Inverse geochemical modeling of high arsenic groundwater: a case study of the arsenic endemic area in western Jilin Province

Abstract：A study area in Jilin was selected from lots of arsenic endemic regions, which are mainly distributed in Taiwan, Xinjiang, Inner Mongolia, Shanxi and Jilin. The area is physiogeographically located along the western flank of Songnen plain, and hydrogeochemically regarded as a basin with groundwater generally flowing eastward. A total of 196 groundwater samples were collected, which not only covered the whole study area but also extended to different depths/aquifers that included Quaternary phreatic groundwater, Quaternary Baitushan Formation confined groundwater and Neogene confined groundwater. Cluster analysis was also performed to identify the degree of relationship between each chemical constituent and arsenic by the SPSS statistical package. The result reveals that the distribution of arsenic at the present time has a close relationship with the spatial variation of Fe, Mn as well as Cl-, PO3-4, HCO-3, SO2-4 and Se. An inverse geochemical model was established to demonstrate the above relationship by using the PHREEQC software. The simulation results have confirmed that the arsenic presence and its distribution in the groundwater of this area result largely from the leaching-migration-accumulation from the edge to the central area of the basin. The dissolution of the redox sensitive ferric oxide compounds and hydrous ferric oxides as well as the arsenic compounds (arsenate or arsenide) is probably the major mechanism for the control of the spatial variation of arsenic in the study area. As groundwater flows stagnantly in the low-lying central area, the afore-mentioned minerals become less stable due to lower Eh and move into the groundwater with relatively high solubility under the lower Eh condition. At the same time, the arsenic complexes adsorbed by these minerals are released and migrate with the movement of the groundwater. It is concluded that the presence of arsenic in the regional groundwater flow regime exhibits the highest concentration in chloride-sodium bicarbonate groundwater in the central area, which is consistent with the above findings and many previous studies in this special field of the international community.