Anoxic Limestone Drain. A deep trench, filled with limestone. The trench is covered with a clay cap to prevent the entrance of oxygen, hence the term "anoxic." seepage enters through one wall of the trench and passes out the other. During the time the water is in the trench it acquires alkalinity from the dissolving limestone. This alkalinity permits metal precipitation at a later stage. An ALD may be used in the treatment sequence for TP1/TP2.
Anoxic Limestone Drain. a buried bed of limestone constructed to intercept subsurface mine water flows and prevent contact with atmospheric oxygen. Keeping oxygen out of the water prevents oxidation of metals and armoring of the limestone.
anoxic limestone draine. An anoxic limestone drain (ALD) is a buried bed of limestone constructed to intercept subsurface mine water flows. ALD's are used to prevent contact with atmospheric oxygen and retain carbon dioxide, which in turn, generates more alkalinity. Sediment ponds are constructed after an ALD to accumulate the iron oxide precipitates.