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Relation Between Water Level Fluctuation and Variation in Fluoride Concentration in Groundwater—A Case Study from Hard Rock Aquifer of Telangana, India

  • Ankita ChatterjeeEmail author
  • Md. Arshad
  • Adrien Selles
  • Shakeel Ahmed
Conference paper
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Part of the Advances in Science, Technology & Innovation book series (ASTI)

Abstract

In this study, groundwater level and fluoride data of fifteen years (from 2003 to 2017) have been used to identify the influence of water level and its fluctuation on the variation of fluoride (F) concentration in groundwater. For this purpose, five locations have been chosen along the groundwater flow direction and amongst these locations, two locations are situated at or near the recharge area, having F concentration below 1.5 mg/l (most of the time), two other locations are situated around the discharge area, having F concentration above 1.5 mg/l (most of the time). At the transitional location between recharge and discharge, F concentration went above or below 1.5 mg/l in a proportional way. The time series plot of the water level and F concentration at each location show that the addition of freshwater during monsoon generally dilutes F concentration in groundwater. The positive relation between water level fluctuation and fluctuation in F concentration also reflects that fluoride release in groundwater is mostly due to water-rock interaction. The average fluctuation in F concentration increases along the flow line, which reflects more water-rock interaction in the discharge area than in the recharge area. The points in the discharge area showed the highest water level fluctuation, fluctuation in F concentration and the highest hydraulic conductivity.

Keywords

Fluoride Water level Fluctuation Telangana 

1 Introduction

Several studies have documented the general characteristics of fluoride in groundwater, like the fluoridated area must have the presence of crystalline basement rocks/volcanic bedrocks that contain most of the fluoride-containing minerals. Fluoride comes to groundwater through an anion exchange or the dissolution of minerals. The fluoride accumulation further promoted by calcium (Ca2+) deficient sodium (Na+)—bicarbonate (\({{{\text{HCO}}_{3}}^{ - }}\)) type groundwater, long residence time of groundwater, strong evapo-transpiration in a semi-arid/arid climate [1, 4, 7]. But very few studies have documented [2] the influence of hydraulic properties (water level, hydraulic conductivity) on the behavior of fluoride in groundwater. Therefore, this study is conducted only for fifteen years water level and F concentration data to understand the effect of water level fluctuation on fluoride occurrence and its behaviour in the aquifer. Hydraulic conductivity of the aquifer is also considered to get an idea about the fracture network and its influence on F concentration.

2 Methodology

The study area (Maheshwaram watershed) is situated in the Ranga Reddy district of Telangana, at a distance of about 35 km from Hyderabad. The watershed has an area of 53 km2. The study area is situated between longitude 78° 24′ 30″E–78° 29′ 00″E and latitude 17° 06′ 20″N–17° 11′ 00″N. The laminated saprolite and the fissured layer together form the two-tier aquifer system in this region and they coexist almost in the entire area [6]. The methodologies of groundwater level and sample collection from the field and the analysis of groundwater samples for fluoride are discussed in detail in Chatterjee et al. [3]. Hydraulic conductivities (in meter/second) are obtained by a slug test in the study area [5]. The graphs were prepared in Microsoft excel 2007 (Fig. 1).
Fig. 1

The study area along with its geology and sample locations

3 Results

It is seen from the graph (Fig. 2) that F concentration was either 1.5 or below 1.5 mg/l most of the time, at locations W19 and W16 (located around the recharge area or at a high elevation). Whereas, at locations W6 and W2 (located around the discharge area or at a low elevation), most of the time, F concentrations were above 1.5 mg/l. However, the location W11, which falls in between the recharge and discharge area, has F concentration below or above 1.5 mg/l in a proportional way. The water level ranges from 5 to 30 m, 5 to 27 m and 7 to 24 m at locations W19 and W16, W6 and W2, and W11, respectively, within the time period of 2003–2017. The water level fluctuation, ∆h (difference between pre and post-monsoon water level) and the fluctuation of F concentration, ∆F (difference between pre and post-monsoon water level) were plotted (Fig. 3) to understand the influence of increase or decrease of water level on F concentration. Most of the samples show a positive relation between ∆h and ∆F, which indicates that fluoride is released into groundwater through the rock-water interaction and it generally decreases due to the dilution after the increase of water level.
Fig. 2

Time series plot of water level (m) represented along the left y- axis, fluoride concentration (mg/l) represented along right y-axis. Time is given in year along the x-axis. From left to right of the figure represents flow direction

Fig. 3

Relationship between water level fluctuation and fluctuation in fluoride concentration at five locations

Moreover, the relations between the hydraulic conductivity (K) of the aquifer, the average ∆h and average ∆F (Table 1) show that, near the discharge area, K values are high with higher ∆h and ∆F values. This reflects the fact that, if fracture connectivity is good, then during monsoon there will be high recharge into the aquifer which leads to high ∆h (as groundwater usage depends on availability) and high recharge dilutes fluoride concentration in groundwater which leads to high ∆F.
Table 1

Table showing relationship amongst hydraulic conductivity (K), water level fluctuation and fluctuation in F concentration

Location

Elevation

K(M/S)

Average ∆h

Average ∆F

W19

654

0.313

3

0.29

W16

647

0.432

4.5

0.29

W11

641

0.169

2.8

0.38

W6

614

2.243

6

0.62

W2

601

1.334

5.2

0.39

4 Conclusions

This study has used groundwater level and fluoride concentration data, and showed that, in this study area, high water level fluctuation is related to high fluctuation in fluoride concentration. However, these high fluctuations are occurring at the discharge area of the watershed, where water gets more time to interact with rocks. Hence, this results in high fluoride in groundwater. Therefore, it can be concluded that high water level fluctuation, high fluctuation in fluoride concentration and high fluoride content are mutually dependent. The discharge area of this watershed needs more attention regarding drinking water sources. Decision makers and planners may implement an alternate drinking water source for the villagers around the discharge area, as this region has high fluoride content most of the time.

References

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Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Ankita Chatterjee
    • 1
    Email author
  • Md. Arshad
    • 2
  • Adrien Selles
    • 3
  • Shakeel Ahmed
    • 1
  1. 1.Academy of Scientific and Innovative Research (AcSIR), CSIR-National Geophysical Research InstituteHyderabadIndia
  2. 2.CSIR-National Geophysical Research InstituteHyderabadIndia
  3. 3.IFCGR, NGRI-BRGM, D3E/NREHyderabadIndia

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