Investigation of groundwater quality considering the influence of nearby pit latrine and septic tank latrine system

In Khulna, pit latrines and septic tanks are prominent onsite sanitation options. These modes of onsite sanitation are becoming source of Groundwater contamination. In this study the groundwater of Khulna City Corporation has been investigated for the assessment of hydrochemistry and degree of fecal contamination in groundwater due to the influence of nearby pit and septic tank latrines. Water samples were collected from 10 spots considering the proximity of pit latrine and septic tank latrine systems. Water samples were collected from the tube wells and analyzed for determination of Total coliform, Fecal coliforms, E. coli and major cations and anions. All of the tested samples failed to ensure the quality of acceptable level for drinking water recommended by World Health Organization (WHO) due to the presence of higher load of Total coliform (4.46 × 10³ CFU/10 0ml), Total fecal coliform (2.9 × 10³ CFU/100 ml) and E. coli (1.84 × 10³ CFU/100 ml) near pit latrines and Total coliform (7× 10² CFU/10 0ml), Total fecal coliform (3.9 × 10² CFU/100 ml) and E. coli (3.5 × 10² CFU/100 ml) near septic tank latrine.  It has been found that pit latrines built near tube wells have a substantial impact on the quality of the tube well water compare to septic tank latrine systems. The results of a hydro-chemical analysis of water samples collected during the monsoon and winter seasons revealed that water quality parameters differ significantly. The accuracy of the analysis was maintained by checking the ionic balance and was eventually found within ±10% throughout the sampling seasons. Regardless of the seasonal pattern, the sequence of major ions in the monsoon and winter seasons was Na⁺> Ca²⁺> Mg²⁺> K⁺. In case of anions the sequence was observed to be HCO^3-> Cl^-> NO₃^-> SO₄^2-> PO₄^2- in monsoon and HCO^3-> Cl^-> SO₄^2-> PO₄^2- > NO₃^-> in winter. Correlation matrix recognized strong and moderate correlation among the most water quality parameters. Gibbs diagram designated that 60% of the water samples were controlled by evaporation and crystallization process and the rest of the water samples were governed rock weathering mechanism. Analytical data indicated that hydro-chemical facies of groundwater samples in monsoon and winter season we found that water samples are Na-Cl and Ca-Na-HCO₃^- type. In terms of EC, TDS, Na⁺, HCO₃^-, and Cl-  the ground water quality in monsoon and winter of the study area is unsatisfactory as it exceeded the standards of Bangladesh and WHO drinking water standard.

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