M. Nepolian

Identification of the geochemical processes in groundwater by factor analysis in hard rock aquifers of Madurai District, South India

A study was carried out in the Madurai district of Tamil Nadu, India to identify the hydrogeochemical processes using factor analysis as a predictive tool. It also focuses on characterizing the samples of these factors with respect to standard geochemical plots. In order to obtain a synoptic view of the statistics and the geochemical processes, a total of 53 groundwater samples are collected representing the entire district. The major ions were analyzed; the order of ion dominance are Ca2+u2009>u2009Na+u2009>u2009Mg2+u2009>u2009K+u2009=u2009Cl−u2009>u2009HCO−3u2009>u2009H4SiO−4u2009>u2009NO−3u2009>u2009SO2−4u2009>u2009P3−4. The samples are classified according to three factors. Factor 1 shows strong positive loadings of Cl−, Ca2+, Mg2+, and NO−3 with 36.98xa0% of the total variance (TV); factor 2 accounts for 13.72xa0% of TV with high loadings of Na+, K+, and HCO−3; and factor 3 shows strong positive loadings of PO3−4 and SO2−4 with TV of 13.1xa0%. In the Piper plot, few samples fall in the mix region as evidenced by the mixing proportion of two samples using AQUACHEM software. The results suggest that different hydrogeochemical processes, like weathering, ion exchange processes, and anthropogenic activities (like sewage infiltration and agriculture), has predominant impact in the study area. Thus, the study highlights the factor analysis technique as a predictive and effective tool for groundwater evolution.

A study on the impact of weathering in groundwater chemistry of a hard rock aquifer

Hydrogeochemistry of groundwater in hard rock terrain are mainly governed by lithology and land use practices. A study area near Madurai region of central Tamil Nadu was selected with various litho-units and a hard rock sedimentary contact with an unconformity. Land use practices in these regions are also varied with lithology. The study was conducted by collecting 54 groundwater samples spatially covering the major litho-units. Collected samples were analyzed for electrical conductivity, pH, total dissolved solids (TDS), temperature, Ca, Mg, Na, K, Cl, HCO3, NO3, H4SiO4, PO4, and SO4. The results of the samples analyzed found to vary spatially. Dominance of ion shows that the alkalies are predominant and HCO3 is the dominant anion. Piper facies show that the samples are alkali-carbonate type indicating the predominance of weathering. Most of the parameters exceed the drinking water permissible limit. Standard plots and statistical analysis also indicate weathering as the major process governing the hydrogeochemistry of the groundwater in the region. Relative mobility of cations indicates that the rate of liberation of alkalies from the lithology is more prominent.

A multivariate statistical approach to identify the spatio-temporal variation of geochemical process in a hard rock aquifer

A study has been carried out in crystalline hard rock aquifers of Madurai district, Tamil Nadu, to identify the spatial and temporal variations and to understand sources responsible for hydrogeochemical processes in the region. Totally, 216 samples were collected for four seasons [premonsoon (PRM), southwest monsoon (SWM), northeast monsoon (NWM), and postmonsoon (POM)]. The Na and K ions are attributed from weathering of feldspars in charnockite and fissile hornblende gneiss. The results also indicate that monsoon leaches the U ions in the groundwater and later it is reflected in the 222Rn levels also. The statistical relationship on the temporal data reflects the fact that Ca, Mg, Na, Cl, HCO3, and SO4 form the spinal species, which are the chief ions playing the significant role in the geochemistry of the region. The factor loadings of the temporal data reveal the fact that the predominant factor is anthropogenic process and followed by natural weathering and U dissolution. The spatial analysis of the temporal data reveals that weathering is prominent in the NW part and that of distribution of U and 222Rn along the NE part of the study area. This is also reflected in the cluster analysis, and it is understood that lithology, land use pattern, lineaments, and groundwater flow direction determine the spatial variation of these ions with respect to season.

Occurrence of the radionuclides in groundwater of crystalline hard rock regions of central Tamil Nadu, India

A study was conducted to understand the occurrence of the radionuclides in groundwater of crystalline hard rock region. Samples were collected to analyze major cations, anions, U, 222Rn and stable isotopes of oxygen, hydrogen. It was inferred that few samples have U and 222Rn concentrations higher than the permissible limit of drinking water standard. High degree of weathering of granitic rocks and long contact time of groundwater with the aquifer matrix could be the reason for enhanced U and 222Rn levels in groundwater. The association of U with SO4 also proves that there exists anthropogenic influence in groundwater composition.

Identification of Recharge Processes in Groundwater in Hard Rock Aquifers of Madurai District Using Stable Isotopes

Stable isotopes of H and O are the integral parts of water molecule and serve as ideal tracers to understand the recharge processes in groundwater. Hence, a study has been conducted in hard rock aquifers of Madurai District of Tamilnadu to identify the recharge processes using stable isotopes. A total of 54 groundwater samples were collected representing the entire district from various lithounits during post monsoon. Samples were analysed for pH, EC, Ca2+, Mg2+, Na+, K+, Cl− HCO3−, SO42−, PO43−, H4SiO4, F−, δ18O and δD. Cl− and HCO3− were the dominant ions in groundwater samples. Average values of Cl− and HCO3− ranged from 247 and 244xa0mg/L in fissile hornblende biotite gneiss, 262 and 268xa0mg/L in Charnockite, 75 and 185xa0mg/L in quartzite, 323 and 305xa0mg/L in granite, 524 and 253xa0mg/L in floodplain alluvium rock types. Geochemical signatures of groundwater were used to identify the chemical processes that control hydrogeochemistry. Interpretation of δ18O and δD indicates recharge from the meteoric water in charnockite, quartzite, granite and some samples of fissile hornblende biotite gneiss. It is also inferred that recharge take place from evaporated water in floodplain alluvium and fissile hornblende biotite gneiss.

A study on variation in dissolved silica concentration in groundwater of hard rock aquifers in Southeast coast of India

Ground water of hard rock aquifers due to its lesser permeability results in the increased residence time, which leads to the higher concentration of ions. Hence in order to understand the hydro-geochemistry of the groundwater of a hard rock aquifer in India, 23 groundwater samples were collected from different locations of the study area and subjected to analysis of major cations and anions. The results of silica showed different range of concentration and was plotted in different groups. In order to understand the reason for this variation, different techniques like Thermodynamics, Statistics and GIS were adopted and it was inferred that the concentration was mainly governed by lithology and land use pattern of the study area.

Assessment of hydrogeochemical status of groundwater in a coastal region of Southeast coast of India

A study was conducted in a coastal region of Cuddalore district of Tamil Nadu, India, to identify the hydrogeochemical processes controlling the groundwater chemistry. The major geological units of the study area are sandstone, clay, alluvium, and laterite soils of Tertiary and Quaternary age. A total of 64 groundwater samples were measured for major ions and stable isotopes. Higher electrical conductivity values indicate the poor quality groundwater along the coastal region. Saline water intrusion mainly affects the hydrochemical composition of the aquifer water reflected by Na–Cl-type waters. Cl−/(Cl−xa0+xa0HCO3−) ratio also indicates the mixing of fresh groundwater with saline water. The results of δD and δ18O analyses show that isotopic compositions of groundwater ranges from −xa07.7 to −xa02.1‰ for δ18O and from −xa055.6 to −xa018.5‰ for δD. Correlation and factor analysis were carried out to find the association of ions and to determine the major factors controlling the groundwater chemistry of the region. The study indicates that ion exchange, weathering, salt water intrusion along the coast, and anthropogenic impacts are the major controlling factors for the groundwater chemistry of the region.

Spatio-temporal Identification of Regions with Anomalous Values of 222Rn in Groundwater of Madurai District, Tamilnadu, India

Measurement of dissolved radon (222Rn) activity concentration in groundwater samples from private and public hand pumps, and in bore wells located at Madurai district of Tamilnadu, India, are presented. The study attempts to identify the background value of 222Rn in groundwater of hard rock terrain and the main aquifer contributing 222Rn, and to determine if any correlation exists with observed field parameters. Measured parameters included pH, TDS, Temperature and 222Rn in 42 samples for two seasons (South West Monsoon [SWM] and North East Monsoon [NEM]). The results show that the 222Rn activity concentration of the samples ranged from 0.049 to 59.952xa0Bq/L in South west monsoon and 0.12 to 211.60xa0Bq/L in North east monsoon. The higher activity was noted in NEM and the highest 222Rn concentrations were observed in granitic terrains in both seasons. The average values of the parameters studied shows that there is a general decrease of TDS and Temperature, but an increase in 222Rn and pH during NEM. The spatial representation of the activity shows that maximum values are in the north eastern part of the study area. Further, correlations between the measured parameters show that temperature has a negative correlation to the samples of charnockite formation during both seasons; pH and TDS also show negative relationships to 222Rn during SWM.

Spatial and temporal variations of radon concentrations in groundwater of hard rock aquifers in Madurai district, India

Radon (222Rn) and other radionuclides in groundwater can lead to health problems if present in higher concentrations. A study was carried out in Madurai district of Tamilnadu by collecting groundwater samples for four different seasons and aims to identify the regions with higher 222Rn concentration along with their spatial and seasonal variations. 222Rn has been compared with field parameters, log pCO2, major ions and uranium to detect the factors responsible for the higher concentration in groundwater. The weathering process induces the release of higher uranium ions from the granitic terrain from the rock matrix which enhances the 222Rn levels in groundwater.