Geochemistry and quality of groundwater of Gummanampadu sub-basin, Guntur District, Andhra Pradesh, India

Groundwater survey has been carried out in the area of Gummanampadu sub-basin located in Guntur District, Andhra Pradesh, India for assessing the factors that are responsible for changing of groundwater chemistry and consequent deterioration of groundwater quality, where the groundwater is a prime source for drinking and irrigation due to non-availability of surface water in time. The area is underlain by the Archaean Gneissic Complex, over which the Proterozoic Cumbhum rocks occur. The results of the plotting of Ca²⁺ + Mg²⁺ versus HCO₃ ^? + CO₃ ^2?, Ca²⁺ + Mg²⁺ versus total cations, Na⁺ + K⁺ versus total cations, Cl^? + SO₄ ^2? versus Na⁺ + K⁺, Na⁺ versus Cl^?, Na⁺ versus HCO₃ ^? + CO₃ ^2?, Na⁺ versus Ca²⁺ and Na⁺: Cl^? versus EC indicate that the rock–water interaction under alkaline condition is the main mechanism in activating mineral dissociation and dissolution, causing the release of Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃ ^?, CO₃ ^2?, SO₄ ^2? and F^? ions into the groundwater. The ionic relations also suggest that the higher concentrations of Na⁺ and Cl^? ions are the results of ion exchange and evaporation. The influences of anthropogenic sources are the other cause for increasing of Mg²⁺, Na⁺, Cl^?, SO₄ ^2? and NO₃ ^? ions. Further, the excess alkaline condition in water accelerates more effective dissolution of F^?-bearing minerals. Moreover, the chemical data plotted in the Piper’s, Gibbs’s and Langelier–Ludwig’s diagrams, computed for the chloro-alkaline and saturation indices, and analyzed in the principal component analysis, support the above hypothesis. The groundwater quality is, thus, characterized by Na⁺ > Ca²⁺ > Mg²⁺ > K⁺: HCO₃ ^? + CO₃ ^2? > Cl^? > SO₄ ^2? > NO₃ ^? > F^? facies. On the other hand, majority of groundwater samples are not suitable for drinking with reference to the concentrations of TDS, TH, Mg²⁺ and F^?, while those are not good for irrigation with respect to USSL’s and Wilcox’s diagrams, residual sodium carbonate, and magnesium hazard, but they are safe for irrigation with respect to permeability index. Thus, the study recommends suitable management measures to improve health conditions as well as to increase agricultural output.     

Seasonal variation of groundwater quality in a part of Guntur District, Andhra Pradesh, India

The area in Guntur district, Andhra Pradesh, India, is selected to discuss the impact of seasonal variation of groundwater quality on irrigation and human health, where the agriculture is the main livelihood of rural people and the groundwater is the main source for irrigation and drinking. Granite gneisses associated with schists and charnockites of the Precambrian Eastern Ghats underlie the area. Groundwater samples collected seasonally, pre- and post-monsoons, during three years from forty wells in the area were analyzed for pH, EC, TDS, TA, TH, Ca²⁺, Mg²⁺, Na⁺, K⁺, CO₃²⁻, HCO₃⁻, Cl⁻, SO₄²⁻, NO₃⁻and F⁻. The chemical relationships in Piper’s diagram, Chebotarev’s genetic classification and Gibbs’s diagram suggest that the groundwaters mainly belong to non-carbonate alkali type and Cl⁻ group, and are controlled by evaporation-dominance, respectively, due to the influence of semi-arid climate, gentle slope, sluggish drainage conditions, greater water–rock interaction, and anthropogenic activities. A comparison of the groundwater quality in relation to drinking water quality standards proves that most of the water samples are not suitable for drinking, especially in post-monsoon period. US Salinity Laboratory’s and Wilcox’s diagrams, and %Na⁺ used for evaluating the water quality for irrigation suggest that the majority of the groundwater samples are not good for irrigation in post-monsoon compared to that in pre-monsoon. These conditions are caused due to leaching of salts from the overlying materials by infiltrating recharge waters. A management plan is suggested for sustainable development of the area.     

Geochemistry of groundwater in parts of Guntur district, Andhra Pradesh, India

Hydrogeochemical investigations, which are significant for the assessment of water quality, have been carried out to study the sources of dissolved ions in groundwaters of some rural areas of Guntur district, Andhra Pradesh, India. Groundwaters in the area are mostly brackish. High contents of SiO₂, and Na⁺ and Cl^- ions in groundwater, in comparison with those of seawater, suggests a meteoric origin of groundwater. The high concentration of SiO₂ and various geochemical signatures reflect the weathering of minerals. However, the Na⁺+K⁺ vs Cl^- ratio suggests weathering, has occurred only to some extent. The chemistry of groundwater favours the formation of clay minerals (montmorillonite, illite and chlorite), because of evapotranspiration. The positive saturation index of CaCO₃ and the high signatures of Ma²⁺:Ca²⁺ and Na⁺:Ca²⁺ reveals the occurrence of evaporation. The evaporation enhances the concentration of ions (which occurred originally in the water) in the soils during summer. The very high % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY-Hhbbf9v8qqaqFr % 0xc9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8 % frFve9Fve9Ff0dmeaabaqaciGacaGaaeqabaqabeaadaaakeaacqqG % tbWucqqGpbWtdaqhaaWcbaGaeeinaqdabaGaeeOmaiJaeeyla0caaa % aa!2EC5! SO₄^{2 -} {\rm SO}_{\rm 4}^{{\rm 2 - }} and Cl^- contents in some groundwaters and the occurrence of kankar (CaCO₃) in the area suggest a long history of evaporation. Greater ionic concentration in the groundwaters of post-monsoon compared with pre-monsoon indicates the increasing addition of leachates into the groundwater from the soils in the monsoon and anthropogenic activities, which leads to a deteriorating quality of groundwater. According to the Gibbs' diagrams, rock weathering, to some extent, and evaporation are the dominant phenomena responsible for the higher ionic concentrations found in groundwater. Measures that benefit sustainable management of groundwater quality are suggested in this study.     

Geochemical assessment of groundwater around Macherla-Karempudi area,Guntur district,Andhra Pradesh

Groundwater in Palnad sub-basin is alkaline in nature and Na⁺-Cl⁻-HCO₃⁻ type around Macherla-Karempudi area in Guntur district, Andhra Pradesh. Total dissolved solids (TDS) show strong positive correlation with Cl⁻, Na⁺, Ca²⁺ and Mg²⁺, and positive correlation with SO₄²⁻, K⁺ and HCO₃⁻. Calcareous Narji Formation is the dominant aquifer lithology, and water-rock interaction controls the groundwater chemistry of the area. Chloro-alkaline indices (CAI) are positive at Miriyala, Adigopula, Mutukuru, Macherla and Durgi suggesting replacement of Na⁺ and K⁺ ions from water by Mg⁺⁺ and Ca⁺⁺ ions from country rock through base exchange reactions. Negative CAI values are recorded at Terala, Rayavaram and Nehrunagar, which indicate exchange of Na⁺ and K⁺ from the rock as cation-anion exchange reaction (chloro-alkaline disequilibrium). TDS range from 91 to 7100 ppm (Avg. 835 ppm) and exceed the prescribed limit of drinking water around Mutukuru, Durgi, Rayavaram, Khambampadu and Ammanizamalmadaka areas. Scanty rainfall and insufficient groundwater recharge are the prime factors responsible for high salinity in the area. Fluoride content ranges from <1 to 3.8 ppm and contaminated areas were identified around Macherla (1 sq km; 3.8ppm), Mandadi (1 sq km, 2.1ppm) and Adigopula (2 sq km, <1 to 3.7 ppm). The % Na⁺ content varies from 17 to 85 with the mean value of 57, and eighty (80) samples showed higher %Na⁺ in comparison to the prescribed limit of 60 for irrigation water. Sodium Adsorption Ratio (SAR) and % Na⁺ in relation to total salt concentration indicate that groundwater (51%) mostly falls under doubtful to poor quality for irrigation purpose. Groundwater of Adigopula village is fluoride contaminated and remedial measures are suggested to improve the water quality.     

Quality characterization of groundwater in Koilsagar project area,Mahabubnagar District,Andhra Pradesh,India

Studies of groundwater chemistry in the Koilsagar project area of Andhra Pradesh indicate that the waters are sodium bicarbonate, sodium chloride, mixed cationic-mixed anionic, mixed cationic Na dominating bicarbonate, and mixed cationic Ca dominating bicarbonate types. Of them, sodium bicarbonate and mixed cationic Mg dominating bicarbonate types of waters are more prevalent.Isocone mapping of specific conductance indicates that the ionic concentration increases from east to west in the area. Graphical treatment of chemical data reveals that, in general, the area has basic water, whereas the left flank canal area is dominated by secondary alkaline water, and Pallamarri and Pedda Rajmur villages have strongly acidic waters. Ion-exchange studies show that cation-anion exchanges exist all over the area except for two places, which have a base exchange hardened type of water.Graphical representation further shows that most of the area has medium salinity-low sodium (C₂S₁) water useful for irrigation purposes. High salinity-low sodium (C₃S₁) and high salinity-medium sodium (C₃S₂) waters are present in some areas, which need adequate drainage to overcome the salinity problem.     

Geochemical characteristics and controlling factors of chemical composition of groundwater in a part of Guntur district,Andhra Pradesh,India

A survey on quality of groundwater was carried out for assessing the geochemical characteristics and controlling factors of chemical composition of groundwater in a part of Guntur district, Andhra Pradesh, India, where the area is underlain by Peninsular Gneissic Complex. The results of the groundwater chemistry show a variation in pH, EC, TDS, Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃ ^?, Cl^?, SO₄ ^2?, NO₃ ^? and F^?. The chemical composition of groundwater is mainly characterized by Na⁺?HCO₃ ^? facies. Hydrogeochemical type transits from Na⁺–Cl^?–HCO₃ ^? to Na⁺–HCO₃ ^?–Cl^? along the flow path. Graphical and binary diagrams, correlation coefficients and saturation indices clearly explain that the chemical composition of groundwater is mainly controlled by geogenic processes (rock weathering, mineral dissolution, ion exchange and evaporation) and anthropogenic sources (irrigation return flow, wastewater, agrochemicals and constructional activities). The principal component (PC) analysis transforms the chemical variables into four PCs, which account for 87% of the total variance of the groundwater chemistry. The PC I has high positive loadings of pH, HCO₃ ^?, NO₃ ^?, K⁺, Mg²⁺ and F^?, attributing to mineral weathering and dissolution, and agrochemicals (nitrogen, phosphate and potash fertilizers). The PC II loadings are highly positive for Na⁺, TDS, Cl^? and F^?, representing the rock weathering, mineral dissolution, ion exchange, evaporation, irrigation return flow and phosphate fertilizers. The PC III shows high loading of Ca²⁺, which is caused by mineral weathering and dissolution, and constructional activities. The PC IV has high positive loading of Mg²⁺ and SO₄ ^2?, measuring the mineral weathering and dissolution, and soil amendments. The spatial distribution of PC scores explains that the geogenic processes are the primary contributors and man-made activities are the secondary factors responsible for modifications of groundwater chemistry. Further, geochemical modeling of groundwater also clearly confirms the water–rock interactions with respect to the phases of calcite, dolomite, fluorite, halite, gypsum, K-feldspar, albite and CO₂, which are the prime factors controlling the chemistry of groundwater, while the rate of reaction and intensity are influenced by climate and anthropogenic activities. The study helps as baseline information to assess the sources of factors controlling the chemical composition of groundwater and also in enhancing the groundwater quality management.     

Geoenvironmental effects of groundwater regime in Andhra Pradesh, India

 The Indian subcontinent has the largest semi-arid tropical (SAT) area among developing nations. The State of Andhra Pradesh falls under the SAT region in India and is mostly covered by compact and hard rocks, characterized by seasonal rainfall of a highly fluctuating nature, in both space and time. As a consequence of the green revolution and an increase in industrial activity, there has been an increase in the utilization of groundwater resources during the last two decades in Andhra Pradesh. The development has also caused a number of problems, such as water table decline, decrease in well yields and seawater intrusion. Although major irrigation projects have contributed to improved agricultural production, the associated problems of waterlogging, salinization and loss of valuable bioresources have led to the gradual degradation of the land, affecting agricultural productivity. Surface water and groundwater have also been polluted in several parts of the State because of untreated discharge of effluents from the industries into nearby streams or open lands. A brief account of the overall scenario of the hydrogeological framework and geo-environmental effects on the groundwater regime in Andhra Pradesh is presented. Possible management practices and conservation methods are suggested. Received: 9 August 1999 · Accepted: 10 July 2000     

The Purimetla gabbros,Prakasam District,Andhra Pradesh,India

Gabbros at Purimetla occur in close association with the alkaline pluton. Petrography and petrochemistry of these gabbros indicate their tholeiitic nature. Chemical variation of these tholeiites suggests that an initial undersaturated tholeiitic magma yielded oversaturated fractions in the final stages of differentiation. Their regional distribution suggests that basic magmatism preceded the emplacement of the alkaline rocks in the Prakasam alkaline province.     

The impact of paleo-channel on groundwater contamination,Andhra Pradesh,India

 Nakka vagu, a tributary of the River Manjira in the Medak district of Andhra Pradesh, has a catchment area of ∼500 km². Patancheru is an industrial development area (IDA) near the vagu. There are about 350 industries of varied nature (pulp, plastic, bulk drugs, pharmaceuticals, paints and steel rolling mills) that are engaged in the manufacture/processing of their respective products and that use water extensively. The hydrogeological setup has a bearing on the widespread contamination in the area because of discharge of industrial effluents into open land and streams. Several dug wells and boreholes situated in the study area have been monitored for water level fluctuations and quality variations. Pumping tests have been conducted to evaluate aquifer parameters. The geology, drainage, chemistry and other related anthropogenic factors play a major role in the spread of pollution in the area. Hence, it is very important to determine the degree of vulnerability to pollution based on hydrogeological factors. Amidst the granite terrain, the Nakka vagu has been identified as a paleo-channel (composed of clay–silt–sand facies); its presence in the area has immensely increased the spread of groundwater contamination. The transmissivity of the alluvial aquifer varies from 750 to 1315 m²/day. The adjoining granite has a transmissivity that varies from 30–430 m²/day. The thickness of the valley fill in the discharge region is about 10–12 m, with a lateral spread of 500–700 m, east of Nakka vagu. Received: 17 November 1999 · Accepted: 14 March 2000     

Fluorine distribution in waters of Nalgonda District, Andhra Pradesh, India

Geochemical and hydrochemical studies were conducted in Nalgonda District (A.P.), to explore the causes of high fluorine in waters, causing a widespread incidence of fluorosis in the local population. Samples of granitic rocks, soils, stream sediments, and waters were analyzed for F and other salient chemical parameters. Samples from the area of Hyderabad city were analyzed for comparison. The F content of waters in areas with endemic fluorosis ranges from 0.4 to 20 mg/l. The low calcium content of rocks and soils, and the presence of high levels of sodium bicarbonate in soils and waters are important factors favoring high levels of F in waters.     

Electrical resistivity surveys to delineate groundwater potential aquifers in Peddavanka watershed,Anantapur District,Andhra Pradesh,India

Vertical electrical resistivity soundings were conducted in order to delineate groundwater potential aquifers in Peddavanka watershed, which is a catchment of about 398 km² in Anantapur District, Andhra Pradesh, India. The main lithologic units in the watershed are quartzite, limestone, shale, and alluvium. Ninety-nine vertical electrical soundings were conducted using the Schlumberger configuration, covering the entire watershed. The data were interpreted with the help of master curves and auxiliary point charts. Interpretations of VES were used to generate a top layer apparent resistivity contour map and longitudinal conductance map. Isoresistivity contour maps were prepared and interpreted in terms of resistivity and thickness of various sub-surface layers using computer software (SURFER), and isocontour diagrams depicting the depth to bedrock were prepared. Resistivity results were correlated with the existing lithology. Based on the depth to bedrock, the thickness of the saturated layer and the resistivity of the second layer, a groundwater potential map has been prepared, in which good, moderate, and poor zones are classified. The study reveals that the weathered and fractured portions in shale and limestone that occur in the southernmost and central portions of the watershed area constitute the productive water-bearing zones categorized as good groundwater potential aquifers.     

Integrated approach for identification of potential groundwater zones in Seethanagaram Mandal of Vizianagaram District,Andhra Pradesh,India

Identifying a good site for groundwater exploration in hard rock terrain is a challenging task. In hard rocks, groundwater occurs in secondary porosity developed due to weathering, fracturing, faulting, etc., which is highly variable within short distance and contributing to near-surface inhomogeneity. In such situations topographic, hydrogeological and geomorphological features provide useful clues for the selection of suitable sites. Initially, based on satellite imagery, topographical, geomorphological and hydrogeological features, an area of about 149 km² was demarcated as a promising zone for groundwater exploration in the hard rock tract of Seethanagaram Mandal, Vizianagaram District, Andhra Pradesh, India. A total of 50 Vertical Electrical Soundings (VES) were carried out using Wenner electrode configuration. An interactive interpretation of the VES data sharpened the information inferred from geomorphological and hydrogeological reconnaissance. Ten sites were recommended for drilling. Drilling with Down-The-Hole Hammer (DTH) was carried out at the recommended sites down to 50 to 70 m depths. The interpreted VES results matched well with the drilled bore well lithologs. The yields of bore wells vary from 900 to 9000 liters per hour (lph).     

Alkaline basic intrusives of Elchuru,Prakasam District,Andhra Pradesh,India

The igneous alkaline rocks at Elchuru start from a parent ijolite-melteigite association to basic malignite, melalusitanite and shonkinite followed by nepheline syenites and then biotite lamprophyres (as dykes) at the waning phase of the evolutionary course of the complex. The distinct alkalinity of the rocks is manifested by the development of modal nepheline and calcic amphibole (kaersutite). For both the basic rocks,i.e. alkali gabbro and biotite lamprophyre, the percentages of normative nepheline are always higher than modal nepheline, indicating silica deficiency and alkali enrichment of the mafics. It is evident from detailed petrological and geochemical studies that the two basic members are very much akin to each other and there is no major deviation in their bulk chemistry.     

Hydrogeochemical parameters for assessment of groundwater quality in the upper Gunjanaeru River basin,Cuddapah District,Andhra Pradesh,South India

In the management of water resources, quality of water is just as important as its quantity. In order to know the quality and/or suitability of groundwater for domestic and irrigation in upper Gunjanaeru River basin, 51 water samples in post-monsoon and 46 in pre-monsoon seasons were collected and analyzed for various parameters. Geological units are alluvium, shale and quartzite. Based on the analytical results, chemical indices like percent sodium, sodium adsorption ratio, residual sodium carbonate, permeability index (PI) and chloroalkaline indices were calculated. The pre-monsoon waters have low sodium hazard as compared to post-monsoon season. Residual sodium carbonate values revealed that one sample is not suitable in both the seasons for irrigation purposes due the occurrence of alkaline white patches and low permeability of the soil. PI values of both seasons revealed that the ground waters are generally suitable for irrigation. The positive values of Chloroalkaline indices in post-monsoon (80%) and in pre-monsoon (59%) water samples indicate absence of base-exchange reaction (chloroalkaline disequilibrium), and remaining samples of negative values of the ratios indicate base-exchange reaction (chloroalkaline equilibrium). Chadha rectangular diagram for geochemical classification and hydrochemical processes of groundwater for both seasons indicates that most of waters are Ca–Mg–HCO₃ type. Assessment of water samples from various methods indicated that majority of the water samples in both seasons are suitable for different purposes except at Yanadipalle (sample no. 8) that requires precautionary measures. The overall quality of groundwater in post-monsoon season in all chemical constituents is on the higher side due to dissolution of surface pollutants during the infiltration and percolation of rainwater and at few places due to agricultural and domestic activities.     

Nitrate pollution and its distribution in the groundwater of Srikakulam district, Andhra Pradesh, India

The complex depositional pattern of clay and sand in most of the areas controlled the vertical and lateral movement of nitrate in groundwater. The variation of nitrate concentration at different groundwater levels and the lateral distribution of nitrate in the groundwater at two sites indicated the filtration of nitrate by clayey formations. A rural agricultural district located in the Vamsadhara river basin, India was selected for studying the lateral and vertical distribution of nitrate in the groundwater and the association of nitrate with other chemical constituents. The nitrate concentrations in the groundwater are observed to vary between below detectable limit and 450 mg NO₃/L. The sources for nitrate are mainly point sources (poultry farms, cattleshed and leakages from septic tanks) and non-point sources (nitrogenous fertilisers). The nitrate concentrations are increased after fertiliser applications. However, very high concentrations of nitrate are derived from animal wastes. Relatively better correlations between nitrate and potassium are observed (R = 0.74 to 0.82). The better relationship between these two chemical constituents in the groundwater may be due to the release of potassium and nitrate from both point and non-point sources. The nitrate and potassium concentrations are high in the groundwater from clayey formations.     

Geotechnical investigations at the Kalyani dam site, Chitoor District, Andhra Pradesh, India

Details are presented of site investigations carried out for the Kalyani Dam, Chittoor District, Andhra Pradesh, India. Geologically, the dam-site region forms a triple junction of the Dharwar, Easternghat and Cuddapah orogenies and it is tectonically disturbed; the course of the Kalyani river is guided by a major strike-slip fault. The geophysical studies reveal the presence of several fault and shear zones in the area. Laboratory studies on the physical and engineering properties of the rocks disclose distinct differences in the sheared (Zone I) rocks as against those that are relatively undisturbed (Zone III). Zone I samples, in general, show high porosity and elastic an isotropy, low values of density, elastic wave velocity, elastic moduli, fracture strength and high absorption, while the reverse is noticed in the undisturbed samples of Zone III. Samples from the shear zone further show large variations in compressional velocity and amplitude, as a function of compressive stress. The laboratory velocities are in good agreement with the field seismic refraction results. These studies helped in estimating the soundness of the rock formations, delineating the structurally weak zones and suggesting remedial measures.     

Integrated approach for delineating potential zones to explore for groundwater in the Pageru River basin, Cuddapah District, Andhra Pradesh, India

Hydrogeomorphological, hydrogeological and geophysical investigations were carried out in the Pageru River basin of Cuddapah district, Andhra Pradesh, to delineate potential zones for future groundwater exploration. The study area is underlain by Proterozoic formations of the Indian Peninsula comprising limestones and shales as the sedimentary cover. Limestone and shale formations of the Cuddapah Super group that are later overlain by the Kurnool group (shale, limestone and quartzite) are exposed extensively. The high drainage density (2.61 km/km²) in the western region also suggests that the area is characterized by low permeable zones compared with low drainage density (1.04 km/km²) of the flood plains, which form the potential aquifers in the east. The hydro-geomorphological data are further supported from evidence of the water-table fluctuation in wells and resistivity of the saturated formations. The results indicate that the favourable, moderately favourable and poor zones characterized geomorphologically, have water-level fluctuations in the range of 0–2, 2–6 and above 6 m, respectively. The resistivities of these zones are also in the range of 1–26, 40–466, and >1,900 ohm-m. A few pumping tests have also been conducted to assess the broad range in the values of aquifer parameters. Based on these data, good to poor potential zones for obtaining groundwater have been delineated in the study area.

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Resumen Se llevaron a cabo investigaciones hidrogeomorfológicas, hidrogeológicas y geofísicas en la cuenca del Río Pageru del distrito Cuddapah, Andhra Pradesh, con objeto de delimitar zonas potenciales para exploración futura de aguas subterráneas. El área de estudio consiste de formaciones Proterozoicas de la Península India con calizas y lutitas como cubierta sedimentaria. Las formaciones de caliza y lutita del Grupo Cuddapah Superior afloran extensamente y están cubiertas por el Grupo Kurnool (lutita, caliza, y cuarcita). La alta densidad de drenaje (2.61 km/km²) en la región occidental también indica que el área se caracteriza por zonas de baja permeabilidad en comparación con las planicies de inundación de baja densidad (1.04 km/km²) que forman los acuíferos potenciales del oriente. Los datos hidrogeomorfológicos tienen apoyo adicional a partir de evidencia proveniente de la fluctuación del nivel freático en pozos y resistividad de las formaciones saturadas. Los resultados indican que las zonas caracterizadas geomorfológicamente como zonas favorables, moderadamente favorables, y pobres tienen fluctuaciones de niveles de agua en el rango de 0–2, 2–6, y mayor de 6 m, respectivamente. Las resistividades de estas zonas también se encuentran en el rango de 1–26, 40–466, y mayores de 1,900 ohm-m. Se realizaron algunas pruebas de bombeo para evaluar los amplios rangos que tienen los valores de los parámetros de los acuíferos. Basado en esta información se delimitaron zonas con potencial bueno a pobre para obtener agua subterránea en la zona de estudio.

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Résumé Des investigations hydrogéomorphologiques, hydrogéologiques et géophysiques ont été menées sur le bassin de la rivière Pageru du district de Cuddapah, Andhra Pradesh, pour délimiter les zones potentielles dans la future recherche deaux souterraines. La zone étudiée est, à la base, constituée par les formations protérozoïques de la péninsule indienne comprenant les calcaires et les shales de la couverture sédimentaire. Les calcaires et les shales du Super Groupe Cuddapah qui sont recouverts par le Groupe Kurnool (shale, calcire, quartzite) sont exposés de manière extensive. La densité importante de drainage (2.61 km/km²) dans la région ouest montre également que la zone est caractérisée par des perméabilités faibles par comparaison avec les plaines dinondation (densité de drainage: 1.04 km/km²), formant les aquifères potentiels de lEst. Les données hydrogéomorphologiques vont également dans le sens des données de fluctuation de la nappe et de résistivité des formations saturées. Les résultats indiquent que les zones caractérisées géomorphologiquement comme favorables, moyennement favorables et pauvres, possèdent des fluctuations respectives de lordre de 0 à 2, 2 à 6 et de plus de 6 m. La résistivité de ces zones est également de lordre de 1 à 26, 40 à 466 et de plus de 1900 ohm-m. Quelques pompages dessais ont également été conduits pour déterminer les valeurs moyennes des paramètres de laquifère. En se basant sur ces données, des zones potentielles bonnes à pauvres pour lexploitation des eaux souterraines ont été délimitées.

     

A case study on changes in quality of groundwater with seasonal fluctuations of Pageru river basin, Cuddapah District, Andhra Pradesh, India

A study was conducted at Pageru river basin, Cuddapah District, Andhra Pradesh, to monitor seasonal fluctuations of groundwater and to determine how the fluctuation in the water levels will affect the groundwater quality. Groundwater levels were found to be influenced by rainfall and pumping of water from the wells for irrigation and domestic uses. Ninety-nine water samples were collected from different wells and analysed for major chemical constituents both in pre- and post-monsoon seasons to determine the quality variation. All major chemical constituents, such as Ca, Mg, Na, K etc., are significantly increased after post-monsoon recharge. According to the overall assessment of the basin, water quality was found to be useful both for drinking and irrigation.     

Fluoride levels in the groundwater of the south-eastern part of Ranga Reddy district,Andhra Pradesh,India

The fluoride level in groundwater is controlled by the distribution of Ca²⁺ and SO₄^2?, ionic strength and the presence of complex ions in its composition. In the study area, situated in the Ranga Reddy district, Andhra Pradesh, India, the concentrations of fluoride in the groundwater vary from 0.7 to 4.80 mg/l and from 0.4 to 4.20 mg/l during the pre- and post-monsoon seasons respectively. From the correlation coefficient studies, it is observed that fluoride is inversely related with Ca²⁺ and positively related with HCO₃^?, whereas the correlation coefficient between fluoride and other ions is very poor during both seasons. The difference in F^? concentrations between pre- and post-monsoon seasons could be because the ionic concentrations in the groundwater during the post-monsoon period were generally less than their counterparts during the pre-monsoon period, because of dilution by rainwater. By contrast, the fluoride concentration in many places was relatively high during the post-monsoon period. This indicates contamination of groundwater from surface pollutants.