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FIG. 3. Plot for the determination of apparent first-order rate constants k for CH4 oxidation from three pairs of gas push-pull tests (GPPTs). Residence time is the total time the gas stayed in the subsurface (see "Materials and Methods"). Slopes from linear regressions (solid lines) are apparent first-order rate constants k. C*(CH4)a and C*(CH4)i are relative CH4 concentrations from an active and the corresponding inactive GPPT, respectively. For better readability, early data from GPPT 1 and 2 are not shown. First-order rate constants k are given with 95% confidence intervals.
