Hydrogeochemistry and isotope geochemistry of Velenje Basin groundwater

Abstract

The geochemical and isotopic composition of groundwater in the Velenje Basin, Slovenia, was investigated between the years 2014 to 2015 to identify the geochemical processes in the major aquifers (Pliocene and Triassic) and the water-rock interactions. Thirty-eight samples of groundwater were taken from the aquifers, 19 in the mine and 19 from the surface. Groundwater in the Triassic aquifer is dominated by HCO , and Si, and has high alkalinity, with δ 13C DIC values in the range of -14.4 to +4.6 ‰. Based on the δ 13C DIC values in all the aquifers (Pliocene and Triassic), both processes influence the dissolution of carbonate minerals and dissolution of organic matter and in the Pliocene aquifers, methanogenesis as well. Based on Principal Component Analysis (PCA), and on geochemical and isotopic data we conclude that the following types of groundwater in Velenje Basin are present: Triassic aquifers with higher pH and lower conductivity and chloride, Pliocene, Pliocene 1 and Pliocene 2 aquifers with lower pH and higher conductivity and chloride contents, and Pliocene 3 and Pliocene 2, 3 aquifers with the highest pH values and lowest conductivities and chloride contents.

The effect of geochemical processes on groundwater in the Velenje coal basin, Slovenia: insights from mineralogy, trace elements and isotopes signatures

“…To date, Giammanco et al [50] investigated the interactions between gas-water-rock in shallow aquifers in the Šaleška valley and used multivariate PCA to determine different geochemical processes affecting groundwater quality. Later, Kanduč et al [40] performed a geochemical, isotopic characterization of surface waters and deep groundwater in aquifers dewatering Pliocene and Triassic strata. They found that in the Triassic aquifer HCO 3 − , Ca 2+ and Mg 2+ ions prevail and groundwater δ 18 O and δ 2 H values are close to those of surface waters when plotted on the meteoric global meteoric line and that the 3 H data indicate recent recharge.…”

“…Temperature, pH, dissolved oxygen (DO) and electrical conductivity were measured with Multiset 3430 (WTW) in the field and are reported in [40]. For trace elements, all sampling bottles were pre-cleaned with 10% HCl and washed with ultra-pure distilled water.…”

“…Major ion chemistry of Velenje basin groundwater was published in [40,46]. Additional surface water was analyzed for As in 2018 as part of this study.…”

“…Groundwater in the Pliocene aquifer has dissolved oxygen (DO) concentrations (1.0 to 6.92 mg/l), while groundwater in the Triassic aquifer contains higher DO (2.95 to 7.50 mg/l) and is suboxic [40]. The SO 4 2− and NO 3 − concentrations in the Pliocene aquifer were < 0.27 and 0.29 mM, respectively, compared to surface waters and Triassic aquifer waters [40]. These values are consistent with bacterial sulfate reduction and methanogenic redox conditions [71,72].…”

Chemical and isotopic composition of CO2-rich magnesium–sodium–bicarbonate–sulphate-type mineral waters from volcanoclastic aquifer in Rogaška Slatina, Slovenia

“…The ratio of 0.71942 ± 0.00026 is a result of silicate weathering. Moreover, groundwaters from a coal mine in Velenje were investigated; outflowing from the Pliocene clastic aquifer have Sr ratio of 0.70820–0.71056, while from the Triassic carbonates 0.70808–0.70910 (Kanduč et al, 2016 ).…”