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The unplanned Bhalswa landfill is located in one of the most urbanized area of Delhi, and its influence on the huge population are inevitable in the capital city of India lying in flood plain of the Yamuna River, and its alluvial lithology makes it more susceptible to contamination by leaching of pollutants. The present study highlights to assess the impact of non-engineered Bhalswa landfill site on the groundwater quality and associated potential health risk by its consumption to local residents of New Delhi, by collecting four leachate and sixty groundwater samples for pre- and post-monsoon seasons in the year 2013. The contamination potential of the leachate samples and the groundwater quality were evaluated with the help of leachate pollution index (LPI) and water quality index (WQI), respectively. The value of LPI is high in both the seasons but more in pre-monsoon (31.51) as compared to post-monsoon (29.36). The Obtained results of groundwater samples showed elevated level of Electrical conductivity (EC), major cations and anions. The EC of groundwater samples display concentration as follows: (pre-monsoon, 456–10870, average 3772; post-monsoon, 465–10450, average 3747). The groundwater samples close to the Bhalswa landfill shows very high value of EC and other chemical parameters. WQI calculated (using 17 physico-chemical parameters and WHO standards) to distinguish the areas of excellent and unsuitable for drinking purposes which will be helpful for the management of water resources. Our results showed that the concentration of majority of heavy metals exceed the WHO permissible limit except Cr and Cu which may be due to redox conditions that control the mobility of these ions in aqueous solutions. The average target hazard quotient (THQ) value of heavy metals were found in the order of Cd > Mn > Pb > Cu > Ni > Fe > Zn > Cr in both the seasons. The tube wells with more than one THQ value for Cd (100%), Mn (63%) and Pb (37%) will have potential human health risks. Hazard index (HI) shows greater than one value for all the samples and the average HI values are 10.241 for pre- and 10.402 for post-monsoon season. THQ and HI values suggest that the residents are highly susceptible to ingestion pathway. A conceptual model is used to describe the dispersal of leachate pollutants with reference to various kinds of geo-environmental features which degrades the groundwater quality. The health risk associated with metals in near future can be a serious threat for this region if this groundwater is being used for long run without proper remedial measures. [ABSTRACT FROM AUTHOR]