Hydro-geochemical characteristics of the groundwater resources in the southern part of the Red River’s Delta plain, Vietnam

• Published in: Environmental earth sciences 2018-10, Vol.77 (19), p.1-21, Article 674
• Main Authors: Hoang, Hoan V., Nguyen, Lam V., Dang, Nhan D., Wagner, Frank, Pham, Nhan Q.
• Format: Article
• Language: English
• Subjects: Aquifer recharge; Aquifers; Biogeosciences; Calcite; Calcium; Carbon 14; Chemical analysis; Composition; Deltas; Dye dispersion; Earth and Environmental Science; Earth Sciences; Electrical resistivity; Environmental Science and Engineering; Fluvial deposits; Fresh water; Freshwater; Freshwater environments; Geochemistry; Geology; Groundwater; Groundwater chemistry; Groundwater management; Groundwater mining; Groundwater quality; Groundwater recharge; Groundwater resources; Holocene; Hydrology/Water Resources; Inland water environment; Iron; Isotope composition; Isotopes; Local population; Local precipitation; Neogene; Organic chemistry; Original Article; Pleistocene; Pore water; Precipitation; Recharge areas; Resource management; Rivers; Saline groundwater; Saline water; Saline water intrusion; Salt water intrusion; Saltwater intrusion; Sea level; Seawater; Sediments; Terrestrial Pollution; Total dissolved solids; Triassic; Water analysis; Water flow; Water resources
• ISSN: 1866-6280; 1866-6299
• DOI: 10.1007/s12665-018-7857-9

In this study, the origin and recharge areas as well as the chemistry of the groundwater in the southern part of the Red River Delta plain, in Thai Binh, Nam Dinh and Ninh Binh provinces (North Vietnam) was investigated by using isotopic techniques combined with geochemical analysis. Groundwaters under the study were those that are available in the Holocene, Pleistocene, Neogene and Triassic aquifers. Groundwater in the Holocene aquifer is brackish of Na–Cl type with an electric conductivity as high as up to 6000 µS cm −1 . The water in the shallow aquifer comprises three end-members: the local precipitation, Red River’s water and intruded seawater. Groundwater in the Pleistocene, Neogene and Triassic aquifers in the Southwest of the study region is fresh containing less than 1 g L −1 of total dissolved solids and is characterized by the Ca–Na–HCO 3 type. However, groundwater in the deep aquifers in the Northeast area is brackish of Na–Ca–Cl–HCO 3 ion type containing more than 1 g L −1 TDS. The chemistry of groundwater in the study region is controlled by three processes, namely the incongruent dissolution of the biogenic high Mg-calcite, the reduction of sulphate and iron oxyhydroxide with organic matters present in the aquifers. The salinity in deep aquifers in the NE was attributed to the diffusion of saline pore water from aquifer or/and aquitard deposits to the recharge water. Groundwater in the Pleistocene, Neogene and Triassic aquifers in the study region seem to have meteoric origin with long traveling time and it mixed with the saline pore water that migrated from the aquifers sediments, as it was evident from the water isotopic compositions. The isotopic compositions of water (δ 2 H and δ 18 O) in the Neogene and Triassic aquifers are similar to that found in the Pleistocene aquifer suggesting the aquifers are hydraulically connected to each other due to the over-extraction rate of fresh water from the latter aquifer. Recharge area of groundwater in the Pleistocene and Neogene aquifers is suggested to be from the NW extension of the region and out crops at a highland at an altitude of 140–160-m above sea level (masl). The recharge water flows from northwesterly towards southeasterly to the sea coast. The results of the 14 C-dating for groundwater combined with the hydraulic heads distribution in the deep aquifers revealed that the saline groundwater is flowing from the NE and backwards from the sea side to the production well field in the center