Groundwater protection in fractured media: a vulnerability-based approach for delineating protection zones in Switzerland

Abstract

A vulnerability-based approach for delineating groundwater protection zones around springs in fractured media has been developed to implement Swiss waterprotection regulations. It takes into consideration the diversity of hydrogeological conditions observed in fractured aquifers and provides individual solutions for each type of setting. A decision process allows for selecting one of three methods, depending on the spring vulnerability and the heterogeneity of the aquifer. At the first stage, an evaluation of spring vulnerability is required, which is essentially based on spring hydrographs and groundwater quality monitoring. In case of a low vulnerability of the spring, a simplified method using a fixed radius approach ("distance method") is applied. For vulnerable springs, additional investigations must be completed during a second stage to better characterize the aquifer properties, especially in terms of heterogeneity. This second stage includes a detailed hydrogeological survey and tracer testing. If the aquifer is assessed as slightly heterogeneous, the delineation of protection zones is performed using a calculated radius approach based on tracer test results ("isochrone method"). If the heterogeneity is high, a groundwater vulnerability mapping method is applied ("DISCO method"), based on evaluating discontinuities, protective cover and runoff parameters. Each method is illustrated by a case study.

Delineating Groundwater Vulnerability and Protection Zone Mapping in Fractured Rock Masses: Focus on the DISCO Index

“…The fractured media parameter (Fm) was derived from the map of tectonic lineaments density, and collected into four classes, with ratings ranging from 4 to 10, depending on the tectonic lineament density [8,26,28,48,50]; • SINTACS was created for vulnerability assessments and mapping in medium and large scale maps, and the multiplier weights of normal string were used [29,30]; • SI, where the Land Use (LU) parameter was derived from land cover maps [32]; • DISCO is carried out in the vulnerable springs and in the mineral water wells related to a highly heterogeneous and fractured media aquifer [33,34].…”

“…The GOD-S, DRASTIC-Fm, SINTACS and SI multi-criteria indexes are often used for local and regional mapping purposes (medium to small-scale), and the DISCO index [34] is very useful for in situ environmental hydrogeological investigations (large-scale maps). The most efficient methodology is an integrative approach encompassing all previous multi-criteria indexes [22].…”

“…The SI index shows only a very small area in the high vulnerability category. In this study a groundwater vulnerability assessment was carried out by means of the DISCO index [34]. The delineation of groundwater protection zones in the study site was applied for two hydromineral water wells ( Figure 7) and for an important shallow groundwater spring (0.5-1 L•s −1 ) (Figure 8).…”

“…Locally, both mineral water wells and normal groundwater springs are located along major deep fractures, or near the intersections between tectonic lineaments. The application of the DISCO method includes three main steps (details in [33,34]):…”

“…The delineation of protection zones at the site (D0, D1, D2 and D3) was defined according to the rating and criterion defined by Pochon et al [34] (Figure 7A). Therefore, buffers were assigned for each category: 25 m for D0, 10 m for D1 and 5 m for D2, while D3 was assigned to the rest of the area.…”