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dries out completercause usually the top of the ~ layer is at about the <br />same elevation as the water table. This process can take anywhere from several <br />months to a year oz more. <br />Once it has dried adequately, the overburden and soil is carefully placed <br />over the silt. The depth of this material is very critical to the <br />revegetation. The material should be between afoot deep and two feet deep. <br />The reason for this will be clear later. <br />The result of this process is a deep silt layer extending from the shale <br />underneath the gravel to about the top of the water table. It appears to still <br />be quite porous and holds considerable amounts of vater. No evidence has ever <br />been found which would indicate the silt produces a barrier to groundwater <br />movement. On top of the silt is a layer of sandy loam soil which is from one <br />to two feet deep. Although large equipment can detect the Telly like <br />consistency of the silt layer under the overburden, standard farm equipment has <br />no difficulty operating on top of the backfilled pits. <br />SOIL ~1 The original soil on the site was an unstructured sandy loam. <br />The original structure was destroyed by repeated plowing during periods when <br />the land was farmed. The original distance from the surface to the water table <br />averaged about 9 to 5 feet so the original soil medium tended to be rather dry <br />and often needed irrigation to yield good production of crops. <br />With the backfill approach, however, this distance from the surface to the <br />water table is reduced to an average of about 18 inches. This means plant <br />roots can easily reach the water table and take advantage of what amounts to <br />subirrigation. <br />The soil material tends to be somewhat saline, but upward migration of <br />water in the sandy loam is not significant. This means saline spots on the <br />surface generally do not occur except where the medium is less than about 6 <br />inches above the water table. By carefully monitoring the depth of overburden <br />replacement the areas of thin overburden can be reduced to almost zero and <br />thereby eliminate the occurrence of saline crust on the surface. This is a <br />critical factor is the successful revegetation of the area and the maintenance <br />of good growths over time. <br />5 <br />