There are eight famous thermal water sources, with medium temperature, neutral pH, high ranges of TDS values located in different carbonate formations in Northern Vietnam. The chemical composition results showed the major elements present were Na, K, Mg, Ca, Sr, while trace amounts of rare earth elements (REE), Ag, As, Pb, Th, U were observed. The 210Po activity concentration and the annual committed effective doses for adults, children, and infants in all study areas were far less than 100 mBq L−1 and 0.1 mSv y−1, respectively. Some significant correlations between 210Po and other chemical components have been observed.
This study applied an integrated surface water-groundwater (SW-GW) model, SWAT-MODFLOW to study interaction of surface and groundwater than simulate saltwater intrusion at a regional scale in Da Nang coastal city, center of Vietnam. Model components were calibrated and validated using monthly river flow data and hydraulic head data for the 2005-2020 period and showed good agreement with observed data. The results demonstrated that GW-SW exchange in the upstream areas had the most pronounced fluctuation between the wet and dry months under historical conditions. The combined potential impact is that intensive groundwater use may have more immediate effects on river flow than those of climate change, which has important implications for water resources management and supply in the future. The results showed that the total average recharge to groundwater from the rivers was varied from 12046 to 23147 m3/d relative to 50 – 74% of water resources in rain and dry season. Saltwater intrusion intrusion in 2020 is about 100 km2. In the area of Son Tra and Ngu Hanh Son districts, groundwater pumping must be reduced to zero, in some other areas, pumping rate do not exceed 250 to 1000 m3/day with distance to coastline at least 500 to 1400m depends on each area.
Muong Thanh valley located in the middle of Dien Bien is home to 80.000 people, including Kinh, Thai, Dao, and H’Mong ethnic groups. Here, underground water is the main source of food and drink for local people. The groundwater in porous formations in the Muong Thanh valley area mainly exists in two aquifers qh, qp belonging to Holocene (aQ21-2) and Pleistocene (aQ13, apQ13) formations. Hydrogeological survey results and groundwater monitoring data showed that groundwater in these formations is mainly from i) Rainwater sources, ii) Seepage from Nam Rom river, and iii) Percolate from outside. Applying numerical methods by using Visual Modflow to estimate inflow and outflow components exhibited that the total underground water reserves in the detached formations in the Muong Thanh valley area vary from 25,154 to 30,973 m3/day between dry and rainy seasons, including recharge from rainfall (from 191 to 5,418 m3/day) and seepage from Nam Rom river (from 12,046 to 23,147 m3/day). The total amount of replenished water fluctuates seasonally, from 13,112 to 29,464 m3/day. The current exploitation water flow is about 2,000 m3/day, much smaller than the total amount of replenished water, showing that the exploitation level is within safe limits.
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