2013-04-09_REVISION - M1977215 (4)

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The front of the pad directly south of the mill facility is very steep and erosion is evident on this bare surface. The materials are quite varied but generally fine textured in conjunction with large rocks. Either the angle of this slope will have to be altered to discourage active rifling and soil loss or some structural amendment such as riprap will have to be constructed. The bulk of area's B, C, and D contain similar soil types. This entire south facing hill is part of the Creede Caldera and most soils on site are volcanic in origin though they may have been transported and reworked alluvially. As materials washed off the hillside to the north, they have been mixed and stratified. Consequently, soils are extremely variable. The organic surface soil is quite thin over most of the area. The A horizon is usually a loam approximately 4 inches thick. Subsoils range from silty sands and sandy clays to silty clays. An unconsolidated coarse grained clayey sand seems to be the most common material. Due to the method of deposition, sand and coarse frequent content will vary greatly. These fine textured materials have a high moisture holding capacity and therefore can provide stored water for plants. This is probably the reason revegetation efforts on the dam and elsewhere have been so successful despite the dry moisture cor4H esson this southerly aspect. Although these subsoils are only slowly permeable, there is enough sand and gravel in the profile to aid downward drainage and facilitate necessary aeration for plants. Due to the plasticity of these materials, compaction on roadways will be severe to moderate. In order to restore the original productive capabilities ripping and harrowing will be necessary prior to reseeding to prepare the seedbed. Erosion risk is considered to be moderate in these areas. The hazard is partially offset by the fact that these soils are quite deep and can accommodate large quantities of the water. The successful initiation and perpetuation of vegetation on the actual tailings (areas B and D) involves correcting a number of adverse factors. Wastes usually (I) are deficient in plant nutrients, especially Phosphorus and Nitrogen and (2) have poor soil structure. Lower water holding capacity than normal turf (due to poor soil structure) and low organic matter content of spoils, together with poor head. and hydraulic conductivity characteristics, provide an environment in which available soil water for plant growth is one of the most important limiting factors. These poor soil characteristics are compounded by high radiation loads on this southerly slope andresultant high soil surface temperatures. -37- . •