Fig. 7. Simulated (curves) and measured (points) changes in limestone mass, detention time, and alkalinity with age of Howe Bridge, Morrison, and Buck Mountain anoxic limestone drains (ALDs). Plots include exponential decay and the rate constants, k' and k'', derived from cubitainer tests and assuming constant flow rate (Q), particle density (_S = 2650 kg m^-3), and porosity ( = 0.49). (A) Limestone mass versus age. (B) Detention time versus age. (C) Alkalinity versus age. Dashed curves estimated using k' (Eq. [7]); solid curves use k'' (Eq. [10]). Measured data in A, B, and C are based on annual averages for effluent (Table 2).