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ATTACHMENT A <br /> RESPONSE TO NOV C-93-130 AND OCTOBER 4, 1993 MODIFICAITON <br /> Survey of Erosional Features on Downslopes <br /> Using site measurements, aerial photography and photographs <br /> taken at all minesites in the summer of 1993, a rill and gully <br /> survey has been completed. Mines #1, 3 and 4 have pre-law <br /> downslopes that have developed gullies over the past 30 years. <br /> However, erosion on such areas has been relatively minor. This is <br /> evident from the fact that BAT ponds placed at the toe of these <br /> areas in the past have not had extremely high sediment cleanout <br /> rates. Also, the portal benches have remained virtually intact <br /> since the 1950's. <br /> The enclosed topographic map sections show the portal <br /> downslope areas for Mines 11, 3, and 4 . Mine #2 does not contain <br /> a steep, disturbed downslope that is prone to erosion. <br /> 1) Mine #4 <br /> Mine 14 contains a pre-law spoil slope created when the portal <br /> bench was excavated. The slope material consists of Mancos Shale, <br /> weathered coal from the seam outcrop and some sandstone material <br /> from minor beds excavated above the coal seam. The spoil slope <br /> extends from the upper portal bench to a point approximately 60 <br /> feet below the coal loading bench. The enclosed photo shows the <br /> downslope area in detail. The total length of the slope is <br /> approximately 300 feet at the deepest point and the overall grade <br /> is roughly 1.OH: 1.OV. Some clump grasses have been established <br /> naturally on the slope. Approximately 15-20 gullies of depths <br /> greater than 3 feet exist, with lengths greater than 100 feet. For <br /> the most part, the gully depths do not exceed 5 feet. A crust has <br /> built up on the surface of the slope over the years which is <br /> helpful in controlling erosion. Close site inspection reveals no <br /> evidence of significant recent (last five years) erosion. Most of <br /> the gullies have reached a relative equilibrium and are not <br /> expected to produce significant erosion during normal runoff <br /> events. <br /> 2) Mine #3 <br /> Mine #3 contains a steep spoil slope which also consists of <br /> Mancos Shale, weathered coal from the seam outcrop, sandstone <br /> material from minor beds excavated above the coal seam and coal <br /> waste from a pre-law coal screening operation located on the bench. <br />