Soil gas measurements of radon (²²²Rn), CO₂, and hydrocarbon concentrations, as well as gamma-ray spectrometry, were conducted at two separate locations to estimate the measurement results for known locations of hydrocarbon accumulations in the subsurface and oil seepage on the surface. The aim of the study was to confirm the applicability of the method for identifying migration pathways (e.g., faults) and to detect possible seepages of hydrocarbons to the surface as well as to investigate possible health issue potential about the soil gas analysis results. Site A investigations were performed with a large number of sampling points to provide sufficient spatial coverage to capture the influence of subsurface lithologic variability as well as the influence of the migration pathway on the measured parameters. For the investigation of site B, sampling points were positioned to reflect the situation between the area above producing hydrocarbon fields and areas with no confirmed accumulation. The results presented show that it is possible to distinguish the near-surface lithology (gamma-ray spectrometry), characterize the migration pathway, and indicate the area of oil seepage at the surface. Areas above the known hydrocarbon accumulations generally have elevated radon concentrations and detectable heavier hydrocarbons with sporadic methane in soil gas, which contrasts with the lower radon levels and lack of detectable heavier hydrocarbons in soil gas in the area with no confirmed hydrocarbon accumulation in the subsurface.

Natural potential sources of nitrate contamination involve decaying of organic matter, bacterial production, atmospheric deposition, and soil N. The study presents the first results of nitrate distribution and migration through soil horizons of the Eutric Cambisols, one of the most common soils developed in the area of the Zagreb aquifer and situated in an area without potential anthropogenic sources of nitrate (first sanitary protection zone of the Velika Gorica well field). A total of 16 parameters of soil water and 16 parameters of soil were used to conduct statistical techniques and analyse associated factors within the soil zone. The results indicate that in the deepest soil horizon, nitrogen is present mostly as nitrate due to nitrification under aerobic conditions which promote stability and the potential for nitrate transport. It was found that nitrate concentrations are the result of soil N nitrification, caused by a NO₃⁻/Cl⁻ molar ratio higher than 1 and the absence of precipitation isotopic signature. The results also show that within the coarse-grained Eutric Cambisols N primarily migrates to deeper parts of unsaturated zone in the form of nitrate and nitrite.

Gamma-ray parameters are widely used to screen organic-rich intervals, yet the influence of lithofacies heterogeneity on the reliability of gamma-ray-based TOC predictions remains incompletely evaluated. This study aims to (1) assess the relationships between gamma-ray parameters and TOC, (2) evaluate how lithofacies heterogeneity influences predictive reliability, and (3) establish practical screening criteria for identifying organic-rich intervals in two Middle Miocene marine successions from the Croatian part of the Pannonian Basin System. Outcrop gamma-ray spectrometry measurements (K, U, Th) and dose rate (DR) were paired with co-located laboratory TOC analyses (Voćin n = 45; Podsused n = 96). Pearson correlation, multiple and simple linear regression, logistic regression for TOC ≥ 1 wt.%, and threshold analysis were applied to evaluate relationships between gamma-ray parameters and organic matter enrichment. U and DR show moderate positive relationships with TOC in both sections, whereas K and Th are not statistically significant predictors. Regression and threshold analyses identify U as the primary predictor of TOC and show more stable and systematic predictive behaviour in the homogeneous Podsused succession than in the heterogeneous Voćin section. The results indicate that lithofacies heterogeneity primarily influences predictive stability rather than the existence of TOC–gamma-ray relationships. The study demonstrates that lithofacies heterogeneity is an important factor influencing the reliability of gamma-ray-based TOC screening and provides a framework for assessing the suitability of uranium and dose-rate proxies in different sedimentary settings.

Deep saline aquifers in the eastern part of Drava Basin were screened for potential storage sites. The input dataset included three seismic volumes, a rather extensive set of old seismic sections and 71 wells. Out of all identified potential storage objects, only two sites were found to be situated in the favorable geological settings, meaning that the inspected wells drilled through structural traps had a seal at least 20 m thick which was intersected by only a few faults with rather limited displacement. Many more closed structures in the area were tested by exploration wells, but in all other wells, various problems were encountered, including inadequate reservoir properties, inadequate seal or inadequate depth of the identified trap. Analysis was highly affected by the insufficient quality and spatial distribution of the seismic input data, as well as in places with insufficient quality of input well datasets. An initial characterization of identified storage sites was performed, and their attributes were compared, with potential storage object B recognized as the one that should be further developed. However, given the depth and increased geothermal gradient of the potential storage object B, it is possible that it will be developed as a geothermal reservoir, and this brings forward the problem of concurrent subsurface use.