Monitoring of the groundwater chemical status in the Azores archipelago (Portugal) in the context of the EU water framework directive

A main challenge associated to EU Water Framework Directive corresponds to groundwater monitoring, both quantitative and chemical. The need for monitoring was also stressed by the Azores Water Plan. Monitoring of the chemical status of groundwater in Azores started in 2003 and has been progressively enlarged to all islands, totalizing 72 springs and 32 wells. A large number of parameters are analysed biannually, as major, minor and trace elements, pesticides and total hydrocarbons, as well as microbial indicators. Spring waters are mainly from HCO₃–Na type; instead water from wells is predominantly from the Cl–Na type, been differences attributed to their respective hydrogeologic framework. Springs discharge mainly from perched-water bodies, been influenced mainly from CO₂ in soils, silicate weathering, and seawater spraying and aerosols. Wells are in basal bodies, therefore subject to seawater intrusion influence, and 9% of Cl analyses made in wells exceed the standard value. Heavy metals, metalloids, hydrocarbons and pesticides all comply with standard values. Agriculture pollution also influences groundwater quality, as revealed by both NO₃ and PO₄ content, been the guide value exceeded respectively in 8 and 9% of the analyses. Despite the discontinuous variation of coliforms over time microbial indicators present an impact on water quality.