Hydrogeochemical and microbial risk assessment of arsenic-contaminated groundwater in Chakdah block, Nadia District, India

The study addresses depth dependent arsenic, and microbial (coliform) contamination of groundwater in the shallow aquifers of Chakdah block of the Bengal Delta Plain, an issue of undeniable public health significance. Groundwater samples were collected from six gram panchayats in the Chakdah block, Nadia district, India to estimate the dissolved ions, total and fecal coliform. The risk associated with groundwater use pattern from six sites was analyzed by the sanitary risk score and the fecal coliform score. Dissolved arsenic levels in the groundwater ranges from 0.069 to 0.178 mgL−1 (Mean: 0.119 mgL−1). The primary anion detected was HCO3− (Mean: 222 mgL−1), followed by Cl− (Mean: 21 mgL−1), SO42− (Mean: 8.96 mgL−1) and PO43− (Mean: 2.26 mgL−1). Chloride varies significantly (up to 147 mgL−1), indicating local anthropogenic sources of pollution. Groundwater sources near surface water bodies (~ 2–3 m) have high total and fecal coliform count. Coliform count varies seasonally in groundwater and shows higher count during post-monsoon season. The fecal coliform count at all sites ranged from 10 to 100/100 mL of groundwater. According to sanitary risk analysis, the monitored tube wells could be categorized as very high risk-25.0%, high risk-58.3%, intermediate risk-11.1%, and low risk-5%. The occurrence of arsenic contamination corresponds with high coliform count, particularly in the tube wells of high risk areas. The study advocates that arsenic and microbial contamination of groundwater in the aforementioned region is a serious public health issue which needs attention (policy) at local and global platforms.