Identification of major sources controlling groundwater chemistry from a hard rock terrain — A case study from Mettur taluk,Salem district,Tamil Nadu,India

The study area Mettur forms an important industrial town situated NW of Salem district. The geology of the area is mainly composed of Archean crystalline metamorphic complexes. To identify the major process activated for controlling the groundwater chemistry an attempt has been made by collecting a total of 46 groundwater samples for two different seasons, viz., pre-monsoon and post-monsoon. The groundwater chemistry is dominated by silicate weathering and (Na + Mg) and (Cl + SO₄) accounts of about 90% of cations and anions. The contribution of (Ca + Mg) and (Na + K) to total cations and HCO₃ indicates the domination of silicate weathering as major sources for cations. The plot for Na to Cl indicates higher Cl in both seasons, derived from Anthropogenic (human) sources from fertilizer, road salt, human and animal waste, and industrial applications, minor representations of Na also indicates source from weathering of silicate-bearing minerals. The plot for Na/Cl to EC indicates Na released from silicate weathering process which is also supported by higher HCO₃ values in both the seasons. Ion exchange process is also activated in the study area which is indicated by shifting to right in plot for Ca + Mg to SO₄ + HCO₃. The plot of Na-Cl to Ca + Mg-HCO₃-SO₄ confirms that Ca, Mg and Na concentrations in groundwater are derived from aquifer materials. Thermodynamic plot indicates that groundwater is in equilibrium with kaolinite, muscovite and chlorite minerals. Saturation index of silicate and carbonate minerals indicate oversaturation during pre-monsoon and undersaturation during post-monsoon, conforming dissolution and dilution process. In general, water chemistry is guided by complex weathering process, ion exchange along with influence of Cl ions from anthropogenic impact.     

Hyperspectral satellite data (Hyperion) preprocessing—a case study on banded magnetite quartzite in Godumalai Hill, Salem, Tamil Nadu, India

This paper deals with many calibration methods involved in preprocessing of hyperspectral remote sensing data, while radiation calibration with respect to magnetite minerals without altering image reflectance. Radiometric calibration is the basis and important for both hyperspectral data applications and quantitative remote sensing. While at present there are many methods available for radiometric calibration in the spaceborne hyperspectral data, here, we used the highest spectral resolution Hyperion EO-1 satellite data using a variety of calibration models, which include the calibration model based on atmospheric radiation theory, conversion model as scene dependent such as flat field model, internal average reflectance model, logs residual modified model, and linear model based on the experience of the ground calibration, and so on, and hyperspectral data calibration study was implemented with magnetite mineral. After the above three models contrast, we have arrived at the conclusion that calibration model based on atmospheric radiation theory is the finest radiation calibration method for Hyperion satellite data preprocessing.     

Geotechnical characterization and analysis of rainfall—induced 2009 landslide at Marappalam area of Nilgiris district,Tamil Nadu state,India

Landslides are frequently occurring natural hazards in Nilgiris district of Tamil Nadu, India, particularly during monsoon season. The present study describes the geotechnical characterization and analysis of rainfall-induced landslide that occurred at Marappalam location of Nilgiris district on November 10, 2009. The detailed investigation comprises mapping of landslide, topographical survey, field and laboratory investigations, characterization of soil and rock, and numerical analysis. Field study comprises borehole and geophysical investigations. Detailed laboratory investigation was performed to identify index and engineering properties of soil and rock. Based on the results obtained from field and laboratory investigations, the generalized subsoil profile of Marappalam slope has been plotted. The investigations revealed that loose and soft soil layer with low permeability and plasticity interspersed with boulders could be the main source of debris flow. Scanning electron microscopic analysis and x-ray diffraction analysis were performed to study the influence of weathering on slope failure. Failure mechanism of Marappalam 2009 landslide was identified from the numerical analysis performed using landslide simulation program LS-RAPID. The analysis revealed that the 5-day antecedent rainfall (303 mm) and intense rainfall on 10th November 2009 (405 mm) saturate the slope due to infiltration of rainwater. This leads to a decrease in the matric suction and subsequent development of positive pore water pressure, which in turn reduces the shear resistance of the soil along with shear displacement, and resulted in a progressive failure.     

Tidal effects on groundwater dynamics in shallow coastal aquifers—southeast coast of Tamilnadu,India

Tides play a significant role in the coastal environment; the mangroves, back waters, creeks, and the coastal groundwater interface. Tidal range has been calculated by using TIDECAL software. This study attempts to find the relation between water table condition and tides in the shallow coastal aquifers. The study was conducted by selecting 12 open wells along the coast of the southern part of Cuddalore to the northern part of Nagapattinam district of Tamilnadu. Observations were made in situ for water table fluctuation, dissolved oxygen (DO), and electrical conductivity (EC) for 24 h during full moon (FM) and new moon (NM) of every 2 h. The present study shows the relationship between tidal variations with respect to water table fluctuations and helps to understand the behavior of DO and EC. An interpolation technique, inverse distance weighted (IDW) method was used to obtain the spatial distribution map. The temporal and the spatial relationships between water table fluctuation, EC, and DO were also used in order to understand the coastal ecosystem in the natural environment.     

Impact assessment of a saline waste lagoon on groundwater pollution near a coastal aquifer in India—synthesis of geoelectrical and hydrochemical studies

The present study is an attempt to assess the impact of a saline waste lagoon on the near subsurface through electrical resistivity tomography (ERT). Resistivity and IP imaging data have been collected on profiles close to the lagoon and at a far off location (control location). Water samples have been collected from the lagoon and a municipality drinking well close to it and analysed for the water chemistry. The geoelectrical sections indicate very low resistivity formations in the near subsurface in the vicinity of the lagoon as compared to the control profile. The water chemistry data from the monitoring well close to the profile also indicates very high total dissolved solids (8658 mg/L) and qualitatively supports the contamination of the near subsurface. The conductive formations in the vicinity of the lagoon can be attributed to the overflow from the lagoon or the seepage.     

Palaeomagnetic and rock magnetic study of charnockites from Tamil Nadu,India, and the ‘Ur’ protocontinent in Early Palaeoproterozoic times

Palaeomagnetic and magnetomineralogical results are reported from charnockites in basement terrane at the eastern sector of the WSW–ENE granulite belt of South India. Magnetite is the dominant ferromagnet identified by rock magnetic and optical study; it is present in several phases including large homogeneous titanomagnetites and disseminated magnetite in microfractures linked to growth stages ranging from primary charnockite formation to uplift decompression and exhumation within the interval ～2500–2100 Ma. Several components of magnetization are resolved by thermal demagnetization and summarized by four pole positions; in the northern (Pallavaram) sector these are P1 (33°N, 99°E, dp/dm = 8/9°) and P2 (79°N, 170°E, dp/dm = 3/6°), and in the southern (Vandallur) sector they are V1 (23°N, 116°E, dp/dm = 8/9°) and V2 (26°S, 136°E, dp/dm = 5/10°). These magnetizations are linked to uplift cooling of the basement and unblocking temperature spectra suggest acquisition sequences P1 → P2 and V1 → V2 in each case implying movement of the shield from higher to lower palaeolatitudes sometime between 2500 and 2100 Ma. Palaeomagnetic poles from the cratonic nuclei of Africa, Australia and India all identify motion from higher to lower palaeolatitudes in Early Palaeoproterozoic times, and this is dated ～2400 and ～2200 Ma in the former two shields. The corresponding apparent polar wander (APW) segments match the magnetization record within the charnockite basement terranes of southern India to yield a preliminary reconstruction of the ‘Ur’ protocontinent, the oldest surviving continental protolith with origins prior to 3000 Ma. Although subject to later relative movements these nuclei seem to have remained in proximity until the Mesozoic break-up of Gondwana.     

Influence of Shannon’s entropy on landslide-causing parameters for vulnerability study and zonation—a case study in Sikkim, India

Landslide is a common hazard in the hilly regions, which causes heavy losses to life and properties every year. Since 1980, various researches and analyses have been carried out in the geographic information systems (GIS) environment to identify factors responsible for causing landslides. The important conditioning factors identified by the researchers are slope, geological, geomorphologic structures, and land use coupled with triggering factors like rainfall and a few of the anthropogenic activities. Almost all landslides vulnerability studies carried out so far used parameters of landslide events of the past as essential inputs and advanced methods like information value, regression analysis, fuzzy logic, etc. The present research is an attempt to investigate the landslide vulnerabilities in different slope areas with simple and realistic method of assignments of weights to the parameters based on experts?? opinion and generic logic, without using the parameters of past landslide events as inputs. The identified factors were assigned appropriate weights based on experts?? opinion and these weights were further balanced with respect to the Shannon??s entropy of their occurrences within the study area. The study area was finally classified into three zones namely least vulnerable zone, moderately vulnerable zone, and most vulnerable zone. When compared with the actual landslide history of the past, it was found that Shannon??s entropy applied zonation model matched to real landslide events with higher value of landslide density as compared to the model developed without Shannon??s entropy.     

Variation in groundwater levels and water quality in Chhatna Block, Bankura district, West Bengal — a GIS approach

Ground water levels and quality in Chhatna Block of West Bengal were studied based on different indices for irrigation and drinking purposes. A detailed hydrogeological investigation was carried out to have an overall idea of the aquifer system of the area. The ground water occurs under shallow to moderately deep water table condition. The groundwater is stored mostly in the weathered residuum and fractured — hard rock. Sodium absorption ratio (SAR), soluble sodium percentage (SSP), residual sodium bi-carbonate (RSBC), electrical conductance (EC), magnesium adsorption ratio (MAR) Kelly’s ratio (KR), total hardness (TH), permeability index (PI) were calculated as derived parameters, to investigate the ionic toxicity. From the results of chemical analysis, it was revealed that the values of Sodium Adsorption Ratio indicate that, ground water of the area falls under the category of low sodium hazard. So, there was neither salinity nor toxicity problem of irrigation water, and hence the ground water can safely be used for long-term irrigation. Plotting of analytical results of the groundwater collected from different areas in Piper’s trilinear diagram (1944) indicate that, the waters of the study area fall under fresh and sulphate rich region of the rhombus.     

Mapping of fluoride ions in groundwater of Dindigul district, Tamilnadu, India—using GIS technique

The accurate information through water quality analysis, scientific study on F ^? distribution in groundwater and geochemical knowledge with spatial information on geology and climate are necessary to understand the source/cause, type and level of F ^? contamination. The Dindigul district is a hard-rock terrain and marked as one of the fluoride-rich area in Tamilnadu due to occurrence of various rock types including fluoride-bearing minerals. The F ^? content of groundwater can thus originate from the dissolution of fluoride-bearing minerals in the bed rock. Eighty-six representative groundwater samples from Dindigul district was collected during two different seasons. Samples were analysed for F ^?, other major cations and anions. The study area is chiefly composed of hornblende biotite gneiss and charnockite, apart from this untreated tannery effluents also let from many places in the study area. Geographical Information System technique was adopted to study the sources of F ^?, and it was found that F ^? in the study is mainly attributed to geogenic source.     

Seasonal impact on beach morphology and the status of heavy mineral deposition – central Tamil Nadu coast,India

The aim of the present research was to investigate the seasonal impact on nearshore beach dynamics and the status of heavy mineral distribution along central Tamil Nadu coast, India. Beach profile measurements were made in 10 profiling sites between Thirukadaiyur and Velankanni on monthly and seasonal basis from January 2011 to July 2012. Using beach profile data, variation in beach width, slope and volumetric changes have been calculated. Beach slope and nearshore wave parameters were used to quantify the longshore sediment transport rate. Beaches between Thirukadaiyur and Karaikkal attained predominant transport rate in northern direction whereas, the rest of the beaches are in southern direction. The seasonal action of wind and wave currents create nearshore bar during northeast (NE) monsoon and frequent berms at tidal zone during southwest (SW) monsoon. Surface sediment samples were collected in each location for quantifying the heavy mineral weight percentage during the period of pre- and post-Thane cyclone. Sediments were also studied by X-ray diffraction (XRD) to evaluate the changes and occurrence of heavy minerals in beach sands. The XRD results show that sediments in the study area have enriched heavy mineral distribution even after strong cyclonic event. It confirms the redistribution of heavy mineral deposits present in the coast. The results suggested that monsoonal action has influenced the seasonal changes in beach morphology and it does not affect the heavy mineral distribution.     

A numerical simulation of landslide-prone slope in Himalayan region—a case study

Stability of slope will always a problem due to its geodynamic nature of Himalayan region. The area investigated belongs to the Lower Siwalik formation, which is prone to failure due to presence of various weak planes or structures present in the rock mass. Frequent landslides causing loss of life, property, disturbance of morphological, surface and subsurface water flow pattern. A huge landslide in the Amiyan area occurred in 1999 and blocked the Gaula River which caused loss of agricultural land and other properties as well as waterlogged upstream side. The debris of Amiyan slope contains soil and sandstones of various types. This article deals with instability analysis of slopes of the Amiyan area, near Kathgodam, Nainital, Uttarakhand. This area experiences a number of local as well as regional slides. Extensive field surveys have been carried out to understand the geological detail. Laboratory experiments have been conducted to determine the various physicomechanical properties of rock mass. These properties have been used as input parameters for the numerical simulation. A number of researchers have used two-dimensional numerical models to simulate the slide area. Three-dimensional slope stability studies provide a better understanding of the mechanism of failure as well as zone of influence. The computed deformations and stress distribution, along the failure surface, have been compared with the field measurements and found to be in good agreement with field observations. In this case, finite difference method has been applied on the stability analysis of Amiyan slope. The study indicates that the slope is vulnerable and needs proper protection.     

An integrated study on the characterization of freshwater lens in a coastal aquifer of Southern India

The hydrogeochemical characterization of groundwater helps to assess the trend of salinization and freshening of the groundwater. The present study was carried out to understand the lateral and vertical variation of groundwater salinity and the process of salinization and freshening of the groundwater in a coastal aquifer comprising a freshwater lens. The partially isolated unconfined aquifer selected for the present study is lying just south of the Chennai City, one of the densely populated cities on the east coast of South India. Critical problems affecting this aquifer include a thin aquifer which is connected/surrounded by saltwater on all the sides, overexploitation of the groundwater, surface impermeabilization due to increasing residential areas, and destruction of existing dune morphology by conversion of barren land to the residential area which causes a reduction in their barrier effect to seawater intrusion. The process of salinization and freshening of the groundwater was studied and monitored by using electrical resistivity survey and hydrogeochemical analysis. The vertical electrical sounding was carried out at 17 locations, and 400 water samples were collected and analyzed from 50 locations during the period from August 2008 to May 2010 for this study. The apparent resistivity values were analyzed and compared with groundwater quality to demarcate the zone of seawater intrusion. The regional flow direction of the groundwater is westward and eastward with respect to the central stretch and groundwater level ranges from 4.96 m MSL at the dune morphology to 0 m MSL along the boundary on all the sides. Base exchange index indicates that salinization trend in the northern part of the study area is due to the extensive groundwater pumping which increases the possibility of seawater intrusion. The increase of base exchange index towards southern part indicates a better groundwater quality of the aquifer due to proper land use practices. A strong trend of quality alteration is clearly visible from the base exchange index in response to the seasonal change between monsoon and dry season. In the western side, the monsoonal variation in the salinization and freshening of the groundwater was not noticed; however, the salinity is slightly higher than freshwater due to the presence of clay.     

Hydrogeochemistry and quality of groundwater of coastal unconfined aquifer in Amol–Ghaemshahr plain,Mazandaran Province,Northern Iran

Groundwater of the unconfined aquifer (1,100 sq. km) of a two-tier coastal aquifer located in the Amol–Ghaemshahr plain, Mazandaran Province, Northern Iran, is classified into fresh and brackish water types. Fresh groundwater (FGW) samples (n = 36) are characterized by Ca²⁺ > Na⁺ > Mg²⁺ > K⁺ and HCO₃ ^? > Cl^? > SO₄ ^2? > NO₃ ^?. Spearman’s rank correlation coefficient matrices, factor analysis data, values of the C-ratio (av. = 0.89) and CAI and values of the molar ratios of Ca²⁺/HCO₃ ^?, Ca²⁺/SO₄ ^2?, Mg²⁺/HCO₃ ^? and Mg²⁺/SO₄ ^2? indicate that the ionic load in the FGW is derived essentially from carbonic acid-aided weathering of carbonates and aluminosilicates, saline/sea water trapped in the aquifer sediments (now admixed with the groundwater) and ion exchange reactions. Values of the CAI and Na⁺/Cl^? molar ratio suggest that the part of the Ca²⁺ (±Mg²⁺) content in 23 FGW samples is derived from clay minerals of the aquifer matrix, and part of the Na⁺ content in 20, 12, and 3 FGW samples is derived, respectively, from alkali feldspar weathering, clay minerals of the aquifer matrix and rain water and/or halite. Brackish groundwater (BGW) samples (n = 4) contain Cl^? as the dominant anion and their average total ionic concentration (38.65 meq/L) is 1.79 times higher than that of the FGW samples (21.50 meq/L). BGW pockets were generated by non-conservative mixing of FGW with the upconed saline water from the underlying saline groundwater zone of the semi-confined aquifer along bore wells involved in excessive extraction of groundwater from the unconfined aquifer. Groundwater belongs essentially to “high salinity, low sodium” irrigation water class.     

Spatiotemporal development of mine water inrush and its mechanism—a case study in Ganhe coal mine,Shanxi, China

Mine water inrush is one of the main hazards in coal mining industry. The mechanism and the processes are complex. Investigation of the spatiotemporal development of the hydrological process could lead to a better understanding of mine water inrush and effective countermeasures. For this reason, we investigated spatial and temporal characteristics (i.e., the changes of flow rate, groundwater level, and water quality) during a water inrush event in China, which had a flow rate of 730 m³/h at maximum and 300m³/h under a steady condition. The result shows that the water inrush developed in several stages. A mathematical model of the dynamic change between the water table and the inrush flow rate was constructed. Based on this model, we found the relationship of highly conductive flow channels between some observation boreholes and the water inrush point. In addition, the recharge velocity of the highly conductive flow channels and the equivalent mean flow velocity of the whole mine were determined. A comprehensive analysis of geological, hydrodynamic, and crustal stress conditions was conducted to study the development of the water channel near the F₁₃ fault and the nonlinear process from seepage stage to inrush stage. The result reveals the water inrush is likely caused by activation of faults under combined influences of high crustal stress and high hydraulic pressure.     

The variation in thickness and composition of coal seams and its use in interpretation of palaeocurrents — A case study from the Raniganj Coalfield,West Bengal,India

The petrological and chemical composition of a coal reflects all its inherent characters. Together with the variation in thickness of the coal seams, these aspects have been studied in detail around Salanpur (Raniganj Coalfield), India. The data reveal that any coal seam having its mother material supplied continuously from the same source will show a variation in its composition, the resultant being closely related to the environmental factors of the site of deposition, namely its morphology, including the disposition of its channel axis, and the palaeocurrent direction. Thus, it is suggested that these coal-seam properties may be used just as other sedimentary parameters in interpreting the characteristics of the site of deposition and depositing current.     

Mangrove sediments a sink for heavy metals? An assessment of Muthupet mangroves of Tamil Nadu,southeast coast of India

Mangrove forests are one of the most productive and biodiverse wetlands on earth. Yet, these unique coastal tropical forests are among the most threatened habitats in the world. Muthupet mangroves situated in the southeastern coast of India, has a reverse “L” shaped structure. Four cores were collected in 2008, sliced and subsampled at 2.5 cm length. The heavy metals (Mn, Cu, Zn, Ni, Pb, Cr, Cd) and other associated geochemical parameters were evaluated to determine pollution history of Muthupet. An evaluation of the status of heavy metal pollution through the index analysis approach was attempted by computing geoaccumulation index, anthropogenic factor, enrichment factor, contamination factor and degree of contamination, pollution load index and metal pollution index. To compensate for the natural variability of heavy metals in the core sediments, normalization using Al was carried out so that, any anthropogenic metal contributions may be detected and quantified. Results of the study reveal that significant metal contamination exists, and all the metals are found to be higher than continental crustal values. The fine sediments of Muthupet vary between uncontaminated and moderately contaminated with almost no enrichment (EF < 1) to severe enrichment (EF > 10). On comparison, the core collected close to aquafarms and dense mangrove forest (C3) is the most polluted core and the core retrieved where minor rivers drain (C2) is the least polluted.     

Hydrochemistry of groundwater in the Savelugu–Nanton District, Northern Ghana

Calcite (CaCO₃), dolomite [CaMg(CO₃)₂], silicate dissolution, ion-exchange and reverse ion-exchange reactions are the predominant processes influencing groundwater quality in the Savelugu?CNanton District. The main objective of this study is to characterize groundwater and delineate water?Crock interactions responsible for the chemical evolution of groundwater in the District. Eighty-one (81) boreholes were sampled for quality assessment. Results showed that, the pH of the boreholes are slightly acidic to basic ranging from 6.1?C8.3?pH units. Conductivity values are low to high ranging from 147?C23,200???S/cm with, 23.5?% of groundwater within the study area being either brackish (1,500?C5,000???S/cm) or saline (>5,000???S/cm) and therefore, unsuitable for potable purposes. TDS values in groundwater varied widely, ranging from 62?C11,900?mg/L. 61.7?% of groundwater within the study area are fresh (TDS?<?500?mg/L). The chemical constituents generally, have low concentrations and are within the WHO (Guidelines for drinking water quality. Revision of the 1993 Guidelines. Final Task Group Meeting. Geneva, 2004) Guideline values. The relative abundance of cations and anions in the groundwater are in the order: Ca²⁺?>?Na⁺?>?Mg²⁺?>?K⁺ and HCO₃ ^??>?Cl^??>?SO₄ ^2??>?NO₃ ^? respectively. Multivariate statistical analysis showed expected process-based relationship derived mainly from the geochemical and biochemical processes within the aquifer. Hydrochemical facies using piper plot of major ions showed one major hydrochemical water type. The Ca?CMg?CHCO₃ water type. Due to the high cost of drilling of boreholes coupled with the high percentage (×1?%) of people without access to potable water in the Northern Region, it is recommended that the Government of Ghana and other stakeholders within the Water Sector take immediate measures to reduce (to recommended limits for potable uses) the levels of dissolved solids either by installing Reverse Osmosis equipments on such boreholes or employ other relatively known cheaper methods to reduce the dissolved solids to recommended limits. High yielding boreholes with hydrochemical parameters within WHO guideline limits in the Savelugu?CNanton District could also be mechanized to serve a wider area.     

PAHs contamination in groundwater from a part of metropolitan city,India: a study based on sampling over a 10-year period

Presence of polycyclic aromatic hydrocarbons (PAHs) in the soil and water is of serious environmental concern as they are carcinogenic in nature. The present study was carried out with an aim to identify the presence of PAHs in groundwater of Chennai, Tamil Nadu, India. This is an industrialised area where petrochemical storage tanks are located. Groundwater sampling was carried out in the years 2001, 2011 and 2012 to understand the variation in PAHs content in this area. Concentration of major ions, pH and EC were measured during the year 2001. Of the 24 groundwater samples collected in the year 2001, most of them were alkaline and 62.5 % were not permissible for drinking based on pH and EC, respectively. Influence of seawater was the major reason for the Na–Cl dominant nature of groundwater. TPH and PAHs analysis of groundwater carried out in 2001 and 2011, and physical examination of groundwater in 2012 indicate the increased level of contamination in the eastern part of the study area. The contamination in the eastern part persists because of the fact that groundwater is flowing towards the east and also due to the presence of petrochemical storage tanks near the coast. Thus this area is affected by PAHs pollution which has endured over the past 50 years. An underground storage tank that was functioning in this area was closed about 50 years ago and leakage of PAHs from this tank was reported in the year 1993. However, the present study indicates the decrease in the area of zone of pollution, possibly due to natural flushing of groundwater zone.