Development of a groundwater quality index: GWQI, for the aquifers of the state of Bahia, Brazil using multivariable analyses

Abstract

This work elaborated a groundwater quality index—GWQI, for the aquifers of the state of Bahia, Brazil, using multivariable analyses. Data from 600 wells located in the four hydrogeological domains: sedimentary, crystalline, karstic, and metasedimentary, were subjected to exploratory statistical analysis, and 22 out of 26 parameters were subjected to multivariable analysis using Statistica (Version 7.0). From the PCA, 5 factors were sufficient to participate in the index, due to sufficient explanation of the cumulative variance. The matrix of factorial loads (for 1–5 factors) indicated 9 parameters related to water quality and 4 hydrological, with factor loads above ± 0.50, to be part of the hierarchical cluster analysis. The dendrogram allowed to choose the 5 parameters related to groundwater quality, to participate in the GWQI (hardness, total residue, sulphate, fluoride and iron). From the multivariable analyses, three parameters from a previous index—NGWQI, were not selected for the GWQI: chloride (belongs to the hardness hierarchical group); pH (insignificant factor load); and nitrate (significant factor load only for 6 factors), also, not a regionalized variable. From the set of communality values (5 factors), the degree of relevance of each parameter was extracted. Based on these values, were determined the relative weights (wi) for the parameters. Using similar WQI-NSF formulation, a product of quality grades raised to a power, which is the weight of importance of each variable, the GWQI values were calculated. Spatialization of 1369 GWQI values, with the respective colors, on the map of the state of Bahia, revealed good correlation between the groundwater quality and the index quality classification. According to the literature on water quality indexing, the GWQI developed here, using emerging technologies, is a mathematical tool developed as specific index, as it was derived using limits for drinking water. This new index was tailored to represent the quality of the groundwater of the four hydrogeological domains of the state of Bahia. Although it has a regionalized application, its development, using, factor analysis, principal component analysis, and hierarchical cluster analysis, participates of the new trend for WQI development, which uses rational, rather than subjective assessment. The GWQI is a successful index due to its ability to represent the groundwater quality of the state of Bahia, using a single mathematical formulation, the same five parameters, and unique weight for each parameter.

Groundwater Quality Assessment using SPSS based on multivariate statics and water quality index of Gaya, Bihar.

“…Based on the Water quality values of the groundwater samples, dendrograms was created to display the different water sample quality categories. The interdependencies between various water quality measurements can be used to categorise them, as can the chemical similarity of samples collected from different sampling locations (Barbosa Filho & de Oliveira, 2021;Rahbar et al, 2020). Total 99 sites included in cluster 1, while the second cluster had 46 sites.…”

“…groundwater quality of the region under investigation and its appropriateness for drinking purposes are investigated using the water quality index (WQI), which is calculated from experimental data and drinking water standards (APHA, 2005;WHO, 2011). Many groundwater quality indices (GWQIs) have been used to measure groundwater quality have been improved by a number of researchers (Honarbakhsh et al, 2019;Tripathi & Singal, 2019;Barbosa Filho & de Oliveira, 2021;Harun et al, 2021). WQI is one of the criteria for classifying groundwater, and it also denotes the relative quality of water.…”

Evaluation of karst spring water quality in northeast Tennessee using water quality indices

“…Because of the relative simplicity in computation and easy‐to‐understand output, which reveals a composite influence of various water quality parameters on water quality, the WQI technique has been widely used. Applications of the WQI technique include surface water quality (Akkoyunlu & Akiner, 2012; Amadi et al., 2010; Berry et al., 2020; Boyacioglu & Boyacioglu, 2007; Iticescu et al., 2013; Kumar & Dua, 2010; Lermontov et al., 2011) and groundwater quality (Adimalla & Qian, 2019; Filho & de Oliveira, 2021; Jha et al., 2020; Mohebbi et al., 2013). Despite WQI's status as a nonregulatory measurement (Akkoyunlu & Akiner, 2012; USF Water Institute, 2022), it is widely used because it helps the public and policymakers better understand critical water quality information.…”

“…Despite differences in the type and number of parameters selected and purpose of use as either specific‐ or general‐water use indices, all WQI employ commonly monitored physical, chemical, and microbial water quality parameters. In practice, WQIs have been developed on the basis of either specific regional/local water quality guidelines or specific/designated uses of water (Filho & de Oliveira, 2021; Uddin et al., 2021). As an example of a specific water use indicator, a variant of NSFWQI includes radionuclides as one of the parameters (Nasirian, 2007), developed in line with ideas in Stoner (1978) arguing for inclusion of radionuclides in public water supply (PWS) indices.…”

“…Recognizing these as issues that may affect WQI outputs, some studies have utilized factor analysis, principal components analysis, and cluster analysis to determine water quality parameter significance, using results to objectively select parameters or groups of parameters for WQI analysis (see, for example, Debels et al. (2005); Filho and de Oliveira (2021); Gupta et al. (2015); Kocer and Sevgili (2014)).…”