T183 Geochemistry of Geologic Sequestration of CO2: Understanding Gas-Water-Mineral Interactions over Wide Temporal and Spatial Ranges (Posters)

Tuesday, 2 November 2010
8:00 AM - 6:00 PM
Hall D

CO2 FLUX FROM COAL MINE DRAINAGE, ALLEGHENY COUNTY, PA

Paper number: T183-7
Program: Technical Sessions
Time: 8:00 AM – 6:00 PM

Authors

Abstract

Coal mine drainage can contain dissolved CO2 at concentrations above equilibrium with atmospheric pressure. The CO2 flux was measured at two Allegheny County, PA discharges that drain abandoned mines in the Pittsburgh coal seam. Both calcium sulfate-type waters emanate from collapsed mine portals located on a hillside above the Youghiogheny River and flow over waterfalls of approximately 10 to 15 meters before discharging into the river. Site 1 portal water had a pH of 6.1 and 159 mg/L CaCO3 alkalinity; Site 2 portal water had a pH of 5.1, but no measurable alkalinity. An Anton Paar CarboQC™ CO2 meter was used to measure the concentration of dissolved CO2 . The flux of CO2 was calculated using discharge data and the difference in dissolved CO2 from the portals to the bottom of each waterfall. The CO2 concentrations at the source portals were ca. 0.21 g/L at Site 1 and ca. 0.14 g/L at Site 2. The CO2 concentrations decreased by ~85% from the portals to the bottoms of the falls at both sites. The estimated CO2 flux was 225 kg/day at Site 1 and 20 kg/day at Site 2. The ratio of CO2 (dissolved)/CO2(atmospheric) was ≈ 300 and 230 at Sites 1 and 2, respectively.

Using data for Pennsylvania (Cravotta, 2008), we calculated CO2 fluxes for 90 other mine drainage sources and obtained values ranging between 5 and 30,000 kg/day, with an average of 1,300 kg/day. The estimated total daily flux from all sites with available data was ca. 110,000 kg. The calculation assumed that the CO2 in these mine waters completely degassed to atmospheric equilibrium and therefore represents a maximum flux value. The data indicate that mine drainage can contain dissolved CO2 orders of magnitude greater than atmospheric equilibrium; further study is needed to evaluate its importance to the overall carbon cycle.

Cravotta, C.A., (2008) Dissolved metals and associated constituents in abandoned coal-mine discharges, Pennsylvania, USA. Part 1: Constituent quantities and correlations: Applied Geochemistry, v. 23, p. 166-202.