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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos

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Referência Bibliográfica

COUTINHO, R., FONTIELA, J., FREIRE, P., CRUZ, J.V. (2015) - Hydrogeology of São Miguel Island, Azores: a review. In: Gaspar, J.L., Guest, J.E., Duncan, A.M., Barriga, F.J.A.S., Chester, D.K. (eds.) Volcanic Geology of São Miguel Island (Azores Archipelago), Geological Society of London Memoir, 44: 289-296, doi: 10.1144/M44.21.​

Resumo

​Groundwater is the main source of water supply on São Miguel. Groundwater abstraction (25 hm3 a-1) relies almost exclusively on springs discharging from perched aquifers. A total of 1100 springs (1.5 springs/km2) are located on São Miguel, mainly in the Água de Pau and the Furnas–Povoação groundwater bodies. Only 26 wells have been drilled, distributed principally in the west-central zone. Specific capacity ranges between 0.49 and 100 l (s m)-1 (median = 1.11 l (s m)-1), while transmissivity ranges between 5.98 x 10-4 and 1.22 x 10-1 m2 s-1 (median = 1.35 x 10-3 m2 s-1). Groundwater is predominantly of the Na-Cl and Na-HCO3 types and electrical conductivity in springs ranges from 36 to 440 µS cm-1 (median = 152 µS cm-1), which is lower than in wells (211–9670 µS cm-1; median = 515 µS cm-1). These values result from seawater spray, a CO2 soil contribution and limited dissolution of primary silicate minerals from volcanic rocks. In the case of wells, seawater intrusion may also influence electrical conductivity. One of the main problems in groundwater quality is total and faecal coliform microbial contamination. A pollution risk map constructed for São Miguel as a whole showed that risk in the majority of the groundwater bodies is only very low to moderate.

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