Investigating Perched Aquifers in Volcanic Terrains using TDEM Geophysical Exploration Technique

Precise location of perched fresh water aquifers in volcanic islands facilitates the design of well drilling and the decision to choose the optimal target production zones, thus reducing drilling risk. Among the most effective exploration techniques to investigate aquifers, geophysical methods as Time Domain Electromagnetic (TDEM) provides underground resistivity distribution at different depths depending on the frequencies range for a specific area, which highlights the water presence. Here we present a case study where TDEM technique was successfully used to locate a perched aquifer in Terceira Island, Azores, helping TERAMB Company to decide the position of a new well for freshwater. The well was requested by Azores government authorities aimed to aquifer water monitoring due to possible fluid leakage and consequently water pollution by urban waste disposal materials at surface. The modelled top aquifer surface based on the TDEM data interpretation fits with the observed water table measured in the vicinity wells. The perched aquifer shows an abrupt water level decreasing due to the presence of a fault plane and pyroclastic rocks that produces a weakness plane where the water escapes. This comprehensive study facilitates the design of new drilling for groundwater contamination monitoring in volcanic complexes.