Central Ground Water Board, Hyderabad, Andhra Pradesh, India.
Environ Monit Assess. 2010 Dec;171(1-4):561-77. doi: 10.1007/s10661-009-1300-3. Epub 2010 Jan 13.
The groundwater of Nalgonda district is well known for its very high fluoride content for the past five decades. Many researchers have contributed their scientific knowledge to unravel causes for fluoride enrichment of groundwater. In the present paper, an attempt has been made to relate the high fluoride content in the groundwater to hydrogeochemical characterization of the water in a fracture hard rock terrain--the Wailpally watershed. Groundwater samples collected from all the major geomorphic units in pre- and post-monsoon seasons were analyzed for its major ion constituents such as Ca(2+), Mg(2+), Na(+), K(+), CO3-, HCO3-, Cl(-), SO4(-2), NO3-, and F(-). The groundwaters in the watershed have the average fluoride content of 2.79 mg/l in pre-monsoon and 2.83 mg/l in post-monsoon. Fluoride concentration in groundwater does not show perceptible change neither with time nor in space. The ionic dominance pattern is in the order of Na(+) > Ca(2+) > Mg(2+) > K(-) among cations and HCO3- Cl(-) > SO4(-2) NO3- F(-) among anions in pre-monsoon. In post-monsoon, Mg replaces Ca(2+) and NO3- takes the place of SO4(-2). The Modified Piper diagram reflect that the water belong to Ca(+2)-Mg(+2)-HCO3- to Na(+)-HCO3- facies. Negative chloralkali indices in both the seasons prove that ion exchange between Na(+) and K(+) in aquatic solution took place with Ca(+2) and Mg(+2) of host rock. The interpretation of plots for different major ions and molar ratios suggest that weathering of silicate rocks and water-rock interaction is responsible for major ion chemistry of groundwater in Wailpally watershed. Chemical characteristics and evolution of this fluoride-contaminated groundwater is akin to normal waters of other hard rock terrain; hence, it can be concluded that aquifer material play an important role in the contribution of fluoride in to the accompanying water. High fluoride content in groundwater can be attributed to the continuous water-rock interaction during the process of percolation with fluoride-bearing country rocks under arid, low precipitation, and high evapotranspiration conditions.
在过去的五十年中，纳尔贡达地区的地下水以其极高的氟含量而闻名。许多研究人员都贡献了他们的科学知识，以揭示地下水富氟的原因。在本文中，我们试图将高氟地下水与断裂硬岩地形——瓦利帕利流域的水地球化学特征联系起来。在旱季和雨季前，从所有主要地貌单元采集地下水样本，分析其主要离子成分，如 Ca(2+)、Mg(2+)、Na(+)、K(+)、CO3-、HCO3-、Cl-、SO4(-2)、NO3-和 F(-)。流域内的地下水在旱季的平均氟含量为 2.79mg/L，在雨季为 2.83mg/L。氟在地下水中的浓度无论是时间上还是空间上都没有明显变化。旱季阳离子的离子优势顺序为 Na(+)>Ca(2+)>Mg(2+)>K(-)，阴离子的离子优势顺序为 HCO3->Cl->SO4(-2)>NO3->F(-)。雨季时，Mg 取代了 Ca(2+)，NO3-取代了 SO4(-2)。修正后的 Piper 图反映出水属于 Ca(+2)-Mg(+2)-HCO3-到 Na(+)-HCO3-相。两季的负氯碱指数均证明，水溶液中 Na(+)与 K(+)的离子交换与母岩中的 Ca(+2)和 Mg(+2)发生了作用。对不同主要离子和摩尔比的图的解释表明，硅酸盐岩石的风化和水岩相互作用是导致瓦利帕利流域地下水主要离子化学性质的原因。这种受氟污染地下水的化学特征和演化与其他硬岩地形的正常水相似；因此，可以得出结论，含水层物质在氟进入伴生水的过程中起着重要作用。地下水中的高氟含量可归因于在干旱、低降水和高蒸散条件下，含氟围岩在渗流过程中与水的持续相互作用。
