Audio magneto telluric and geoelectric signatures of un-consolidated coastal sedimentary formations-an integrated geophysical approach for targeting freshwater phreatic aquifers
Paper Details
Audio magneto telluric and geoelectric signatures of un-consolidated coastal sedimentary formations-an integrated geophysical approach for targeting freshwater phreatic aquifers
Abstract
For exploring groundwater resources in any terrain, employing vertical electrical sounding [VES] technique is the common practice. This study pertains to comparing and correlating Audio magneto telluric [AMT] profiling with 1D vertical electrical sounding to prospect the groundwater potential pocket for an irrigation project in an unconsolidated coastal sedimentary terrain for targeting freshwater phreatic aquifers in saline environment. The area falls in Chinnamanulur village of Kilvelur block in Nagappattinam district, Tamil Nadu, South India. A borewell drilled to a depth of 150 feet was not successful as good sand aquifers could not be met. The area of investigation is with an extent of about twenty acres of agricultural land. There are two shallow tubewells of about 16 feet depth and with these two sources only water need is managed. The TDS [Total dissolved solids] of this well is 385 PPM [parts per million]. An attempt has been made to prospect the freshwater aquifers by an integrated geological, hydrogeological and geophysical approach with combined geoelectric and AMT sounding/scanning. Three two-dimensional audio magneto telluric imaging followed by three 1 dimensional vertical electrical soundings [1D VES] were conducted. A shallow sand aquifer zone could be explored and one pilot borehole was drilled engaging calyx drill to a depth of 30 meters. A good medium to coarse grained sand with a thickness of 10 meters was encountered from 18 to 28 meters below ground level. As the soil samples and water were tasted frequently for every two meters, found to be good without any brackish/salinity taste and no marine gastropod shells were encountered in soil samples, a tubewell of 178 mm diameter was bravely constructed to a depth of 29m without conducting electrical well logging. The well was developed and completed after 4 days. As the attempt, findings and results were encouraging and positive; the tubewell was constructed successfully and fruitfully. The discharge of well is reported to be 63 liters per minute [LPM] and the quality of water is also good and fresh. It is recommended to test the water sample physiochemically tested for suitability for agriculture.
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