceptual model of the enrichment process of As and F−. The main conclusions are as follows: hydrochemical type of unconfined and confined groundwater in Guide basin is Ca–Na–HCO3 and Na–Cl–HCO3 type, respectively. Main minerals in sediments are quartz and plagioclase. Concentrations of As and F− are lower in unconfined groundwater, but higher in confined groundwater, and which show a gradual increasing trend along the groundwater flow path. The mineralization of natural organic matter in confined aquifer causes iron and manganese oxide minerals containing As to dissolve gradually, which leads to the gradual release of As into groundwater. Large amount of HCO3− produced by mineralization of organic matter precipitate with Ca2+ in groundwater, resulting in reduction of Ca2+ content, promoting the dissolution of fluoride-containing minerals such as fluorite (CaF2), and continuously releasing F− into groundwater. Meanwhile, competitive adsorption reactions in confined aquifers causes more As and F− to be released from mineral surface into groundwater, which gradually migrate and accumulate along groundwater flow. Finally, it is established that a conceptual model for the formation of high As and F− groundwater in the confined aquifer of Guide basin. The research results not only help to improve our understanding of the formation and evolution of groundwater with high As and F− with similar geological background, but also provide scientific basis for rational development and utilization of groundwater, and prevention and control of chronic As and F− poisoning in local and similar areas.

Hydrogeochemical and isotopic characterization of the Gioia Tauro coastal Plain (Calabria - southern Italy): A multidisciplinary approach for a focused management of vulnerable strategic systems

This work pursues the hydro-geochemical and isotopic characterization of the complex groundwater system of the Gioia Tauro Plain, one of the most important industrialized and agricultural coastal areas of southern Italy. The anthropic pressure exposes the water resources at risk of depletion and quality degradation making the plain groundwater a system of high scientific and social interest.The plain is characterized by a shallow aquifer, mostly recharged by local rains and a deep aquifer apparently less influenced by local precipitation. Both aquifers are mainly Ca-HCO3 waters except for localized sectors where Na-HCO3, Na-Cl and Ca-SO4 waters are present. In deep aquifer, both prolonged interaction with sedimentary rocks, mainly deriving from the erosion of crystalline rocks, and direct cation exchange represent the primary factors controlling the formation of Na-HCO3 waters. Mixing processes between these waters and either connate brine and/or deep thermal waters contribute to the formation of isolated high salinity Na-Cl-rich waters. In shallow aquifer, inputs of N-rich sewage and agriculture-related contaminants, and SOx emissions in proximity of the harbor are responsible of the increasing nitrate and sulphate concentrations, respectively. The Cl/Br and NO3/Cl ratios highlight contamination mainly linked to agricultural activities and contribution of wastewater.Along the northern boundary, the warmest groundwater (Na-Cl[SO4]) were found close to a bend of the main strike-slip fault system, locally favouring the rising of B- and Li-rich deep waters, testifying the influence of geological-structural features on deep water circulation.Despite the high-water demand, a direct marine intrusion is localized in a very restricted area, where we observed an incipient groundwater-seawater mixing (seawater contribution ≤7 %). The qualitative and quantitative conditions of the shallow aquifer still have acceptable levels because of the relatively high recharge inflow. A reliable hydrogeochemical conceptual model, able to explain the compositional variability of the studied waters, is proposed.

Hydrogeochemical surveys of shallow coastal aquifers: A conceptual model to set-up a monitoring network and increase the resilience of a strategic groundwater system to climate change and anthropogenic pressure

Salinization is a main concern for coastal aquifers due to climate change and incremental anthropogenic pressure. The Mediterranean area is particularly sensitive to this process, being several coastal aquifers already affected by seawater intrusion. The Fano coastal aquifer, located in the northern part of the Adriatic Sea (Italy), has a regional importance since it supplies drinkable water to the local communities and may be subjected to salinization given its intrinsic vulnerability and the awaited human and climate pressure. In this work, for the first time a detailed hydrogeochemical and isotopic study on the Fano shallow aquifer is presented to highlight the quality of this groundwater system. The hydrological, geochemical and isotopic data indicate a strong nitrate contamination in the central part of the basin, forcing the local water management company to inject low-NO3 waters from the main river course (Metauro River) to reduce the impact due to the N-bearing species. Differently from other coastal aquifers located along the Adriatic Sea where the seawater wedge is deteriorating most groundwater systems, our results and geochemical modeling suggest that the shallow aquifer of Fano is not apparently affected by salinization. This achievement makes this aquifer suitable for assessing whether the groundwater system might be evolving toward a seawater-contaminated aquifer. According to the proposed hydrogeochemical conceptual model, a monitor network should be deployed by the local authorities and the water management company to take appropriate measures to minimize the risk of seawater intrusion, should the hydrogeochemical and isotopic parameters indicate an incipient ingression of seawater.

Construction of a hydrogeochemical conceptual model and identification of the groundwater pollution contribution rate in a pyrite mining area

To effectively restore the groundwater environment of the Shiping Mine (SPM) area, which is contaminated by acid mine drainage (AMD), a hydrogeochemical conceptual model was constructed based on groundwater chemistry and environmental stable isotopes. The contribution rate of various pollution sources in the groundwater environment was quantitatively analyzed using an optimized stable isotope mass balance model. A total of 68 groups of water samples were collected. The sampling period covered the dry, intermediate, and wet periods of a complete hydrological year. Samples were taken from rain, springs, mine drainage, tailings leachate, and surface water; and the detection and analysis indicators included 24 parameters, such as inorganic salts, heavy metals, and isotopes. A hydrogeochemical and statistical data analysis was performed. The main source of groundwater replenishment was found to be atmospheric precipitation, with the water-rock interaction of calcite and pyrite, and mining activities being the main controlling factors of hydrogeochemical processes. Acid mine drainage significantly enhanced the dissolution of various minerals, and the detection rate of Zn, Cu, As, Cd, and Pb increased from 0–30%–100% when compared with groundwater in the area upstream of the mines. The optimized mass balance model results revealed that the contribution rates of upstream groundwater, mine water and leachate were 0.78–0.86, 0.08–0.18, and 0.04–0.06 for Heidong underground river, respectively; were 0.27–0.36, 0.62–0.68, and 0.03–0.05 for Tiantang underground river, respectively. Furthermore, based on the water balance analysis, 34–70% of the mine water was found to infiltrate directly through karst fissures and karst pipes and could not be collected at the mine entrance. Acid mine drainage that directly infiltrated through runoff could easily be ignored due to the hidden migration path, which may cause the groundwater environment to be remediated less effectively than expected.

Construction of a Hydrogeochemical Conceptual Model and Identification of the Groundwater Pollution Contribution Rate in a Pyrite Mining Area

Construction of a Hydrogeochemical Conceptual Model and Identification of the Groundwater Pollution Contribution Rate in a Pyrite Mining Area

Recharge sources and hydrogeochemical evolution of groundwater in a heterogeneous karst water system in Hubei Province, Central China

Although numerous studies on hydrogeochemistry in karst catchments have been performed, some challenges in understanding their hydrogeochemical behavior remain due to the unique architecture of karst groundwater systems and the high heterogeneity of the karst medium. Here we used a multicriteria approach combining hydrodynamic, hydrochemical, and stable isotopic tools to investigate the impact of heterogeneity on karst hydrogeochemistry in a mountainous area of Hubei Province, Central China. Our results showed that groundwater was dominated by Ca2+, Mg2+, HCO3−, and SO42−, and typically characterized by HCO3–Ca·Mg type in the shallow aquifer and by SO4–Ca·Mg type in the deep aquifer. With increasing circulation depth, water-rock interactions and the heterogeneity of the karst medium produced water with increased Ca2+, Mg2+, Sr2+, and SO42− concentrations, and also increased the dissolved total solids. Calcite, dolomite, and gypsum dissolution in local and intermediate flows were important geochemical processes in groundwater evolution, and calcite precipitation occurred in the regional flow due to dedolomitization, supported by PHREEQC modeling of minerals. The decreased major ions and increased nitrate with increasing δ18O due to the dilution of shallow groundwater by high δ18O recharge and nitrogen fertilizer required during the summer rainy season were found relying on Plots of δ18O vs major ions, which offer an alternative approach to learn seasonal effects of hydrogeochemistry. All advances presented were integrated into a hydrogeochemical conceptual model, including local, intermediate, and regional flows, hydrogeochemical evolution, horizontal and vertical karst zones, hydrochemistry, and stable isotopes of groundwater, providing a typical model for multiple karst groundwater systems in Central China.

First conceptual hydrogeological model of two intermountain Andean basins based on isotopes and hydrochemistry

ABSTRACT Mountains arid environments are vulnerable under climate change scenarios. Variations in the recharge sources and the rising temperature can affect the water availability, threaten the socio-productive systems on local and regional scales. In this sense, two hydrological systems were studied in the Andes Range, Argentina, by hydrochemical and isotope techniques, with the purpose to understand the origin of water, the groundwater recharge, and to conceptualize the groundwater flow system. In the two sampling periods (winter and summer seasons) most of the waters were characterized by low mineralization and a HCO3-Ca type. The isotopic composition showed wide ranges of variation consistent with the altitudinal differences existing in the study systems. However, no significant isotope changes were observed between the samples collected in winter and summer periods. Therefore, little influence of liquid precipitation is inferred in the recharge source of both hydrological systems. This means that the western sector of the valley, where the ice bodies and permafrost are located, is the main recharge area for groundwater of both basins. This confirms the former hypothesis used for the hydrogeochemical conceptual model proposed, and highlights the importance of protecting these environments to ensure the provision of water in arid lands.

Preliminary conceptual model of the Cerro Blanco caldera-hosted geothermal system (Southern Puna, Argentina): Inferences from geochemical investigations

The Cerro Blanco Caldera (CBC) is the youngest collapse caldera system in the Southern Central Andes (Southern Puna, Argentina). The CBC is subsiding with at an average velocity of 0.87 cm/year and hosts an active geothermal system. A geochemical characterization of emitted fluids was carried out based on the chemical and isotopic compositions of fumaroles, and thermal and cold springs discharged in this volcanic area with the aim of constructing the first hydrogeochemical conceptual model and preliminary estimate the geothermal potential. The main hydrothermal reservoir, likely hosted within the pre-caldera basement rocks, has a Na+-Clˉ(HCO3)ˉ composition with estimated temperatures ≥135 °C. The unconsolidated, fine-grained Cerro Blanco ignimbrite likely acts as the cap-rock of the hydrothermal system. The presence of phreatic eruption breccias in the surrounding area of the geothermal fumaroles supports the effectiveness of the pyroclastic deposit as sealing rocks. The isotopic data of water (δ18O and δD) indicate a meteoric recharge of the hydrothermal reservoir, suggesting as recharge areas the sectors surrounding the CBC, mainly towards the W and NW where large outcrops of the pre-caldera basement exist. A fault-controlled hydraulic connection between the hot springs and the hydrothermal reservoir is proposed for the Los Hornitos area. The fumaroles show the typical compositional features of hydrothermal fluids, being dominated by water vapor with significant concentrations of H2S, CH4 and H2. Considering the high geothermal gradient of this area (∼104 °C/km) and the relatively high fraction of mantle He (∼39%) calculated on the basis of the measured R/Ra values, the hydrothermal aquifer likely receives inputs of magmatic fluids from the degassing magma chamber. The preliminary geothermal potential at CBC was evaluated with the Volume Method, calculating up to E = 11.4*1018 J. Both the scarce presence of superficial thermal manifestations and the occurrence of an efficient cap-rock likely contribute to minimize the loss of thermal energy from the reservoir. The results here presented constitute the necessary base of knowledge for further accurate assessment of the geothermal potential and ultimately the implementation of the geothermal resource as a viable energy alternative for small localities or mining facilities isolated from the National Interconnected System due to their remote localization.

Establishing complex compartments-aquifers connectivity via geochemical approaches towards hydrogeochemical conceptual model: Kasserine Aquifer System, Central Tunisia

Located in an arid region in Central Tunisia, the Kasserine Aquifer System (KAS) represents the most available source of water supply in the area. The main regional reservoir of the KAS is the deep aquifer of Miocene sandstone that extends into the northeast of Algeria. The system consists of four compartments, namely: Oum Ali-Thelepte (OT), Feriana-Skhirat (FS), the Plateau (PL) and the Plaine (PK) of Kasserine.The challenge of this study is to investigate hydrogeochemical and isotopic data to highlight the mechanisms leading to connection between the different compartments of the KAS. The results of the hydrogeochemical assessment were integrated into a 3D geological model to develop a 3D hydrogeochemical conceptual model of the KAS. Besides, mixing between the four-groundwater compartments was also highlighted using a binary mixing hypothesis and an End Member Mixing Analysis method including two tracers Cl and δ18O and three end-members.These methods indicate the importance contribution of the upstream compartment of OT into the other aquifer units. It also allowed the estimation of direct recharge ratios in every compartment and the quantification of diffuse and concentrated recharge in the KAS. Hence, the main factors affecting the KAS studied in this paper are, mixing, dedolomization and cation exchange processes.This study helps understanding the hydrogeochemical processes of the KAS and informs groundwater managers where better targeted groundwater monitoring programs are required in the future.

Five-year performance monitoring of a high-density polyethylene (HDPE) cover system at a reclaimed mine waste rock pile in the Sydney Coalfield (Nova Scotia, Canada).

Cover systems are commonly placed over waste rock piles (WRPs) to limit atmospheric water and oxygen ingress and control the generation and release of acid mine drainage (AMD) to the receiving environment. Although covers containing geomembranes such as high-density polyethylene (HDPE) exhibit the attributes to be highly effective, there are few, if any, published studies monitoring their performance at full-scale WRPs. In 2011, a HDPE cover was installed over the Scotchtown Summit WRP in Nova Scotia, Canada, and extensive field performance monitoring was conducted over the next fiveyears. A range of parameters within the atmosphere, cover, waste rock, groundwater and surface water, were monitored and integrated into a comprehensive hydrogeochemical conceptual model to assess (i) atmospheric ingress to the waste rock, (ii) waste rock acidity and depletion and (iii) evolution of groundwater and surface water quality. Results demonstrate that the cover is effective and meeting site closure objectives. Depletion in oxygen influx resulted in slower sulphide oxidation and AMD generation, while a significant reduction in water influx (i.e. 512 to 50mm/year) resulted in diminished AMD release. Consistent improvements in groundwater quality (decrease in sulphate and metals; increase in pH) beneath and downgradient of the WRP were observed. Protection and/or significant improvement in surface water quality was evident in all surrounding watercourses due to the improved groundwater plume and elimination of contaminated runoff over previously exposed waste rock. A variably saturated flow and contaminant transport model is currently being developed to predict long-term cover system performance.

Nitrogen and sulphur cycling in the saline coastal aquifer of Ferrara, Italy. A multi-isotope approach

The origin of high ammonium and sulphate concentrations, characterizing the saline groundwater of the Po River floodplain coastal aquifer, are documented. A detailed understanding of the hydrogeochemical conceptual model is built up using a hydrochemical (major ions, DOC, DIC and methane) and isotopic (δ15NNO3, δ15NNH4, δ18ONO3, δ34SSO4, δ18OSO4 and δ13CDIC) approach. Based on previous hydrogeological investigations, two boreholes located in contrasting environments (urban and agricultural) have been sampled at high vertical resolution.Groundwater is mostly under reducing conditions, characterized by high DOC and DIC concentrations but low to moderate methane content. Dissolved ammonium, as high as 87.8 mgL−1, derives by the mineralization of N-organic rich fine sediments, as indicated by its N isotopic signatures (1÷3‰). Attenuation processes of ammonium are ruled by dilution and by partial nitrification, supported by the enrichment in δ15NNH4 (∼+7‰). Apart from dilution/oxidation processes, the positive correlation between δ15NNO3 and δ18ONO3 agreed with the occurrence of denitrification in the shallow part of the aquifer. δ34SSO4 and δ18OSO4 data highlight that oxidation of pyrite occurs but is not necessarily linked to nitrate removal. The isotope data showed that sulphate (>2500 mgL−1) is of marine origin. In the deeper part of the aquifer, sulphur and oxygen isotopes enrichment patterns, demonstrated that sulphate reduction (SR) occurs in the aquifer and it is also possible that SR occurred in the underlying clay units. δ13CDIC pattern toward depleted δ13CDIC values even as low as −40.4‰ documented the occurrence of SR mediated by organic carbon and SR coupled to oxidation of methane (AOM) are involved in the sulphur and carbon cycles. The present study shows the advantage of using stable isotopes complemented with geochemical data to characterize the solutes' origins, both natural and anthropogenic, and giving insights on biogeochemical transformations involving nitrogen, sulphur and carbon in coastal sediments.

Estimating groundwater residence time and recharge patterns in a saline coastal aquifer

AbstractA detailed study using environmental tracers such as chloride (Cl−) and tritium (3H), deuterium (2H) and oxygen (18O) isotopes was performed in an alluvial coastal aquifer in two contrasting environments (urban and agricultural). These environmental tracers combined with a high‐resolution multi‐level sampling approach were used to estimate groundwater residence time and recharge patterns and to validate the hydrogeochemical conceptual model already proposed in previous studies. δ18O and δ2H combined with Cl− data proved that the hypersaline groundwater present in the deepest part of the aquifer was sourced from the underlying hypersaline aquitard via an upward flux. Both chemical and isotopic data were employed to calibrate a density‐dependent numerical model based on SEAWAT 4.0, where 3H and Cl− were helped quantifying solutes transport within the modelled aquifer. Model results highlighted the differences on estimated recharge in the two contrasting environments, with the urban one exhibiting concentrated recharge because of preferential infiltration associated to the storm water drains network, while scarce local recharge characterized the agriculture setting. In the urban field site, is still possible to recognize at 9 m b.g.l. the input of the atmospheric anthropogenic 3H generated by testing of thermonuclear weapons, while in the agricultural field site, the 3H peak has been washed out at 6 m b.g.l. because the groundwater circulation is restricted only to the upper fresh part of the aquifer, drained by the reclamation system. The presented approach that combined high‐resolution field monitoring, environmental tracers and numerical modelling, resulted effective in validating the conceptual model of the aquifer salinization. Copyright © 2016 John Wiley & Sons, Ltd.

Multivariate statistical analysis of hydrogeochemical data towards understanding groundwater flow systems in granites

The present study focuses on hydrogeochemical data from a Hercynian granitic mass where a new underground hydraulic circuit for a hydropower plant is being developed between two reservoirs and near another existing and operating underground hydraulic circuit. The main goal of this work is to assess the use of multivariate statistics to distinguish groundwater from different flow systems, to aid in evaluating the possible infiltration of water from the existing hydraulic circuit into the new one. Sampling points were selected inside the tunnels (eight points at the new circuit and one point at the existing circuit), near the surface (five points along the new circuit major axis) and on Venda Nova dam reservoir (one point). Based on laboratory determinations of major ions, three distinct groups of waters with different physicochemical characteristics and spatial distribution were established by cluster analyses. The relations of these groups with the characteristics of the occurrences are discussed with the support of principal component analysis. A hydrogeochemical conceptual model for groundwater flow systems related to infiltration and water–rock interaction in this granite rock mass is proposed based on multivariate statistical analyses and geological information. Supplementary material: Sample point coordinates, data results of physical–chemical parameters and elements, statistical data results of physical–chemical parameters and elements, and isotope data are available at https://doi.org/10.6084/m9.figshare.c.2857303.v1 .

Carbon dioxide and helium dissolved gases in groundwater at central Tenerife Island, Canary Islands: chemical and isotopic characterization

Seismic-volcanic unrest was detected between 2004 and 2005 in the central and northwest zones of Tenerife Island (Canary Islands, Spain). With the aim of strengthening the program of geochemical and seismic-volcanic surveillance, a study of the origin, characteristics, and spatial distribution of dissolved carbon dioxide (CO2) and helium (He) gases in the volcanic aquifer of central Tenerife Island and around Teide volcano was carried out. This work also improves the hydrogeological and hydrogeochemical conceptual model of groundwater flow. Dissolved CO2 concentrations in sampled groundwater are several orders of magnitude higher than that of air-saturated water (ASW) suggesting a significant contribution of non-atmospheric CO2, mainly magmatic, confirmed through measurement of isotopic compositions (δ13CTDIC) and total dissolved inorganic carbon (TDIC) concentrations. A vertical stratification of dissolved CO2 and δ13CTDIC values was observed in the volcanic aquifer at the eastern region of Las Canadas Caldera. Stratification seems to be controlled by both degree of magmatic CO2-water interaction and CO2 degassing and the original δ13Cco2(g) isotopic composition. The highest dissolved helium (4He) concentrations in groundwater seem to be related to radiogenic contributions resulting from water-rock interactions, and increase with residence time, instead of with endogenous magmatic inputs. Isotopic systematics show that the dissolved gases in groundwater of central Tenerife are variable mixtures of CO2–3He-rich fluids of volcanic-hydrothermal origin with both organic and atmospheric components. The results suggest that the eastern area of Las Canadas Caldera, the South Volcanic Ridge, and the Teide summit cone are the areas most affected by degassing of the volcanic-hydrothermal system, and they are therefore the most suitable zones for future geochemical monitoring.

The origin of groundwater composition in the Pampeano Aquifer underlying the Del Azul Creek basin, Argentina

The Pampean plain is the most productive region in Argentina. The Pampeano Aquifer beneath the Pampean plain is used mostly for drinking water. The study area is the sector of the Pampeano Aquifer underlying the Del Azul Creek basin, in Buenos Aires province. The main objective is to characterize the chemical and isotopic compositions of groundwater and their origin on a regional scale. The methodology used involved the identification and characterization of potential sources of solutes, the study of rain water and groundwater chemical and isotopic characteristics to deduce processes, the development of a hydrogeochemical conceptual model, and its validation by hydrogeochemical modelling with PHREEQC. Groundwater samples come mostly from a two-depth monitoring network of the “Dr. Eduardo J. Usunoff” Large Plains Hydrology Institute (IHLLA). Groundwater salinity increases from SW to NE, where groundwater is saline. In the upper basin groundwater is of the HCO3-Ca type, in the middle basin it is HCO3-Na, and in the lower basin it is ClSO4–NaCa and Cl–Na. The main processes incorporating solutes to groundwater during recharge in the upper basin are rain water evaporation, dissolution of CO2, calcite, dolomite, silica, and anorthite; cationic exchange with Na release and Ca and Mg uptake, and clay precipitation. The main processes modifying groundwater chemistry along horizontal flow at 30m depth from the upper to the lower basin are cationic exchange, dissolution of silica and anorthite, and clay precipitation. The origin of salinity in the middle and lower basin is secular evaporation in a naturally endorheic area. In the upper and middle basins there is agricultural pollution. In the lower basin the main pollution source is human liquid and solid wastes. Vertical infiltration through the boreholes annular space during the yearly flooding stages is probably the pollution mechanism of the samples at 30m depth.

Development of a Management Tool to Support the Beneficial Use of Treated Coal Seam Gas Water for Irrigation in Eastern Australia

An infiltration and salinity transport model (ISTM) based on the HYDRUS modeling platform was developed to support the beneficial use of treated coal seam gas (CSG) water to irrigate perennial forage plots in eastern Australia. The ISTM was used to support the expansion of irrigated areas under the CSG industry’s first specific irrigation beneficial use approval issued by the Queensland environmental regulatory administering authorities in March 2009. To support meeting regulatory requirements for expansion beyond the original irrigation area, forward modelling within the vadose zone was used to evaluate the fate and transport of the irrigation water as it migrates through the shallow soils and unsaturated bedrock toward the saturated zone; simulations beneath three agricultural systems with contrasting infiltration capacities were assessed. The model simulation results were used to guide irrigation activities to maximize water use in the readily available soil water capacity range for these agroecosystems, without detrimental impacts to plant growth or surface water/groundwater and soil resources. In this paper, a practical irrigation and rainfall systems-driven hydrogeochemical conceptual model is presented to identify processes that are likely to govern infiltration from the land surface, root water uptake, and solute transport into, and potentially through, the unsaturated zone. A numerical model is then parameterized to represent the primary processes hypothesized to affect water and salinity movement in the vadose zone. Finally, a series of simulations, conducted to identify the key parameters and processes governing the potential movement of water and salt through the root zone and into the bedrock vadose zone, are discussed. The simulations are used to support continuous improvement in modeling approaches for sustainably managing treated CSG extraction water allocated to irrigation.

Geochemistry of Mississippi Valley-type mineralizing fluids of the Ozark Plateau: A regional synthesis

The compositions of fluid inclusions hosted in ore and gangue minerals from Mississippi Valley--type (MVT) Pb-Zn-Ba deposits of the Ozark Plateau region were measured to develop a regional hydro-geochemical conceptual model for ore emplacement. This model may explain the diverse compositions of fluids involved in mineral precipitation, the ore precipitation mechanism, and the temporal change in composition of fluids invading the ore districts. The conceptual model additionally provides evidence for what factors may have controlled deposit size, stratigraphic location, and Zn/Pb ratio. High Pb concentrations up to 1,0009s of ppm were identified in sphalerite-hosted fluid inclusions from all of the region9s districts. If these high Pb concentrations were transported in the same fluid with sulfide, then total sulfur concentration in the fluid must have been low. Mass balance calculations demonstrate that the Arkoma Basin, a presumed source basin for the mineralizing fluids, is too small to have contained enough fluid to precipitate the observed masses of sulfur in the larger MVT districts, given the low sulfide concentrations that could coexist in the fluid with such high concentrations of Pb. High methane concentrations in sphalerite-hosted fluid inclusions from all of the region9s districts, in dolomite-hosted fluid inclusions from the Tri-State and Northern Arkansas districts, and quartz-hosted fluid inclusions from the Northern Arkansas district suggest that the prevailing redox conditions during MVT mineralization were reducing, making it unlikely that sulfate was transported in large concentrations in the fluids. During sphalerite precipitation, assuming saturation with respect to carbon dioxide, measured methane concentrations in sphalerite-hosted fluid inclusions would have required oxygen fugacity to have been at least two log units below the sulfate predominance field boundary. Fluid inclusion methane concentrations can also be used to estimate minimum burial depths of mineralization of about 0.08 to 1.2 km. Available evidence indicates that sulfide mineral precipitation in the Ozark Plateau MVT districts most likely occurred primarily as a result of the introduction of sulfide into a Pb- and Zn-rich ore fluid. In the two larger MVT districts, sulfide may have been supplied by local organic- and sulfur-rich carbonate facies. An apparent mixing line between high Ca/Na ratio and low Ca/Na ratio fluids hosted predominantly in main stage sulfide minerals and paragenetically late minerals, respectively, indicates the ore fluid was relatively Ca enriched. The lack of continuity in high Pb concentrations in fluid inclusions in sulfide and nonsulfide minerals from across the mineral parageneses suggests that the ore fluids entered the districts intermittently and/or had variable metal contents over time.

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.

Groundwater Quality, Geochemical Processes and Groundwater Evolution in the Chateauguay River Watershed, Quebec, Canada

A hydrogeochemical study was carried out in the Quebec portion of the Chateauguay River watershed. The objective was to characterize the chemical composition of groundwater in order to evaluate its quality and assess geochemical variations related to the geological and hydrogeological settings. Bulk groundwater samples were collected from 144 wells distributed evenly over the study area. Nine of the wells were sampled with a multi-level packer system, for a total of 22 multi-level samples. Samples were analysed for a comprehensive set of chemical inorganic parameters: dissolved major, minor and trace constituents, bacterial content, and stable (δ2H, δ13C, δ18O) and radioactive (3H, 14C) isotopes. Major dissolved constituents Ca, Mg, Na, K, Cl, SO4 and HCO3– ions represent more than 92% of total dissolved solids and their concentrations seem controlled by both hydrogeological and geological factors. Most water quality problems are related to aesthetic standards for potable water use (hardness, total dissolved solids (TDS), Fe and Mn concentrations) and TDS and Cl for irrigation use. Analyses of tritium (3H) and 14C confirm the inferred recharge zones and indicate the presence of variable water ages. Groundwater shows a wide range of compositions as indicated by 12 water types defined on the basis of major ions with a weak variation of chemical composition with depth. The predominant water type, Ca-HCO3, occurs in most geological and hydrogeological settings. Principal Component Analysis (PCA) and geochemical graphs were used to identify the major processes that exert a control over the chemical composition of the groundwater. Approximately 80% of the geochemical variation can be explained by mixing between fresh recharge water with more saline water associated with the former Champlain Sea, which invaded the aquifer. Secondary processes are related to ion exchange and the potential dissolution of minerals. A cross-section along a major flow path shows that the geochemical evolution of groundwater leads to relations between water type groups, geochemical processes, and groundwater flow conditions. The hydrogeochemical conceptual model infers that carbonate dissolution during recharge leads to one end-member, a Ca-HCO3 type water, which further evolves along its flow path due through ion exchange and mixing with remnant Champlain Sea water (Na-Cl), the other end-member.