Early in the CMI grant, Catherine Peters, Peter Jaffe, and Satish Myneni carried out geochemical experiments to mimic the effects of CO2 injections on aquifers and assess potential hazards of leakage.

Catherine Peter’s group tested the theoretical prediction that metals released from silicate minerals could react with carbon in the aquifer to form new carbonate minerals and sequester CO2. Calculations indicated that these reactions could take up 10-20% of the carbon injected into aquifers, but the team’s experiments showed that solutions had to be highly supersaturated before new carbonate minerals would form. Their work indicated that sequestration via carbonate mineral formation may be difficult to achieve in real aquifers.

The group’s findings also indicated that, although temperature and pH have strong influences on dissolution rates, pressure has only a minor effect. Models can thus scale up existing rate laws for lower pressure conditions, making simulation of aquifers less complicated.

Peter Jaffé and colleagues investigated the impacts of leaks of CO2 from deep aquifers into the shallow subsurface, and their possible environmental risks. The team’s work involved identifying contaminants that might be released if minerals in shallow aquifers were dissolved by CO2-rich fluids. Initial analysis of a USGS dataset indicated that arsenic was the only common element likely to exceed recommended maximum concentrations. However, as arsenic also becomes less mobile with increasing acidity, the group found that leakage of CO2 into shallow aquifers is not likely to impact water quality adversely. The Jaffe group also investigated how leakage into shallow soils impacts biogeochemical cycling.

Satish Myneni led an effort to study the impacts of high CO2 concentrations on soil chemistry and plant growth. Since the 1990’s, large amounts of carbon dioxide have leaked up from an active underground magma chamber beneath the Mammoth Mountain resort area in California, causing high concentrations of CO2 in local soils and the die-off of large numbers of trees.

Myneni’s team investigated the soil chemistry in regions with high CO2 fluxes. They found that minerals are more intensely weathered in these areas and that the nutrients released from this weathering were washed away rather than retained in soils. In addition, root systems of certain trees were altered by high CO2 concentrations in soils, spreading out at shallow depths rather than growing down into deep layers as they normally would. Such signals encountered in areas over a CO2 storage aquifer could be indicators of CO2 leakage.