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• use of contour furrowing, contour drainage ditches, chisel plowing and <br />revegetation. <br />This application contains calculations used to determine runoff volumes <br />and flow rates for a theoretical 10-year, 24-hour precipitation event and <br />subsequent sediment volumes. The precipitation data were obtained from <br />the NOA Atlas 2, Volume 3 for Colorado; soil types were obtained from the <br />Soil Conservation Service, and are shown on the Soils - South Map (Map <br />6) and the Soils - North Map (Map 5). <br />The ongoing mining activities within each watershed of the permit area <br />will create constantly changing hydrologic conditions. The design models <br />are generally based on a static, theoretical scenario, utilizing SEDCAD+ <br />Version III which considers a final reclamation and pit closure scenario <br />in each watershed. Refer to Drawing 41 - Watershed Boundaries for <br />Hydrologic Modeling for a delineation of the areas used for these <br />modeling purposes as well as the individual maps associated with each <br />SEDCAD run. <br />It is Colowyo's contention that the proposed models represent nothing <br />more than our best hydrologic estimates for a described range of <br />conditions. According to Agplied Hydrologv and Sedimentology for <br />Disturbed Areas, Barfield, Warner and Haan, 1981, "Hydrologic <br />calculations are estimates, with the error in these estimates increasing <br />as the degree of approximation increases or as the estimation procedure <br />is applied beyond the range of conditions for which it is intended." <br />Accordingly, it would be inappropriate for these modeling scenarios to <br />be used or relied upon other than for their intended purpose which is as <br />an aid in the design of sedimentation pond structures to predict <br />compliance with applicable effluent standards. Colowyo believes it <br />would be an inappropriate use of the SEDCAD models to use them as an <br />enforcement tool for such operations as topsoil stripping, backfilling, <br />grading, reclamation, etc. <br />The scenario used for the work area pond and loadout ponds correspond to <br />an active, disturbed operation. In terms of ground water, Colowyo's pits <br />have remained essentially dry. Pumping of pit water (precipitation <br />induced surface runoff) into sedimentation ponds is unlikely but, <br />nevertheless, should it be necessary to pump the following ponds are <br />designed to handle a base flow of 0.03 cfs for points 001, 002, 007, 008, <br />009 and 010. Colowyo's CDPS Discharge Permit (to be renewed in 1998) <br />will provide for pumping of pit water from both precipitation induced <br />surface runoff and groundwater sources should they be encountered. <br />Discharges from Colowyo's ponds will remain in compliance with the <br />applicable CDPS Discharge Permit requirements. The use of flocculents in <br />sedimentation ponds may also be used in accordance with the provisions <br />• of the CDPS Permit. <br />Sediment will be removed from all sedimentation ponds on an as needed <br />basis or when sediment will not allow effective treatment of the runoff <br />4 . O5 - 6 Flevisgn SubmrGed 7 •~~ 9rQ <br />