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Fir, Jerry Koblitz - 2 - June 21, 1990 3. Please re-work the soii erosion analysis. The bond release regulations (Rule 3.03.1(3)(b)) discuss comparisons of pre-mine and post-mine contributions of suspended solids to surface drainage outside of the permit area. The pond removal regulations (4.05.2(2)) require two demonstrations. Like bond release, a comparison must be generated between suspended solids generation on the pre-mine and post-mine topography, but in addition a demonstration must be made that untreated drainage from the disturbed areas meets state and federal water quality standards for receiving streams at Canadian Strip. This means that you must address all NPDES parameters as well as the receiving stream standards as listed in the enclosure. While Wyoming Fuels must address suspended solids generation as apart of the bond release, it is not mandatory to evaluate the pond removal criteria at this time. (However, I thought that was your intention.) The Division's Bond Release Memorandum suggests that the suspended solids comparison be performed using Williams' modified Universal Soil Loss Equation (MUSLE). This equation predicts sediment yield from a specific storm event. USLE, the equation you utilized, predicts average annual soil loss from a watershed. The Division recommended the use of MUSLE to enable predictive modeling which would satisfy the pond removal criteria. There have been manly modifications to the Universal Soil Loss Equation (USLE), as you are well aware. MUSLE was developed following the evaluation of 778 storms on watersheds ranging in size from 2.7 acres to 2,380 acres and slopes ranging from 0.94ti-5.44. The post-mining topography at Canadian has some slopes of 250, so it may be inappropriate to use MUSLE. A modification of MUSLE entitle RUSLE was developed to handle steeper slopes and may be more appropriate. a. Comparison of erosion loss should be made on similar watersheds. Either compare the disturbed area's pre~nine and post-mine topography throughout its entire extent or compare the post-mine topography at Canadian with a Jackson County watershed of similar size, shape, soil type and slope. Map those watersheds and delineate the subwatersheds which are used in your evaluation as you did previously. b. If Wyoming Fuels desires a pond removal evaluation from the Division, please utilize a soil loss equation which incorporates a 16-year, 24-hour event in the calculations. The 1D-year, 24-hour event is requested as our regulations require that sediment ponds be sized to handle an event of that size. Results should be listed as mg/1 for Total Suspended Solids or mg/m1 for Total Settleable Solids. c. In addition, if Wyoming Fuels desires a pond removal evaluation from the Division, please provide results of influent water quality sampling for both Ponds 001 and 002. Include all parameters for which there are NPDES requirements as well as receiving stream standards.