Estimated hydraulic properties for the surficial-and bedrock-aquifer system, Meddybemps, Maine

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.

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Comprehensive Geohydrological Study of Consolidated Sedimentary Rocks in Bornholm

Hydrology Research ◽

10.2166/nh.1977.0010 ◽

1977 ◽

Vol 8 (2) ◽

pp. 117-128

Author(s):

Tage Sørensen ◽

Hans Ole Hansen

Keyword(s):

Groundwater Pollution ◽

Hydraulic Properties ◽

General Procedure ◽

Sedimentary Rocks ◽

Well Logging ◽

Pumping Test ◽

Test Evaluation ◽

Aquifer System ◽

Aquifer Systems

Problems and procedures conserning planning and execution of geohydrological investigations of aquifer systems composed of consolidated sedimentary rocks are discussed. The discussion is illustrated by investigations in an area on the island of Bornholm, Denmark, where the aquifer system is composed of inclined and faulted beds of sand-, silt-and claystone. The investigations includes the following elements:Hydrogeological mapping.Geophysical investigations and well-logging (gamma-, resistivity-, flow- and conductivity-log).Pumping-test Evaluation of hydraulic properties of the aquifers. Construction of mathematical model.Deliniation of infiltration areas and evaluation of potential infiltration. Protection against groundwater-pollution. The paper emphasises the general procedure for engineering geohydrological investigations of consolidated sedimentary rocks and the correlation of the information collected by different methods.

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

Archives of Environmental Contamination and Toxicology ◽

10.1007/s00244-021-00887-3 ◽

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.

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Characterizing Hydraulic Properties and Ground-Water Chemistry in Fractured-Rock Aquifers: A User's Manual for the Multifunction Bedrock-Aquifer Transportable Testing Tool (BAT3)

Open-File Report ◽

10.3133/ofr20071134 ◽

2007 ◽

Cited By ~ 1

Author(s):

Allen M. Shapiro

Keyword(s):

Water Chemistry ◽

Ground Water ◽

Hydraulic Properties ◽

Fractured Rock ◽

Testing Tool ◽

Fractured Rock Aquifers ◽

Bedrock Aquifer

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

10.21203/rs.3.rs-381091/v1 ◽

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.

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