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Size and Performance of Anoxic Limestone Drains to Neutralize Acidic Mine Drainage

United States Geological Survey, 215 Limekiln Rd., New Cumberland, PA 17070

View larger version (46K): [in a new window]   Fig. 1. Schematic of nominal 3.78-L (1-gallon) cubitainer containing 4 kg limestone and filled with mine discharge water to evaluate alkalinity production rates (after Watzlaf and Hedin, 1993). Limestone sized to 1.3 x 3.5 cm.

View larger version (19K): [in a new window]   Fig. 2. Changes in alkalinity with detention time of mine drainage within limestone drains at Howe Bridge, Morrison, and Buck Mountain sites. Detention time (td) computed as product of porosity (), downflow distance (L), and cross-sectional area (A) divided by flow rate (Q): td = LA/Q, assuming = 0.49.

View larger version (45K): [in a new window]   Fig. 3. Generalized alkalinity data (points) for cubitainer tests of the influent to Howe Bridge, Morrison, and Buck Mountain anoxic limestone drains (ALDs) and corresponding estimates of alkalinity concentration (Ct) computed on the basis of first-order (Eq. [7], dashed curves) and second-order (Eq. [10], solid curves) rate models and corresponding rate constants derived from cubitainer data (Fig. 4 and 5). (A) Howe Bridge and Morrison tests conducted under static–closed conditions (after Watzlaf and Hedin, 1993). (B) Buck Mountain tests conducted under static–closed and circulated–closed conditions.

View larger version (37K): [in a new window]   Fig. 4. First-order rate constant for cubitainer tests: (A) Howe Bridge and Morrison; (B) Buck Mountain negative value of slope indicates rate constant (k') for computation of alkalinity as a function of detention time (Ct) on the basis of Eq. [7].

View larger version (39K): [in a new window]   Fig. 5. Second-order rate constant for cubitainer tests: (A) Howe Bridge and Morrison; (B) Buck Mountain value of slope indicates rate constant (k'') for computation of alkalinity as a function of detention time (Ct) on the basis of Eq. [10].

View larger version (20K): [in a new window]   Fig. 6. Simulated (curves) and measured (points) changes in alkalinity with detention time in Howe Bridge, Morrison, and Buck Mountain anoxic limestone drains (ALDs) including exponential decay and the rate constants, k' and k'', derived from cubitainer tests. Dashed curves were computed for the first-order rate model (Eq. [7]) and solid curves for the second-order rate model (Eq. [10]). Measured data are typical values along the profile as shown in Fig. 2.

View larger version (47K): [in a new window]   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).