Groundwater Exploration in Hard Rock Areas 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 and varies sharply within very short distances, 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 the satellite imageries, topographical, geomorphological and hydrogeological inference promising zones were demarcated in hard rock areas of three Mandals (Seethanagaram, Salur and Pachipenta) of Vizianagaram District, Andhra Pradesh, India, an area of about 750 km2 to identify good locations for groundwater exploration. Total 100 Vertical Electrical Soundings (VES) were carried out using Wenner electrode configuration and an interactive interpretation of the VES data sharpened the information inferred from geomorphological and hydrogeological reconnaissance. Out of them 42 sites were recommended for drilling. Drilling with Down-The-Hole hammer (DTH) drill method was carried out for drilling in the recommended sites. 42 bore wells are drilled down to 50 to 80 m depths. The interpreted VES results are also correlated with the drilled bore well lithologs, showing good agreement with them. The yields of these bore wells vary from 1500 to 8000 lph, which are obtained from step draw down pumping test.