Combining boron isotopes and carbamazepine to trace sewage in salinized groundwater: A case study in Cap Bon,Tunisia

The Korba aquifer on the east coast of Cape Bon has been overexploited since the 1960s with a resultant reversal of the hydraulic gradient and a degradation of the quality due to seawater intrusion. In 2008 the authorities introduced integrated water resources planning based on a managed aquifer recharge with treated wastewater. Water quality monitoring was implemented in order to determine the different system components and trace the effectiveness of the artificial recharge. Groundwater samples taken from recharge control piezometers and surrounding farm wells were analyzed for their chemical contents, for their B isotopes, a proven tracer of groundwater salinization and domestic sewage, and their carbamazepine content, an anti-epileptic known to pass through wastewater treatment and so recognized as a pertinent tracer of wastewater contamination. The system equilibrium was permanently disturbed by the different temporal dynamics of continuous processes such as cation exchange, and by threshold processes linked to oxidation–reduction conditions. The B isotopic compositions significantly shifted back-and-forth due to mixing with end-members of various origin. Under the variable contribution of meteoric recharge, the Plio-Quaternary groundwater (δ¹¹B of 35–40.6‰, a mean B concentration of 30 μmol/L, no carbamazepine, n = 7) was subject to seawater intrusion that induced a high δ¹¹B level (δ¹¹B of 41.5–48.0‰, a mean B concentration of 36 μmol/L, and n = 8). Fresh groundwater (δ¹¹B of 19.89‰, B concentration of 2.8 μmol/L, no carbamazepine) was detected close to the recharge site and may represent the deep Miocene pole which feeds the upper Plio-Quaternary aquifer. The managed recharge water (δ¹¹B of 10.67–13.8‰, n = 3) was brackish and of poor quality with a carbamazepine content showing a large short term variability with an average daily level of 328 ± 61 ng/L. A few piezometers in the vicinity of the recharge site gradually acquired a B isotopic composition close to the wastewater signature and showed an increasing carbamazepine content (from 20 to 910 ng/L). The combination of B isotopic signatures with B and carbamazepine contents is a useful tool to assess sources and mixing of treated wastewaters in groundwaters. Effluent quality needs to be greatly improved before injection to prevent further degradation of groundwater quality.     

Naturally occurring arsenic: Mobilization at a landfill in Maine and implications for remediation

Elevated levels of dissolved arsenic (∼300 μg L⁻¹) have been detected beneath and in groundwater plumes extending away from a closed landfill in southern Maine. This study sought to determine the source of arsenic to the aquifer, the processes responsible for arsenic mobilization, and to evaluate the effectiveness of remediation efforts that have occurred at this site. The As appears to originate in the natural (glacial) aquifer solids, which contain ∼5 mg kg⁻¹ As on a dry weight basis. This conclusion is supported by the relatively uniform distribution of As in sediment samples, results of laboratory batch incubation experiments, and comparisons with groundwaters in nearby wetlands, which also have high levels of dissolved As that do not appear to originate within the landfill. The As is mobilized in the subsurface by strongly reducing conditions beneath the landfill and in nearby wetlands. In the aquifer beneath the landfill, the average oxidation–reduction potential (ORP) is −95 mV (Eh + 105 mV), and these reducing conditions were primarily induced by landfill leachate. Remediation efforts at this site have included installation of a low permeability clay cap; groundwater extraction, oxidation, and re-injection; and subsurface oxidation by injection of magnesium peroxide. The natural source of arsenic within the aquifer solids, coupled with widespread reducing conditions, has severely limited the effectiveness of these interventions on groundwater arsenic concentrations.     

Metal binding to dissolved organic matter and adsorption to ferrihydrite in shallow peat groundwaters: Application to diamond exploration in the James Bay Lowlands,Canada

The speciation and solubility of kimberlite pathfinder metals (Ni, Nd, Ba and K) in shallow peat groundwaters is investigated over the Yankee, Zulu and Golf kimberlites in the Attawapiskat region, James Bay Lowlands, Canada. The purpose of this study is to examine the relationship between dissolved organic matter (DOM) complexation with kimberlite pathfinder metals and determine the spatial distribution of those metals in shallow peat groundwaters along sampling transects over subcropping kimberlites. Nickel, Nd, Ba and K complexation with DOM and the adsorption of these metals onto ferrihydrite were calculated using Visual MINTEQ 3.0 and the NICA-Donnan database. Calculations predict almost 100% of soluble Nd, Ni and Ba form complexes with DOM at sampling sites with little to no contribution from upwelling groundwater (i.e., dissolved organic C (DOC) concentrations = 40–132 mg/L, pH = 3.9–5.5, and log ionic strength ??3). In only the most ombrotrophic peat groundwater conditions does a majority fraction of K bind to DOM. By contrast, under conditions with large contributions from upwelling groundwaters (i.e., DOC concentrations ?40 mg/L, pH = 5.5–6.5, and log ionic strength = ?3 to ?2), as little as 10% of Nd and Ni, and 0% K and Ba are predicted to complex with DOM. The modeling calculations suggest the dominant control on metal–DOM complexation, particularly with respect to Ni and Nd, is competitive effects for DOM binding sites due to elevated ionic strength where there is evidence of strong groundwater upwelling. Visual MINTEQ modeling of metal adsorption on ferrihydrite surfaces predicts that under strong upwelling conditions, Ni and Nd are scavenged from solution due to increased ferrihydrite precipitation and decreased fractions of metals complexed with DOM. Analytical geochemical data are consistent with model predictions of metal adsorption on ferrihydrite. Total dissolved Ni and Nd concentrations at sites of strong upwelling are up to five times lower than waters with little to no upwelling and log ferrihydrite saturation indices (logSI_ferr) indicate precipitation (values up to 5) at sites of strong groundwater upwelling. Where the majority of Ni and Nd complex with DOM and ferrihydrite is highly under saturated (logSI_ferr = ?18 to ?5), the concentrations of total Ni and Nd are elevated compared to other sites along sampling transects. Metal complexation with DOM effectively inhibits metal scavenging from solution via adsorption and/or from forming secondary mineral precipitates. Also, because alkaline earth metals do not compete strongly with Ni and Nd for adsorption sites on ferrihydrite surfaces, but do compete strongly for insoluble organic sites, Ni and Nd are more likely to adsorb onto ferrihydrite.     

Fluoride dynamics in the granitic aquifer of the Wailapally watershed,Nalgonda District,India

High concentrations of fluoride (up to 7.6 mg/L) are a recognized feature of the Wailapally granitic aquifer of Nalgonda District, Andhra Pradesh, India. The basement rocks provide abundant sources of F in the form of amphibole, biotite, fluorite and apatite. The whole-rock concentrations of F in the aquifer are in the range 240–990 mg/kg. Calcretes from the shallow weathered horizons also contain comparably high concentrations of F (635–950 mg/kg). The concentrations of water-soluble F in the granitic rocks and the calcretes are usually low (1% of the total or less) but broadly correlate with the concentrations observed in groundwaters in the local vicinity. The water-soluble fraction of fluoride is relatively high in weathered calcretes compared to fresh calcretes.Groundwater major-ion composition shows a well-defined trend with flow downgradient in the Wailapally aquifer, from Na–Ca–HCO₃-dominated waters in the recharge area at the upper part of the catchment, through to Na–Mg–HCO₃ and ultimately to Na–HCO₃ and Na–HCO₃–Cl types in the discharge area in the lowest part. The evolution occurs over a reach spanning some 17 km. Groundwater chemistry evolves by silicate weathering reactions, although groundwaters rapidly reach equilibrium with carbonate minerals, favouring precipitation of calcite, and ultimately dolomite in the lower parts of the watershed. This precipitation is also aided by evapotranspiration. Decreasing Ca activity downgradient leads to a dominance of fluorite-undersaturated conditions and consequently to mobilisation of F. Despite the clear downgradient evolution of major-ion chemistry, concentrations of F remain relatively uniform in the fluorite-undersaturated groundwaters, most being in the range 3.0–7.6 mg/L. The rather narrow range is attributed to a mechanism of co-precipitation with and/or adsorption to calcrete in the lower sections of the aquifer. The model may find application in other high-F groundwaters from granitic aquifers of semi-arid regions.     

Volcanic degassing at Somma–Vesuvio (Italy) inferred by chemical and isotopic signatures of groundwater

A geochemical model is proposed for water evolution at Somma–Vesuvio, based on the chemical and isotopic composition of groundwaters, submarine gas emission and chemical composition of the dissolved gases. The active degassing processes, present in the highest part of the volcano edifice, strongly influence the groundwater evolution. The geological–volcanological setting of the volcano forces the waters infiltrating at Somma–Vesuvio caldera, enriched in volcanic gases, to flow towards the southern sector to an area of high pCO₂ groundwaters. Reaction path modelling applied to this conceptual model, involving gas–water–rock interaction, highlights an intense degassing process in the aquifer controlling the chemical and isotopic composition of dissolved gases, total dissolved inorganic C (TDIC) and submarine gas emission. Mapping of TDIC shows a unique area of high values situated SSE of Vesuvio volcano with an average TDIC value of 0.039 mol/L, i.e., one order of magnitude higher than groundwaters from other sectors of the volcano. On the basis of TDIC values, the amount of CO₂ transported by Vesuvio groundwaters was estimated at about 150 t/d. This estimate does not take into account the fraction of gas loss by degassing, however, it represents a relevant part of the CO₂ emitted in this quiescent period by the Vesuvio volcanic system, being of the same order of magnitude as the CO₂ diffusely degassed from the crater area.     

Groundwater fluxes into a submerged sinkhole area,Central Italy,using radon and water chemistry

The groundwater contribution into Green Lake and Black Lake (Vescovo Lakes Group), two cover collapse sinkholes in Pontina Plain (Central Italy), was estimated using water chemistry and a ²²²Rn budget. These data can constrain the interactions between sinkholes and deep seated fluid circulation, with a special focus on the possibility of the bedrock karst aquifer feeding the lake. The Rn budget accounted for all quantifiable surface and subsurface input and output fluxes including the flux across the sediment–water interface. The total value of groundwater discharge into Green Lake and Black Lake (∼540 ± 160 L s⁻¹) obtained from the Rn budget is lower than, but comparable with historical data on the springs group discharge estimated in the same period of the year (800 ± 90 L s⁻¹). Besides being an indirect test for the reliability of the Rn-budget “tool”, it confirms that both Green and Black Lake are effectively springs and not simply “water filled” sinkholes. New data on the water chemistry and the groundwater fluxes into the sinkhole area of Vescovo Lakes allows the assessment of the mechanism responsible for sinkhole formation in Pontina Plain and suggests the necessity of monitoring the changes of physical and chemical parameters of groundwater below the plain in order to mitigate the associated risk.     

Isotopic and geochemical identifications of groundwater salinisation processes in Salalah coastal plain,Sultanate of Oman

A detail investigation was carried out to improve the current knowledge of groundwater salinisation processes in coastal aquifers using hydrochemical and isotopic parameters. Data of major ions for 40 wells located in the Salalah plain aquifer, Sultanate of Oman, were collected during pre-monsoon 2004 and analysed. The groundwater changes along the general flow path towards the coast from fresh (EC < 1500 μS/cm), brackish (EC: 1500–3000 μS/cm) and saline (EC > 3000 μS/cm). Results of inverse modeling simulations using PHREEQC show that dissolution of halite may be the main source of Cl and Na in the study area. Ionic delta calculation indicates that the depletion of Na and K and enrichment of Ca and Mg in groundwater were probably attributed to reverse ion exchange reactions. During a sampling campaign conducted in October 2015, 11 groundwater samples were collected for Cl, Br and isotopic analysis (²H/¹⁸O). Molar Cl/Br ratios in fresh groundwater were higher than those of seawater, indicating the impact of halite dissolution on the groundwater quality. For saline groundwater, these ratios were less than those of seawater, showing the influence of anthropogenic input from agriculture on the same. Relatively depleted isotopic signature of all groundwater samples show that the monsoon precipitation is the main source of groundwater recharge in the study area.     

Arsenic-rich groundwater in an urban area experiencing drought and increasing population density,Perth, Australia

Groundwater in the Gwelup groundwater management area in Perth, Western Australia has been enriched in As due to the exposure of pyritic sediments caused by reduced rainfall, increased groundwater abstraction for irrigation and water supply, and prolonged dewatering carried out during urban construction activities. Groundwater near the watertable in a 25–60 m thick unconfined sandy aquifer has become acidic and has affected shallow wells used for garden irrigation. Arsenic concentrations up to 7000 μg/L were measured in shallow groundwater, triggering concerns about possible health effects if residents were to use water from household wells as a drinking water source. Deep production wells used for public water supply are not affected by acidity, but trends of progressively increasing concentrations of Fe, SO₄ and Ca over a 30-a period indicate that pyrite oxidation products extend to the base of the unconfined aquifer. Falling Eh values are triggering the release of As from the reduction of Fe(III) oxyhydroxide minerals near the base of the unconfined aquifer, increasing the risk that groundwater used as a drinking water source will also become contaminated with high concentrations of As.     

Joint use of TEM and MRS methods in a complex geological setting

Transient Electromagnetic (TEM), known also as Time Domain Electromagnetic (TDEM) and Magnetic Resonance Sounding (MRS) methods were applied jointly to investigate variations in lithology and groundwater salinity in the Nahal Hever South area (Dead Sea coast of Israel). The subsurface in this area is highly heterogeneous and composed of intercalated sand and clay layers over a salt formation, which is partly karstified. Groundwater is very saline, with a chloride concentration of 100–225 g/l. TEM is known as an efficient tool for investigating electrically conductive targets like saline water, but it is sensitive to both the salinity of groundwater and the porosity of rocks. MRS, however, is sensitive primarily to groundwater volume, but it also allows delineating of lithological variations in water-saturated formations. MRS is much less sensitive to variations in groundwater salinity in comparison with TEM. We show that MRS enables us to resolve the fundamental uncertainty in TEM interpretation caused by the equivalence between groundwater resistivity and lithology. Combining TEM and MRS, we found that the sandy Dead Sea aquifer filled with Dead Sea brine is characterized by a bulk resistivity of ρ_x > 0.4 Ωm, whereas zones with silt and clay in the subsurface are characterized by a bulk resistivity of ρ_x < 0.4 Ωm. These observations are confirmed by calibration of the TEM method performed near 18 boreholes.     

Geochemical and isotopic variations in shallow groundwater in areas of the Fayetteville Shale development,north-central Arkansas

Exploration of unconventional natural gas reservoirs such as impermeable shale basins through the use of horizontal drilling and hydraulic fracturing has changed the energy landscape in the USA providing a vast new energy source. The accelerated production of natural gas has triggered a debate concerning the safety and possible environmental impacts of these operations. This study investigates one of the critical aspects of the environmental effects; the possible degradation of water quality in shallow aquifers overlying producing shale formations. The geochemistry of domestic groundwater wells was investigated in aquifers overlying the Fayetteville Shale in north-central Arkansas, where approximately 4000 wells have been drilled since 2004 to extract unconventional natural gas. Monitoring was performed on 127 drinking water wells and the geochemistry of major ions, trace metals, CH₄ gas content and its C isotopes (δ¹³C_CH4), and select isotope tracers (δ¹¹B, ⁸⁷Sr/⁸⁶Sr, δ²H, δ¹⁸O, δ¹³C_DIC) compared to the composition of flowback-water samples directly from Fayetteville Shale gas wells. Dissolved CH₄ was detected in 63% of the drinking-water wells (32 of 51 samples), but only six wells exceeded concentrations of 0.5 mg CH₄/L. The δ¹³C_CH4 of dissolved CH₄ ranged from −42.3‰ to −74.7‰, with the most negative values characteristic of a biogenic source also associated with the highest observed CH₄ concentrations, with a possible minor contribution of trace amounts of thermogenic CH₄. The majority of these values are distinct from the reported thermogenic composition of the Fayetteville Shale gas (δ¹³C_CH4 = −35.4‰ to −41.9‰). Based on major element chemistry, four shallow groundwater types were identified: (1) low (<100 mg/L) total dissolved solids (TDS), (2) TDS > 100 mg/L and Ca–HCO₃ dominated, (3) TDS > 100 mg/L and Na–HCO₃ dominated, and (4) slightly saline groundwater with TDS > 100 mg/L and Cl > 20 mg/L with elevated Br/Cl ratios (>0.001). The Sr (⁸⁷Sr/⁸⁶Sr = 0.7097–0.7166), C (δ¹³C_DIC = −21.3‰ to −4.7‰), and B (δ¹¹B = 3.9–32.9‰) isotopes clearly reflect water–rock interactions within the aquifer rocks, while the stable O and H isotopic composition mimics the local meteoric water composition. Overall, there was a geochemical gradient from low-mineralized recharge water to more evolved Ca–HCO₃, and higher-mineralized Na–HCO₃ composition generated by a combination of carbonate dissolution, silicate weathering, and reverse base-exchange reactions. The chemical and isotopic compositions of the bulk shallow groundwater samples were distinct from the Na–Cl type Fayetteville flowback/produced waters (TDS ∼10,000–20,000 mg/L). Yet, the high Br/Cl variations in a small subset of saline shallow groundwater suggest that they were derived from dilution of saline water similar to the brine in the Fayetteville Shale. Nonetheless, no spatial relationship was found between CH₄ and salinity occurrences in shallow drinking water wells with proximity to shale-gas drilling sites. The integration of multiple geochemical and isotopic proxies shows no direct evidence of contamination in shallow drinking-water aquifers associated with natural gas extraction from the Fayetteville Shale.     

Temporal and geochemical evolution of the Cenozoic intraplate volcanism of Zealandia

In order to constrain better the distribution, age, geochemistry and origin of widespread Cenozoic intraplate volcanism on Zealandia, the New Zealand micro-continent, we report new ⁴⁰Ar/³⁹Ar and geochemical (major and trace element and Sr–Nd–Hf–Pb isotope) data from offshore (Chatham Rise, Campbell and Challenger Plateaus) and onland (North, South, Auckland, Campbell, Chatham and Antipodes Islands of New Zealand) volcanism on Zealandia. The samples include nephelinite, basanite through phonolite, alkali basalt through trachyte/rhyolite, and minor tholeiite and basaltic andesite, all of which have ocean island basalt (OIB)-type trace element signatures and which range in age from 64.8 to 0.17 Ma. Isotope ratios show a wide range in composition (⁸⁷Sr/⁸⁶Sr = 0.7027–0.7050, ¹⁴³Nd/¹⁴⁴Nd = 0.5128–0.5131, ¹⁷⁷Hf/¹⁷⁶Hf = 0.2829–0.2831, ²⁰⁶Pb/²⁰⁴Pb = 18.62–20.67, ²⁰⁷Pb/²⁰⁴Pb = 15.54–15.72 and ²⁰⁸Pb/²⁰⁴Pb = 38.27–40.34) with samples plotting between mid-ocean-ridge basalts (MORB) and Cretaceous New Zealand intraplate volcanic rocks.Major characteristics of Zealandia's Cenozoic volcanism include longevity, irregular distribution and lack of age progressions in the direction of plate motion, or indeed any systematic temporal or spatial geochemical variations. We believe that these characteristics can be best explained in the context of lithospheric detachment, which causes upwelling and melting of the upper asthenospheric mantle and portions of the removed lithosphere. We propose that a large-scale seismic low-velocity anomaly, that stretches from beneath West Antarctica to Zealandia at a depth of > 600 km may represent a geochemical reservoir that has been in existence since the Cretaceous, and has been supplying the upper mantle beneath Zealandia with HIMU-type plume material throughout the Cenozoic. In addition, the sources of the Cenozoic intraplate volcanism may be at least partially derived through melting of locally detached Zealandia lower lithosphere.     

Using dual isotopic data to track the sources and behaviors of dissolved sulfate in the western North China Plain

This paper investigated the sources and behaviors of sulfate in groundwater of the western North China Plain using sulfur and oxygen isotopic ratios. The groundwaters can be categorized into karst groundwater (KGW), coal mine drainage (CMD) and pore water (subsurface saturated water in interstices of unconsolidated sediment). Pore water in alluvial plain sediments could be further classified into unconfined groundwater (UGW) with depth of less than 30 m and confined groundwater (CGW) with depth of more than 60 m. The isotopic compositions of KGW varied from 9.3‰ to 11.3‰ for δ³⁴S_SO4 with the median value of 10.3‰ (n = 4) and 7.9‰ to 15.6‰ for δ¹⁸O_SO4 with the median value of 14.3‰ (n = 4) respectively, indicating gypsum dissolution in karst aquifers. δ³⁴S_SO4 and δ¹⁸O_SO4 values of sulfate in CMD ranged from 10.8‰ to 12.4‰ and 4.8‰ to 8.7‰ respectively. On the basis of groundwater flow path and geomorphological setting, the pore water samples were divided as three groups: (1) alluvial–proluvial fan (II₁) group with high sulfate concentration (median values of 2.37 mM and 1.95 mM for UGW and CGW, respectively) and positive δ³⁴S_SO4 and δ¹⁸O_SO4 values (median values of 8.8‰ and 6.9‰ for UGW, 12.0‰ and 8.0‰ for CGW); (2) proluvial slope (II₂) group with low sulfate concentration (median values of 1.56 mM and 0.84 mM for UGW and CGW, respectively) and similar δ³⁴S_SO4 and δ¹⁸O_SO4 values (median values of 9.0‰ and 7.4‰ for UGW, 10.2‰ and 7.7‰ for CGW); and (3) low-lying zone (II₃) group with moderate sulfate concentration (median values of 2.13 mM and 1.17 mM for UGW and CGW, respectively) and more positive δ³⁴S_SO4 and δ¹⁸O_SO4 values (median values of 10.7‰ and 7.7‰ for UGW, 20.1‰ and 8.8‰ for CGW). In the present study, three major sources of sulfate could be differentiated as following: sulfate dissolved from Ordovician to Permian rocks (δ³⁴S_SO4 = 10–35‰ and δ¹⁸O_SO4 = 7–20‰), soil sulfate (δ³⁴S_SO4 = 5.9‰ and δ¹⁸O_SO4 = 5.8‰) and sewage water (δ³⁴S_SO4 = 10.0‰ and δ¹⁸O_SO4 = 7.6‰). Kinetic fractionations of sulfur and oxygen isotopes as a result of bacterial sulfate reduction (BSR) were found to be evident in the confined aquifer in stagnant zone (II₃), and enrichment factors of sulfate–sulfur and sulfate–oxygen isotopes calculated by Rayleigh equation were −12.1‰ and −4.7‰ respectively along the flow direction of groundwater at depths of 60–100 m. The results obtained in this study confirm that detailed hydrogeological settings and identification of anthropogenic sources are critical for elucidating evolution of δ³⁴S_SO4 and δ¹⁸O_SO4 values along with groundwater flow path, and this work also provides a useful framework for understanding sulfur cycling in alluvial plain aquifers.     

Processes affecting groundwater chemistry in a zone of saline intrusion into an urban sandstone aquifer

Samples have been collected from inflows into railway tunnels in the Triassic sandstone aquifer beneath Liverpool and the Mersey Estuary, England, U.K. These provide a profile through a saline–freshwater mixing zone. Analyses were made of major anions and cations, δ³⁴S and δ¹⁸O in SO₄, δ¹³C in dissolved inorganic C and ⁸⁷Sr/⁸⁶Sr. The data demonstrate that the presence of a low permeability fault exerts a strong control on the local groundwater chemistry. On the estuary side of the fault, groundwater chemistry is dominated by mixing of intruding estuary water, which is modified by SO₄ reduction and calcite dissolution, with fresh groundwater. The environment of SO₄ reduction in the tidal estuary is one of repeated reduction and re-oxidation of S in an open system and has resulted in virtually no change in S isotopic composition, but an enrichment in residual SO₄ δ¹⁸O of 1.5‰. Groundwater chemistry on the landward side of the fault is primarily the result of recharge in an urban environment. There is also evidence that saline water has been present in this region of the aquifer in the past and that this has now been flushed by fresh groundwaters. This saline water was either transported along the landward side of the fault from nearer the estuary or more probably transmitted across the fault. Both mechanisms would have been driven by large landward head gradients caused by heavy industrial abstraction earlier this century. This has produced a zone of groundwaters depleted in Ca and radiogenic Sr and enriched in Na as a result of ion exchange between the fresh groundwaters and the aquifer previously occupied by more saline water. Sulphur isotopic composition, however, shows no variation since SO₄ does not undergo significant ion exchange. A tracer test from a borehole to the tunnels showed multiple breakthroughs to some locations indicating a number of different flow paths through the aquifer. The maximum flow velocity recorded in this test was 140 m/d suggesting flow along fractures.     

Groundwater flow system under a rapidly urbanizing coastal city as determined by hydrogeochemistry

In the Jakarta area (Indonesia), excessive groundwater pumping due to the rapidly increasing population has caused groundwater-related problems such as brackish water contamination in coastal areas and land subsidence. In this study, we adopted multiple hydrogeochemical techniques to demonstrate the groundwater flow system in the Jakarta area. Although almost all groundwater existing in the Jakarta basin is recharged at similar elevations, the water quality and residence time demonstrates a clear difference between the shallow and deep aquifers. Due to the rapid decrease in the groundwater potential in urban areas, we found that the seawater intrusion and the shallow and deep groundwaters are mixing, a conclusion confirmed by major ions, Br^?:Cl^? ratios, and chlorofluorocarbon (CFC)-12 analysis. Spring water and groundwater samples collected from the southern mountainside area show younger age characteristics with high concentrations of ¹⁴C and Ca–HCO₃ type water chemistry. We estimated the residence times of these groundwaters within 45 years under piston flow conditions by tritium analysis. Also, these groundwater ages can be limited to 20–30 years with piston flow evaluated by CFCs. Moreover, due to the magnitude of the CFC-12 concentration, we can use a pseudo age indicator in this field study, because we found a positive correlation between the major type of water chemistry and the CFC-12 concentration.     

A conceptual framework of groundwater flow in some crystalline aquifers in Southeastern Ghana

A conceptual groundwater flow model was developed for the crystalline aquifers in southeastern part of the Eastern region, Ghana. The objective was to determine approximate levels of groundwater recharge, estimate aquifer hydraulic parameters, and then test various scenarios of groundwater extraction under the current conditions of recharge. A steady state groundwater flow model has been calibrated against measured water levels of 19 wells in the area. The resulting recharge is estimated to range from 8.97 × 10^?5 m/d to 7.14 × 10^?4 m/d resulting in a basin wide average recharge of about 9.6% of total annual precipitation, which results in a basin wide quantitative recharge of about 2.4 million m³/d in the area. This compares to recharge estimated from the chloride mass balance of 7.6% of precipitation determined in this study. The general groundwater flow in the area has also been determined to conform to the general northeast–southwest structural grain of the country. The implication is that the general hydrogeology is controlled by post genetic structural entities imposed on the rocks to create ingresses for sufficient groundwater storage and transport. Calibrated aquifer hydraulic conductivities range between 0.99 m/d and over 19.4 m/d. There is a significant contribution of groundwater discharge to stream flow in the study area. Increasing groundwater extraction will have an effect on stream flow. This study finds that the current groundwater extraction levels represent only 0.17% of the annual recharge from precipitation, and that groundwater can sustain future increased groundwater demands from population growth and industrialization.     

Brachinite meteorites: Partial melt residues from an FeO-rich asteroid

Brachinites are ultramafic, dunitic to wherlitic, unbrecciated and essentially unshocked rocks that are low in SiO₂ (∼36–39 wt.%), high in MgO (∼27–30 wt.%) and notably high in FeO (∼26–37 wt.%), and low in Al₂O₃ (∼0.2–2.5 wt.%) and combined alkalis Na₂O and K₂O (∼0–0.7 wt.%). They consist mostly of olivine (∼71–96 vol.%; ∼Fo_64–73), major clinopyroxene (minor to ∼15 vol.%; ∼En_40–63Wo_36–48), with variable small amounts of plagioclase (0 to ∼10 vol.%; ∼An_15–33), and minor to trace amounts of orthopyroxene (none to ∼20 vol.%; En_69–73Wo_2–4), Fe-sulfides (trace to ∼7 vol.%), chromite (none to ∼5 vol.%), phosphates (none to ∼3 vol.%) and metallic Fe,Ni (trace to ∼2 vol.%). Minerals tend to be homogeneous, and textures are medium to coarse-grained (∼0.1–1.5 mm), with olivine commonly displaying triple junctions. Brachina has near-chondritic lithophile element abundances, whereas other brachinites show variable depletions in Al, Ca, Rb, K, Na, and LREE. Siderophile element abundance patterns vary and range from ∼0.01 to ∼0.9 CI. Oxygen isotope composition (Δ¹⁷O) ranges from ∼−0.09 to −0.39‰, with the mean = −0.23 ± 0.14‰. Brachinites are ancient rocks, as was recognized early by the detection, in some brachinites, of excess ¹²⁹Xe from the decay of short-lived ¹²⁹I (half-life 17 Ma) and of fission tracks from the decay of ²⁴⁴Pu (half-life 82 Ma) in phosphate, high-Ca clinopyroxene and olivine. The first precise crystallization age was determined for Brachina using ⁵³Mn–⁵³Cr systematics, relative to the Pb–Pb age of the angrite LEW 86010, and yielded an age of 4563.7 ± 0.9 Ma. Thus, Brachina is at most ∼4 Ma younger that the CAIs whose age is 4567.2 ± 0.6 Ma. There is no consensus on the origin of brachinites, but they most likely are primitive achondrites, i.e., ultra-mafic residues from various low degrees of partial melting. Partial melting experiments suggest that they possibly formed from a parent lithology chemically similar but not identical to the Rumuruti (R) chondrites, although the different oxygen isotopic compositions of the R chondrites and the brachinites put a serious constraint on this hypothesis. The apparent lack of abundant rocks representing the partial melts suggests that brachinites may have formed on a parent body <∼100 km in radius, where early partial melts were removed from the parent body by explosive pyroclastic volcanism. Graves Nunataks 06128 and 06129 are felsic, andesitic basalts which have properties that suggest a relationship to brachinites and thus, may be samples of the elusive partial melts.     

Is 222Rn a suitable tracer of stream–groundwater interactions? A case study in central Italy

River water infiltration into an unconfined porous aquifer (∼73% gravels, ∼12% sands, ∼15% silts and clays) in the Petrignano d’Assisi plain, central Italy, was traced combining isotopic techniques (²²²Rn) with hydrochemical and hydrogeologic techniques in order to characterize the system under study. The ²²²Rn gave information about the river water residence times within the aquifer and hydrochemical data, in a two-component mixing model, which allowed estimating the extent of mixing between surface waters and groundwater in wells at increasing distances from the river. The mixing measured in the well closer to the riverbank indicated a higher contribution of river water (up to 99%) during the groundwater recession phase and a moderate contribution (up to 64%) during the recharge phase. A model describing ²²²Rn concentrations in groundwater as the result of both parent/daughter nuclide equilibrium and mixing process (²²²Rn mixing/saturation model) was used to describe observed Rn concentrations and mixing index trends with the aim of evaluating water mean infiltration velocities along the transect. The stream bank infiltration velocities obtained by the model ranged from 1 m day⁻¹ during groundwater recharge periods, when river water infiltration is lower, to 39 m day⁻¹ during recession phases, when river water infiltration is larger.     

Study of the surface properties of enargite as a function of pH

The surface properties of enargite as a function of pH were investigated. The zeta potential values increased from − 10 mV (pH = 3) to − 45 mV (pH = 12) and no isoelectric point (iep) was detected. The zeta potential of enargite was highly sensitive to pH and interesting peaks/valleys, unusual in common sulfide minerals, were observed. In the present study, these results were interpreted on the basis of the chemistry of enargite, which is a tetra-thioasenate of Cu(I). A thermodynamic approach, including the Eh–pH diagram for enargite, and the hydrolysis diagrams for arsenic, thioarsenic, and oxo-thioarsenic acids was employed. An interpretation based on the simultaneous ionization and dissociation reactions of the hydrolysis products of arsenic and thioarsenic acids on the enargite surface was discussed. On the other hand, covellite (CuS), under low concentrations of arsenate ions, showed similar zeta potential peaks. Additionally, enargite's zeta potential showed sign reversal for a certain pH range, with the addition of low concentrations of Cu(I) and Cu(II) ions, suggesting that other hydrolysis and precipitation reactions may also be involved.     

Petrology and geochemistry of Abyssal Peridotites from the Manipur Ophiolite Complex,Indo-Myanmar Orogenic Belt,Northeast India: Implication for melt generation in mid-oceanic ridge environment

The Manipur Ophiolite Complex (MOC) located in the Indo-Myanmar Orogenic Belt (IMOB) of Northeast India forms a section of the Tethyan Ophiolite Belt of the Alpine–Himalayan orogenic system. Whole rock compositions and mineral chemistry of mantle peridotites from the MOC show an affinity to the abyssal peridotites, characterized by high contents of Al₂O₃ (1.28–3.30 anhydrous wt.%); low Cr# of Cr-spinel (0.11–0.27); low Mg# of olivine (∼Fo₉₀) and high Al₂O₃ in pyroxenes (3.71–6.35 wt.%). They have very low REE concentrations (∑REE = 0.48–2.14 ppb). Lherzolites display LREE-depleted patterns (La_N/Sm_N = 0.14–0.45) with a flat to slightly fractionated HREE segments (Sm_N/Yb_N = 0.30–0.65) whereas Cpx-harburgites have flat to upward-inflected LREE patterns (La_N/Sm_N = 0.13–1.23) with more fractionated HREE patterns (Sm_N/Yb_N = 0.13–0.65) than the lherzolite samples. Their platinum group elements (PGE) contents (<50 ppb) and distinct mantle-normalised PGE patterns with the Pd/Ir values (1.8–11.9) and Pt/Pt^* values (0.2–1.1) show an affinity to the characteristic of the residual mantle material. Evaluation of mineralogical and petrological characteristics of these peridotites suggests that they represent the residues remaining after low degree of partial melting (∼2–12%) in the spinel stability field of a mid-oceanic ridge environment. The well-preserved mid-oceanic ridge characteristics of these peridotites further suggest that the mantle section was subsequently trapped in the forearc region of the subduction zone without undergoing significant modification in their chemistry by later subduction-related tectonic and petrological processes before its emplacement to the present crustal level.     

Estuarine–fluvial floodplain formation in the Holocene Lower Tagus valley (Central Portugal) and implications for Quaternary fluvial system evolution

We present a brief synthesis of the Quaternary fluvial record in the Lower Tagus Basin (central Portugal), concentrating on factors controlling infill and incision. The Holocene part of the record forms the focus of this paper and guides the questioning of the basic assumptions of the established Quaternary fluvial evolution model, in particular the link between sea-level change and fluvial incision-deposition. We suggest that several incision-aggradation phases may have occurred during glacial periods. Major aggradation events may overlap with cold episodes, while incision appears to concentrate on the warming limb of climate transitions. The complex stratigraphy of the Quaternary record in the Lower Tagus valley is influenced by repeated base-level and climate changes.This paper submits the first chronostratigraphic framework for valley fill deposits in the Lower Tagus area. Sea-level rise forced aggradation and controlled deposition of the fine-grained sedimentary wedge underlying the low-gradient Lower Tagus floodplain. Investigations have focused on the lower Muge tributary, where rapidly aggrading estuarine and fluvial environments were abruptly established (∼8150 cal BP) as sea level rose. Base level at the valley mouth controlled the upstream extent of the fine-grained backfill. Tidal environments disappeared abruptly (∼5800 cal BP) when the open estuary at the Muge confluence was infilled by the Tagus River. The decrease and final still stand of sea-level rise led to floodplain stabilisation with peat (∼6400–5200 cal BP) and soil formation (∼5200–2200 cal BP). Localised renewed sedimentation (∼2200–200 cal BP) is linked to human activity.