Laserfiche WebLink
Hydrologic Impact Assessment <br />Blue Flame Mine, Permit C-81-053 <br />Proposed Release of Liability <br />Prepared by Tom Kaldenbach <br />Environmental Protection Specialist <br />Colorado Division of Minerals and Geology <br />January 29, 2004 <br />Preminina versus Postminin¢ Sediment Yield <br />One requirement for release of a reclamation liability is that the reclaimed area not yield more <br />suspended solids to offsite surface water than it did prior to mining (Rule 3.03.1(b)). An alternative <br />requirement is that the reclaimed area not yield more suspended solids than adjacent nonmined land. <br />Approximately 4.1 acres of land surface were disturbed and reclaimed at the Blue Flame Mine site. <br />The premining sediment yield of this disturbed area is unknown because the area was disturbed prior <br />to the enactment of the Surface Mining Control and Reclamation Act (SMCRA). (Mining began in <br />the 1940s.) <br />A chief cause of soil loss is transport of solids in suspension; therefore, calculated soil loss rates can <br />be valid indicators of the premining and postmining yields of suspended solids. In order to compare <br />premining and postmining soil loss from the disturbed azea, the Division has calculated premining <br />and postmining soil loss rates using the Universal Soil Loss Equation (LISLE). The LISLE is the <br />product of the following five factors: rainfall-runoff (R), soil erodibility (K),slope-length-steepness <br />(LS}, cover-management (C), and erosion control practice (P). Only the cover (C) factor is varied <br />between the Division's pre- and post-mining calculations; all other variables are held constant. The <br />premining and postmining C-factors used in the calculations both assume cover at the surface is <br />grass, rather than weeds. A premining C-factor of 0,018 is used, based on75% canopy cover and <br />80% ground cover. (This premining C-factor is very conservative when pre-SMCRA disturbance is <br />considered.) A postmining C-factor of 0.013 is used, based on no appreciable canopy, with 80% <br />ground cover. (DMG found grass and litter cover totaled 79.8% during its 2003 Vegetation Sampling <br />study conducted at the Blue Flame Mine.) The calculated premining soil loss rate is 0.7 <br />tons/acre/year (40R X 0.30K X 3,O~s X 0.018c X 1.OP = 0.7 tons/acre/year). The calculated <br />postmining soil loss rate is 0.5 tons/acre/year (40R X 0.30K X 3.O~s X 0.013c X O1.OP = 0.5 <br />tons/acre/year). The premining rate is less than the postmining rate, thus indicating postmining soil <br />loss (and sediment yield) is no more than premining conditions. The postmining rate of 0.5 <br />tons/acre/yeaz is a moderate soil loss rate for steep-sloped rangeland in southwest Colorado. <br />The Division's field observations during regular inspections have corroborated the calculated low <br />sediment yield from the Blue Flame site. There have been no problems with rilling or gullying. <br />Sediment fans or deltas aze not present. The vegetative cover appears to adequately protect the site <br />from erosion. Based on these field observations, and the calculated soil loss rates, the Division finds <br />1 <br />