Groundwater changes caused by flow through naturally occurring gas (±water) leakage points

Results from the EC-funded RISCS project are presented regarding groundwater sampling across two naturally occurring gas (±water) leakage points in central Italy to measure potential impacts, and evolution, of near surface groundwater chemistry. One site consists of gas only leakage in the Latera caldera, characterised by shallow alluvial sediments of volcanic (silicate) origin. The other site consists of gas and deep water leaking into a sinkhole in the San Vittorino valley, with surface sediments consisting of carbonate fluvial-lacustrine deposits. These contrasting characteristics permitted an evaluation of how site specific conditions can influence and control the potential impact of a CO2 leak on groundwater resources. Concentrations of most parameters were higher at the carbonate site despite having the higher, buffered pH. This is due to the flow of the deep-origin acidified waters through the thick carbonate stratigraphy and the higher solubility of the associated mineral phases. At the silicate site pH values less than 4 were found in the leakage area, with a clear control of major element chemistry exerted by the local potassium-rich volcanic sediments. Further down gradient the pH and dissolved concentrations for both major and trace elements approached that up gradient, non-impacted groundwaters