Chemical impacts of subsurface CO and brine on shallow groundwater quality.

Leakage from geologic CO sequestration (GCS) sites to overlying shallow drinking water aquifers is a tangible risk. A primary purpose of this study is to assess the potential impacts of CO leakage into a fresh-water aquifer with associated CO-water-sediment interactions. The study site is the Ogallala aquifer overlying an active demonstration-scale GCS site in north Texas, USA. Using the results of combined batch experiments and reactive transport simulations, we discuss the effects of salinity on potential trace metal release and the potential for groundwater quality recovery after leakage ceases. RESULTS: suggest that trace metals are released from sediment due to impure carbonate mineral dissolution and cation exchange with exposure to aqueous CO. Concentrations of Mn, Zn and Sr might exceed the U.S. Environmental Protection Agency's (EPA) limits. After CO leakage stops, most cation concentrations decrease to levels observed before leakage quickly, suggesting that water quality may not be a long-term concern. However, saline water that co-leaks with CO may increase salinity of a shallow aquifer and induce more trace metals release from the sediment. In most cases, pH is sensitive to even small increases of CO, suggesting that pH may be a sufficiently sensitive parameter for detecting CO leakage.