Assessing phreatic and confined water quality in the Guanzhong Basin, China: a novel integrated-weight water quality index approach

Abstract

Distinction between phreatic and confined water provide a better understanding of groundwater quality for drinking purposes. This study assessed groundwater quality in the Guanzhong Basin, China, using a novel integrated-weight water quality index (IWQI) designed to address limitations in previous parameter weighting methods. Based on 163 groundwater samples, thirteen health-related water quality parameters were analyzed, including major ions, nitrogen contaminants, As, and I⁻. Results show that groundwater quality was primarily influenced by TDS, Cl⁻, SO₄²⁻, Na⁺, TH, and NH₄⁺, with SO₄²⁻ and Na⁺ as dominant ions contributing to elevated TDS and Cl⁻ levels. Confined groundwater has better quality than phreatic groundwater. The lower percentage of excellent confined water quality was linked to agricultural pollution in the central and northeastern basin, particularly in the ancient irrigation district. Moreover, some of the deep wells are very old, indicating a probable gradually slow contamination of groundwater. The IWQI approach was found to be a solution to the overweighting of some chemical parameters such as COD_Mn, NO₂–N, As, and I⁻, NH₄–N, and As noticed in traditional EWQI. These chemicals had concentrations under the detection limit for the majority of samples, which means that they should not greatly affect the comprehensive groundwater quality for the entire basin. These findings can support groundwater management decisions, while the IWQI method offers a valuable tool for similar global assessments.