Natural conditions in North and Central Kazakhstan and the energy potential of chestnut soil testify to the efficiency of agriculture, especially on irrigated lands. The humus horizon of chestnut soils is 35–50 cm, and the humus content is 3.0–3.5%. The majority of the humus (75%) is contained in a half-meter layer, which emphasizes the short humus level. The phosphorus content, both gross and mobile, is very low at 0.98–0.031%. Potassium is in elevated amounts. Soils are most susceptible to the application of nitrogen–phosphorus fertilizers. According to the mechanical composition, chestnut soils are predominantly lightly loamy, light clays with substrates of souses. Salinization is low, with a salt content in the 0–100 cm soil layer of 0.10–0.20%. The mass of the arable soil layer is 1.3–1.4 g/cm³. Deep plowing and loosening of soils improve the water and nutrition regime, creating good conditions for arid agriculture. With deep autumn plowing up to 30 cm, the accumulation of sediment and spring meltwater reaches 1200–1500 m³/ha more than in spring disposal. Deep plowing ensures absorption of irrigation water, eliminates run-off during irrigation, and reduces the number of crops requiring extra irrigation. In an average dry year, at 50% water availability and 70% soil moisture content (MC), the number of irrigations is 4, and the irrigation rate is 300–470 m³/ha; at 60% MC, 2 irrigations are performed, and the irrigation rate is 600–650 m³/ha. On irrigated land, the yield of cereals is 2.8–2.6 t/ha; perennial grasses, 3.0–4.5 t/ha; potatoes, 23.2–24.1 t/ha; carrots, 35.0–40.0 t/ha; and cabbage, 50.0–75.0 t/ha.

An integrated field–analytical framework was applied to quantify the impact of two small-settlement treatment facilities (TF1 and TF2) on the Irtysh River (East Kazakhstan). The main objective of this study is to quantify effluent-driven dilution and non-conservative changes in key water-quality indicators downstream of TF1 and TF2 and to evaluate parsimonious models for predicting effluent-outlet BOD and COD from upstream measurements. Paired upstream–downstream control sections are sampled in 2024–2025 for 22 indicators, and plant influent–effluent records are compiled for key wastewater variables. Chloride-based conservative mixing indicated very strong dilution (approximately $D\approx 2.0\times {10}^3$ for TF1 and $D\approx 4.2\times {10}^2$ for TF2). Deviations from the mixing line were summarized using a transformation diagnostic $\theta$. At TF1, several constituents exceeded mixing expectations ($\theta \approx 13$ for COD, $\theta \approx 42$ for ammonium, and $\theta \approx 6$ for phosphates), while nitrate shows net attenuation $\theta <0$. At TF2, $\theta$ values cluster near unity, indicating modest deviations. Under a small-sample regime $\left(\mathrm{N}=10\right)$ and leave-one-out validation, regularized regression provided accurate forecasts of effluent-outlet BOD and COD. Lasso under LOOCV performed best (BOD_after: RMSE = 0.626, MAE = 0.459, and $R^2=0.976$; COD_after: RMSE = 0.795, MAE = 0.634, and $R^2=0.997$). The results reconcile strong reach-scale dilution with constituent-specific local departures and support targeted modernization and operational forecasting for water-quality management in small facilities.