## 1 Introduction
The advantage of MODFLOW modeling over groundwater filtration analytical calculations is that the model takes into account the modeled object's actual configuration, including its filtration heterogeneity, the wellfields' interaction, and the change in the aquifer transmissivity with head fluctuations during pumping. The latter circumstance is especially important to consider when assessing the potential operational groundwater reserves, since the maximum permissible head drawdowns, as a rule, make up half of the aquifer thickness. A unified geographic information system of fresh groundwater resources and reserves in Kazakhstan was created in the ArcGIS environment. Data entered into the system were used to calculate various groundwater reservoir characteristics and to create fresh groundwater resource thematic maps [22]. Groundwater resources distribution in Kazakhstan is not uniform, with approximately 37% of groundwater resources being concentrated in the Balkhash-Alakol Basin in southeastern Kazakhstan [23]. Hydrogeological zoning and regional groundwater resource assessment of natural exploitable groundwater resource reserves indicate that as of 2001, 623 groundwater reservoirs were utilized for various purposes, totaling 43,383.5 thousand m\({}^{3}\)/day [23; 24]. The Zhem Artesian Basin, located in the Aktobe region of western Kazakhstan, is also a significant groundwater resource. According to the Republic of Kazakhstan Groundwater Deposits Cadaster, 131 groundwater reservoirs and sites have been explored within the Zhem Artesian Basin, with operational reserves of 755 thousand m\({}^{3}\)/day confined to Albian-Canomanian strata and, to a lesser extent (8%), to the aquifer complex of Albian-Canomanian-Quaternary deposits. The bulk (79%) of groundwater reserves is fresh, with mineralization of up to 1 g/L. Reserves with mineralization of 1-3 g/L make up 14%, and according to Kazakh regulations, these reserves are also suitable for domestic and drinking water supply after minimal water treatment. To date, the Zhem Artesian Basin's degree of groundwater resources development has been determined according to the total amount drinking, industrial and agricultural needs, which is approximately 8.6% of the operational reserves [18; 25] Other regions in western Kazakhstan, such as Mangistau and Atyrau, have 4.8, 5.2, and 7.4 times less exploitable groundwater reserves, respectively, than the Aktobe region. By 2030, the drinking water demand in the Aktobe region is predicted to double and reach 321,000 m\({}^{3}\)/day [25]. This increase is due to the region's population growth and the development of industrial and agricultural areas. Although mineralization reaches 3 g/L, the Cretaceous Albian-Canomanian aquifer complex is the most promising water source for this growing demand. By 2070, the freshwater supply projected demand in these administrative regions will increase from 640 to 901 thousand m\({}^{3}\)/day. According to a reliability assessment, with the known operational groundwater reserves, once all Zhem Artesian Basin aquifers and wellfields are exploited simultaneously, this poses a very real problem. A sustainable operation scheme will allow a realistic assessment of the potential of the available groundwater resources for ensuring a future water supply to the water-deficient regions of western Kazakhstan. The Zhem Artesian Basin's exploitable groundwater resources consist of several Cretaceous aquifers comprising an aquifer complex. The utilization of the Emba site, located in the northeastern Kokzhide aquifer, started in 2008 after a reassessment (following the initial assessment in 1983). In 2021, the exploitable reserves of the Kokzhide aquifer were re-estimated based on MODFLOW modeling results [26]. MODFLOW models have also been used to determine the exploitable reserves of Kundaktakyrskoye [27], Kandagachskoye [28], Saybulakskoye [29], and Moiseevskoye [30].