DBPapers
DOI: 10.5593/SGEM2015/B13/S5.109

ERT INVESTIGATION OF A BURIED WATER RESERVOIR

A. Serban, F. Chitea, D. Ioane
Friday 7 August 2015 by Libadmin2015

References: 15th International Multidisciplinary Scientific GeoConference SGEM 2015, www.sgem.org, SGEM2015 Conference Proceedings, ISBN 978-619-7105-33-9 / ISSN 1314-2704, June 18-24, 2015, Book1 Vol. 3, 839-846 pp

ABSTRACT
In order to prevent land deterioration, when searching for buried objects with imprecise location, non-invasive and non-destructive geophysical methods can be applied. The success of these methods depends on the target dimensions, its properties in certain induced or natural physical fields and their contrast with the surrounding material, as well on the measurements profiles design.
Such a test was executed for a buried water reservoir formed by two unequal wells with the maximum height of 3m. Each column was built up by concrete tubes having a diameter of 1.2m.
Geophysical measurements, consisting in apparent electrical resistivity measurements, were executed using a multielectrode system. Several Electrical Resistivity (ERT) profiles, with different orientations, were delineated in order to intersect the area where the buried water reservoir was suspected to be located. ERT measurements were performed using Schlumberger, Wenner or Dipole-Dipole arrays, positioning the electrodes at an equidistance of 1m each.
Two ERT profiles were previously executed in an undisturbed area in order to understand the local shallow geology illustrated by resistivity variations. ERT sections depicted an electrical layered structure formed by 3 distinct layers till the investigated depth of 7m.
Despite the fact that the groundwater is often classified as electrically conductive, samples of water collected from the studied area showed low electrical conductivity properties. Due to the unexpected values obtained from the water collected during the geophysical measurements (32µS/cm, at a pH of 6.868) from a nearby spring, a new water probe was analyzed after 3 months of the completion of geophysical campaign. The results showed a small change, the electrical conductivity of the water taken from the reservoir being 30 µS/cm, at a pH of 6.673, 0.0 salinity and TDS of 23ppm). The high electrical resistivity value of the phreatic aquifer from the studied location is a consequence of its refilling mainly by the raining water (electrical conductivity of
mountain rain water collected from the study location was 20 µS/cm at a pH of 6.759 and TDS of 10ppm).
Despite the challenging environment and unexpected low conductance of the groundwater, by means of ERT data interpretation the buried water reservoir was successfully located.

Keywords: Electrical Resistivity Tomography, electrical detection of water reservoir, environmental geophysics, near-surface geophysics