Shallow hydrogeological and hydrochemical characterization of the Aquistore CO2 sequestration site in Estevan, Saskatchewan
Gabrielle Klappstein, Ben Rostron
Carbon dioxide sequestration refers to the process of capturing CO
2
before it is released into the atmosphere and storing it in a suitable media, typically geological formations deep in the subsurface.
Aquistore is Canada’s first dedicated CO
2
storage project, with the purpose of post-combustion capture of
CO
2
from a coal-fired electrical generating station in southeast Saskatchewan. The storage site is located in the Williston Basin, and the target injection zones consist of deep saline aquifers within the basal
Cambro-Ordovician succession at depths of 3.2 - 3.4 km.
An essential component of Aquistore’s measurement, monitoring, and verification (MMV) program is the characterization of shallow hydrogeology as part of a monitoring strategy to trace the migration of CO
2 injected into deep brine formations. Although the site’s geological storage security has been rigorously investigated, there remains a risk of CO
2
leaking into shallow groundwater via unanticipated permeable conduits. Therefore, it is critical to demonstrate that geologically sequestered CO
2
has not leaked into overlying shallow aquifers and altered the quality of groundwater resources. Baseline data provide a framework in which hydrogeological changes, and thus CO
2
intrusion, can be assessed.
In order to establish the baseline hydrochemistry of the Aquistore site, samples were collected from a network of groundwater wells. Several existing monitoring and domestic wells were included in the network, and an additional twenty piezometers were installed specifically for the Aquistore project. These piezometers were located at the CO
2
injection well site and surrounding area in order to cover a 3-km radius of the site. Two major monitoring events were completed for the baseline survey, one in the
Spring, and one in the Fall of 2013. A total of 40 wells were monitored and sampled, with field measurements including water level depths, pH, conductivity, and temperature. Samples were collected and submitted for laboratory analyses of a suite of chemical parameters including major and minor elements and compounds, dissolved organic (DOC) and inorganic carbon (DIC), and stable isotopes. This presentation will provide an overview of water chemistry results along with details of the shallow groundwater monitoring program.