International Environmental Modelling and Software Society (iEMSs) 7th Int.Congress on Env. Modelling and Software, San Diego, CA, USA, Daniel.P. Ames, Nigel W.T. Quinn and Andrea E. Rizzoli (Eds.) http://www.iemss.org/society/index.php/iemss-2014-proceedings Modeling Potential Environmental Impacts of Deep Aquifer CO2 Sequestration Nigel W.T. Quinn PhD, P.E., D.WRE Research Group Leader, HydroEcological Engineering Advanced Decision Support, Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 9472., nwquinn@lbl.gov Abstract: A promising measure for mitigating climate change is to store large volumes of CO 2 captured from large point-source carbon emitters in deep saline aquifers. In vulnerable systems, water resources impacts of large-scale CO 2 storage need to be evaluated and assessed before industrial- size storage projects get under way. In California’s southern San Joaquin Basin the land surface uplift caused by large CO 2 injection projects land deformation could have the potential to create reverse flow along certain canal reaches, or to reduce canal deliveries to agricultural land and managed wetlands. The impact of CO 2 storage on shallow water resources was compared to the expected stresses on the groundwater and surface water systems from ongoing pumping using a version of the Central Valley Hydrological Model CVHM extended vertically to capture reservoir geology. Results of simulations demonstrated that such pumping-related deformations in the area might be one order of magnitude larger than those from CO 2 injection. In the basin the low permeability geological layers between shallow effectively limit pressure changes from migrating far in vertical directions, downward or upward. Keywords: CO 2 sequestration; groundwater modeling; environmental impacts; land subsidence. 1. BACKGROUND In California, the thick sediments of the Central Valley have been identified as prime targets for future geological carbon sequestration (GCS). The San Joaquin Basin has multiple saline aquifers and oil and gas reservoirs, which guarantee a large injection volume. Widespread shale seals found in the basins can serve as structural trapping, ensuring the natural long-term confinement of injected CO 2 . In addition, there have been significant geological data collected from oil and gas operations, which facilitate reliable environmental assessments. Regionally, California's Central Valley has the largest CO 2 storage resource potential, in the range of 2.0 billion–4.1 billion metric tons. The southern portion of the Basin, the focus of our modeling study, is home to some of California’s largest natural gas fields. California’s Central Valley is currently the home to over six million people, and generates over $20 billion in agricultural crops each year. The agricultural and urban development in the area depends on an intricate surface water distribution system that routes water from surrounding watersheds to the Central Valley, and on the presence of extensive aquifers that provide substantial amounts of irrigation water supply. Water resources impacts of large-scale CO 2 storage need to be evaluated and assessed before industrial-size storage projects get under way (Birkholzer et al., 2008, 2009; Zhao et al., 2011). Storing additional fluids in deep saline aquifers causes pressure changes and displacement of native brines, affecting subsurface volumes that can be significantly larger than the CO 2 plume itself. Environmental impacts on groundwater resources may result if the deep parts of the basin communicate effectively with shallower units. The deep sediments overlying the crystalline bedrock would be the main target of future CO 2 storage in the area. These sediments deposited in a marine environment form a succession of thick, porous and permeable, mostly saline aquifers separated by laterally persistent aquitards represented by marine shales (Birkholzer et al., 2008, 2009).