The geochemical and isotopic composition of surface waters and groundwater in the Velenje Basin, Slovenia, was investigated seasonally to determine the relationship between major aquifers and surface waters, water-rock reactions, relative ages of groundwater, and biogeochemical processes. Groundwater in the Triasic aquifer is dominated by HCO3-, Ca2+, Mg2+ and d13CDIC indicating degradation of soil organic matter and dissolution of carbonate minerals, similar to surface waters. In addition, groundwater in the Triassic aquifer has d18O and dD values that plot near surface waters on the local and global meteoric water lines and detectable tritium, likely reflecting recent (below 50 years) recharge. In contrast, groundwater in the Pliocene aquifers is enriched in Mg2+, Na+, Ca2+, K+ and Si and has high alkalinity and d13CDIC values, with low SO42- and NO3- concentrations. These waters have likely been influenced by sulfate reduction and microbial methanogenesis associated with coal seams and dissolution of feldspars and Mg-rich clay minerals. Pliocene aquifer waters are also depleted in 18O and 2H and have 3H concentrations near the detection limit, suggesting these waters are older, had a different recharge source, and have not mixed extensively with groundwater in the Triassic aquifer. Since in this paper the problem with detection limit of 3H method with detrmining age of groundwater - we have dead waters (which were determined in Velenje sedimentary basin) with lower detection limit. This data is important for dewatering, subsidence of sedimentary basin and engineering aspect.
COBISS.SI-ID: 27531303
Coal gas outbursts (especially CO2) present a high risk in mining of lignite in the Velenje Coal Mine, located in the Velenje Basin in the northern Slovenia. A programme of monitoring geochemical parameters was set up to help understand the behaviour of the coalbed gas distribution in advance of the working face using mass spectrometric methods to study its molecular and isotopic compositions and origins. Coalbed gas samples from four different exavation fields (G2/C and K.-130/A from the north and south Preloge mining area and K.-5/A and K. -50/C from the Pesje mining area), which were operational between the years 2010 and 2011 were investigated. The major gas components are CO2 and methane. Temporal changes in the chemical and isotopic composition of free seam gases were observed within boreholes as a function of the advancement of the working face. The study also revealed that at the distance of around 120 m from the working face, the influence of coal exploitation by the Velenuje Longwall Mining Method causes coalbed gas to migrate. At the distance of 70 m the lignite structure is crushed causing desorption of fixed CO2 from the coal. Differences in coalbed gas composition at the longwall panels which underlie the unmined area or under previoulsy mined area were found. A high CDMI (=CO2/(CO2+CH4)*100%) index with values up to 95.6% was typical for areas of pre-mined excavation fields (South Preloge K. -130/A) and Pesje area K -50/C fields (South Preloge K. -130/A and Pesje area K-50/C) up to 61.9 vol. % of CH4 was detected. The concentration measurements and isotopic studies revealed endogenic CO2 (including CO2 originating from dissolution of carbonates) with d13CCO2 values ranging from -7.0‰ to 5.5‰, microbial methane and CO2 with values ranging from -70.4‰ to -50‰ and from -11.0‰ to -7.0‰, respectively. Higher d13CCH4 values ranging from -50‰ to -19.8‰ could be attributed to so-called secondary processes influencing the d13CCH4 values, such as migration due to lignite excavation (escape of isotopically lighter methane). In excavation fields (G2/C and K. -50/C) with no premining activity higher d13CCH4 value could also be explained by migration of methane from deeper strata. The d13CCH4 value also depend on the depth of the excavation field; at shallower levels of excavation field (K. 5/A) a lower d13CCH4 value was traced indicating microbial gas, while at deeper levels higher d13CCH4 values were found. Similar methods will be used to desipher composition, gas origin at active mining areas (dynamic mining system) in the scope of this applied project.
COBISS.SI-ID: 27862823
Since the first software that has been documented in detail and widely accessible to all engineers in the world, the PLASM, and until recently the mainstream in matematical modelling of underground water have been clearly the finite difference and finite elements methods. In 1988 the MODFLOW software package appered and due to a soft estimation nowdays some 10 000 engineers are using this software package. Besides the fact that other methods have only been used in scientific circles and that no other software gained such popularity as MODFLOW did, all of those have been based on the method of finite difference or finite elements. In the early 2013 the USGS (United States Geological Survey) website published the world premiere of MODFLOW USG. The abbrevation USG is for unstructred grid what represents a new approach in mathematical modelling of underground water. The reaction of GUI (graphical user interface) software developers was rapid and the new version of Groundwater Vistas (ver. 6) implemented this software package. In this paper, the basic characteristics of MODFLOW USG software package that tends to set new standards in groundwater modelling are presented.
COBISS.SI-ID: 1506143