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Major and trace elements in groundwater from basaltic aquifers in pristine conditions were investigated in a volcanic island to evaluate sources, sinks, and mobility of elements over a wide range of mineralization conditions with total dissolved solids from 50 mg/L to 3400 mg/L. Groundwater was highly undersaturated with respect to primary silicate minerals, indicating that dissolution of basaltic rocks may continue under conditions with precipitation of calcite and secondary silicates. Evolution of B/Cl ratio in groundwater from marine aerosols to basaltic rocks showed that the ratio could be used as a conservative tracer for interactions between water and basaltic rocks. Relative mobility (RM) of elements calculated using the concentrations of elements in the local basaltic rocks and those in groundwater showed that mobility decreased in the order of B > Rb > Na > K > Mg > Ca > Mo > V > Si > Sr > Sc > P > U > Zn > Pb > Cr > Cu > Ba > Ni > Ti > (Mn, Al, Fe, Co, Th) indicating that oxyanion-forming elements and alkali metals had the highest mobility. Compared to average RM, V had decreased mobility, and Fe and Mn had increased mobility in anoxic groundwater while V, Mo, and U had higher mobility in oxic-alkaline water. The sources of V, Cr, Cu, and Zn in rocks were estimated using the partition coefficients between minerals and basaltic melt, and the disparity between sources and mobility indicated that sinks are more important for controlling the concentrations of these elements in groundwater than the contents in the rocks. Principal component analysis (PCA) of hydrogeochemical parameters in groundwater produced three principal components (PC) which represent dissolution of basaltic rocks without significant attenuation of released solutes, higher degree of water–rock interactions resulting in oxic-alkaline conditions, and attenuation of Zn and Cu in higher pH, respectively. Spatial distribution of PCs revealed that groundwater with elevated concentrations of mobile elements was concentrated in the southwestern area and that concentrations of V and Cr were more scattered, which is likely to be controlled by pH and redox states of groundwater as well as degree of water–rock interactions. [ABSTRACT FROM AUTHOR]

In order to evaluate groundwater quality and geochemical reactions arising from mixing between seawater and dilute groundwater, we performed a hydrochemical investigation of alluvial groundwater in a limestone-rich coastal area of eastern South Korea. Two sites were chosen for comparison: an upstream site and a downstream site. Data of major ion chemistry and ratios of oxygen–hydrogen isotopes (δ18O, δD) revealed different major sources of groundwater salinity: recharge by sea-spray-affected precipitation in the upstream site, and seawater intrusion and diffusion zone fluctuation in the downstream site. The results of geochemical modelling showed that Ca2+ enrichment in the downstream area is caused by calcite dissolution enhanced by the ionic strength increase, as a result of seawater–groundwater mixing under open system conditions with a constant PCO2 value (about 10−1.5 atm). The results show that, for coastal alluvial groundwater residing on limestone, significant hydrochemical change (especially increased hardness) due to calcite dissolution enhanced by seawater mixing should be taken into account for better groundwater management. This process can be effectively evaluated using geochemical modelling. Editor D. Koutsoyiannis; Associate editor Y. Guttman Citation Chae, G.-T., Yun, S.-T., Yun, S.-M., Kim, K.-H., and So, C.-S., 2012. Seawater–freshwater mixing and resulting calcite dissolution: an example from a coastal alluvial aquifer in eastern South Korea. Hydrological Sciences Journal, 57 (8),1–12. [ABSTRACT FROM AUTHOR]

Abstract: Basic oxygen furnace (BOF) slag media were studied as a potential treatment material in on-site sanitation systems. Batch and column studies were conducted to evaluate attenuation of the bacteriophage PR772 and 0.190 μm diameter microspheres by BOF media, and to delineate the relative contributions of two principle processes of virus attenuation: inactivation and attachment. In the batch studies, conducted at 4°C, substantial inactivation of PR772 did not occur in the pH 7.6 and 9.5 suspensions. At pH 11.4, bimodal inactivation of PR772 was observed, at an initial rate of 2.1 log C/C0 day−1 for the first two days, followed by a much slower rate of 0.124 log C/C0 day−1 over the following 10 days. Two column studies were conducted at 4°C at a flow rate of 1 pore volume day−1 using two slag sources (Stelco, Ontario; Tubarão, Brazil) combined with sand and pea gravel. In both column experiments, the effluent microsphere concentration approached input concentrations over time (reductions of 0.1–0.2 log C/C0), suggesting attachment processes for microspheres were negligible. Removal of PR772 virus was more pronounced both during the early stages of the experiments, but also after longer transport times (0.5–1.0 log C/C0). PR772 reduction appeared to be primarily as a result of virus inactivation in response to the elevated pH conditions generated by the BOF mixture (10.6–11.4). On-site sanitation systems using BOF media should be designed to maintain sufficient contact time between the BOF media and the wastewater to allow sufficient residence time of pathogens at elevated pH conditions. [Copyright &y& Elsevier]

Abstract: Major ions and stable isotopic (δDwater, δ18Owater, δ15Nnitrate, δ18Onitrate) measurements in concert with hydrochemical modeling were used in order to elucidate the sources and geochemical processes controlling nitrate contamination of shallow alluvial groundwater underneath a riverside agricultural field in the Buyeo area, Korea. Beneath vegetable fields in the sandy soil, the mean nitrate concentration of groundwater was 148.6mg/L, which is significantly higher than in groundwater (mean 28.8mg/L) beneath silty soils underneath rice paddy fields. Nitrogen isotope data indicate that synthetic fertilizers are the predominant source of groundwater nitrate in the study area. Denitrification during recharge through rice paddy soils appears to be responsible for the lower nitrate concentrations in groundwater beneath the silty soil zone. The relationship between nitrogen and oxygen isotope data of nitrate also suggests mixing of two different groundwater bodies with nitrates from the silt zone and the sand zone. Geochemical mass balance modeling on hydrochemical data indicates that various agricultural chemicals such as urea, lime, magnesium sulfate and potassium chloride dissolve in vegetable fields of the sandy zone, resulting in significant enrichment of various solutes such as K+, Ca2+, Mg2+, NO3 −, SO4 2− and Cl−. As a consequence of over-utilization of synthetic nitrogen fertilizers, the sand zone is characterized by very high nitrate concentrations in the groundwater. This study suggests that a reduction of over-fertilization especially on vegetable fields in the riverside sand zone is required to minimize the nitrate contamination of groundwater. This study also shows that combination of geochemical and isotopic techniques with simple mass balance modeling provides information about the causes and processes of nitrate contamination of groundwater underneath a riverside agricultural field. The study also provides sustainable measures to optimize fertilization rate as an important basis of eco-friendly agriculture. [Copyright &y& Elsevier]

Summary: Hydrogeochemical characteristics of groundwater were investigated to elucidate baseline quality for basaltic aquifers of a mountainous area dominated by natural land cover in the volcanic island of Jeju, South Korea. Principal component analysis (PCA) resulted in four principal components (PC) of which PC1, PC3 and PC4 represented natural mineralization by water–rock interaction, while PC2 corresponded to anthropogenic contamination from nitrate sources. Hierarchical cluster analysis (HCA) was performed to assess the effect of the geochemical and hydrologic processes on each sample. Six sample groups, distinguished by total dissolved solids (TDS), nitrate concentration, and water type, resulted from the HCA: high-altitude springs, low-mineral water, nitrate-contaminated water, intermediate-mineral water, and two groups of high-mineral water. Water types were transformed from Na(Mg, Ca)–HCO3 for low-mineral water to Na–HCO3 for high-mineral water. Nitrate-contaminated water occurred near the boundary of natural and agricultural land uses of the western area. High-mineral water had higher calcite saturation states than other groups. The high-mineral water also had tritium (3H) values lower than 1.5TU, indicating a significant contribution of old groundwater. In contrast, low-mineral water had tritium values of about 3TU, which is close to those of rainwater. Geographically, the high-mineral water was concentrated in the southwestern area, where intermediate-mineral water was also found. This distribution was likely related to the presence of extensive trachytic rocks, which could have formed locally isolated aquifers, enabling prolonged water–rock interactions; the higher location of low-permeability hydrovolcanic tuffs in the subsurface of the southern area would also increase chances of tapping aquifers below the hydrovolcanic tuffs. The cumulative probability of TDS showed two breakpoints of 50 and 150mg/L that distinguished high-altitude springs, low-mineral water, and high-mineral water. The cumulative probability of nitrate provided possible threshold values for anthropogenic contamination of 2.5 and 5.5mg/L. That 32% of samples had nitrate concentrations higher than 2.5mg/L indicated high vulnerability to surface contamination sources in this mountainous area. HCA seems to be more effective for interpreting the baseline chemistry of groundwater than other threshold-calculating statistics in that HCA revealed geochemical processes including natural mineralization and anthropogenic contamination. Our study suggests that the cumulative probability and HCA are useful as complementary methods for determining threshold values. [Copyright &y& Elsevier]

Abstract: Hydrogeologic and hydrochemical data for subway tunnel seepage waters in Seoul (Republic of Korea) were examined to understand the effect of underground tunnels on the degradation of urban groundwater. A very large quantity of groundwater (up to 63 million m3 year−1) is discharged into subway tunnels with a total length of 287 km, resulting in a significant drop of the local groundwater table and the abandonment of groundwater wells. For the tunnel seepage water samples (n =72) collected from 43 subway stations, at least one parameter among pathogenic microbes (total coliform, heterotrophic bacteria), dissolved Mn and Fe, NH4 +, NO3 −, turbidity, and color exceeded the Korean Drinking Water Standards. Locally, tunnel seepage water was enriched in dissolved Mn (avg. 0.70 mg L−1, max. 5.58 mg L−1), in addition to dissolved Fe, NH4 +, and pathogenic microbes, likely due to significant inflow of sewage water from broken or leaking sewer pipes. Geochemical modeling of redox reactions was conducted to simulate the characteristic hydrochemistry of subway tunnel seepage. The results show that variations in the reducing conditions occur in urban groundwater, dependent upon the amount of organic matter-rich municipal sewage contaminating the aquifer. The organic matter facilitates the reduction and dissolution of Mn- and Fe-bearing solids in aquifers and/or tunnel construction materials, resulting in the successive increase of dissolved Mn and Fe. The present study clearly demonstrates that locally significant deterioration of urban groundwater is caused by a series of interlinked hydrogeologic and hydrochemical changes induced by underground tunnels. [Copyright &y& Elsevier]

Abstract: Fluorescent microspheres are increasingly used in environmental studies to evaluate threats of viral and bacterial pathogens in drinking water and to investigate colloid-facilitated contaminant transport. A commonly accepted technique for the enumeration of viruses, bacteria, and virus- and bacteria-sized particles by microscopy involves a field-of-view (field) approach to estimate concentration. Few studies have focused on those factors that are most important in ensuring precise and accurate measures of concentration. Microsphere counts in suspensions of artificial groundwater and deionized water were contrasted in this study to gain a greater understanding of the effect of ionic strength and the presence of precipitates in groundwater matrices that can bias microsphere enumerations. To investigate microsphere enumeration with minimal bias from other factors, a commonly used standard method was used to prepare slides and enumerate microspheres, with particular care to randomly select fields for counting. A factorial experiment evaluated two factors, (1) the density of microspheres in each field and (2) the number of counts in an enumeration. Two parameters, relative standard deviation and percent error, were used to assess methodological precision and accuracy. Visual observations of the slides indicated that some biases, such as undulation in the filter membrane or bubble entrained in the mounting medium, create biases in microsphere enumeration. Additional biases were introduced by the presence of precipitates that form in artificial groundwater saturated with calcite. Microsphere density was found to be critical for ensuring methodological precision, whereas the total number of microspheres counted was essential to ensuring methodological accuracy. The results suggested that to minimize variability using the field approach, the enumeration of at least 350 microspheres and 25–40microspheresfield−1 is necessary. [Copyright &y& Elsevier]

High fluoride concentrations (median=4.4 mg/L) in deep bedrock groundwater of South Korea prevent the usage of it as a drinking water source. The hydrogeochemistry of deep thermal groundwaters (N =377) in diverse bedrocks has been studied in order to evaluate the geologic and geochemical controls on fluoride concentrations in groundwater. The groundwater samples were clustered geologically, and the average and median concentrations of fluoride were compared by the Mann–Whitney U test. The order of median fluoride concentration with respect to geology is as follows: metamorphic rocks≥granitoids≥complex rock≫volcanic rocks≥sedimentary rocks. This result indicates that the geological source of fluoride in groundwater is related to the mineral composition of metamorphic rocks and granitoids. With respect to groundwater chemistry, the fluoride concentration was highest in Na-HCO3 type groundwater and lowest in Ca-HCO3 type groundwater. Ionic relationships also imply that the geochemical behavior of fluoride in groundwater is related to the geochemical process releasing Na and removing Ca ions. The thermodynamic relationship between the activities of Ca and F indicates that fluoride concentration is controlled by the equilibrium of fluorite (CaF2). In other words, the upper limits of fluoride concentration are determined by the Ca ion; i.e., Ca concentrations play a crucial role in fluoride behavior in deep thermal groundwater. The result of this study suggests that the high fluoride in groundwater originates from geological sources and fluoride can be removed by fluorite precipitation when high Ca concentration is maintained. This provides a basis for a proper management plan to develop the deep thermal groundwater and for treatment of high fluoride groundwater frequently found in South Korea. [Copyright &y& Elsevier]

Abstract: The Pocheon spa-land area, South Korea occurs in a topographically steep, fault-bounded basin and is characterized by a hydraulic upwelling flow zone of thermal water (up to 44°C) in its central part. Hydrogeochemical and environmental isotope data for groundwater in the study area suggested the occurrence of two distinct water types, a Ca-HCO3 type and a Na-HCO3 type. The former water type is characterized by relatively high concentrations of Ca, SO4 and NO3, which show significant temporal variation indicating a strong influence by surface processes. In contrast, the Na-HCO3 type waters have high and temporally constant temperature, pH, TDS, Na, Cl, HCO3 and F, indicating the attainment of a chemical steady state with respect to the host rocks (granite and gneiss). Oxygen, hydrogen and tritium isotope data also indicate the differences in hydrologic conditions between the two groups: the relatively lower δ18O, δD and tritium values for Na-HCO3 type waters suggest that they recharged at higher elevations and have comparatively long mean residence times. Considering the geologic and hydrogeologic conditions of the study area, Na-HCO3 type waters possibly have evolved from Ca-HCO3 type waters. Mass balance modeling revealed that the chemistry of Na-HCO3 type water was regulated by dissolution of silicates and carbonates and concurrent ion exchange. Particularly, low Ca concentrations in Na-HCO3 water was mainly caused by cation exchange. Multivariate mixing and mass balance modeling (M3 modeling) was performed to evaluate the hydrologic mixing and mass transfer between discrete water masses occurring in the shallow peripheral part of the central spa-land area, where hydraulic upwelling occurs. Based on Q-mode factor analysis and mixing modeling using PHREEQC, an ideal mixing among three major water masses (surface water, shallow groundwater of Ca-HCO3 type, deep groundwater of Na-HCO3 type) was proposed. M3 modeling suggests that all the groundwaters in the spa area can be described as mixtures of these end-members. After mixing, the net mole transfer by geochemical reaction was less than that without mixing. Therefore, it is likely that in the hydraulic mixing zone geochemical reactions are of minor importance and, therefore, that mixing regulates the groundwater geochemistry. [Copyright &y& Elsevier]

Alluvial groundwaters in the area where intensive agricultural activity takes place were geochemically investigated to evaluate factors regulating groundwater quality of alluvial aquifers. For this study, 55 groundwater samples were taken from the uniformly distributed irrigation wells and were classified into three distinct groups according to their geochemical characteristics. This study reveals that the groundwater quality and the geochemical characteristics of the clustered groups are consistent with the geology of the area. The samples collected from the area where a thick silt bed overlies the sand aquifer are clustered into Group II and show water quality that is only slightly affected by the contaminants originating from the land surface. However, groundwaters of this group are very high in Fe and Mn levels due to strong anoxic condition caused by the thick silt bed. In contrast, Group I shows water quality largely influenced by agricultural activities (i.e., fertilization, liming) and occurs in the area adjacent to the river where the silt bed is not observed and the sand aquifer is covered with sandy soils. Group III mostly occurs in the upgradient of Group I where a thin, silty soil covers the sand aquifer. In overall, the results show that the clustered groups closely reflect the groundwater susceptibility to the contaminants originated from the land surface. This suggests that groundwater clustering based on water chemistry could be applied to the contamination susceptibility assessment for groundwaters in the agricultural area. [Copyright &y& Elsevier]

The spatial variations in the chemistry of first- and second-order stream waters (N=65) were investigated in the easterly bound of Seoul in order to assess the effects of urban air pollution on surface water chemistry. The sulfate (SO42−) was high (range 3.9–17.8 mg l−1, mean 11.8 mg l−1) within 30 km away from the center of Seoul, compared to the levels (range 1.1–7.7 mg l−1, mean 4.3 mg l−1) observed in remote areas (30–70 km away). Both graphical examination and statistical evaluation (variogram) of sulfate concentration data consistently showed the decrease of sulfate concentration with increasing distance. The results of mass balance modeling also indicate that the concentrations of SO42−, Cl− and Na+ may be affected mainly by dry/wet deposition. However, the spatial variations of major cations such as Ca2+ and Na+ are well explained by the reaction of rainwater with diverse rocks in the watercourse. The water type was found to change from Ca(–Na)–SO4 type to Ca(–Na)–HCO3 type with the increasing distance. It is thus inferred that the pollutants like SO2 emitted from strong man-made source areas of Seoul are transported to the considerable distance (at least 30 km away) by westerlies and that such mechanism may lead to the changes of the anion composition in surface water. In the remote area (>30 km away from Seoul), the stream water chemistry appears to be influenced more effectively by the weathering of rock-forming minerals. [Copyright &y& Elsevier]

Portland cement is a common sealing material used in wellbores for geological carbon sequestration. Two types of portland cement were reacted with carbon dioxide () in supercritical, gaseous, and aqueous phases, under various pressure and temperature conditions, to simulate a cement- reaction along the wellbore from the carbon injection depth to the near surface. In this study, two types of cement were used: Korean Standard (KS) portland cement (Type I) and American Petroleum Institute (API) class G portland cement. The top halves of hydrated portland cement sample columns (), including additives such as fly ash, were reacted with in an unsaturated (dry, no contact with water) condition. The bottom halves of the columns were reacted with in a saturated (wet, in contact with water) condition. These conditions were maintained under high pressure (8 MPa) and temperature (40°C) for 10 and 100 days to determine the potential of this process for carbon sequestration. To perform a relative quantitative analysis (RQA) of cement carbonation, an aragonite-calcite equation was proposed. The degree of carbonation was determined according to the type of cement, the reaction period, and the amount of fly ash. The characterization of the cement was performed using X-ray diffraction spectroscopy (XRD), field emission scanning electron microscopy (FE-SEM) with an energy dispersive spectrometer (EDS), and thermogravimetry-differential thermal analysis (TG-DTA). The relative quantitative analysis of cement carbonation proposed in this study has the advantages of being easier and faster to perform than the general quantitative method. [ABSTRACT FROM AUTHOR]

Abstract: Using a variety of chemical geothermometers and statistical analysis, we estimate the temperature of a possible deeper geothermal reservoir at Bugok, Southern Korea. Shallow thermal aquifers (down to about 400m depth) are under exploitation in this area; the temperatures (up to 78°C) of the produced fluids are the highest found in South Korea. Based on hydrochemical data and occurrence, the groundwaters at Bugok can be classified under three groups: Na-SO4 thermal groundwaters (CTGW) occurring in the central (about 0.24km2) part of the area; Ca-HCO3 cold groundwater (SCGW) found in shallow peripheral parts of the CTGW; the intermediate-type groundwater (STGW). The CTGW type is typical of the Bugok thermal waters; they have the highest discharge temperatures and contain very high concentrations of Na (75.1–101.0mg/L), K (2.9–6.9mg/L) and SiO2 (62.0–84.5mg/L) and are rich in sulfates. The major ion composition of the CTGW suggests that these waters are in partial equilibrium with rocks at depth. The application of various alkali-ion geothermometers yields temperature estimates in the 88–198°C range for the thermal reservoir. Multiple-mineral equilibrium calculations indicate a similar but narrower temperature range (from about 100 to 155°C). These estimates for CTGW are significantly higher than the measured discharge temperatures. Considering the heat losses occurring during the ascent of the waters, one can infer the presence of a deeper (around 1.8km) thermal reservoir in the Bugok area that could be developed for district heating or other direct applications of geothermal heat. [Copyright &y& Elsevier]

Abstract: In order to evaluate the salinization in the western coastal area of South Korea, we performed a regional hydrochemical study on a total of 356 shallow groundwaters sampled within 10km from the coastline. About 13, 5, and 37% of the samples exceed the drinking water standards for total dissolved solids, chloride, and nitrate, respectively, indicating significant deterioration and salinization of groundwaters. The concentrations of analyzed solutes are very wide in range, suggesting that the hydrochemistry is controlled by several intermixed processes such as seawater mixing, anthropogenic contamination, and water–rock interaction. Based on the interpretation of cumulative probability curves for Cl− and NO3 − concentrations, groundwaters are grouped into four types, as follows: (1) type 1 waters (37.6%) that are relatively poor in Cl− and NO3 −, which indicates little contamination due to seawater mixing and/or anthropogenic pollution; (2) type 2 waters (2.8%) enriched in Cl−, indicating considerable effects of seawater mixing; (3) NO3 −-rich, type 3 waters (58.1%) which show significant anthropogenic pollution; and (4) type 4 waters (1.4%) enriched in both Cl− and NO3 −, demonstrating the effects of both seawater mixing and anthropogenic contamination. The results of water-type classification are well confirmed by statistical analyses of hydrochemical data. As an effective tool for evaluating the relative degree of seawater mixing, we propose the ‘Seawater Mixing Index’ (SMI) based on the concentrations of Na, Mg, Cl, and SO4. Most type 2 and type 4 waters have SMI values greater than 1. At least about 5 and 60% of well groundwaters are considered to be affected by salinization due to seawater mixing and anthropogenic contamination, respectively. [Copyright &y& Elsevier]

[Display omitted] • Natural mineral springs in a tectonically stable area have diverse water types. • CO 2 -rich and thermal waters are associated with Jurassic granitic rocks and faults. • CO 2 -rich water has variable mineralization and no relationships with thermal water. • F concentration is higher in thermal water and controlled by calcite precipitation. • Elevated Mg in CO 2 -rich water is derived from silicate mineral interactions. Springs and hot spas have been used worldwide since ancient times as sources of potable, medicinal and bathing water, as well as for industrial purposes. They also sustain spring-dependent ecosystems and provide water flow to downstream ecosystems. We investigated the major element hydrogeochemistry of traditional springs, CO 2 -rich waters, and hot spas in South Korea and their relationships with features of bedrock geology and structural settings at the national scale to classify water types and identify the major factors controlling the occurrence of each water type. Three criteria—mineral content, CO 2 (aq), and water temperature—defined six major water types. Alkaline mineral water in carbonate rocks and sedimentary rocks result from readily weatherable lithology. The majority of mineralized waters are CO 2 -rich or thermal waters with a wide range of mineral contents. Their occurrence was found to be mainly concentrated near faults and boundaries between Early to Middle Jurassic granitic rocks and other rocks of much older ages, and this pattern was quantitatively identified through proximity analysis. This finding indicates that younger granitic rocks provide sources of heat and deep-seated CO 2 , and faults link these deep sources to groundwater flow. Hydrolysis of primary silicate minerals, including feldspar and biotite, is likely to supply major and minor solutes including Mg2+, F-, and Fe to CO 2 -rich and thermal waters. F- concentration appears to be regulated by the saturation states of calcite and fluorite, and Mg2+ concentration in alkaline thermal water is driven by the formation of Mg-bearing secondary silicates. We demonstrated that natural mineral water in tectonically stable regions has diverse thermal and hydrogeochemical properties that are mainly controlled by their lithological and structural settings at the regional scale. These results may help elucidate the generation processes of natural mineral waters with high cultural and ecological values, leading to their sustainable use and protection. [ABSTRACT FROM AUTHOR]

Tracers are used to tag the injected carbon dioxide (CO2) for verification of the storage performance and containment in geosequestration. Yet the characterization of the transport behavior of a chemical tracer in two‐phase flow system has not been fully investigated. We present experimental observations together with numerical results for both homogeneous and heterogeneous media from core scale to field scale. The key features of the breakthrough curves (BTCs) that include the tracer arrival time, peak concentration, and tailing pattern were examined. We identify distinct differences in BTCs depending on whether the formation was previously swept by CO2. When the tracer is released before CO2 sweeps the formation, the tracer transports at the front of gas‐liquid interfaces with a narrow tracer plume distribution and the BTCs reflect the effect of local heterogeneity. Furthermore, a series of tracer pulse can be used to identify whether new pathways have been developed during CO2 injection. Plain Language Summary: Geologic storage of carbon dioxide (CO2) has become an attractive climate change mitigation option, and ensuring the containment of injected CO2 is of prime importance for successful geological storage. Tracers are an effective means of tracking injected CO2 and verifying containment within the storage formation. Here we show that distinctive features in observed tracer data are highly related to whether or not the storage formation was previously swept by CO2. When the tracer is released at the beginning of CO2 injection, the tracer moves with narrow distribution and is advantageous for the tracer data to reflect multiple pathways. By contrast, once the CO2 sweeps the formation, the tracer moves much faster with a wider dispersion pattern. Key Points: We present experimental observations with numerical results for characterizing the tracer transport behavior in two‐phase flow systemThe key features of breakthrough curves and tracer velocity highly depend on whether the formation was previously swept by CO2A series of tracer pulse can be used to identify whether new pathways have been developed during CO2 injection [ABSTRACT FROM AUTHOR]

Abstract: Hydrochemical and multivariate statistical interpretations of 16 physicochemical parameters of 45 groundwater samples from a riverside alluvial aquifer underneath an agricultural area in Osong, central Korea, were performed in this study to understand the spatial controls of nitrate concentrations in terms of biogeochemical processes occurring near oxbow lakes within a fluvial plain. Nitrate concentrations in groundwater showed a large variability from 0.1 to 190.6 mg/L (mean=35.0 mg/L) with significantly lower values near oxbow lakes. The evaluation of hydrochemical data indicated that the groundwater chemistry (especially, degree of nitrate contamination) is mainly controlled by two competing processes: 1) agricultural contamination and 2) redox processes. In addition, results of factorial kriging, consisting of two steps (i.e., co-regionalization and factor analysis), reliably showed a spatial control of the concentrations of nitrate and other redox-sensitive species; in particular, significant denitrification was observed restrictedly near oxbow lakes. The results of this study indicate that sub-oxic conditions in an alluvial groundwater system are developed geologically and geochemically in and near oxbow lakes, which can effectively enhance the natural attenuation of nitrate before the groundwater discharges to nearby streams. This study also demonstrates the usefulness of multivariate statistical analysis in groundwater study as a supplementary tool for interpretation of complex hydrochemical data sets. [Copyright &y& Elsevier]