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November 1993 Raton C>eek * Small A>ea Exemption • l <br />• SMALL AREA EXEMPTIONS <br />TRAILER AND ADJACENT TOPSOIL STOCKPILE AREAS <br />In response to a notice of violation (NOV C-93-46) relating to drainage design concerns, EFMC <br />reviewed the existing disturbance configuration and completed hydrologic modeling of the trailer <br />and adjacent topsoil stockpile areas loca[ed near the mine entrance on the south side of the mine <br />access road, as shown on Map 12, Mine Site Water Systems and Refuse Area. <br />The trailer area consists of a graded pad and access road, both of which are surfaced with <br />approximately 2-inches of gravel, disturbing a total of approximately 0.2 acres. The existing <br />topsoil stockpile, which has a total surface disturbance area of approximately 0.75 acres, was <br />constructed with approximately 3H:1V sideslopes and has been stabilized with temporary <br />vegetative cover. <br />Given that mining operations have ceased, the trailer and topsoil stockpile areas are not <br />currently being utilized and future activities in these areas coil] be ]imi[ed to recovery of <br />stockpiled topsoil materials for site reclamation and final reclamation of associated disturbance <br />areas. <br />In order to adequately control run-on from adjacent undisturbed upgradient areas and runoff <br />from the trailer and topsoil stockpile disturbance areas, EFMC has designed and will construtt <br />• or modify the following drainage structures: <br />• Watershed Diversion 5 <br />• Topsoil Containment Ditches TS-1 and TS-2 <br />• Sediment Fences on the lower portion of Ditch TS-1 <br />• Containment Berm on the west side of the trailer area <br />Watershed Diversion 5 is a temporary diversion designed to safely pass the peak flows resulting <br />from the 10 year, 24 hour storm event. This diversion will intercept runoff from undisturbed <br />areas to the south and upgradient from the trailer/stockpile area, rou[ing resulting flows around <br />the upper edge of the disturbance area to a natural drainage to [he west. The lower portion of <br />the diversion where it enters the natural drainage will be relatively steep, however, in this area <br />it will be excavated in natural bedrock and supplemental erosion protection will not be required. <br />In order to control disturbed area runoff from the trailer and topsoil stockpile areas and prevent <br />it from mixing with runoff from adjacent and downgradient undisturbed areas, EFMC has <br />designed and will construct two topsoil containment ditches, TS-1 and TS-2. <br />Ditch TS-1 will extend from the southeast corner of the topsoil stockpile and is designed in <br />three segments to facilitate control of both flow velocities and sediment transport through the <br />use of sediment fences which will att as sediment [raps. The sediment fences at the lower ends <br />of both the upper and lower segments of Ditch TS-1 will be placed and maintained to provide <br />effettive sediment control. The placement mill involve anchoring of sediment fences across the <br />. entire ditch flow channel at the locations designated on Map 12, Mine Site Water Systems and <br />Refuse Area. The sediment fences will be inspected at least semi-annually <br />A:~856BTRO7.PG5 <br />tti7yy~ tom,,, TenaMatrix/ACZ /nr. * P.O. Box 774018 * Steamboat Sp>ingx Co(o>ado 80477 * (303J 8796260 <br />