Assessment of shallow groundwater quality from six wards of Khulna City Corporation, Bangladesh

Abstract

Water supply in the Khulna City Corporation (KCC) is adversely affected by the plentiful presence of salinity in the groundwater (GW) as well as surface water (SW) sources. Other water quality parameters, which are also present in GW that has a direct impact on the city's water supply and industrial development. In this regard, a study is undertaken to assess the water quality of shallow aquifers in the KCC area for drinking and industrial purposes. Six wards (ward no. 14 to 19) of KCC covering central part of Khulna city are selected and 36 GW samples (5 samples in each ward) from shallow depth are collected on a monthly basis for a period of eight months (July 2010 to February 2011). Samples are tested for pH, iron, chloride, TDS, hardness, color, alkalinity, turbidity and electrical conductivity using standard testing procedures. The analysis reveals that salinity varies from 1012 mg/L to 160 mg/L with an average value of 556 mg/L and 76% of all samples exceeds BDS allowable limit for chloride. The result demonstrates that salinity is lower in monsoon (May to October) season due to heavy rainfall and upstream freshwater flow. However, limited freshwater flow from upstream and less rainfall causes significant increase of salinity in dry (November to April) period. During the study period, 45% and 17% of all samples exceed the BDS and WHO recommended iron limit for drinking water. However, TDS classification of GW shows that maximum samples lie within good (300–600 mg/L) and fair (600–900 mg/L). The hardness values depict that 58% samples exceed BDS allowable limit, which makes GW unsuitable for public and industrial use. In addition, maximum and minimum values of electrical conductivity are found as 3120 and 320 μS/cm, respectively and about 57% sample exceeds BDS recommended value. The results also show that except very few cases, other water quality parameters such as pH, turbidity, color and alkalinity of almost all samples satisfy the allowable limits recommended by WHO and BDS guidelines.