scholarly journals Occurrence, Geochemistry and Speciation of Elevated Arsenic Concentrations in a Fractured Bedrock Aquifer System

2021 ◽  
Author(s):  
Ellen McGrory ◽  
Tiernan Henry ◽  
Peter Conroy ◽  
Liam Morrison
Keyword(s):  
Solid Phase ◽  
Arsenic Speciation ◽  
Eastern United States ◽  
Aquifer System ◽  
Fractured Bedrock ◽  
North Eastern ◽  
Major Controlling Factor ◽  
Fe Oxyhydroxides ◽  
Geologic Setting ◽  
Bedrock Aquifer

Abstract The presence of elevated arsenic concentrations (≥10 µg L-1) in groundwaters has been widely reported in areas of south east Asia with recent studies showing its detection in fractured bedrock aquifers mainly in regions of north-eastern United States. Data within Europe remains limited; therefore, the objective of this work was to understand the geochemical mobilisation mechanism of arsenic in this geologic setting. Physiochemical (pH, Eh, d-O2), trace metals, major ion and arsenic speciation samples were collected and analysed using a variety of field and laboratory-based techniques and evaluated using statistical analysis including multivariate analysis. Elevated dissolved arsenic concentrations (up to 73.95 µg L-1) were observed in oxic-alkali groundwaters with the co-occurrence of other oxyanions (e.g. Mo, Se, Sb and U), low dissolved concentrations of Fe and Mn and low Na/Ca ratios indicating that arsenic was mobilised through alkali desorption of Fe oxyhydroxides. Arsenic speciation using a solid-phase extraction methodology (n=20) showed that the dominant species of arsenic present in groundwater was arsenate, with pH being a major controlling factor. The expected source of arsenic is sulfide minerals within fractures of the bedrock aquifer with transportation of arsenic and other oxyanion-forming elements facilitated by secondary Fe mineral phases. However, the presence of methylarsenical compounds detected in the groundwaters illustrates that microbially mediated mobilisation processes were also (co)-occurring. This study demonstrates how field speciation of arsenic can be utilised to overcome analytical limitations of conventional laboratory speciation and to facilitate in the interpretation of the environmental mobility of arsenic within groundwaters.

scholarly journals Occurrence, Geochemistry and Speciation of Elevated Arsenic Concentrations in a Fractured Bedrock Aquifer System

2021 ◽  
Vol 81 (3) ◽  
pp. 414-437
Author(s):  
Ellen McGrory ◽  
Tiernan Henry ◽  
Peter Conroy ◽  
Liam Morrison
Keyword(s):  
Solid Phase ◽  
Groundwater Resources ◽  
Arsenic Speciation ◽  
Aquifer System ◽  
Fractured Bedrock ◽  
North Eastern ◽  
Eastern Usa ◽  
Major Controlling Factor ◽  
Geologic Setting ◽  
Bedrock Aquifer

AbstractThe presence of elevated arsenic concentrations (≥ 10 µg L−1) in groundwaters has been widely reported in areas of South-East Asia with recent studies showing its detection in fractured bedrock aquifers is occurring mainly in regions of north-eastern USA. However, data within Europe remain limited; therefore, the objective of this work was to understand the geochemical mobilisation mechanism of arsenic in this geologic setting using a study site in Ireland as a case study. Physicochemical (pH, Eh, d-O2), trace metals, major ion and arsenic speciation samples were collected and analysed using a variety of field and laboratory-based techniques and evaluated using statistical analysis. Groundwaters containing elevated dissolved arsenic concentrations (up to 73.95 µg L−1) were characterised as oxic-alkali groundwaters with the co-occurrence of other oxyanions (including Mo, Se, Sb and U), low dissolved concentrations of Fe and Mn, and low Na/Ca ratios indicated that arsenic was mobilised through alkali desorption of Fe oxyhydroxides. Arsenic speciation using a solid-phase extraction methodology (n = 20) showed that the dominant species of arsenic was arsenate, with pH being a major controlling factor. The expected source of arsenic is sulphide minerals within fractures of the bedrock aquifer with transportation of arsenic and other oxyanion forming elements facilitated by secondary Fe mineral phases. However, the presence of methylarsenical compounds detected in groundwaters illustrates that microbially mediated mobilisation processes may also be (co)-occurring. This study gives insight into the geochemistry of arsenic mobilisation that can be used to further guide research needs in this area for the protection of groundwater resources.

Multi-scale hydrogeologic characterization of a leaky till–mantled fractured bedrock aquifer system

2015 ◽  
Vol 52 (12) ◽  
pp. 1945-1955 ◽  
Author(s):  
William G. Lukas ◽  
Don J. DeGroot ◽  
David W. Ostendorf ◽  
Erich S. Hinlein
Keyword(s):  
Hydraulic Conductivity ◽  
Coarse Grained ◽  
Small Scale ◽  
Data Sets ◽  
Aquifer System ◽  
Monitoring Wells ◽  
Fractured Bedrock ◽  
Decadal Scale ◽  
Fractured Bedrock Aquifer ◽  
Bedrock Aquifer

The paper presents hydrogeologic properties for a leaky till–mantled fractured bedrock aquifer system based on geophysical and hydraulic tests performed at a drumlin located in northeastern Massachusetts, USA. The site profile consists of a fractured bedrock aquifer overlain by a 30 m thick unweathered, coarse-grained till aquitard. Steady state, decadal scale, hydraulics varied little until seasonal irrigation pumping was initiated in recent years, causing a substantial annual drawdown in the aquifer and leakage from the overlying till. High frequency hydraulic head data sets collected in monitoring wells record the hydraulic response to the irrigation pumping. These data sets, together with results from small scale slug and purge tests performed in monitoring wells, are used to characterize the hydrogeologic behavior of this groundwater system. Geophysical logging performed in bedrock wells confirmed the presence of numerous flowing fractures. The large-scale continuum analysis of the fractured bedrock aquifer response to the irrigation pumping yields transmissivity values consistent with those determined from the small-scale, short-term purge test results. The low hydraulic conductivity till has a significant impact on the drawdown behavior of the fractured bedrock aquifer. Calibrated values from the collective data sets and analyses result in the following properties for the 30 m thick unweathered till: hydraulic conductivity K′ = 7.2 × 10−9 m/s, transmissivity T′ = 2.3 × 10−8 m2/s, and storativity S′ = 2.7 × 10−4, and for the underlying fractured bedrock aquifer: T = 6.5 × 10−6 m2/s with an average fracture aperture of 46 μm and hydraulic conductivity Kf = 1.3 × 10−3 m/s. These results should describe similar unweathered coarse-grained till–mantled fractured bedrock aquifer systems and provide useful data for preliminary analyses prior to any site-specific investigations.

Hydrogeochemical and isotopic evaluation of VOC commingled plumes in a weathered fractured bedrock aquifer treated with thermal and bioremediation

2022 ◽  
pp. 103940
Author(s):  
SashaT. Hart ◽  
Reginaldo A. Bertolo ◽  
Maria S. Agostini ◽  
Roland Feig ◽  
Paulo Lojkasek-Lima ◽  
...  
Keyword(s):  
Fractured Bedrock ◽  
Fractured Bedrock Aquifer ◽  
Bedrock Aquifer

scholarly journals Kherzet Youcef Mine Flooding of 2nd June 1990 Revisited (Northeastern of Algeria) Origine and Hydrogeological Consequences

2021 ◽  
Author(s):  
CHEDDAD Souhila ◽  
Haouchine Abdelhamid
Keyword(s):  
Aquifer System ◽  
Ore Bodies ◽  
Lead And Zinc ◽  
Hydrogeological Study ◽  
Zn Content ◽  
North Eastern ◽  
Mine Flooding ◽  
Hydrogeological Studies ◽  
Eastern Algeria ◽  
And Storage

Abstract This work is part of the hydrogeological study of the Kherzet Youcef deposit. The polymetallic deposit of Kherzet Youcef, known, since the beginning of the 20th century, by the exploitation of Lead and Zinc ore, is located 50 Km southeast of Setif (North-eastern Algeria) and 5.5 Km west of Ain Azel. Mineralization is represented by some ore bodies (about 25). The thickness variate from a few centimeters up to 3m. These bodies are located on the layers of dolomites and dolomitized marls and along the Kherzet Youcef fault. The geological reserves of Zinc and Lead ore are of the order of 1.6 million tons. This ore has a Pb content of 3.6% and Zn content of 18.4%. The projected annual exploitation was 100 thousand tons per year. Hydrogeological studies carried out successively (1973-1977) and (1981-1983) revealed the existence of an aquifer system located west of the Kherzet Youssef fault characterized by the presence of Karts and by strong cracking due to local brittle tectonics. These two characteristics define the filtration and storage capacity of very abundant groundwater. This groundwater represented a major handicap for mining in view of the large amounts of water that required the installation of major pumping and drainage devices. The Kherzet Youssef mine has experienced frequent flooding in the past at a time when technology could not pump efficiently. It caused the mine to close several times. In June 1990, the mine experienced a flood of great magnitude that has never been observed and despite the large installed means of pumping, this "water cost" led to the total drowning of the mine, the death of 19 workers and the stoppage of the exploitation of this deposit since. Pitting attempts were carried out with a pumping capacity of 1100 m3/h, then 1800 m3/h but without success. The interpretation of the drawdown data and field observations made it possible to conclude that this accident was only the result of the general destabilization of the massif. Our complementary work by geophysical prospecting made it possible to represent the configuration of the underground layers and demonstrate the hydrodynamic communication between the two East and West compartments of the deposit.

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