Coexistence of High Fluoride Fresh and Saline Groundwaters in the Yuncheng Basin, Northern China

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Procedia Earth and Planetary Science 7 ( 2013 ) 280 – 283

Water Rock Interaction [WRI 14] Coexistence of high fluoride fresh and saline groundwaters in the Yuncheng Basin, northern China

X.B. Gaoa, F.C. Zhangb, C.Wangb,Y.X. Wanga,*

aState Key Laboratory of Biogeology and Environmental Geology & School of Environmental Studies, China University of Geosciences, Wuhan, 430074 P. R. China bCenter for Hydrogeology and Environmental Geology, CGS, Baoding, 071051 P. R. China

Abstract

Fluoride contaminated groundwater is a serious health issue worldwide. However, little is known about the coexistence of fresh and saline elevated fluoride groundwaters. In this case, fresh and saline groundwaters with elevated F concentrations (up to 14.1mg/l) in the Yuncheng Basin (YB) were investigated. The enrichment and mobility of F in groundwater are controlled by natural water-rock interaction processes in the aquifers, which were - indicated by the positive correlation of high F and high HCO3 concentrations, and the negative correlation between F and nitrate concentrations in groundwater.

© 20132012 The The Authors. Authors. Published Publis byhed Elsevier by Elsevier B.V. B.V. Selection and/or and/or peer-review peer-review under under responsibility responsibility of the Organizing of Organizing and Scientific and Scientific Committee Committee of WRI 14 of – 2013WRI 14 - 2013

Keywords: fluoride; high fluoride water; fresh groundwater; saline groundwater; Yuncheng Basin; China

1. Introduction

Fluoride contaminated groundwater is a serious health issue worldwide.[1,2] High fluoride concentration in potable groundwater has caused serious endemic poisoning cases in Africa, Bangladesh, India, Mongolia and China. High fluoride content water was observed in fresh and saline groundwater from Quaternary aquifers in the Yuncheng Basin (YB), a semi-arid area of Shanxi Province in northern China, where groundwater is the major source of drinking and irrigation water. Endemic fluoride poisoning was first confirmed in the YB in the early 1980s. 70.0 % of the total tested quaternary water in the study area contained F concentrations exceeding 1.0mg/L, the F maximum contaminant level (MCL)

* Corresponding author. Tel.: +86-27-62879198; fax: +86-27-87481392. E-mail address: [email protected]; [email protected].

1878-5220 © 2013 The Authors. Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Organizing and Scientific Committee of WRI 14 – 2013 doi: 10.1016/j.proeps.2013.03.052 X.B. Gao et al. / Procedia Earth and Planetary Science 7 ( 2013 ) 280 – 283 281 for drinking water in China. Various studies have been done to understand the occurrence of fluoride in fresh groundwater. However, little is known about the coexistence of fresh and saline high F groundwaters. In this study, field investigation of F distribution in fresh and saline groundwater was carried out with water samples from YB. This will help to understand the chemical characteristics of F in groundwater in inland arid and semi-arid basins. The basin comprises a Quaternary aquifer of inter-layered sediments that is up to 500 m thick. The sediment is mostly aeolian loess containing quartz, feldspar, calcite, clays and mica, comprising a series of depositional layers, mostly 2-5 m thick, separated by thinner (<1 m) paleosol layers. The loess in the YB is also inter-layered with alluvial sands and lacustrine clay lenses.

Fig. 1. A simplified hydrogeology map of the YB.

Historically, regional groundwater flows from the east to the west, towards the Yellow River (Figure 1), while intermediate-scale flow also occurred from the sloping southern and northern margins to the flatter interior (China Geological Survey, 1980). However, due to the over exploitation of shallow and deep groundwater since the 1980s, horizontal groundwater flow is now mostly towards a cone of depression to the west of Yuncheng City. Groundwater in the shallow aquifer is generally modified by evapotranspiration and heavy irrigation.

2. Sampling and methods

136 water samples, including 100 groundwaters, 30 surface waters and 6 fissure waters, were collected from the YB in August 2011. Before sampling, the groundwater was pumped over one hour. When sampling, all water samples were filtered through 0.45 μm membranes on site. Samples were collected in two new 500 ml polyethylene bottles. For metallic element analysis, reagent-quality HNO3 was added to one of these polyethylene bottles until pH of samples reached 1. These bottles had been rinsed with deionized water twice before sampling. Unstable hydrochemical parameters including water temperature, pH, Eh, and electrical conductivity (EC) were measured in-situ using portable Hanna EC Eh, and pH meter that had been calibrated before use. Alkalinity was measured on the sampling day using the Gran titration method. Concentration of fluoride and other anions of the samples were determined using IC 282 X.B. Gao et al. / Procedia Earth and Planetary Science 7 ( 2013 ) 280 – 283

(Dionex 120). A PerkinElmer SCIEX model Elan® DRC II ICP-MS was used for trace elements measurements.

3. Results and discussion

The fluoride concentration in the groundwater ranges between 0.24 and 14.1mg/L with a mean value of 1.51 mg/L (Table 1). Seventy groundwater samples had F concentrations above the MCL for drinking water in China (1 mg/L), including 42 from shallow wells (depth < 60 m), and 9 from deep wells (depth > 120 m), and 19 from intermediate wells (60 < depth < 120 m), occupying 70.0 % of the total samples. Most of the groundwater with high F concentrations is from the central or western part of the YB.

Table 2. Parameters of high fluoride groundwater from YB

Parameters Max Min Average value St dev. T(OC) 39.00 15.9 19.7 3.67 pH 8.52 7.29 7.99 0.29 EC (ms/cm) 6.15 0.08 1.98 1483 - HCO3 (mg/L) 1094 15.4 420 244 Cl- (mg/L) 46,269 6.59 570 3883 2- SO4 (mg/L) 19,212 24.0 379 1620 F- (mg/L) 14.10 0.24 1.63 1.51 K (mg/L) 37.69 0.35 3.58 5.90 Na (mg/L) 1530 8.28 326 349 Ca (mg/L) 129.8 6.61 48.2 32.55 Mg (mg/L) 308.6 1.32 57.25 54.18 B (μg/L) 7019 12.7 1104 1422 Al (μg/L) 222.1 0.04 6.59 26.41 Si (mg/L) 17.64 0.18 4.79 2073 Sr (μg/L) 19,265 15.1 3116 3687

According to the relationship between F concentration and TDS value, groundwater in YB can be divided into three groups: group A, high F content with low TDS value; group B, high F content with medium to high TDS value; group C, low F content with medium to high TDS value. Most of the groundwater in group B and group C come from low land areas while groundwater in group A partly comes from high land areas. There is no significant positive correlation between F concentrations and - HCO3 concentrations. But, high fluoride water normally belongs to groundwater with high bicarbonate concentration. In addition, F concentrations correlate positively with pH values. Groundwater with high F concentrations was generally of Na type water, with low Ca concentration. Positive correlation between F concentrations and Na/Ca ratios was also found in the high fluoride groundwater. Therefore, cation exchange may play an important role in the genesis of high F groundwater. There is no significant correlation between F and NO3 concentrations, which indicates that input from agricultural activity is unlikely to be a major source of F in groundwater. So the enrichment and mobility of F in groundwater are under the control of natural water-rock interaction processes in the aquifers. X.B. Gao et al. / Procedia Earth and Planetary Science 7 ( 2013 ) 280 – 283 283

Fig. 2. F concentration vs. TDS in groundwater samples from Fig. 3. F vs. HCO3- concentration in groundwater samples from YB YB

Fig. 4. F vs. NO3- concentration in groundwater samples from YB

4. Conclusions

About 70.0 % of the total samples have F concentrations above the MCL for drinking water in China (1.0 mg/L), including 42 from shallow wells, 9 from deep wells, and 19 from intermediate-depth wells. The enrichment and mobility of F in groundwater are under the control of natural water-rock interaction - processes in the aquifers as indicated by the positive correlation between F concentrations and HCO3 concentrations, and the negative correlation between F concentrations and nitrate concentration in groundwater.

Acknowledgement

The research work was financially supported by National Natural Science Foundation of China (No.40120124003), State Key Laboratory of Biogeology and Environmental Geology (No. BGEG201107), China Geological Survey (1212011220949), and Ministry of Education of China (111 project, No. CUGNGM201216).

References

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