Project "Improvement of Groundwater Protection in Vietnam" (IGPVN), National Center for Water Resources Planning and Investigation (NAWAPI), No. 93, Lane 95, Vu Xuan Thieu, Long Bien, Hanoi, Vietnam.
Federal Institute for Geosciences and Natural Resources (BGR), Hannover, Germany.
Environ Geochem Health. 2019 Feb;41(1):325-341. doi: 10.1007/s10653-018-0167-z. Epub 2018 Aug 12.
Environmental isotope techniques were applied to study the hydrochemical characteristics of groundwater in Soc Trang Province, Southern Vietnam, in frame of the project Improvement of Groundwater Protection in Vietnam (IGPVN). Groundwater samples were collected from various monitoring wells (newly drilled by the IGPVN project), national monitoring wells, private tube wells and production wells. Surface water samples were collected from rivers, ponds or canals. The aquifer system is more complex than presumed as the hydrochemical and stable isotope compositions of groundwater samples in the Middle-Upper Pleistocene (qp) aquifer differ significantly in lateral direction. Furthermore, observed changing redox reactions within the target aquifer from dry to wet season make it probable that some interaction with overlying aquifers exists. The stable isotope signatures of the qp groundwater samples can be divided into two distinct groups which, respectively, originated from paleo-meteoric water and either was located in paleo-salinized areas of the qp aquifer or resulted from evaporation effect of recharging water prior or during infiltration process. In fact, individual parts of "the same" aquifer seem not to be hydraulically connected to each other. The environmental isotope data provided neither evidences of hydraulic connection between the rivers and the qp aquifer nor of recent groundwater recharge in the Province. As a result, saltwater from the sea intruded inland to some extent via the Hau River during the dry season, but it did not affect the target aquifer. Any recharge from surface water to the qp aquifer in Soc Trang should occur outside the boundaries of Soc Trang Province. Considering the low groundwater transit velocities roughly estimated in this study (3.6 m/year and 7.8 m/year), it may take several ten thousands to hundred thousands of years for recharging water from beyond the Vietnam's national border to reach the qp aquifer in Soc Trang Province. Consequently, natural recharge cannot help to reduce groundwater declining in the short-to-middle term.
环境同位素技术被应用于研究越南南部朔庄省地下水的水文地球化学特征，该研究是越南地下水保护改善项目（IGPVN）的一部分。地下水样本取自各种监测井（由 IGPVN 项目新钻取的）、国家监测井、私人管井和生产井。地表水样本取自河流、池塘或运河。含水层系统比预想的更为复杂，因为中更新世（qp）含水层的地下水样本在横向方向上的水文地球化学和稳定同位素组成有显著差异。此外，在旱季到雨季的目标含水层中观察到的不断变化的氧化还原反应，使得与上覆含水层存在某种相互作用的可能性增大。qp 地下水样本的稳定同位素特征可分为两个截然不同的群组，分别源自古大气水，或者位于 qp 含水层的古盐化区，或者是补给水在渗透过程之前或期间蒸发的结果。事实上，“同一”含水层的各个部分似乎彼此没有水力联系。环境同位素数据既没有提供河流与 qp 含水层之间存在水力联系的证据，也没有提供该省近期地下水补给的证据。因此，旱季期间，海水通过黑河部分向内陆侵入，但没有影响目标含水层。地表水向朔庄 qp 含水层的任何补给都应该发生在朔庄省边界之外。考虑到本研究中大致估计的地下水迁移速度较低（分别为 3.6 米/年和 7.8 米/年），来自越南边境以外的补给水到达朔庄省的 qp 含水层可能需要数万到数十万年来实现。因此，在短期到中期内，自然补给无助于减少地下水的下降。
