AWWA WQTC71338

Commercial-scale geological carbon sequestering (GCS) projects are now being seriously considered as a means of reducing carbon dioxide emissions to help mitigate climate change. In GCS systems, large amounts of super-critical carbon dioxide would be injected primarily into deep saline formations (TDS greater than or equal to 10,000 mg/L) where the CO₂ would be contained for decades to centuries. Although the CO₂ injection zones will be separated from underground sources of drinking water (USDW or sources with TDS <10,000 mg/L) and the GCS systems will be designed to minimize the risk of CO₂ leakage, there is the potential for some of the stored CO₂ to leak into USDWs over the project lifetime (several decades). The potential CO₂ leakage routes include the following: gaps in the confining layer; fault and fracture zones; abandoned wells; slow diffusion through confining layers or through injection well casings; and, down-gradient flow of inject zone water to other groundwater aquifers through long distance transport. The proposed regulations for GCS injection wells are expected to address these potential leakage routes through site assessments, monitoring, and mitigation measures. Nevertheless, it is important to understand how potential increased levels of CO₂ in groundwater supplies could affect their water quality and beneficial uses. Includes extended abstract only.