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DIAGNOSTIC MONITORING OF BIOGEOCHEMICAL INTERACTIONS OF A SHALLOW AQUIFER IN RESPONSE TO A CO2 LEAK
Impact/Purpose:
CO2 injection into deep geological formations capped by low permeability formations is one of the most promising alternatives for mitigation of anthropogenic climate change. Several deep pilot and demonstration projects are underway. However, the upward leakage of CO2 or mobilized brines through the cap rock could lead to vulnerability of shallow, overlying drinking water aquifers. Elevated levels of dissolved CO2 might affect microbial community dynamics and mobilize natural-radioisotopes, metals, and other non-potable elements and compounds. The proposed research will investigate a shallow potable water aquifer system in sand/clay sequences of the Newark Basin group using laboratory and in situ methods and test how it would respond to a high-level CO2 condition caused by a hypothetical leakage of CO2 from deep injection reservoirs. In particular, we will (1) determine metal release rates as a function of pCO2 and pH under laboratory and field conditions, (2) measure microbial community dynamics as a function of increased acidity and dissolved metal concentrations, (3) determine the role and persistence of microbial communities in the mobilization or immobilization of metallic elements, (4) measure in situ/ex situ mobilization and immobilization of metals under high-level CO2 conditions, (5) determine the extent to which leaked CO2 is geochemically trapped in the aquifer, and (6) develop diagnostic monitoring techniques to advance assessments of groundwater contamination risks and water quality deterioration due to a CO2 leakage event.
Description:
Results from these coupled laboratory and field experiments will greatly improve our understanding of the geochemical and microbiological reactions under low pH - high CO2 stress. We anticipate that this research will: (1) provide criteria for site selection for geological CO2 sequestration, (2) identify aquifers that would be least vulnerable to risks of CO2 leakage and subsequent contamination, and (3) provide a small number of diagnostic testing parameters that may be used in other potable aquifer systems associated with deep CO2 injection.