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Studies in west-central New Mexico show that the hydrologic parameters of a coal sequence do not change appreciably
as a result of strip mining or by erosion and deposition.
The Dilco, Gibson, and Cleary coal deposits are part of an intertonguing sequence of Upper Cretaceous marine and non-marine deposits consisting principally of fine-grained clastics. Aquifer tests have established a range for the hydrologic parameters of strata in the coal sequence. Chemical quality of the ground water also has been determined.
Natural erosion of the coal deposits generally occurs in the form of mass wasting, sheet wash, and eolian deposition. This material is periodically reworked by ephemeral streams to produce thin valley-fill deposits. Infiltration of runoff into the underlying sediment creates a perched ground-water aquifer that is likely to go dry during periods of limited runoff. These ephemeral aquifers have hydrologic characteristics and water quality similar to the undisturbed coal sequences.
Through conventional reclamation processes, spoil material replaces the original coal sequence. The spoil material has been found to have hydrologic characteristics and water quality similar to the natural coal-bearing deposits and the valley-fill material.
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