A preliminary review was conducted of the occurrence and importance of slaking in coal refuse dumps. Of 21 disposal sites visited to evaluate environmental problems of aging refuse dumps, 5 were selected for intensive study. Laboratory testing included specific gravity, gradation, maximum and minimum density tests, 9-inch drained triaxial tests, 9- and 10-inch permeability tests, slake- durability tests, and accelerated slaking tests. Some refuse sites had significantly lower shear strengths and permeabilities in old, slaked, or weathered material than in fresh refuse. Testing did not show useful correlations between strength and permeability changes and other material properties that could serve as predictors. Testing of refuse under accelerated slaking conditions showed promise as a comparative tool and as a potential means of preparing artificially aged samples for evaluations of long-term behavior.