The quality of water is a vital concern for mankind since it is directly linked to human health. The present work is carried out with an objective to assess and map the spatial variability in the groundwater quality parameters in Mandvi Taluka, Surat district Gujarat, India. A total fifty-seven representative ground-water samples from different bore wells and hand pumps from Mandvi Taluka has been collected and analyzed for major cation and anions with fluoride concentration for the pre-monsoon and post-monsoon seasons. Ground water in the region is found alkaline, with presence of bicarbonates in nature and very hard. Weathering and leaching of F - bearing minerals under the alkaline conditions favors the high F - concentration. Presence of low total hardness, low calcium hardness, high chlorides, high bicarbonates and some anthropogenic factors such as intensive and long-term irrigation, heavy use of fertilizers are the supplementary factors to further enhance the F - concentrations in the groundwater. Moreover, GIS spatial distribution maps give better visual image to understand the spatial distribution pattern to overlook better conclusion.
Fluoride though occurs in minor quantities in natural water; due to its impact on human health it gained significant interest. Fluoride in drinking water has both benefit and drawbacks on human health. Low quantity of F− is good for the formation of dental enamel and mineralization of bone [
Geospatial technology in the context of today’s need is the state of the availability and providing service to the end users. The spatial variability and the GIS maps can be used for monitoring of ground water quality and effective decrease of contamination related threats can be achieved. However, GIS includes managing, compiling and analyzing the spatial data. With the help of tools such as Arc GIS Spatial Analyst extension analyzing and modeling of spatial data can be done. In addition, interpolation tools can be used for a set of sample points describing changes in population, landscape, or environmental parameters to visualize the pattern, trend, and variability in the observed data along the surface. Thus, variability in the data like lithology, morphology and their characteristics can be extrapolated along the geographic surface. Thus, it can be said that facility to generate surfaces from the observed sample data makes the interpolation tool more efficient, useful and powerful tool in GIS.
Number of studies has been carried out in this context such as Srinivasamoorthy in 2009 have carried a detailed geochemical study for pre monsoon (PRM) and post monsoon (POM) seasons and identify quality of groundwater to determine its suitability for domestic use in Salem district of Tamilnadu, India [
The study area is having Latitude and Longitude of Mandvi Taluka are 21.15˚N 73.18˚E and having geographical area 829.02 sq. Km experiences a semiarid climate. An average annual rainfall is about 1701.8 mm. Temperature in the study area varies from 30˚C to 42˚C. Alluvial plains situated towards the central parts of the district are characterized by flood plains of the Tapi, Kim and Purna rivers. Topography of the study area is normally plain with gentle slope towards the west.
It comprises rocks like Basalt, Rhyolites, Dolerite/Basalt dyke, Laterite, Argillaceous limestone and clay containing nummulites and clay, friable sandstone, pebbly sandstone, a conglomerate which are remarked as fluoride - bearing minerals areas in Mandvi, Surat. Large thick basaltic aquifers are found in the north-eastern, eastern and south eastern parts of the area. Study area is having black clayey to loamy soil which is due to the presence of basaltic lava in the study area. At some places there is change in the color of soil which is due to the presence of high iron content at places. Soil at piedmont sloppy area ranges from shallow-moderately deep, moderate -severely eroded and non-calcareous in nature. Texture of the soil is varies from silt clay loam to clay loams. Besides, the hydro geological area is basically managed by the geological setting, rainfall distribution, circulation facilities and movement of water which further associates with major and minor porosity of the lithological units to forms the aquifers.
Fifty-seven groundwater sample locations (Hand pump and Bore well) during summer season (PRM) and post monsoon (POM) were taken to analyze the fluoride contamination and other parameters in groundwater at Mandvi Taluka, Surat. To find complete representation for the fluoride contaminated location
and intensity of fluoride in groundwater care has been taken to collect the sample from the same locations only. The Samples were taken using acid washed plastic container to avoid unpredictable changes in characteristic as per standard procedures [
The pH shows strength of water to react with acidic and alkaline materials. The alkaline conditions of groundwater are more favorable for solubility of fluorine bearing minerals and Fluoride solubility in groundwater is strongly influenced by the pH. However, during alkaline medium, desorption of fluorine
Chemical Parameters | Pre-monsoon | Post-monsoon | BIS? (10,500, 2012) | WHO (1984) | |||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Min | Max | Mean | Std. Dev. | Min | Max | Mean | Std. Dev. | DL | PL | ||
pH | 6.53 | 7.95 | 7.19 | 0.32 | 6.98 | 8.15 | 7.66 | 0.27 | 6.5 - 8.5 | NG | - |
Temp | 26.5 | 31.5 | 29.30 | 1.12 | 26.6 | 31.2 | 29.34 | 1.06 | - | - | - |
EC | 204 | 3971 | 942.65 | 624.05 | 280.0 | 3890.0 | 937.94 | 578.88 | 500 | 2000 | - |
TA | 160 | 656 | 343.66 | 114.26 | 200.0 | 706.0 | 341.08 | 106.65 | 200 | 600 | - |
TH | 116.2 | 993.5 | 307.86 | 147.8 | 109.2 | 991.6 | 323.52 | 152.96 | 200 | 600 | 500 |
Ca2+ | 28.6 | 186.2 | 70.17 | 30.39 | 28.0 | 190.0 | 70.21 | 32.69 | 75 | 200 | 75 |
Mg2+ | 7.8 | 144.7 | 32.14 | 24.55 | 2.4 | 138.6 | 38.33 | 26.87 | 30 | 100 | 150 |
F− | 0.17 | 4.17 | 0.98 | 0.78 | 0.18 | 4.98 | 0.91 | 0.91 | 1.0 | 1.5 | 1.5 |
TDS | 192 | 3360 | 696.56 | 479.54 | 250 | 3500 | 801.47 | 581.63 | 500 | 2000 | 500 |
HCO 3 − | 195.2 | 800.3 | 4.16 | 136.81 | 207.0 | 800.0 | 419.24 | 130.49 | 200 | 600 | - |
SO 4 2 − | 16 | 70 | 31.96 | 8.95 | 13 | 136 | 43.61 | 16.95 | 200 | 400 | 400 |
NO 3 − | 1.1 | 36.0 | 11.41 | 9.10 | 1.6 | 84.2 | 32.78 | 14.26 | 45 | NG | 45 |
Cl− | 24 | 250 | 65.05 | 47.62 | 43 | 330 | 107.21 | 60.95 | 250 | 1000 | - |
All the anion and cation values are shown in mg/l, except Temperature in ºC & EC in µS/cm at 25˚C; NG-No Guidelines, DL-Desirable Limit, PL-Permissible Limit.
takes place which ultimately favors the solubility of fluoride dissolution activity [
combination of CO2 with water which forms carbonic acid. In present study maximum samples are alkaline in nature during both the seasons. The spatial distribution map of pH shows (
NE part of the study area, there is a change in the color distribution as compared to PRM, and in the remaining area there is a slight increase in the pH which
shows the variations in the pH is due to the rainfall effect. Thus from the spatial distribution map of pH it can be said that study area indicates and favors an alkaline pH conditions.
The EC (Electrical conductivity) is a measure of an ability to conduct current so that the higher EC indicates the enrichment of salts in the groundwater. The
EC value ranges from 204 to 3971 μS/cm which shows an increasing trend along the groundwater flow direction during POM with respect to PRM (
&
interferes with the absorption of water and nutrients from the soil [
The Total Dissolved Solids (TDS), which indicates concentration of TDS in sample water, is between 192 to 3500 mg/l (
permissible limit of TDS according to Indian Standard which is caused due to the consecutive action of weathering and dilution processes or may be due to the
influence of anthropogenic sources, such as domestic sewage, septic tanks, and agricultural activities. To ascertain the suitability of groundwater for any purpose, it is displayed spatially that some parts of north western, the eastern portion of the study area are exceeding the permissible limit and thus not safe for drinking and irrigation purposes. Moreover, the spatial distribution map of TDS shows increasing trend over the study area during POM as compared to the PRM period. Higher value of TDS is observed towards the NW and SE part of the study area.
The Total Hardness (TH) value ranges from 109.2 to 991.6 mg/l which signifies variation is due to the effect of weathering and erosion of soils which is acting for the period of time (
The concentration of Ca2+ is between 28 mg/l to 190.0 mg/l, whereas the concentration of Mg2+ ranges from 2.4 mg/l to 138.6 mg/l respectively. Calcium also participates in cation exchange equilibriums at aluminosilicate and other mineral surfaces. In some locations Mg2+ > Ca2+, this may be due to the influence of sea water and also suggests that study area is having a meteoric origin in groundwater [
The spatial distribution map of calcium hardness (
The major source of alkalinity includes dissolved carbon dioxide species, bicarbonates, and carbonates. Carbon dioxide species are important contributors in reactions that control the pH of natural waters. The concentration of Total Alkalinity ranges from 160 to 706.6 mg/l, which is being controlled by bicarbonates ions. Carbon dioxide is introduced through atmospheric and biological processes contribute to the carbonate alkalinity. The action of CO2 upon the alkaline material of soil and geology in the study area results in high bicarbonates in the groundwater [
Sulphate is generally found in air, soil and water. Large amount of sulfur is released due to the combustion of fossil fuels. These reduced forms of sulfur in atmosphere are oxidized to sulphate in presence of oxygen and gets deposited with precipitation or deposit in dry form. Moreover, it is mobile in groundwater because it occurs as a dissolved ion. In addition to this, gypsum and sodium sulphate minerals are an important source in many aquifers containing high amount of sulphates. For the present study concentration of sulphate ranges from 13mg/l to 136 mg/l during PRM and POM and all the samples are within the permissible recommended limits (
The amount of nitrate-nitrogen approach or exceed due to the nitrogenous organic waste, or animal waste or due to the application of chemical fertilizers. The nitrate ion concentration varies from 1.1 to 84.2 mg/l (
All natural waters contain chloride but low in concentrations. Chloride may originate from various sources such as dissolution of crystalline and shale rocks, clay and other related minerals. Furthermore the concentration of chloride ranges from 24 mg/l to 330 mg/l indicating dissociation and dissolution of Cl− from the upper layer of the soil (
Depending upon the prescribed range of F− concentration given for the drinking water as per BIS-10500 the study area is categorized into three categories: less than 0.60 mg/l as low F− category; between 0.60 - 1.20 mg/l as moderate F− category (optimum range) and greater than 1.2 mg/l as High F− category [
During POM, 33.3% of all the samples fall in moderate F− category i.e. optimum range. Whereas, 45.6% of the total groundwater samples are categorized under low-F− category and falls in the SE and NW region of the study area. The
Chemical Parameter | F− range (mg/l) | |||||
---|---|---|---|---|---|---|
<0.6 | 0.6 - 1.2 | >1.2 | <0.6 | 0.6 - 1.2 | >1.2 | |
Pre-monsoon | Post-monsoon | |||||
pH | 7.15 | 7.16 | 7.29 | 7.67 | 7.69 | 7.62 |
EC | 864.11 | 960.18 | 957.12 | 855.59 | 1009.54 | 1003.01 |
TA | 258.94 | 353.47 | 419 | 291.96 | 374.21 | 395.08 |
TH | 316.93 | 324.88 | 272.78 | 349.32 | 294.17 | 276.08 |
Ca2+ | 78.29 | 67.76 | 59.29 | 83.85 | 70.59 | 53.07 |
Mg2+ | 29.42 | 60.08 | 53.29 | 59.58 | 47 | 52.77 |
F− | 0.38 | 0.91 | 1.98 | 0.34 | 0.92 | 2.12 |
TDS | 650.94 | 706.59 | 718.15 | 879.12 | 747.42 | 718.83 |
HCO 3 − | 315.91 | 431.23 | 511.18 | 352.26 | 452.7 | 511.4 |
SO 4 2 − | 28.24 | 31.71 | 37.69 | 43 | 43.79 | 44.67 |
NO 3 − | 10.84 | 11.48 | 12.23 | 33.84 | 32.83 | 30.43 |
Cl− | 52.59 | 67.97 | 72.77 | 88.12 | 114.06 | 137.75 |
All the anion and cation values are shown in mg/l, except Temperature in ºC & EC in µS/cm at 25˚C.
remaining water samples (21.1%), are classified as high F− category, and are towards the NE, NW and southern parts of the study area. It was observed that Fluoride (F−) concentration was higher during POM which may be due to the dissolution and precipitation of F− bearing minerals along with the adsorption/desorption from metal (hydro) oxides and clay minerals which are found under alkaline conditions and that goes weathering chemical process which leads to higher concentration of Fluoride (
Usually, precipitation of salts, together with fluoride salts, remains in the upper layer of soil is caused due to the high rate of evapotranspiration and this act as source for easily dissolvable fluorine after monsoon. While during POM, an adequate addition of Fluoride with an increase in TDS results in high concentrations of salts due to the leaching of infiltrating waters from the soils [
Moreover, the increase in contact time increases the ion-exchange between OH− in water to F− in the mineral and these results in enhancing the concentration of F− in ground waters. Further, higher values of TDS also increase the dissolution of CaF2 in the ground water [
Also, as shown in
Moreover, intensive and long-term irrigation with heavy application of fertilizers in the district could be another factor that causes weathering and leaching through circulating water from the weathered products which dissolves and leaches the minerals, including fluorine [
From the detailed analysis and study, it can be said that by the action of carbon dioxide in water on carbonate rocks such as Basalt, Rhyolites, Dolerite/Basalt dyke, Laterite, Argillaceous limestone and clay containing nummulites and clay, friable sandstone, pebbly sandstone, conglomerate etc., high amount of bicarbonates ( HCO 3 − ) are produced and thus forming an alkaline environment. In addition this, chemical weathering under semiarid conditions with high TDS, low total hardness in the rocks and soils with hydro-geochemical processes like dissociation, ion-exchange, dissolution, and some anthropogenic inputs like the heavy use of fertilizers, domestic sewage, leakage from septic tank and animal waste which affect the concentration of fluoride and contributing fluoride to the ground water. Thus, due to the dissolution and precipitation of F− bearing minerals along with the adsorption/desorption from metal (hydro) oxides and clay minerals which are found under alkaline conditions and that goes weathering chemical process which leads to higher concentration of Fluoride.
Prajapati, M., Jariwala, N. and Agnihotri, P. (2018) Geochemical Evaluation of Groundwater in the Mandvi Taluka of Surat, India. Journal of Environmental Protection, 9, 67-89. https://doi.org/10.4236/jep.2018.91006