Spatial distribution of uranium and metalloids in groundwater near sandstone-type uranium deposits, Southern Mongolia

Abstract

In the Dornogobi Aimag region of Southern Mongolia, the main source of groundwater contamination by U, As, and Se is hydrogenic- or sandstone-type uranium deposits. These environmentally hazardous deposits, located in close proximity to populated settlements, pose a serious threat to drinking water quality and human health. Fifty samples were analyzed and levels of uranium were found to be elevated in deep and shallow waters (200 and 34.7 mg/L, respectively), with nearly 25% exceeding the World Health Organization (WHO) guideline level for drinking water quality (30 mg/L). Local rocks and soils appear to be the natural source of uranium. In particular, water from deep hydrologic wells near the largest deposits (Dulaan Uul and Zoovch Ovoo) exceeds the WHO guideline levels for U, As, Se, Sb, Cd, and Fe. At the same time, shallow groundwater (Argalant area) contains 50.5 mg/L of As, 34.7 mg/L of U, and 35.9 mg/L of Cd. Although multiple metal and metalloid contamination of groundwater is an issue of global concern, our understanding of the physical-chemical conditions of its accumulation is limited. This study provides a plausible explanation of the geochemical situation at the uranium Dornogobi province based on thermodynamic calculations.