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The choice of the deficiency of 5 tons of calcium carbonate equivalent per 1000 tons of material as the division between toxic and non-toxic material . obviously is arbitrary. However, when applied to the large number of samples studied during the past several years of minesoil research at West Virginia University, it corresponds to other supporting laboratory information about these samples as well as to extensive field experiences with minesoils developing in the different rock types. If rock or soil samples were defined to be toxic at much lower calcium carbonate equivalent deficiencies than 5 tons per 1000 tons, we would be declaring many of our native soils to be toxic. On the other hand, with deficiencies much greater than 5 tone per 1000 tons, toxic concentrations of plant-available aluminum and pH values below 4.0 often develop rapidly. Rock type is incorporated with the acid-base account because it is useful to categorize the materials which comprise coal overburdens. Knowledge of the rock types can provide an estimate of the texture and base status of a future minesoil, as well as stability of rock fragments. For example, sandstones containing moderate amounts of pyrite and lacking sufficient neutralizers become active acid producers when exposed to the atmosphere. The properties previously discussed are represented graphically in Figure 1. There are two zones of acid--toxic materials (the 16.2 to 17.1 m and the 20.7 to 21.6 m depths) indicated by pH values of less than 4.0. Both zones contain enough sulfur to continue to overwhelm the small amount of neutra- - liters present. - Thus, these materials have the potential for remaining acid-toxic unless large amounts of neutralizers (50 and 80 tons calcium carbonate equivalent per 1000 tons of material, respectively) are added. In addition, there is a zone of potentially toxic matefial at a depth of • 13.4 to 16.2 m and two zones below the 23 m depth (underlying the first coal add overlying the bottom coal) , which are defined by a calcium carbonate deficiency of more than 5 tons per 1000 tons of material even though the pH is above 4.0. Non-toxic zones, which exhibit varying amounts of excess neutralizers, exist -T-- _-from-the-surface-to--a=depth-of=13.4-m, from-the17:1to--21-m-depth,—and -- from the 24.4 to 25.4 m depth. These materials can be removed and replaced - in sequential-order, -selectively blended before-replacement,-or totally blended before replacement. Other methods of handling the overburden materials would include utilization of the limestone, after crushing, as a source of neutralizers to be -blended-with the potentially toxic materials. The acid-base accounting method provides a useful tool for evaluating over- burdens in the humid areas of the United States, since it is useless to look for plant toxicities from elements such as aluminum, boron, etc. , until the acid problem is-eliminated.- 4 seliminated. 4