Intrinsic vulnerability mapping for small mountainous karst aquifers, implementation of the new PaPRIKa method to Western Pyrenees (France)

Abstract

The new intrinsic vulnerability mapping method PaPRIKa is proposed as a tool to assess groundwater protection of small karst systems exploited for drinking water supply purposes in the French Pyrenees. The specific characteristics of the discontinuous carbonate aquifers of mountainous areas are here considered and taken into account into the implementation of the methodology. The Orbe site from the French Western Pyrenees area is chosen as a test site because of the relatively well known structure and behavior of the aquifer system. Steep slopes, extremely developed dissolution features, thin soils and strong dipping of geological formations are the main points to be considered. PaPRIKa method appears as a tool to assess and illustrate both the resource and source vulnerability according to the site specificities provided that appropriate field observations at a relatively high density are carried out. The vulnerability of the resource was assessed for the entire catchment area, while source-orientated mapping was attempted for the catchment area of the main capture work used for drinking water supply.

1. Introduction

In the French Pyrenees groundwater from carbonate rocks are considered as a huge potential resource for water supply to satisfy drinking water needs. In the coming years, these resources will be necessary as a substitution to surface water resources which are con- stantly decreasing because of the intense agricultural activity within the area and which quality is more and more unable to meet European drinking water standards (Rey, 2007). The development of carbonate aquifer groundwater is planned through the capture of many springs scattered over large areas and mainly concerns the South of the Béarn Region and more precisely the area of the “Chaînons Béarnais”, here considered as a test zone. The discontinuous structure of these reservoirs is a main obstacle to the development and exploita- tion of groundwater, but since no other aquifer can be tapped in these areas, many communities have decided to improve their knowl- edge of the main springs of the region. A few of them are already used for drinking water supply, but problems linked to the lack of proper management can lead in some cases to water supply disruption because of quality problems especially during strong rain episodes.

The French regulation on potable water quality inherited from the European Water Framework Directive 2000/60/CE and dated from the 23rd October 2000 forces administrations in charge of groundwa- ter management and distribution to pay attention to resource protec- tion. Efficient management is strongly correlated to the proper protection perimeter definition around springs and proactive regula- tion of land uses over the spring’s catchment area (“impluvium”). For water supply managers the objectives are to minimize the poten- tial cost of water treatment and to guaranty the continuous delivery of good quality water to consumers.