## 2 Materials and Methods
### Background and Geographical Framework of the Zhem Artesian Basin
The aquifer thickness varies from 5 to 18 m, and in some deep valley sections, it reaches 50-60 m (Ilek River valley). The aquifer hydraulic conductivity ranges from 1 to 12 m/day, with depths of up to 5 m in the floodplain and the first terrace above the floodplain, and 12-15 m in higher terraces. The pumping well flow rates vary from 1 to 2.5 L/s, with the total salinity of groundwater increasing downstream from 0.8 to 3.0 g/L. The Lower Quaternary alluvial deposit (aQI) aquifer is confined to the third floodplain terrace and geographically coincides with the Kokzhide and Kumzhargan aeolian sand boundaries. Groundwater is confined to heterogeneous sands with lenses of gravel, with an aquifer thickness that reaches 11 m or more. Depending on the hyposometry of the surface,  
Figure 3: Hydrogeological cross-sections along the A–B and C–D lines (in Figure 2). 1—Upper Quaternary–Modern alluvial aquifer; 2—Middle–Upper quaternary alluvial aquifer; 3—Lower Quaternary alluvial aquifer; 4—Quaternary marine sediment aquifer; 5—local Paleogene deposit aquifer; 6—impermeable Paleogene sediments; 7—Upper Cretaceous and Paleogene aquiclude; 8—Upper Cretaceous aquiclude; 9—local Upper Cretaceous aquifer; 10—Lower Cretaceous-Canomanian aquifer complex; 11—Lower Cretaceous aquifer complex; 12—Jurassic aquifer complex; 13—hydrogeological unstudied fault; 14—water-bearing fault; 15—fault hidden under overlying strata and inferred from geophysical data; 16—Borehole with sampling interval; the borehole number is at the top. Lithology: 17—sands; 18—clayey sands; 19—clays; 20—impermeable horizon clays; 21—chalk; 22—marls; 23—sandstones. the groundwater table depth varies from 2.2 to 28.9 m. The pumping well flow rates range from 1 to 13 L/s. The total salinity of the groundwater is 0.1-0.2 g/L. The local Paleogene aquifer and aquiclude (P) have a limited distribution in the eastern and southern Zhem Basin parts in the form of watershed surface remnants. The thickness of the water-bearing sands and sandstones rarely exceeds 3-5 m, with an interlayered unit total thickness of 10-15 m and a pumping flow rate of 0.025-1 L/s. The semi-confined groundwater is at a 5-16 m depth. The groundwater is fresh to slightly brackish, with a total salinity of 0.8-5 g/L. The impermeable layers are Tripoli- and Opoka-like clays with interlaying sands and weakly cemented sandstones, with a total thickness of up to 50 m.  
Upper Cretaceous Campanian to Lower Paleogene regional aquitards (K2-P and K2) underlie the watershed areas, with a thickness that varies from 10 m to 90 m. This aquitard stratum restricts the discharge from the Albian aquifer complex. The local Upper Cretaceous aquifer (K2) has a limited distribution and is composed of sandy marks and clays with a total thickness of up to 40 m. The lower Cretaceous-Cenomanian aquifer complex (K1-K2s) is the most promising and widespread in the Zhem Basin. In places across the basin, the aquifer complex groundwater reaches the surface or is covered by thin alluvial sediments. Clay and marl sediment cover the aquitard, confining the Upper Cretaceous sandstone aquifer vertically and spatially. The sediment thickness varies from 25 to 980 m and is 147 m on average. The groundwater heads range from 4 to 383 m above the complex datum and are 49 m on average. Filtration coefficients vary from 0.8 to 29.8 m/day, and the pumping rates range from 6 to 40-63 L/s. The total salinity of groundwater ranges from 0.2 to 5.3 g/L, with a general increase from the northeast to the southwest in the groundwater flow direction. The lower Cretaceous Aptian-Neocoman aquifer complex (K1) lies at a depth of 90 to 1100 m with a 30 to 100 m thickness range. It is comprised of sands interlaced with pebbles and clay layers. The clay cover separates it from the overlying lower Cretaceous-Cenomanian complex. The Jurassic aquifer (J) is exposed in restricted areas between salt domes, while in other areas, it occurs at great depths.