GIS-based Spatial Variability of COD and Heavy Metals Owing to Larkana City Sewage Drained into the Rice Canal, Sindh, Pakistan

The study was carried out by using multivariate statistical methods, geochemical modeling (GIS maps), WQI and conventional designs to categorize the hydrochemical feature of the region. The drainage water is being dumped into the Rice Canal which is making canal water polluted, and people are consuming the Rice Canal water for drinking purposes; therefore, it is a concern for human health. A total of 18 water samples were composed: 9 from the Rice Canal and 9 from the Larkana drainage water. The sampling was repeated 3 times in a year and investigated for physicochemical and heavy metals. The GIS maps of cations and anions indicated that sewage drained in the Rice Canal showed a high risk to human health and made the Rice Canal water unfit for drinking. The higher level of chemical oxygen demand (COD), particularly during the post-monsoon season was of concern because of low freshwater discharge. The water quality index (WQI) of the Rice Canal water indicated that all samples were found in excellent to good for drinking, and 100% were present in excellent to good for cultivation. The WQI of drainage water indicated that 100% were good for irrigation. The contamination index (Cd) of drainage water of the majority of the samples exhibited a high threat to humans. The HQ value of drainage water of one sample showed a higher level of cadmium. Arsenic in 2 samples crossed the allowable limit and exposed high risk for the human body. The CDI value of drainage water showed risk in some samples, but the Rice Canal water did not show risk for human health, because of dilution by fresh water. The Gibbs diagram showed that the Rice Canal water was found in the rock-dominance category, and drainage water samples were in evaporation dominance. The Piper diagram showed that the majority of samples were present in the mixed-type water category.