- Groundwater, Shallow aquifers, Drinking quality, Coastal part, Karachi.
The aim of present study is to assess groundwater quality of Qayyumabad area for drinking purpose. Groundwater samples (n = 20) were collected from wellbores from variable depths (12-300 feet) occurring on both banks of the Malir River near study area. Water quality was assessed through estimation of physical parameters including, pH, Eh, TDS, EC, hardness, temperature, aesthetic character (taste, color and odor) and chemical parameters including major cations (Na, K, Ca, Mg), anions (Cl, NO₃, SO₄, HCO₃) and minor/trace elements (Fe, As). Data revealed that groundwater of study area has very high TDS content (range: 805-40340 mg/l) and positive Eh (-180 to +125 mV), suggesting the recent recharge. The pH varies in the range of 6.55-7.75 which comply with WHO limit (6.5-8.5) for drinking water. Major solutes varied in the order of Na (mean: 2587 mg/l) > Mg (433mg/l) > Ca (231mg/l) > K (91 mg/l) while anions in the order of Cl (mean: 3385 mg/l) > SO₄ (mean: 580 mg/l) > HCO₃ (mean: 343 mg/l) > NO₃ (11.43 mg/l). Both arsenic and iron contents occur within the WHO permissible limits except two samples which showed elevated Fe (4950 ppb) and As (100 ppb) respectively. These results suggest that groundwater in study area is unfit for drinking purpose. Principal component analysis (PCA) explained four factors where F1 suggests the salts leaching mechanism and F2 indicated anoxia prevalence due to organic matter decomposition. On the other hand, F3 confirmed water rock interaction and F4 supported the prevalence arsenic release associated with anoxia.