Hydrogeochemistry and Quality Assessment ofGroundwater in an Arid Area: A Case Study from the Lower Part of Wadi Siham Basin, Tihama Coastal Plain, Republic of Yemen

The chemical characteristics of groundwater in the study area have been studied to classify waters into different facies using piper's trilinear diagram and to ascertain the suitability of waters for drinking and agricultural purposes. fifty one water samples representing the different domains of the area were collected and analyzed for ph, ec, tds, hco3, co3, cl, po4, so4, no3 ca, mg, na, and k. the major ion chemistry data revealed that: 1. there is only small variation in the values of parameters determined for summer and winter water samples. 2. the values for tds range between 580-8813 (mg/l) indicating slightly saline to moderately saline types. 3. the quality of the groundwater is not suitable for drinking use except the water available in the foothill domain. data have also been subjected to the evaluation of the suitability of groundwater for agricultural purposes using kelly's ratio (kr), sodium absorption ratio (sar), sodium soluble percentage (ssp), permeability index (pi), and residual sodium carbonate (rsc). the calculated values indicate that most of the waters from all the three domains are doubtful to be unsuitable for agricultural purposes, as far as, salinity hazard is concerned and good to doubtful as far as sodium hazard is concerned.