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<br />TR9PPER 1RININPr I1~C. <br />February 12, 1990 <br />CERTIFIED #P568142085 <br />Mr. David Berry <br />Colorado Mined Land Reclamation Division <br />215 Centennial Bldg. <br />1313 Sherman St. <br />Denver, CO 80203 <br />Dear David: <br />Subject: Minor Revision MR-95. Small area exemption in West Pyeatt Gulch. <br />During your last inspection of Trapper Mine (2/7/90) we discussed the adequacy <br />of erosion control measures for a small area exemption (topsoil stockpile) in <br />West Pyeatt Gulch. As reported, no downstream sediment control ponds cur- <br />rently exist in this drainage, however, other means of sediment control are in <br />place. In accordance with MR-72 (6/6/88), Trapper has installed (yearly) a <br />series of hay bale structures and/or other adequate erosion control materials <br />(ex silt fence) in the drainage bottom immediately downstream of the distur- <br />bance area in an attempt to control sediment discharge from this small topsoil <br />stockpile. Additionally, mulching and the placement of hay bales along the <br />downstream toe of the stockpile were performed to further reduce the erosion <br />potential until vegetation became established on the site. <br />The Universal Soil Loss Equation (USLE) was used to evaluate the effectiveness <br />of our conservation measures in reducing the erosion potential on this site. <br />Based on the soil type (Morapos) which makes up this topsoil stockpile, the <br />slope length and steepness of the pile, the existing vegetation cover (358), <br />and the management practice performed to reduce the erosion potential on the <br />site, the soil loss associated with this small area exemption is very slight. <br />The soil loss from this topsoil stockpile is approximately .89 tons/acre/year, <br />well below the acceptable 5 tons/acre/year from this soil type in its natural <br />state as designated by the USDA Soil Conservation Service. The following <br />parameters were used in the USLE to determine the soil loss from this <br />stockpile: <br />A - RKLSCP <br />.89 - 30 x .34 x 1.4 x .125 x .5 where <br />A, soil loss in tons/acre/year <br />R, the rainfall and runoff factor <br />K, soil erodibility factor (based on natural soil conditions) <br />L, slope length - combined into an LS factor <br />S, slope steepness <br />C, the cover and management factor <br />P, erosion control practice factor <br />P.O. Box 187 Craig, Colorado 81626 (303) 824-4401 <br />