Assessment of the impact of on-site sanitation systems on groundwater pollution in two diverse geological settings—a case study from India

On-site sanitation has emerged as a preferred mode of sanitation in cities experiencing rapid urbanization due to the high cost involved in off-site sanitation which requires conventional sewerages. However, this practice has put severe stress on groundwater especially its quality. Under the above backdrop, a study has been undertaken to investigate the impact of on-site sanitation on quality of groundwater sources in two mega cities namely Indore and Kolkata which are situated in two different geological settings. The parameters for the studies are distance of groundwater source from place of sanitation, effect of summer and monsoon seasons, local hydro-geological conditions, and physico-chemical parameters. NO3 and fecal coliform concentrations are considered as main indexes of pollution in water. Out of many conclusions which can be made from this studies, one major conclusion is about the influence of on-site sanitation on groundwater quality is minimal in Kolkata, whereas it is significant in Indore. This difference is due to the difference in hydrogeological parameters of these two cities, Kolkata being on alluvium quaternary and Indore being on Deccan trap of Cretaceous to Paleogene age.