This study reports a synthesis of years-long hydrogeochemical monitoring in northern West Siberia, performed by the Russian Meteorological Service (Rosgidromet) and several academic institutions. Natural factors and intensive human economic activity lead to the disruption of the ecosystems of the northern territories of Western Siberia. The aim of this study is to estimate the background water chemistry parameters in the rivers of northern West Siberia in the beginning of the 21st century. The mean values hydrochemical and geochemical indicators were determined with STATISTICA software, which can be used as background values in assessing the actual and allowable anthropogenic impact on water bodies. We revealed four water chemistry provinces: western Ob Gulf and Ob estuary catchments (I); eastern Ob Gulf and Taz Gulf catchments, except for the Taz River and its tributaries (II); Taz River catchments (III); Yenisei River catchments, right bank (IV). The major-ion chemistry of the sampled river waters records a combination of geological, geomorphological, and hydrological conditions in the four provinces. The features typical of the northern West Siberian Plain are especially prominent in province II, which has the lowest average total of major ions (Σ_mi), the highest chemical oxygen demand (potassium dichromate COD), and the highest contents of Fe and phosphates. The Σ_mi value is the highest in province IV. The river waters from four provinces share similarity in quite high organic contents (both potassium dichromate and permanganate COD), as well as high NH₄⁺ and Fe. The long-term average Σ_mi of the waters is predicted not to change much in the coming one or two decades, though it may decrease slightly in the winter season but increase in the fall and spring time.

The study was focused on groundwaters sampled from boreholes drilled to deep horizons of the Udachnaya kimberlite pipe and the host sedimentary strata. Brines in the rocks significantly complicate underground mining. Analysis of the hydrogeological setting is required to ensure safety during mining to the design levels. The features of chemical composition and the geochemical evolution of brines in the crust can be clarified in a more detail on the basis of new reliable data on strong chloride saline solutions that formed in complex geological and tectonic conditions. Kimberlite and water samples were taken from the ore bodies and host sedimentary strata at the depth of 680–980 m. Conventional methods of quantitative and instrumental analysis were applied to study the chemical composition of brines. Mineral composition of kimberlite was determined by powder diffractography and X-ray fluorescence methods. Geological, structural and tectonophysical methods were used to reveal and describe the tectonic structure of the kimberlite pipe area. Groundwaters with salinity of 280–406 g/L are strong and very strong calcium chloride brines. The chlorine-bromine ratio has a small range of 48–57; the sodium-chlorine ratio varies from 0.11 to 0.18. According to their geochemical features, the studied groundwaters are metamorphosed brines that have analogues across the Siberian platform. Physical and chemical processes were simulated to investigate the degrees of saturation of strong brines relative to the minerals of water-bearing rocks. The simulation results show that the brines in the Western ore body of the Udachnaya pipe are strongly undersaturated in the deep horizons in comparison to carbonate, sulfate and chloride minerals. This suggests possible dilution of brines during their geochemical evolution. A detailed study of the tectonic structure identified structural elements that control the distribution and migration of groundwaters in the rocks. In the mining sites, brines occur mainly in the fault zones, fault junctions and intersections with the contacts of kimberlite bodies. Integration of hydrogeological and geostructural data can provide a basis for prediction and assessment of the sites with increased water inflow in the deep horizons involved in mining.

Detailed analysis of the geological and hydrogeological conditions in the Yurubcheno–Tokhomo zone of oil and gas accumulations showed the osinskii horizon of the Lower Cambrian to be of greatest inter