Geoelectrical resistivity survey of the Chennai Sewage Treatment Plants for identifying reclaimed water recharge

Abstract

An electrical resistivity survey was carried out in the premises of Chennai Metro water Sewage treatment pla nts at Koyambedu, Nesapakkam, Kodungaiyur, Perungudi and Anna University to assess the suitability for reclaimed water recharge and also to understand groundwater conditions, such as depth, thickness and location of the aquifer and the type of water. The geo-electrical methods used in the survey are Vertical Electrical Sounding (VES) in and around the Chennai Sewage Treatment Plants. The 5 VES points were conducted using the Schlumberger c onfiguration in the entire study area. The instrument used is ABEM Terrameter SAS 1000. The VES data were interpreted using IX1Dv2 software which showed that the area is composed of top soil (clay and Alluvium), clay, sandy clay, weathered gneiss, jointed gneiss and massive charnockite. These layer parameters thus obtained from the analysis were used together with existing boreholes to estimate the depth and thickness of each layer as well as correlating water quality with the aquifer apparent resistivity. The curves are prominently of H-type indicating the presence of three layers followed by combination of curves (HA and HK) indicating the four sub-surface layers. Interpretation reveals the number of subsurface layers, their thickness and their water poten tial zone within the study area. The resistivity varying from 3.96 Ωm to 2796.4 Ωm and thickness from 0.58 m to 43.05 m. The EC value for VES 1 (Perungudi) and VES 3 (Koyambedu) are 26 mS/cm and 1.55 mS/cm, and the TDS value for VES 1 and VES 3 are 16,896 mg/l and 993 respectively.