Investigation of the geochemical impact of CO sub(2) on shallow groundwater: design and implementation of a CO sub(2) injection test in Northeast Germany

A small scale and temporally limited CO sub(2) injection test was performed in a shallow aquifer to investigate the geochemical impact of CO sub(2) upon such aquifers and to apply and verify different monitoring methods. Detailed site investigation coupled with multiphase simulations were necessary to design the injection experiment and to set up the monitoring network, before CO sub(2) was injected over a ten-day period at three injection wells, at a depth of 18 m below surface level into a quaternary sand aquifer located close to the town of Wittstock in Northeast Germany. Monitoring methods comprised groundwater sampling and standard analyses, as well as trace element analyses and isotope analyses; geoelectrical borehole monitoring; passive samplers to analyse temporally integrated for cations and multi-parameter probes that can measure continuously for dissolved CO sub(2), pH and electrical conductivity. Due to CO sub(2) injection, total inorganic carbon concentrations increased and pH decreased down to a level of 5.1. Associated reactions comprised the release of major cations and trace elements. Geoelectrical monitoring, as well as isotope analyses and multi-parameter probes proved to be suitable methods for monitoring injected CO sub(2) and/or the alteration of groundwater.