A Novel Approach to Harmonize Vulnerability Assessment in Carbonate and Detrital Aquifers at Basin Scale

Leticia Baena-Ruiz,David Pulido-Velazquez

doi:10.3390/w12112971

Abstract

The DRASTIC (D: Depth to water; R: Net recharge; A: Aquifer media; S: Soil media; T: Topography; I: Impact of vadose zone; C: Hydraulic conductivity) index is usually applied to assess intrinsic vulnerability in detrital and carbonate aquifers, although it does not take into account the particularities of karst systems as the COP (C: Concentration of flow; O: Overlying layers above water table; P: precipitation) method does. In this paper we aim to find a reasonable correspondence between the vulnerability maps obtained using these two methods. We adapt the DRASTIC index in order to obtain reliable assessments in carbonate aquifers while maintaining its original conceptual formulation. This approach is analogous to the hypothesis of “equivalent porous medium”, which applies to karstic aquifers the numerical solution developed for detrital aquifers. We applied our novel method to the Upper Guadiana Basin, which contains both carbonate and detrital aquifers. Validation analysis demonstrated a higher confidence in the vulnerability assessment provided by the COP method in the carbonate aquifers. The proposed method solves an optimization problem to minimize the differences between the assessments provided by the modified DRASTIC and COP methods. Decision trees and spatial statistics analyses were combined to identify the ranges and weights of DRASTIC parameters to produce an optimal solution that matches the COP vulnerability classification for carbonate aquifers in 75% of the area, while maintaining a reliable assessment of the detrital aquifers in the Basin.

Highlights

Groundwater pollution is a widespread problem affecting most aquifers all over the world due to the increasing agricultural and industrial human activity [1,2]
The spatial coincidence (Si ) of the vulnerability classes between the DRASTIC and COP maps rose to 61.31%
The ranges of parameter C in O-DRASTIC support this conclusion given that the new classification of this parameter reduces the rate assigned to conductivity values

Summary

Introduction

Groundwater pollution is a widespread problem affecting most aquifers all over the world due to the increasing agricultural and industrial human activity [1,2]. It is the result of the interaction between the anthroposphere and the hydrosphere, where substances from the different land uses penetrate the groundwater, leading to impacts on environmental water quality and human health. The degree of protection depends on intrinsic groundwater vulnerability, which is defined as the susceptibility of aquifers to pollution arising from anthropogenic activity [6]. Several methods have been proposed to assess intrinsic vulnerability by using conceptual groundwater flow models and taking transport processes into account [7,8]. The most frequently employed methods are the index-based approaches [9,10]

Methods

Results

Conclusion