Assessment of groundwater processes using censored data analysis incorporating non-detect chemical, physical, and biological data

McGrory, Ellen; Morrison, Liam

doi:10.1016/j.jconhyd.2020.103706

Cited by 9 publications

(9 citation statements)

References 45 publications

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“…Arsenic was detected at lower concentrations in dug wells with the maximum concentration reported at 3.7 µg L −1 in 2015, comparable to observations noted in a bedrock aquifer in Quebec, Canada where arsenic concentrations in shallow wells did not exceed 4.1 µg L −1 (Bondu et al 2017). Negligible arsenic concentrations were reported in dug wells as no anthropogenic contamination was noted in this area (McGrory et al 2020). Anthropogenic arsenic contamination (or surface contamination) would show higher arsenic concentrations in dug wells and would mask the positive correlation of arsenic and depth present in this study.…”

Section: Arsenic Geochemistry and Speciationsupporting

confidence: 75%

“…Charge balances were ≤ 10.0%; however, BH-27 (15.3%), DW-7 (15.5%) and BH-46 (12.1%) were higher with the absence of NO 3 not being measured accounting for this discrepancy based on previous work (McGrory et al 2020).…”

Section: Quality Controlmentioning

confidence: 73%

“…The more acidic nature of surface wells may reflect more surface weathering of the acidic soil. Previous work in this area has also identified that surface wells were contaminated with elevated nitrate arising from inorganic fertilisers (McGrory et al 2020). Generally, groundwaters were described as alkaline oxidising (or oxic-alkali) for boreholes and acidic oxidising (or oxic-acidic) groundwaters for the shallower dug wells (Fig.…”

Section: Physicochemical Parametersmentioning

confidence: 91%

“…Most residential homes in the area consist of one-off dwellings with a private well as their primary source of drinking water in addition to an on-site domestic wastewater treatment system (DWWTS). The surrounding area is primarily agricultural (pastures) with forestry to the north (McGrory et al 2020). The climate of the Ireland is generally mild and humid with changeable weather (temperate oceanic climate).…”

Section: Study Sitementioning

confidence: 99%

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

McGrory

Henry

Conroy

et al. 2021

Arch Environ Contam Toxicol

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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 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.

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Section: Arsenic Geochemistry and Speciationsupporting

confidence: 75%

Section: Quality Controlmentioning

confidence: 73%

Section: Physicochemical Parametersmentioning

confidence: 91%

Section: Study Sitementioning

confidence: 99%

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

McGrory

Henry

Conroy

et al. 2021

Arch Environ Contam Toxicol

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show abstract

“…Charge balances were generally within 10.5%; however, BH-27 (15.3%), DW-7 (15.5%), and BH-46 (12.1%) were higher with the absence of NO 3 not being measured accounting for this discrepancy based on previous work(McGrory et al 2020). …”

mentioning

confidence: 70%

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

McGrory

Henry

Conroy

et al. 2021

Preprint

Self Cite

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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.

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Application of geostatistical techniques in the assessment of groundwater contamination in the Afigya Kwabre District of Ghana

Agyemang

2022

Appl Water Sci

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Geostatistical techniques have been applied to successfully assess the groundwater quality in the Afigya Kwabre District of Ghana. Forty boreholes were sampled for physicochemical and bacteriological characteristics of the groundwater. Principal component analysis revealed that seven components contain 81.01% of the variation of the original variables. Factor 1 accounted for 31.34% of the total variance, factor 2 accounted for 10.97%, third and fourth factors explained 8.41% and 8.19%, the fifth factor showed 8.13% while the sixth and seventh components showed 7.76% and 6.21% variances, respectively. R-mode cluster analysis showed five clusters. Cluster 1 was made of Na+, Cl−, TH, SiO2, HCO3− and TDS. Cluster 2 and cluster 3 contained dissolved oxygen (DO), pH, K+ and F−, Br, respectively. Cluster 4 was made of PO43− and NO3−and Cluster 5 had Ca2+, Mg2+, Total. coli, Fecal. coli, SO42−, and salinity. Correlation analysis revealed a strong positive correlation between EC and TDS, Mg2+, Ca2+, Mn, Na+, TH, HCO3−; pH and Ca2+, HCO3−; Mg2+ and Ca2+, Na+, TH, HCO3−, Fe; Ca2+ and Na+, TH, HCO3−; Cu and PO43−; Mn and Na+; F− and SO42− as well as NO3− and PO43−. The study revealed the impact of both natural processes such as rock mineral weathering, ion exchange, and anthropogenic activities such as application of agrochemicals on farmlands and improper waste disposal on the geochemistry of the groundwater. Generally, the groundwater in the District has a low pH. However, it is generally suitable for domestic use with exception of a few samples with high Fe, F-, Pb concentrations and Escherichia coliform and fecal coliform contaminations. The study has shown that the geostatistical technique is useful in determining the state of water contamination, the extent of contamination, and possible source of contaminants, as well as presenting a guideline for effective groundwater resource management.

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Assessment of groundwater processes using censored data analysis incorporating non-detect chemical, physical, and biological data

Cited by 9 publications

References 45 publications

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

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

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

Application of geostatistical techniques in the assessment of groundwater contamination in the Afigya Kwabre District of Ghana

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