Open AccessCorrelation of electrical resistivity and groundwater arsenic concentration, Nawalparasi, Nepal
Author(s) -
Tom H. Brikowski,
Linda S. Smith,
Tai-Chyi Shei,
Surendra Shrestha
Publication year - 2004
Publication title -
journal of nepal geological society
Language(s) - English
Resource type - Journals
ISSN - 2676-1378
DOI - 10.3126/jngs.v30i0.31687
Subject(s) - arsenic , aquifer , groundwater , electrical resistivity and conductivity , geology , hydrogeology , arsenic contamination of groundwater , environmental chemistry , contamination , soil science , environmental science , hydrology (agriculture) , chemistry , materials science , metallurgy , ecology , geotechnical engineering , electrical engineering , engineering , biology
The Asian Arsenic Crisis has expanded into the headwaters of the Ganges River, now including the plains (Terai) of Nepal. This study seeks a non-invasive predictive tool to estimate groundwater arsenic concentration prior to drilling, enabling "arsenic avoidance" in contaminated areas. Detailed chemical studies indicate that in Himalayan-sourced aquifers arsenic is released by microbially-mediated redox reactions. Likely hydrogeological settings for oxidizing chemical conditions (immobile arsenic) should be more porous (higher in filtration rate for oxygenated waters) and contain fewer fine organic sediments (oxygen-consuming material). Both conditions should yield higher electrical resistivity, and such aquifer heterogeneity effects should be most prominent in head water regions such as Nepal. To test this approach, a series of vertical electrical resistivity soundings were made near Parasi, Nepal, constituting a profile extending 2 km across a known high-arsenic area. Correlation of the horizontal and vertical distribution of measured resistivity and ENPHO groundwater arsenic measurements demonstrated a distinct inverse relationship between these variables. Out of 240 arsenic sample points, 75% of those extracted from high resistivity zones (>100 ohm-m, inferred lower clay content) exhibited arsenic 150 ppb. Given these preliminary results, the resistivity technique appears to hold great promise as a predictive tool for finding low-arsenic groundwater zones within contaminated areas, thereby allowing "well-switching" from highly toxic to new safe or more readily treatable wells. The method should be applicable in most circum- Himalayan high-arsenic areas.