Groundwater Quality Baseline Assessment for CO ₂ Injection Operations: Barnett Zero CCS Project Case Study

ABSTRACT The rise in atmospheric carbon dioxide concentrations has driven urgent development of carbon capture and storage (CCS) technologies, yet potential groundwater contamination from leakage remains a critical environmental concern. This study establishes comprehensive baseline groundwater quality conditions for the Barnett Zero CCS project in Wise County, Texas, approximately 13 months after injection commenced in November 2023. We collected groundwater samples from six wells (four monitoring wells within 1.6 km and two control wells at 1.6–3.2 km from the injection site) and conducted laboratory analyses of field parameters, major ion concentrations, heavy metals, organic carbon levels, and organic contaminants. Statistical analyses emphasized effect size estimation over hypothesis testing given small sample constraints, revealing no statistically significant differences between monitoring and control wells for any parameter (), and no detectable organic contaminants were found in any wells. However, monitoring wells showed elevated sodium concentrations (110.9 mg higher) and conductivity levels (608.25 µS ) compared to control wells, with large effect sizes ( d = 1.66, 1.10) suggesting potential early geochemical perturbations. Power analysis revealed critical monitoring limitations (achieved power: 0.31–0.52), indicating substantial detection risk. The study demonstrates that while current CCS operations have not resulted in detectable contamination of shallow aquifer systems, the observed effect sizes warrant continued monitoring and network expansion to achieve adequate detection capabilities. These findings establish essential baseline data and an adaptive monitoring framework, contributing valuable insights for CCS environmental surveillance and regulatory development.