1994-05-02_REVISION - C1981017 - Laserfiche WebLink

Home Browse Search

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