Mitigation and Remedy of Groundwater Arsenic Menace in India

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Mitigation and Remedy of Groundwater Arsenic Menace in India : A Vision Documentmeters are affected. In alluvial formations, possibility of having confined aquifer is a chancephenomenon, and if at all, it would be on a very limited local scale. The aquifers are normally ofunconfined to semi-confined types. Therefore, threat of downward mobilization of arsenic, fromshallow to deeper zones over the years always, prevails. Further, the source being in-situ atlocalized pockets, a large part in a spatially distributed groundwater domain has uncontaminatedgroundwater reserves, which may not be under the influence of arsenic groundwatermobilization due to some obvious chemical portioning leading to self-purging, etc.. Areas barringlarge scale fluvial deposits, accumulated formations of clays, shifted river courses, alreadyexposed by arsenic mobilization, etc. are normally expected to have uncontaminated reserves oraccumulations. Modeling studies of arsenic contamination transport by various researchers showedthat judicious and scientific management of fresh zones of aquifer, both shallow and deep, cansustain withdrawal of fresh groundwater resources for a long period without much aggravationof arsenic contaminated zones. For identification and design of safe locations of groundwaterwithdrawal, wells modeling studies can be the right tool. The caution that one has to take isanalysis of post groundwater development scenarios, particularly with respect to transformedgroundwater direction and movement.Watershed is considered to be the basic unit of land-water management practices. Fromhydrological point of view, watershed possesses all characteristics generally required forconservation and development of water resources. Surface water is arsenic-free, and it is moreso when rainwater is harvested as surface storage. Harnessing, developing and appropriatemanagement of surface water, on a watershed basis, in arsenic affected areas and their usagesin irrigation and other domestic purposes, can be a potential alternative. This can be noted thatthe major application of watershed based approaches and harnessing surface was not atraditional practice in alluvial tracts in Bengal, - major part of which is scourged with Arseniccontamination. On the contrary, in the western part of Bengal and mostly in drier zones and hardrock areas, use of surface water, was a natural option and practice.Supply and usage of surface water exclusive from other sources, particularly due todistributive rain fall pattern, are no doubt a viable alternative, when availability of water from thesource is assured and sustainable. The demand management of some areas from resources ofother areas is linked to certainty of many factors. Creation of alternate surface water systemmay involve considerable money. Conjunctive use of surface water (either from watersheddevelopment or from other sources) and in-situ groundwater can be another potentialalternative. A technical feasibility study, considering risk, cost and benefit of each alternative,would form an important task.Whatever technological options we adopt, the success and effectiveness of that taskcan not be achieved unless end-users and beneficiaries of the schemes are debugged fromconcern and responsibility. No strategic planning of availability of safe and wise use of water canNIH & CGWB 121
A Critical Appraisal- Future Risk, Scope to Remediate, Technological Competence, etc.be sustained by delinking user community and their effective participation in the management oftraditional and new resources. Obviously, for the success of the program, people's awareness,regarding importance of water, its know-how on 'dos and don'ts and rightful uses, need to betagged as a mandatory task.6.6 SummaryThere exist a number of opinions about causes of arsenic induced groundwatercontamination, in the Gangetic and Brahmaputra plains, in Indian sub-continent. However, it isnow generally accepted that the source is of geological origin and percolation of fertilizerresidues may have played a modifying role in its further exaggeration. Identification of parentalrocks or outcrops is yet to be recognized, including their sources, routes, transport, speciation andoccurrence in Holocene aquifers along fluvial tracks of the Ganga-Brahmaputra-Barrak valleyand in scattered places, adjoining to it, in their basins. The speculation of sources in the Gangeticplains ranged from the sulphide belts of Bihar, Uttar Pradesh, and North Bengal to the coalseams of the neighboring Godwana Basins, the basic rocks of the Rajmahal Traps, themetamorphic schists of the Lesser Himalaya. The question of the possible role of excessivewithdrawal of groundwater for its triggering, however, has continued to have divided opinions.The chemical processes such as, Redox potential, sorption, precipitation-dissolution, pH,influence of other competing ions, biological transformation, etc under different soil-waterenvironmental condition; influence the perturbation of arsenic in a system, having presence ofsource material and/or conditions of enrichment. Whether the processes of physicochemicaltransformation were only influenced by excessive groundwater exploitation or there were othercoupled actions of a number of hydro-geological and geo-environmental disturbances, over theperiods, are yet to be recognized. Surfacing new arsenic affected areas, in every additionalsurvey, is a matter of concern. It was reported that the contaminated waters are enriched in Fe,Mn, Ca, Mg, bicarbonates, and depleted in sulphate, fluoride, chloride; pH ranged from 6.5 to 8;redox condition usually in reducing; high on organic matter content; lodged mostly in sandcoatings, or sorbed on clays, HFOs, and organic matters; As-concentration diminishingdown-depth, which brings out a generalized geochemical perception that could help developin-situ remediation of arsenic.It has been proved that arsenic has affinity with iron. The relationship between As-Fecan be interpreted as signifying that in these instances iron played the scavenger role, adsorbingarsenic from water as it precipitated out, again desorbing arsenic into water as it re-dissolved inresponse to appropriate change of Eh-pH conditions. It appears that the reductants and oxidantswere transported / accumulated / diagenetically precipitated components of the process ofbuild-up of the sediment sequence of the delta. The oscillations owe their origin either toresetting of oxidants / reductants as a result of diffusion-dispersion-flux, or combined with, initialvariation of As-Fe contents of the solid phases in the aquifer sediments.122NIH & CGWB
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ACKNOWLEDGEMENTThe Government of In
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nearly 33 villages in 4 districts i
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(iii) Whether ex-situ removal techn
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6.4 Experiences during Arsenic Remo
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List of FiguresFigure no. Figure ca
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List of TablesTable no. Table Capti
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Mitigation and Remedy of Groundwate
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Mitigation and Remedy of Groundwater Arsenic Menace in India

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