HYDROLOGICAL AND GEOCHEMICAL ANALYSIS OF SHALLOW AQUIFER WATER FOLLOWING A NEARBY DEEP CO2 INJECTION IN WELLINGTON, KANSAS

Carbon sequestration experiments require frequent monitoring of nearby shallow water resources to protect potable water supplies. A CO₂ intrusion into the shallow subsurface can acidify water, bring saline water from depth increasing total dissolved solids (TDS) and desorb hazardous quantities of trace metals into solution. Our study aims to collect specific geochemical data from nearby shallow aquifers and surface waters before and after the start of a carbon storage operation where CO₂ will be injected into the Arbuckle aquifer in south-central Kansas to a depth of 4950 feet. Sampling of these shallow waters and subsequent analysis for major and trace elemental data including REE chemistry, δ²H- δ¹⁸O, ⁸⁷Sr/⁸⁶Sr and water quality parameters will provide data necessary to track the geochemical and water quality evolution over time. The results from our analyses will allow us to evaluate controls on shallow water chemistry and construct a model that describes the hydrological setting, including groundwater source and flow direction, to determine if a leakage event has potential to impact nearby potable wells. Results of the pre-injection monitoring within the shallow aquifers indicate a steep salinity gradient with TDS that range from 1,500 to 300,000 mg/L to a depth of 200 feet. The pH ranged from 6.5-7 for the shallow wells and 6.5-8 for the potable wells and surface waters. Sr²⁺, Ca²⁺ and PO₄^3- concentrations are highest in the shallowest well (~50’ TD) which were 155, 4364 and 18.1 mg/L, respectively. Mg²⁺, Ca²⁺ and Br^- concentrations decrease from the shallow to intermediate wells before increasing again to the deepest well. Na⁺ and Cl^- values increase exponentially with depth between the three wells ranging from 5,800 mg/L to 110,612 mg/L for Na⁺ and 16,800 mg/L to 154,800 mg/L for Cl^-. These preliminary data will serve as the basis for comparison against post-injection water samples to determine if there was an abnormal change in water chemistry over time.