HYDROGEOCHEMICAL STUDIES AND GROUNDWATER QUALITY EVALUATION IN HANUR WATERSHED, KOLLEGAL TALUK, CHAMARAJNAGAR DISTRICT, KARNATAKA STATE, SOUTH INDIA

K. Siddaraju, D. Nagaraju, H. M. Bhanuprakash, H. M. Shivaswamy and A. Balasubramanian. Department of Studies in Earth Science, Manasagangotri, Mysuru, 570006 Karnataka, India. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

Groundwater is becoming a scant resource in part of Kollegal taluk, Chamarajnagar District, Karnataka State. This area receives an average annual rainfall of 696 mm. Groundwater has been the major sources of irrigation and drinking purpose for several years almost 80 percent of area is underlain by hard rocks. The study area is drought prone, most of the people in this area depend on groundwater for drinking water and agriculture. Therefore, constant monitoring and assessment of water resource is necessary. The study area is bounded by Yelandur and T. Narasipura Taluk to the west, Mandya and Bangalore to the North, and East and South it is bounded by Dharamapuri District of TamilNadu this area is located in the south eastern corner of Karnataka. The area is located between 77 0 5 1 to 77 0 30 1 East longitude 11 0 45 1 to 12 0 15 1 North latitude with an areal extent of 1026sq km covering 138 villages coming under the Survey of India Toposheet (SOI) numbers are 57 H/4, 57H/7, 57H/8,, 58E/1 and 58E/5. The study area comes under the semiarid region. In recent years, this region has been facing water scarcity as well as water quality problems. The major sources of employment are sericulture, agriculture and horticulture, engaging almost 70% of the workforce. Water samples have been collected from 68 locations of the study area, during the monsoon year 2016, The collected samples were analysed for chemical parameters. In the study area Ca-Mg-HCO3 type of water predominates during the mansoon season of year 2016. On the basis of hydro-chemical facies classification the water is found to be suitable for irrigation.The other evaluated parameters are SAR, RSC, salinity sodium hazard and USSL Classification.

…………………………………………………………………………………………………….... Introduction:-
Water is the most important commodity for all living things, in rural as well as urban areas Because of increase, in agricultural and domestic activities, the demand is increasing. Quantity of water without quality is of no utility and hence chemical quality of water has gained equal importance along with quantity. The quality of any water may be altered due to over usage of fertilizers and other biogenic activity. The chemistry of host rock through which the groundwater flows below the earth surface and the total time of residence of the water with the host material control the chemistry of groundwater. The present study aims to obtain comprehensive information on the quality of Study Area:-Hanur Watershed of Kollegal taluk, Chamarajnagar District is located in the south eastern corner part of Karnataka state between 77 0 5 1 to 77 0 30 1 East longitude 11 0 45 1 to 12 0 15 1 North latitude (Figure 1). It covers an area of 1026 sq.km. Groundwater is influenced by underlaying lithology, structures, soil types thickness and structure of rock formations. Weathered and fractured charnokites, hornblende/ampibolite schist form the main aquifer in Hanur watershed. Groundwater in the study area occurs under water table conditions in the weathered and fractured charnokites, hornblende/ampibolite schist ( Figure 2); there is no perennial river in the study area. Most of the people depend on groundwater resource for their domestic and agricultural requirements, the major ion chemistry of groundwater of Hanur watershed has not been studied earlier. During the monsoon period in the year 2016, 68 Samples were collected from the different locations of the study area. The collected water samples were transferred into precleaned polythene container for analysis of chemical characters. Chemical analyses were carried out for the major ion concentrations of the water samples collected from different locations using the standard procedures recommended by APHA-1994. The analytical data has been used for the classification of water for utilitarian purposes and for ascertaining various factors on which the chemical characteristics of water depend.

Methodology:-
As stated earlier, 68 locations Groundwater samples were collected from Hanur watershed during monsoon period 2016 ( Figure 3). The collected water samples were stored in pre-treated polythene bottles and transferred laboratory for analysis of major chemical elements -Ca +2 , Mg +2 , Cl -1 , HCO 3 -1 Na +1 , K +1 , and SO 4 -2 . Using the standard procedures recommended by APHA-1994.

Results and Discussion:-
The Groundwater quality reveals that the pH varies from 6.28 to 9.4, EC ranges from 86 to 2670 μmho/cm, total dissolved solids(TDS) values range from 385 to 1926 mg/l, calcium varies from 20 to 179 mg/l, Mg varies from 14 to 109 mg/l, Na+k varies from 21 to 546 mg/l, Cl values range from 14 to 376 mg/l, Co3 values range from 0 to 93 mg/l, HCO3 values range from 152 to 646 mg/l, SO4 values range from 0.5 to 552 mg/l, NO3 values range from 0 to 62 mg/l in water of the study area. Chemical data of water samples are given in Table 1. Year -2016 Table 1    Hydrochemical facies are distinct zones that projects the dominating cation and anion concentration in water. To define the composition class, Back and co-workers suggested various sub divisions within the tri-linear diagram ( Figure 5). The interpretation of distinct facies from the 0 to 10% and 90 to 100% domains, on the diamond shaped cation to anion graph, is more helpful than using equal 25% increments. It clearly explains the variations or domination of cation and anion concentrations. Groundwater Hardness is important parameters for water use and consumption. Hardness is caused primarily due to the presence of cations such as calcium and magnesium and anions such as carbonate, bicarbonate, chloride and sulfate in water. Wilcox classified groundwater for irrigation purposes based on % sodium and electrical conductivity. Eaton recommended the concentration of Residual Sodium Carbonate to determine the suitability of water for irrigation purposes. The US-Salinity Laboratory of the Department of Agriculture adopted certain techniques based on which the suitability of water for agriculture is explained. The sodium in irrigation waters is usually denoted as per cent sodium and can be determined using the following formula. % Na = (Na+) X 100/ (Ca 2 + + Mg 2 + + Na +1 + K +1 ) That is the quantities of Ca 2+, Mg 2+ Na + and K + are expressed in milliequivalents per liter (epm).  Figure.7 Sodium Percentage of the study area Table 3:-Groundwater quality based on RSC (Residual Sodium Carbonate).
The classification of groundwater samples with respect to per cent sodium is shown in (Table 2). It is observed that about 10 samples are excellent, 24 samples are good, 30 samples are permissible in this limit and 4 samples are doubtful. In waters having high concentration of bicarbonate, there is tendency for calcium and magnesium to precipitate as the water in the soil becomes more concentrated. As a result, the relative proportion of sodium in the water is increased in the form of sodium carbonate. RSC is calculated using the following equation.

) -(Ca 2 + + Mg 2+ )
That is all ionic concentrations are expressed in epm. The most important characteristics of irrigation water in determining its quality are: (i) Total concentration of soluble salts; (ii) Relative proportion of sodium to other principal cations; (iii) Concentration of boron or other element that may be toxic, and (iv) Under some condition, bicarbonate concentration as related to the concentration of calcium plus magnesium. These have been termed as the salinity hazard, sodium hazard, boron hazard and bicarbonate hazard. In the past, the sodium hazard has been expressed as per cent sodium of total cations. A better measure of the sodium hazard for irrigation is the SAR which is used to express reactions with the soil. SAR is computed as where all ionic concentrations are expressed in epm.  The classification of groundwater samples from the study area with respect to SAR is represented in (Table 4). The SAR value of all the samples are found to be less than 6, and are classified as excellent for irrigation. When the SAR and specific conductance of water are known, the classification of water for irrigation can be determined by graphically plotting these values on the US salinity (USSL) diagram ( Figures 10&11).    Figure 11:-USSL classification of water samples.

RSC
For the purpose of diagnosis and classification, the total concentration of soluble salts (salinity hazard) in irrigation water can be expressed in terms of specific conductance. Classification of groundwater based on salinity hazard is presented in Table 5. It is found from the EC value; only 2 samples are found to be unsuitable for irrigation purposes. Table 5 shows the Salinity hazard classes. In the study area, the groundwater is generally Ca-Mg-HCO 3 type, which is mainly due to the geology of the area which comprises igneous rocks of crystalline nature, in which the major units are Charnokites and hornblende schist. Groundwater in the study area occurs under water table conditions in the weathered and fractured Charnokites and hornblende schist.

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Conclusions:- Ca-Mg-HCO 3 type of water predominates in the study area during the Year 2016,  Though the suitability of water for irrigation is determined based on SAR, %Na, RSC and Salinity hazard, it is only an empirical conclusion. In addition to water quality, other factors like soil type, crop type, crop  Pattern, frequency and recharge (rainfall), climate, etc. have an important role to play in determining the Suitability of water.  Water that is not suitable based on the above classification may be suitable in well-drained Soils.  The suitability of water for irrigation is evaluated based on SAR, %Na, RSC and salinity hazards. Most of  the samples in Study area fall in the suitable range for irrigation purpose either from SAR, % Na or RSC  Values.  About 98% of the samples are grouped within C 2 S 1 and C 3 S 1 classes (Figures 10 & 11).  Most of the samples in study area fall in the suitable range for irrigation purpose from USSL diagram.