Groundwater hydrogeochemical processes, water quality index, and probabilistic health risk assessment in an arid and semi-arid environment (Hamedan, Iran)

Groundwater protection requires an understanding of different hydrogeochemical processes and this study synthesised and analysed a large hydrogeochemical dataset (1030 data points over 15 years) of published data in western Iran, to gain a deeper understanding and reveal the main factors controlling groundwater geochemistry. Furthermore, non-carcinogenic effects on human health related to nitrate (NO₃⁻) concentrations were assessed. In terms of the measured parameters, four distinct clusters were identified Ca–HCO₃, Na–HCO₃, Na–SO₄, and Na–SO₄–Cl. Cluster 1 (68% of samples) had higher average pH while exhibiting lower average electrical conductivities (ECs), cations, and anions than the other clusters and had a lower average weighted arithmetic than the other clusters. 28.5%, 51.9%, 16.3%, 2.1%, and 1.2% of total water samples rated as excellent, good, poor, extremely poor, and undrinkable, respectively, implying that about 80.4% of the groundwater samples are potable. Multi-linear regression models based on pH and EC values can predict cation and anion concentrations in groundwater with high accuracy. The significance of the findings lies in their potential to facilitate the comprehension, modeling, and eventual forecasting of the fate of anions and cations in semi-arid and arid environments, as well as similar groundwaters, using common water characteristics. In order to lower the non-carcinogenic health risks to the local population, the appropriate actions should be taken. The majority of the region's agricultural areas have primary soil textures that are sandy and prone to NO₃⁻ leaching. Therefore, in order to maintain the quality of the groundwater in the study region, excessive use of chemical and organic fertilizers should be avoided. These findings will contribute to understanding and safeguarding groundwater quality, while also informing management strategies in arid and semi-arid regions with similar environmental characteristics.