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1 | P a g e C1981-0 2 2 T R 7 7 M e m o <br /> <br /> <br />To: Leigh Simmons <br />From: Janet Binns <br />Date: May 3, 2019 <br />Re: Elk Creek Mine, TR77 <br /> <br />I have reviewed Oxbow Mining, LLC’s (OM) application for a technical revision to <br />revise and define reclamation success standards for the Elk Creek Mine. Mining at the <br />Elk Creek Mine area began in 1901. As such, much of the facilities area was disturbed <br />prior to the Colorado Surface Coal Mining Reclamation Act and subsequent Regulations <br />were passed. Therefore, in many areas no topsoil was salvaged prior to disturbance, and <br />no baseline vegetation data was collected prior to disturbance. <br />The post-mining land use on many of the areas disturbed pre-law is commercial and <br />industrial, or undeveloped land. OM is proposing a reclamation success standard <br />applicable to the areas disturbed pre-law, and subject to Rule 4.15.10. <br />Since there was no pre-disturbance data for vegetative cover on these areas subject to <br />Rule 4.15.10, OM is proposing to use the modified Universal Soil Loss Equation to <br />develop a vegetative standard that will be adequate to control erosion on the reclaimed <br />area. Considering the lack of acceptable undisturbed land to use as a reference area, and <br />the lack of pre-mining vegetative data, use of an accepted erosion control formula to <br />calculate the necessary vegetative cover to achieve erosion control is an acceptable <br />approach. However, the Division needs additional information regarding the assumptions <br />OM used in solving the equation for “C” (vegetative cover). <br />A=soil loss in Tons/acre/year. OM used data from West Elk Mine from 2011 of A=13.68 <br />tons/acre/year. <br />1. The Division needs additional information regarding how this value was <br />derived. The majority of the slopes at Elk Ridge Mine are south facing, <br />while the majority of the slopes at West Elk Mine are north facing. Was <br />this soil loss calculation derived from similar soils and slopes? The <br />Division needs more detail in order to confirm if this is an acceptable soil <br />loss rate for the Elk Ridge permit area. <br />R= Rainfall factor. Elk Creek used 2-year, 6 hour Type II storm for Somerset, CO <br />=33.30. The Division concurs with using the 2 year, 24 hour storm event, as it is <br />referenced in Barfield and Warner, Applied Hydrology and Sedimentology for Disturbed