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In tilled soils the topsoil layer is typically the uppermost part of the soil ordinarily moved in tillage (discing, etc.) and frequently designated as the plow layer or AP horizon. A maximum depth of 6 to 8 inches of soil is ordinarily moved in cultivation of agricultural soils. The observed plow layer(AP Horizon) is 6 inches or less. Thus the surface 6 inches of soil would be of sufficient depth for separation as topsoil. In accordance with Article 9 Reclamation standards section 3704(c)the topsoil shall be salvaged and stockpiled separately from the subsoils. The topsoil stockpiles left in place for one mining season will be planted to a suitable cover crop mix to reduce erosion and help maintain aeration and microbiological activity. I asked Mr. Glenn Frieberthauser, a plant pathologist with Agri-Analysis in Davis, California to render his professional opinion on the effects of stockpile depth on microbial populations. The following is excerpt from Mr. Frieberthauser's letter. "We have reviewed the information provided with respect to the possible effects of stockpiling soil upon the soil microbial populations. Clearly,soil microbial populations can fluctuate through several orders of magnitude with inputs of organic matter and soil moisture. The soil microbial biomass consisting of the sum total of bacteria,fungi,and actinomycetes will be more influenced by these inputs than by any other factor. It can be expected that the stockpiling of soil will have an effect upon the soil atmosphere. However,D.J. Greenwood(1970)has pointed out that equilibrium with the atmosphere will be quickly restored by gaseous diffusion in soil pores and air channels directly connected with the atmosphere. Soil microorganisms comprise a large and diverse group of species and have been found in previously undisturbed soil at depths of several hundred feet. It is highly unlikely that the stockpiling of soil to a depth of several tens of feet above the soil surface would have any long- term detrimental effects upon the soil microbial populations. There may be a transient reduction in total numbers of microorganisms in stockpiled soil due to the diminution of inputs of soil organic matter and moisture,but these effects would be readily overcome after the soil stockpile was spread out and actively cultivated." Some microbial activity can be reduced over time when soils are stockpiled. However, it is a reduction in populations takes place not a complete elimination of microbes. The temporary reduction in soil microbes can be reversed in the reclamation process through the addition of organic matter and moisture. Biomass building cover crops (e.g. bell beans, oats and vetch)turned back into the soil are intended to serve as a organic matter source for the reclaimed fields. The microbe recovery rate can be further enhanced by the addition of compost, where necessary. Compost would serve as both an organic matter source and an inoculant for soil microbes. It should be noted that the biomass building cover crops alone may be sufficient for microbial recovery. In addition to maintaining microbial activity and reducing soil erosion the cover crops planted on the topsoil stockpiles also function as dust control. Water applied to control dust will be used by the growing cover crops. In turn as the cover crops grow the need for dust control water applications will be reduced. The stockpiles may require light irrigations during the summer months to maintain the cover crops. The cover crop mix selected will include both summer and winter growing plants. 11