Background. The threat of contamination of drinking water sources in the Kalush region is largely determined by the flooding of the Dombrovsky quarry and the possible leakage of highly mineralised brines into the gravel and pebble aquifer and river system from surface man-made reservoirs. Currently, the open pit serves as a drainage for groundwater, but the water level in the mine excavation is rising at a rate of approximately 1 m per year, which requires monitoring, research of the hydrogeological system in the area of drainage influence of the quarry and rapid management decisions to prevent an environmental emergency. The aim of the study was to propose a new method for determining the filtration coefficient (Ff), which would average the filtration properties of large massifs of soils of the gravel-pebble aquifer and take into account their heterogeneity. Methods. Balance methods of instrumental determination of water inflow to the quarry to determine the averaged filtration coefficient for a large area was used. Parameters for its calculation was found. Results. All available literature and fund sources were analysed and summarised, and an integrated approach was applied to determine the filtration coefficient of the gravel and pebble aquifer. Using Darcy's equation, it is determined that the Ff is 5.3 m/day. A method for determining the filtration coefficient of aquifer soils using GIS technologies to determine the flow rate of groundwater that is completely discharged into a quarry or similar reservoirs is proposed. The results of the study were used to create a numerical geofiltration model and predict groundwater salinity. Conclusions. The urgent scientific issue of studying the hydrogeological system of the Kalush region and determining the filtration parameters of the gravel and pebble aquifer, which is the only source of drinking water for the city of Kalush and adjacent settlements, has been solved. The filtration coefficient of the gravel and pebble aquifer of the I, II and III floodplain terraces, which averages the filtration properties of soils over a large area and can be used to make predictions of groundwater salinity, was obtained.