Lazareva, Olesya
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Lazareva, Olesya
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Lazareva, Olesya
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Lazareva, O.
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Item-typ:Veröffentlichung, Determination of arsenic concentration and distribution in the Floridan Aquifer SystemHere we report on the different sampling strategies for almost seven years of sampling rocks/sediments for the determination of As within the Intermediate Aquifer System (IAS) and upper Floridan Aquifer System (FAS), a very large and productive limestone aquifer spanning from Georgia into Florida. In the FAS, As contamination has become a recurring problem during aquifer storage and recovery (ASR), particularly in central and south Florida. To investigate these phenomena, samples from solid drill cores and rock cuttings were collected from the Hawthorn Group, Suwannee Limestone, Ocala Limestone and Avon Park Formation. Samples were taken along drill cores and rock cuttings (referred to as ‘interval’ samples) or from particular drill core sections and rock cuttings (referred to as ‘targeted’ samples) likely to contain elevated concentrations of As as indicated by the presence of pyrite, hydrous ferric oxide, organic matter, clay minerals, fracture surfaces, and high permeable (moldic) zones. Arsenic was present in all of the stratigraphic units at low concentrations, close to the global average for As in limestone of 2.6 mg/kg. The highest As concentration was 69 mg/kg. In all units, however, the average bulk As concentration in the targeted samples was substantially higher than that in the interval samples. Based on direct spot measurements by electron microprobe and indirect calculations, pyrite was identified as the main source of As in the FAS. Concentrations in pyrite ranged from less than 100 mg/kg to more than 11,000 mg/kg. Because pyrite is heterogeneously distributed, both vertically and horizontally in the sampled stratigraphic units, the same was observed for the distribution of As. However, As concentrations generally decreased with depth, i.e., highest As values in the Hawthorn Group and lowest As values in the Ocala Limestone and Avon Park Formation. Compared to pyrite, other trace minerals contained much less As. The average As concentrations of the two types of sample media (solid cores and rock cuttings) were quite similar. These results indicate that if simply the average bulk rock As concentration of a geologic unit is the desired outcome of an investigation, either interval or targeted sampling of rock cuttings, seems to be sufficient. This is particularly important when time and money are a factor. This approach could work equally well for any other trace element. Structural sedimentary information, such as fractures, etc., is likely lost, however, when sampling rock cuttings. Thus, if this information is required, solid core samples need to be collected by hollow core diamond drilling.Wissenschaftlicher ArtikelBand:111Heft:3449 451 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Evaluating Complex Hydrogeological Settings in a Constructed Wetland: An Isotopic/Chemical Mass Balance ApproachThe objective of this study was to investigate the hydrogeological conditions of an artificial wetland, with four possible sources of water: (1) ground water, (2) industrial waste water, (3) seepage from a water body to the north, and (4) seepage from a water body to the south. The wetland was designed to improve the quality of municipal effluent and industrial wastewater. To evaluate and separate the impact of wetland processes from those due to dilution with water from “clean” sources (i.e., rain water or ground water), a combined isotope/chemical mass-balance approach was employed. The δD, δ18O, and Na were monitored for 18 months. Based on the data, the variation of individual proportions of each water type in the wetland and monitor wells was calculated. The isotopic composition of water in the wetland varied throughout the study period changing along the wetland flow path. The wetland contained mainly wastewater (88%–100%) during normal operations; however, hurricanes and inconsistent pumping added low conductivity water directly and triggered enhanced groundwater inflow into the wetland of up to 78%. Finally, the composition of water in monitor wells was mostly groundwater dominated; however seepage from a water body to the north was detected.Wissenschaftlicher ArtikelBand:3164 41 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Understanding arsenic behavior in carbonate aquifers: Implications for aquifer storage and recovery (ASR)Geochemical reactive transport modeling was coupled to bench-scale leaching experiments to investigate and verify the mobilization of geogenic arsenic (As) under a range of redox conditions from an arsenic-rich pyrite bearing limestone aquifer. Modeling and experimental observations showed similar results and confirmed the following: (1) native groundwater and aquifer matrix, including pyrite, were in chemical equilibrium, thus preventing the release of As due to pyrite dissolution under ambient conditions; (2) mixing of oxygen- and nitrate-rich surface water with oxygen-depleted native groundwater changed the redox conditions and promoted the dissolution of pyrite, and (3) the behavior of As along a flow path was controlled by a complex series of interconnected reactions. This included the oxidative dissolution of pyrite and simultaneous sorption of As onto neo-formed hydrous ferric oxides (HFO), followed by the reductive dissolution of HFO and secondary release of adsorbed As under reducing conditions. Arsenic contamination of drinking water in these systems is thus controlled by the re-equilibration of the system to more reducing conditions rather than a purely oxidative process.Wissenschaftlicher ArtikelBand:5261 44 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Long-term performance of a constructed wetland/filter basin system treating wastewater, Central FloridaThis study investigated the efficiency of a constructed wetland/filter basin (CW/FB) treatment system to improve the chemical composition of waste and surface waters. The system was constructed in closed phosphate mines used for clay settling and sand tailings. Monitoring was carried out for 18 months to evaluate the CW/FB performance under a variety of climatic conditions. Water samples were taken bi-monthly. To evaluate possible groundwater input into and water leaking out of the wetland 6 monitor wells were installed along the flow path and sampled monthly. In order to estimate the change of water chemistry along the wetland flow path, water samples along a transect were taken during the dry and rainy seasons. The samples were analyzed for pH, T, oxidation–reduction potential (ORP), conductivity, total dissolved solids (TDS), dissolved oxygen (DO), Fe(II), H2S, major anions, major cations, arsenic, fecal and total coliform. The study showed the following changes in water quality between the input and output: (1) Substantial decrease of water temperature (up to 10 °C); (2) Significant change in pH from about 9 to 6.5–7; (3) Negative ORP confirming the reducing conditions of the treatment system; (4) Substantial increase of H2S (up to 1060 µg/L); (5) Reduction of As from 5 to <2 µg/L (mostly <0.5); (6) Substantial reduction of SO4, F, Cl, NO3, NO2, Br, Na, K, Ca, and Mg; (7) Reduction of fecal and total coliform from 30–730 and 1000–7000 to <2 and <100 count/100 mL, respectively. In general, the performance of the CW/FB treatment system showed great potential to improve the water quality of industrial and municipal wastewater. Despite significant seasonal variations with respect to temperature, rainfall and humidity, the chemical/microbiological composition of the wetland output remained relatively constant.Wissenschaftlicher ArtikelBand:269Heft:1-265 71 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Naturally occurring arsenic in the Miocene Hawthorn Group, southwestern Florida: Potential implication for phosphate miningTo understand the mineralogical association, concentration, and distribution of arsenic (As) in the Hawthorn Group, the chemical and mineralogical composition of 362 samples that were collected from 16 cores in southwestern Florida were examined in detail. In the study area, the Hawthorn Group consisted primarily of a basal carbonate unit (the Arcadia Formation) and an upper siliciclastic unit (The Peace River Formation). The Peace River Formation contains appreciable amounts of phosphate and is currently being exploited for phosphate ore. Samples were taken from cores of each formation at intervals of 7.5 m. In addition, to the interval samples, sections likely to have high As concentrations, such as zones with pyrite crystals, hydrous ferric oxides, green clays, and organic material, were collected and analyzed. Bulk As concentrations were determined by hydride generation-atomic fluorescence spectrometry (HG-AFS) after digestion with aqua regia (3:1 HCl and HNO3). The elements Fe, Al, Si, Mg, Ca, S, and P were measured on the same solutions by inductively coupled plasma optical emission spectrometry (ICP-OES). The identification of discrete minerals was aided by scanning electron microscopy (SEM) and chemical compositions within the sample matrix and in individual minerals were obtained by electron-probe microanalysis (EMPA). This detailed mineralogical and geochemical study demonstrated that: (1) As in the Hawthorn Group varied from formation to formation and was mostly concentrated in trace minerals, such as pyrite; (2) average As concentrations significantly changed from 8.8 mg/kg (σ = 8.6 mg/kg) in the Peace River Formation to 3.0 mg/kg (σ = 3.7 mg/kg) in the Tampa Member of the Arcadia Formation. Arsenic concentrations for all Hawthorn samples varied from 0.1 to 69.0 mg/kg; (3) pyrite, with one exception, occurred as framboids and was unevenly distributed throughout the Hawthorn Group; (4) pyrite framboids were located inside a francolite (carbonate fluorapatite) matrix with As concentrations as high as 3730 mg/kg and as a trace mineral in the sediment matrix concentrations varying from <1 to 8260 mg/kg; (5) hydrous ferric oxides (HFO) contained As concentrations as high as 540 mg/kg; (6) francolite, organic material, and clays contained substantially less As than pyrite; (7) thus, the release of As from pyrite could pose a potential problem for the phosphate industry.Wissenschaftlicher ArtikelBand:22Heft:551 44