Abstract
The present study aims to investigate the applicability of DRASTIC, GOD and SI models in evaluating the groundwater vulnerability and risk of contamination in the Canton of Portoviejo, Ecuador. The groundwater vulnerability to contamination has been evaluated using DRASTIC and GOD models. Both models were able to classify the study area into different sectors of variable vulnerability. The coincidence of the two models is high, especially in the sectors with high vulnerability. Evaluation of the groundwater risk of contamination has been carried out by combining the contaminant load index with the elaborated groundwater vulnerability classes using DRASTIC and GOD methodologies. The resultant maps of both models reveal that in the areas with high vulnerability the land usages tend to introduce high contaminant load and therefore, the groundwater beneath these areas is subject to higher risk of contamination. The risk maps elaborated using DRASTIC and GOD models have more coincidence than vulnerability maps elaborated using the same models. This is partially because of the contaminant load index which is identical in the both cases. The groundwater risk of contamination has been also evaluated using Susceptibility Index (SI) model. The resultant SI risk map was compared with the risk maps elaborated using DRASTIC and GOD. The results indicate a comparable products; however, they have more similarity with DRASTIC outputs. The maps of groundwater risk of contamination in the canton using different models show a comparable results, especially when accepting one risk category shift as acceptable error. The coincidence in this case is 98, 94 and 88% between DRASTIC and GOD, DRASTIC and SI, GOD and SI respectively. The results of the study recommend SI and GOD models to study the risk of groundwater contamination especially in data limitation conditions.
Highlights
In spite of thousands of articles dealt with the term vulnerability, there is no agreement on the exact definition (Albuquerque et al, 2013; Stigter et al, 2006)
To evaluate the groundwater risk of contamination in the study area, three models have been applied: DRASTIC model combined with the contaminant load, GOD model combined with contaminant load and Susceptibility Index (SI) model
The results show that DRASTIC and GOD models are able to classify the groundwater's vulnerability of the study area to distinct levels (Fig. 4)
Summary
In spite of thousands of articles dealt with the term vulnerability, there is no agreement on the exact definition (Albuquerque et al, 2013; Stigter et al, 2006). This is totally coincided with the definition of Foster and Hirata (1988), in which they define the groundwater pollution risk as "the interaction between the natural vulnerability of an aquifer and the pollution loading that is or will be applied on the surface environment as a result of human activity”. Assessing and mapping groundwater vulnerability to contamination help the stakeholders and decision makers to locate where groundwater can be contaminated and where not This in turn helps to decide which activities can be allowed in certain areas in order to maintain or even improve the quality of groundwater in accordance with good land-use practices (Kumar et al, 2015; Aller et al, 1987). The possibility of storing some water cannot be rule out
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