Spatial Evaluation of Groundwater Quality in Indore City Using the Nemerow Pollution Index

Abstract

Introduction: Groundwater is a primary freshwater source in rapidly urbanizing Indian cities; however, increasing anthropogenic pressure and lithological controls significantly influence its quality and associated health risks

Objectives: This study aims (i) to assess and spatially classify groundwater quality across    nineteen urban zones of Indore City using the Nemerow Pollution Index (NPI), and (ii) to identify dominant hydrogeochemical processes and evaluate potential non-carcinogenic health risks.

Methods: Nineteen groundwater samples were analyzed for pH, Total Dissolved Solids (TDS), Total Hardness (TH), Nitrate, Sulphate, Fluoride, and Calcium following APHA (2017) methods. Pollution Index (Pi) and Nemerow Pollution Index (NPI) were computed using BIS (2012) standards. Pearson correlation and Principal Component Analysis (PCA) were applied to determine hydrochemical relationships and controlling mechanisms.

Results: NPI values ranged from 1.615 to 3.969, indicating slight to heavy pollution, with no sampling site classified as safe (NPI < 1). PCA extracted two significant components explaining 81.6% of total variance. PC1 (55.6%) reflected lithogenic control associated with basaltic mineral weathering, while PC2 (26.0%) indicated anthropogenic inputs linked to nitrate and sulphate enrichment. Fluoride-based Hazard Quotient (HQ) values were below unity (HQ < 1)..

Conclusions: Groundwater quality in Indore is predominantly governed by geogenic processes with secondary anthropogenic influence. Continuous monitoring and integrated groundwater management strategies are essential for sustainable urban water security.