Supplementary Paper S1 Electrical Resistivity Tomography (ERT) profiles. Supplementary Paper S2 Details of well construction. Supplementary Paper S3 Groundwater major physico-chemical parameters, ion concentrations and charge balance error (CBE%). All cations analysed by ICP-AES except for Mg 2+ in the first 3 samplings analysed by ICP-MS. Supplementary Paper S4 Groundwater and surface water information with well location, screened interval and abbreviated water type. Supplementary Paper S5 Selected groundwater minor and trace element concentrations. Al, Mn and Fe analysed by ICP-AES, the rest of elements by ICP_MS. BDL (bellow detection limit); no data represent not analysed elements. Supplementary Paper S6 Groundwater dissolved organic carbon (DOC), stable isotopes (δ 13 C DOC , δ 13 C DIC , water δ 18 O and δ 2 H, sulfate δ 34 S and δ 18 O), calculated deuterium excess (d-excess), 87 Sr/ 86 Sr and tritium ( 3 H). Note 3 H is reported in Bq L −1 (1 Bq L −1 = 8.47 TU). Supplementary Paper S7 Water stable isotopes for leachate samples from Harrington's Quarry. The d is the calculated deuterium excess for the corresponding samples. Supplementary Paper S8 Calculated saturation indexes for common mineral phases in LFLS groundwater.
Gypsum rocks are widely exploited in the world as industrial minerals. The purity of the gypsum rocks (percentage in gypsum mineral in the whole rock) is a critical factor to evaluate the potential exploitability of a gypsum deposit. It is considered than purities higher than 80% in gypsum are required to be economically profitable. Gypsum deposits have been studied with geoelectrical methods; a direct relationship between the electrical resistivity values of the gypsum rocks and its lithological composition has been established, with the presence of lutites being the main controlling factor in the geoelectrical response of the deposit. This phenomenon has been quantified in the present study, by means of a combination of theoretical calculations, laboratory measurements and field data acquisition. Direct modelling has been performed; the data have been inverted to obtain the mean electrical resistivity of the models. The laboratory measurements have been obtained from artificial gypsum-clay mixture pills, and the electrical resistivity has been measured using a simple electrical circuit with direct current power supply. Finally, electrical resistivity tomography data have been acquired in different evaporite Tertiary basins located in North East Spain; the selected gypsum deposits have different gypsum compositions. The geoelectrical response of gypsum rocks has been determined by comparing the resistivity values obtained from theoretical models, laboratory tests and field
Sulphate rocks have a sedimentary evaporitic origin and are present in many deposits worldwide. Among them, gypsum (dihydrated calcium sulphate) is the most common and is exploited for industrial purposes. Anhydrite (calcium sulphate) is frequently found in gypsum quarries and in non-outcropping sulphates. The greater hardness of anhydrite compared to gypsum causes a problem for gypsum extraction; quarry fronts have to be halted as soon as anhydrite is found. In this work the electrical properties of calcium sulphates have been studied by means of geoelectrical methods. A direct relationship between the electrical conductivity values of the calcium sulphate rocks and their lithological composition has been established with the lutitic matrix being the main controlling factor when it is well connected. When the matrix is under the percolation threshold the sulphate phases are dominant, and the electrical response of the rocks depends on the percentage of each phase. When the rock is matrix dominant, the electrical resistivity trend fits with the Hashin-2nd revision Click here to view linked References 2 Shtrikman lower bound for multiphase systems (considering gypsum, anhydrite and matrix as the components). On the other hand, when the rock is calcium sulphate dominant the trend shows the one of the Hashin-Shtrikman upper bound. The reference electrical resistivity value of pure anhydrite rocks has been defined as 10 4 Ω.m and geoelectrical classification for calcium sulphate rocks has been elaborated. With this classification it is possible to differentiate between calcium sulphate rocks with different composition from their electrical resistivity value. This classification has been checked with field examples and calculating the theoretical resistivity value of thin section photographs with the program ELECFEM2D. The electrical behavior of calcium sulphate rocks is a good reference for other type of rocks with electrically differentiated components, and similar methods can be used to define their geoelectrical responses.
Abstract. Evaluating the possibility of leakage through low permeability geological strata is critically important for sustainable water supplies, extraction of fuels from strata such as coal beds, and confinement of waste within the earth. Characterizing low or negligible flow rates and transport of solutes can require impractically long periods of field or laboratory testing, but is necessary for evaluations over regional areas and over multi-decadal timescales. The current work reports a custom designed centrifuge permeameter (CP) system, which can provide relatively rapid and reliable hydraulic conductivity (K) measurement compared to column permeameter tests at standard gravity (1g). Linear fluid velocity through a low K porous sample is linearly related to g-level during a CP flight unless consolidation or geochemical reactions occur. The CP module is designed to fit within a standard 2 m diameter, geotechnical centrifuge with a capacity for sample dimensions of 30 to 100 mm diameter and 30 to 200 mm in length. At maximum RPM the resultant centrifugal force is equivalent to 550g at base of sample or a total stress of ~2 MPa. K is calculated by measuring influent and effluent volumes. A custom designed mounting system allows minimal disturbance of drill core samples and a centrifugal force that represents realistic in situ stress conditions is applied. Formation fluids were used as influent to limit any shrink-swell phenomena which may alter the resultant K value. Vertical hydraulic conductivity (Kv) results from CP testing of core from the sites in the same clayey silt formation varied (10−7 to 10−9 m s−1, n = 14) but higher than 1g column permeameter tests of adjacent core using deionized water (10−9 to 10−11 m s−1, n = 7). Results at one site were similar to in situ Kv values (3 × 10−9 m s−1) from pore pressure responses within a 30 m clayey sequence in a homogenous area of the formation. Kv sensitivity to sample heterogeneity was observed, and anomalous flow via preferential pathways could be readily identified. Results demonstrate the utility of centrifuge testing for measuring minimum K values that can contribute to assessments of geological formations at large scale. The importance of using realistic stress conditions and influent geochemistry during hydraulic testing is also demonstrated.
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