Abstract
El-Gassim is the most important agricultural region in Saudi Arabia due to its huge storage of groundwater. The main aquifer, which supplies most wells in the El-Gassim region is of Saq sandstone. Due to the serious increase of water salinity, most landowners abandoned these wells and re-drilled new wells, at considerable cost. Moreover the seepage of saline water from the abandoned wells continues to contaminate the main aquifer in the region. This study has been carried out to evaluate and investigate the reasons of increased salinity in El-Gassim water wells. A random survey has located 310 deep wells in 137 farms. It showed that the average ratio of abandoned wells to the total number of wells is 22 % and has reached 44 % in some locations. An analysis of 150 water samples showed that the total dissolved salts TDS reached 2200 mg/l in 29 % of the farms. The values of TDS reached 7000 - 10000 mg/l in some locations although the Saq aquifer has a low value of TDS (500 - 1000 mg/l).