Use of isotopic techniques for determinig background levels according to groundwater directive. Study of sulfate levels in southern Spain

Abstract

Determine Natural Background Levels (NBL) are a key element in characterization of groundwater bodies, according to Water Framework Directive 2000/60/EC and, more specifically, Groundwater Directive 2006/118/EC. The NBL are the result of numerous factors, such as water-rock interactions, chemical and biological processes in the unsaturated zone, the residence time of water in the aquifer, recharge by rain and relations with other aquifers. In many cases, these levels present very high values for some parameters and types of groundwater, which is significant for their correct determination as a prior step to establishing thresholds, assessing the status of water bodies and subsequently identifying contaminant patterns. Because chemical analyses only provide the concentration of sulphate in water but not its source, four isotopic sampling campaigns ( δ 34S-SO4) were carried out on 2004, 2006, 2009 and 20012 on groundwater bodies in the Upper Guadalhorce river basin in order to trace the origin of sulphate. The objective of the present study is to quantify the percentage of natural (Evaporites) and anthropogenic (Fertilizers) sulphate and match a concentration associated with this percentage that allow to know the NBL on the upper basin.