Changes in the chemistry of shallow groundwater related to the 2008 injection of CO sub(2) at the ZERT field site, Bozeman, Montana

• Published in: Environmental earth sciences 2010-03, Vol.60 (2), p.273-284
• Main Authors: Kharaka, Yousif K, Thordsen, James J, Kakouros, Evangelos, Ambats, Gil, Herkelrath, William N, Beers, Sarah R, Birkholzer, Jens T, Apps, John A, Spycher, Nicholas F, Zheng, Liange, Trautz, Robert C, Rauch, Henry W, Gullickson, Kadie S
• Format: Article
• Language: English
• ISSN: 1866-6280; 1866-6299
• DOI: 10.1007/s12665-009-0401-1

Approximately 300 kg/day of food-grade CO sub(2) was injected through a perforated pipe placed horizontally 2-2.3 m deep during July 9-August 7, 2008 at the MSU-ZERT field test to evaluate atmospheric and near-surface monitoring and detection techniques applicable to the subsurface storage and potential leakage of CO sub(2). As part of this multidisciplinary research project, 80 samples of water were collected from 10 shallow monitoring wells (1.5 or 3.0 m deep) installed 1-6 m from the injection pipe, at the southwestern end of the slotted section (zone VI), and from two distant monitoring wells. The samples were collected before, during, and following CO sub(2) injection. The main objective of study was to investigate changes in the concentrations of major, minor, and trace inorganic and organic compounds during and following CO sub(2) injection. The ultimate goals were (1) to better understand the potential of groundwater quality impacts related to CO sub(2) leakage from deep storage operations, (2) to develop geochemical tools that could provide early detection of CO sub(2) intrusion into underground sources of drinking water (USDW), and (3) to test the predictive capabilities of geochemical codes against field data. Field determinations showed rapid and systematic changes in pH (7.0-5.6), alkalinity (400-1,330 mg/l as HCO sub(3)), and electrical conductance (600-1,800 mu S/cm) following CO sub(2) injection in samples collected from the 1.5 m-deep wells. Laboratory results show major increases in the concentrations of Ca (90-240 mg/l), Mg (25-70 mg/l), Fe (5-1,200 ppb), and Mn (5-1,400 ppb) following CO sub(2) injection. These chemical changes could provide early detection of CO sub(2) leakage into shallow groundwater from deep storage operations. Dissolution of observed carbonate minerals and desorption-ion exchange resulting from lowered pH values following CO sub(2) injection are the likely geochemical processes responsible for the observed increases in the concentrations of solutes; concentrations generally decreased temporarily following four significant precipitation events. The DOC values obtained are 5 +/- 2 mg/l, and the variations do not correlate with CO sub(2) injection. CO sub(2) injection, however, is responsible for detection of BTEX (e.g. benzene, 0-0.8 ppb), mobilization of metals, the lowered pH values, and increases in the concentrations of other solutes in groundwater. The trace metal and BTEX concentrations are all significantly be