Major Ion Chemistry and Groundwater Quality Evaluation for Irrigation

Hydrogeochemical characteristics of Groundwater analyzed in the study area of Coimbatore district by collecting 60 samples from agricultural belt. Groundwater quality for irrigation is determined by several key factors like pH, Electrical conductivity (EC), Total suspended solids (TDS). The cations such as Sodium (Na), Potassium (K), Calcium (Ca), Magnesium (Mg ) and anions are Hydrocarbon (HCO3), Carbonate (CO3), Chlorides (Cl)and Sulphates (SO4) are tested. The irrigation water quality parameters such as Residual Sodium Carbonate (RSC), Sodium Absorption Ratio (SAR), Chloro Alkali Indices (CA I & CAII), Kelley’s Ratio (KR), Magnesium Hazard (MH), Percent sodium (%Na) and Permeability Index (PI), Soluble sodium Percent (SSP) are computed from the key factors, anions and cations. From the USSL Diagram the samples fall in C2S1, C3S1, C4S1 range. Salinity hazard is too elevated in the study area, all the samples are categorized under high to very high with the values greater than 750 μS/cm. Total dissolved solid in the study area indicated that only 2 locations are unfit for irrigation. SAR and % Na shows that there is no hazard related to irrigation watering. Magnesium hazard in the groundwater is high and indicates 51 sample out of 60 is unsuitable for irrigation. From the study it indicates the groundwater is contaminated with salt content and in most of the area it can be used for irrigation. DOI: https://dx.doi.org/10.4314/jasem.v24i4.23 Copyright: Copyright © 2020 Shyamala et al. This is an open access article distributed under the Creative Commons Attribution License (CCL), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Dates: Received: 07 February 2020; Revised: 19 March 2020; Accepted: 27 March 2020

Management of groundwater is vital for the sustainable growth of nation. From the past decade groundwater is becoming an important source of water supply worldwide (Yousif et al., 2013). It is known for its natural protection from contaminants. Gradually the groundwater quality has worsened in some provinces, leading to bitter consequences. Removing pollutants from the groundwater is a challenging task, sometime impossible due to its long residence time (Ahamed and Jayakumar 2015).
Quality of groundwater is likewise significant to its quantity owing to the suitability of groundwater for numerous functions (Shyamala et al.,. 2017). Groundwater is an essential component of our life support system. Groundwater is less contaminated contrasted with surface water, anyway because of fast development of population, urbanization, industrialization and rural growth, groundwater assets are under danger (Srinivas et al., 2015). Soil layers and rock contains minerals which get disintegrated in groundwater as it goes through it. Hurtful contaminants get related with the groundwater through the procedure of leakage from the surface water and natural factors (Selvakumar et al., 2014)(Krishna et al., 2016. The chemical composition of groundwater is constrained by numerous elements, including the precipitation, topographical structure, mineralogy of springs, land forms inside the spring, alongside effect of outside contamination like releases from agricultural activity, industrial activity and urbanization (Aghazadeh and Mogaddam 2010) (Ahamed and Jayakumar 2015). Ramkumar conducted studies to estimate the water quality of Kottur block, Thiruvarur district, Tamil Nadu. Control of cations in the order of Na + >Ca 2+ >K + >Mg 2+ and anions Cl -> So4 2->HCO3 ->No3 was observed in both seasons (Ramkumar et al., 2013). Oyem analysed the concentration of selected heavy metals in the groundwater. The result of this analysis did not reveal any strong or significant inter-metal relationship in the groundwater. (Oyem and Usese, 2015).
Srinivas collected and examined the groundwater samples according to published guide lines. Sodium is the most dominant cation when compared with chlorides and hydrocarbonate. Total dissolved solid ranges between 67 and 2086 mg/l with a mean of 523mg/l (Srinivas et al., 2015). .
Nishanthiny conducted groundwater quality analysis based on irrigation water quality. Residual sodium carbonate was used to find suitability of groundwater for irrigation use. Overall assessment of the tested well indicated very well that 20.6% wells have a good quality of water and 44.1% of the well have permissible to desirable irrigation water quality and 35.3% of the well have a unsuitable irrigation water quality (Ramesh et al., 2020). High SAR in irrigation water transforms the physical construction of the soil particles. Soil particles are attracted towards sodium and adsorbed on the surface, making soil impervious (Mohamed et al. 2018). Salinity condition exists as salt gets accumulated in the root zone of the plants, if the groundwater with high TDS is irrigated continuously. Shanmugasundharam used Wilcox diagram to determine the aptness of groundwater for irrigation purpose. (Shanmugasundharam et al.,. 2015). Venkateswaran and Vediappan (2013) investigated suitability of groundwater quality for agricultural use in lower Bhavani reservoir. He computed sodium kelley ratio, absorption ratio, magnesium hazard, Percentage Sodium Permeability Index and Residual Sodium Carbonate(RSC) along with wilcox diagram and USSL diagram. High salinity was observed in most of the location, hence ample drainage should be provided to improve crop yield  (Shyamala and Jeyanthi 2017).

MATERIALS AND METHODS
Study area: Coimbatore is agriculture based district with the area of 4723 sq km. It is situated at the altitude of 411 meters above mean sea level. It is one of the largest city in Tamil Nadu state Coimbatore District is composed of rocks of Dharwar age, which is of high grade metamorphic rocks. The hydro geological framework of the district is controlled by the distribution of rainfall, geological structure and morphological configuration. The area is covered by metamorphic rock of type archean, alluvium, colluviums, laterite, charnockite, hornblende, biotite gneiss, garnet sillmanite gneiss, pegmatite and quartz veins. To initialize the task of groundwater quality assessment visit was made to the irrigation fields and residential area to identify potential of groundwater in the area. Depth of the sample extraction in the study area was in the range of 30 ft to 250 ft. In total 60 groundwater samples have been drawn from borewells and open wells. The samples were gathered in plastic containers, sanitized with distilled before gathering groundwater.

RESULTS AND DISCUSSION
Irrigation water quality parameters: In the study area of Coimbatore district 60 samples were collected from agricultural belt. Water quality for irrigation is determined by several key factors like Salinity Hazard (SH), Sodium Absorption Ratio (SAR), Total Suspended Solids (TDS), Percent Sodium (%Na), Residual Sodium Carbonate (RSC), Kelley's Ratio (KR), Magnesium Hazard (MH), Chloro Alkali Indices (CAI & CAII), Soluble sodium Percent (SSP) and Permeability Index (PI) (Prasanna et al.,. 2011), (K. Ramesh andVennila 2012), (Magesh and Chandrasekar 2013). Quality of water for irrigation is determined by several key factors as shown in the Table 1. Salinity Hazard: Electrical conductivity is excellent measure to determine salinity hazard to crops as it reveal TDS in groundwater(B Arun Kumar et al. 2018). High EC indicates elevated salt content water. Excess salinity will reduce the osmotic activity of plants and thus hinder with the assimilation of water and nutrients from the soil. EC indicates the presence of sodium & chloride ions, which may be due to the use of fertilizer in turn due to fertilizers. Ions may be positively or negatively charged, which are produced by breaking of compounds that conduct electricity. Mobility of ions dissolved in water increases conductivity. Total dissolved solids can be indirectly measured from electric conductivity. Limiting value for electrical conductivity is provided in the Table 4.4, out of 60 samples tested none of the samples are in the category of low or medium. High electrical conductivity is observed in 54 samples and 6 samples are of very high electrical conductivity i.e. in the range greater than 2250 µS/cm. USSL diagram is plotted for electrical conductivity and sodium absorption ratio.
Most of the samples fall in low SAR and high to very high EC range as shown in Figure 1. Total dissolved solids can be indirectly measured from electric conductivity. Limiting value for electrical conductivity is provided in the Table 2, out of 60 samples tested none of the samples are in the category of low or medium. High electrical conductivity is observed in 54 samples and 6 samples are of very high electrical conductivity i.e. in the range greater than 2250 µS/cm.

Fig. 1 USSL diagram for Salinity Hazard
Total Dissolved Solids: Groundwater contains negligible quantity of suspended solid as these are filtered out by soil strata through mechanical straining action (Omonona et al., 2014). The amount of suspended solids in groundwater increases with input of manmade contamination. Total Suspended Solids in the study location is shown in the Table 4.5. In 60 Samples considered for analysis 58 samples are fit for agricultural usage and 2 samples are unfit for both potable drinking and agricultural usage. Presence of Total Dissolved Solids is owing to sediments or the contact of water with atmosphere or soil.   All the samples in the study location are in 60 % hence it falls in the range of excellent to permissible category ( Table 5). As per sodium concentration the groundwater does not have negative impacts like growth retardation or yield reduction. Table 5 shows the categorization of agricultural water quality based on percent sodium. All the 60 samples fall in the group of excellent to permissible category. Electrical conductivity and percentage sodium is represented in Wilcox diagram. Wilcox diagram (Fig. 2) is used to evaluate the appropriateness of groundwater for irrigation using percent sodium and electric conductivity. It is categorized ad very good to good, Good to permissible, Doubtful to unsuitable, unsuitable and permissible to doubtful. In the study area most of the sample fall in three categories Good to permissible, Doubtful to unsuitable and permissible to doubtful.
Residual Sodium Carbonate: Water with a carbonate concentration larger than the calcium and magnesium concentration is recognized by the term "residual sodium carbonate". Residual Sodium Carbonate index (RCS) refers alkalinity hazard to soil. If the sodium in clayey soil is higher it causes swelling and reduces infiltration capacity. The potential of sodium vulnerability is increased as Residual sodium carbonate (RSC) raise. Residual Sodium Carbonate (RSC) is intended from the formula 3 To identify the aptness of groundwater in clay soil RCS index is used. If the groundwater with elevated RCS is applied for irrigation it leads to alkali soil formation. As per calculated RCS index for the 60 samples collected in agricultural belt, 58 samples have low RCS value less than 1.25 and is apt for irrigation as shown in the Table 6. Kelley's proportion (KR) of more than 1 reveals to an abundance level of sodium in waters. Subsequently, waters with a Kelley's Ratio are most suitable for irrigation, while those with a proportion more than one are unacceptable for irrigation. 60 samples were analysed in the agricultural area and the Kelley ratio falls less than 1 for all the samples which shows the groundwater is apt for irrigation in the study area (Table 7). Magnesium Hazard: Groundwater with elevated concentration of magnesium, if used for irrigation purpose damages soil structure and causes high salinity. Calcium and magnesium are present in water in an equilibrium state and they behave independently in soil system. Magnesium hazard is given by the equation 5 From the analysis MH value for the samples are in the ranges from 35.68 to 77.89. MH value should be less than 50meq/l, Out of 60 samples 9 samples were apt for agriculture as per magnesium hazard revealed in the table 4.10. If the magnesium hazard value is greater than 50 meq/l it affects plant growth and becomes unsuitable for agricultural use, In the widely held number of the samples in the study area i.e in about 51samples the Magnesium Hazard value is above 50meq/l which makes it unsuitable for agricultural use. Total hardness as CaCO3: Hardness in water is brought about by the occurrence of divalent metallic cations like calcium, magnesium, ferrous iron, strontium, manganese and so on. It is relevant to take note of that the greater part of the industrial sector in the zone pre-treat water to evacuate hardness; else it blocks the working of their boilers. In the examination zone 56 examples are in the class of hard to hard. Soluble sodium Percent (SSP): Soluble Sodium Percent (SSP) for groundwater was determined by using the formula 4.6. The groupings of Ca2+, Mg2+ and Na+ are articulated in mill equivalents per liter. The solvent Sodium Percent (SSP) values under 50 or equivalent to 50 signify great quality water and in the event that it is in excess of 50 it denotes the intolerable water quality for water for irrigation (Kshetrimayum and Bajpai 2012).
Permeability Index: Permeability index of the groundwater is calculated using sodium, carbonates, calcium and magnesium. Groundwater for irrigation is investigated dependent on the Permeability Index (PI). PI is computed from the equation 7. Durov diagram: Durov diagram is plotted using rockwork software version 16 as shown in Fig. 4. It has two base triangle and 1 square. All the cation and anion in the samples are projected as points in the triangular portion of the drawing. The plots in the triangular portion are transferred to square grid. The upper part of the triangle represents carbonates, bicarbonates and sulphates.  The horizontal part of the triangle represents calcium and magnesium. The samples of similar ionic composition are clustered together. From the figure Cldominated the HCO3 -, CO3 -, SO4 2in the anionic plot. Cationic plot reveals that magnesium ion and calcium ion dominates the other cations. It is revealed from the plot, that the water quality in the study location is dominated with calcium and magnesium .The weathering of metamorphic rock and the hydrogeological framework in the study location might be the grounds for calcium magnesium dominance. The dominance of ions in ground water is Ca, Mg and Cl as per piper diagram generated from Rockworks 17.
Conclusion: High level of EC and Total Hardness is noted in few areas. The water category is Ca-Mg-Cl type, as it is analyzed by piper diagram. According to the Wilcox graph the greater part of the example falls in the permissible range. In the total sample of 60 tested, 11 sample location SAR value is below 6. Magnesium risk is high in the study area. The outcomes depict that water quality falls in the classification of high in saltiness and low in SAR according to USSL outline.