Aquatic geochemistry status in the south, central, and highland regions of Vietnam.

Aquatic geochemical distribution in the Central, Highland, and Southern regions of Vietnam, including: Da Nang city (Hoa Khanh Industrial Park, Aquaculture Industrial Zone Tho Quang, Do Toa River Deposit Area), Da Lat city (Prenn Pass), Dong Nai province (Suoi Ram hamlet, Cam My district, Long Giao) was investigated by using 2D electrical resistivity tomography (ERT) combined with geochemical analysis. In this research, the correlation between tectonic formation, geochemical composition, and groundwater distribution was assessed between regions. Geochemistry of the Holocene aquifer (from 10 to 30 m underground) was studied considering major ions and trace elements measured in wet and dry seasons. The results of chemometric evaluation show that groundwater in Central Vietnam, Da Nang in particular, has a higher frequency of environmental toxin distribution than in Da Lat and Dong Nai. Groundwater in Da Lat with the advantage of high distribution of K, Ca, Mg, Fe, and Zn. The micro and macro elements such as Co, Mo, Na have high distribution in groundwater in Dong Nai. Meanwhile, groundwater at the study sites in Da Nang showed high concentrations of heavy metals with high toxicity such as, Al, Pb, and Ni. In Da Nang city, the concentration of Pb in groundwater samples from Holocene aquifer ranges between 74 in dry season and 214 ppb in wet season, exceeding the WHO guideline of 21 ppb. There is an increase of mean temperature of groundwater from Holocene aquifer of studied areas, from 17 in wet season to 26.2 °C in dry season. It shows that the ambient temperature effects on the groundwater reflects the relatively surficial character of Holocene aquifer. At the same time, the impact factors, including natural conditions, production methods, customs, and habits were analyzed to formulate the risks and potential risks of geohazards in mechanical construction, infrastructure, civil works, and underground works affecting the social security in the research areas. Through the convection and transfer processes, the electrolyte pollutants such as NaCl, KCl, and acetic acid (the resistivity is about 5.38 Ω m) have been accumulated in groundwater of Da Nang - a developing city with industrial clusters. This problem is similar to Suoi Ram hamlet, where groundwater is also showing signs of pollution due to the use of chemicals in cultivation (mainly cashew nut growth). In terms of density and flow of underground water, according to the results of the electrical images, generally in Suoi Ram Hamlet pollution is much larger than the Hoa Khanh industrial park (Da Nang), which is also quite reasonable because the southern area is lower than the Central and Highland regions. Research contributed importantly in finding the rules of geological distribution, groundwater at elevation topography, of great significance in the earth and environmental science.