Laserfiche WebLink
RULE 2 - PERMITS <br />Based on available information, the potential mining - related impacts to surface water for the PSCM <br />will be localized, temporary, and will not involve any significant long -term adverse impacts. The <br />hydrologic control and mitigation measures proposed in conjunction with mining and related <br />activities should effectively mitigate any potential adverse hydrologic impacts. <br />In general, probable hydrologic consequences to surface water resources resulting from PSCM's <br />operations will be limited by the relatively small surface disturbance area, and will be effectively <br />mitigated by operation of the drainage and sediment control system and ultimate reclamation of <br />mine disturbance areas. Section 2.05.3, Operations Plan, and Section 2.05.4, Reclamation Plan, <br />outline the extent of proposed mining- related surface disturbance. Probable surface water impacts <br />and their significance relative to the hydrologic system are discussed in the following sections. <br />Existing and proposed new mining- related surface disturbance is limited to mine surface facilities <br />areas and involves removal of vegetation and soil /substrate materials and grading of disturbance <br />areas for specific mining- related uses. These disturbance activities reduce infiltration potential and <br />evapotranspiration due to elimination of vegetation, and generally increase surface runoff and <br />erosion potential. For existing disturbance areas associated with the Seneca II mine, these impacts <br />have already occurred and runoff and sediment effects are ongoing, but mitigated by the operation <br />of Ponds 002 and 003, as described in Sections 2.04.7 and 2.05.3. <br />PSCM's primary drainage control practice is to effectively minimize the area of surface disturbance <br />by keeping all surface facilities within a relatively limited area. Provisions for minimizing mine - <br />related surface disturbance are detailed in Section 2.05.3, Mine Facilities. In order to effectively <br />control erosion and increased runoff from those areas which are disturbed, PSCM diverts runoff <br />from undisturbed upgradient areas around areas of disturbance; grades disturbance areas to <br />minimize runoff and erosion; controls surface flow velocities through temporary revegetation and <br />the use of appropriate surfacing materials; uses ditches to collect runoff as close as possible to its <br />source and route it to sedimentation ponds for retention and settlement of suspended solids prior to <br />discharge to natural drainages; and designs, constructs, and maintains diversion/collection ditches to <br />minimize erosion and the resulting sediment loading. Sediment ponds are designed to treat runoff <br />for the 10 -year, 24 -hour event, as described in section 2.05.3, and demonstrated in Exhibit 2.05.3 - <br />E2, Drainage and Sediment Control Plan, and will effectively mitigate any increased sediment yield <br />caused by mining - related surface disturbance. <br />On completion of mining operations, disturbed areas will be reclaimed. Reclamation will involve <br />backfilling and grading, reestablishment of natural drainage patterns, soil /substitute replacement, <br />and revegetation. It is anticipated that reclamation will effectively restore infiltration and runoff <br />patterns to approximate the baseline conditions currently existing for the surface disturbance areas. <br />All presently proposed surface disturbance occurs within the Little Grassy Creek basin, which has a <br />total drainage area of 3,139 acres. The basin of Grassy Creek, at the confluence with the Yampa <br />River, has a drainage area of 20,137 acres. The proposed PSCM surface disturbance totals 276 <br />acres (including some previously - disturbed areas associated with existing Seneca II facilities), or <br />8.8% and 1.4% of the Little Grassy Creek and Grassy Creek drainage areas, respectively. Map <br />2.04.7 -M1, Hydrology, presents the surface disturbance boundary relative to the drainage basins. It <br />• is evident that the disturbed area constitutes a relatively small portion of the total watershed. <br />Increases in runoff from disturbance areas may result in temporary minor increases in stream flows <br />for the receiving drainages, however, any increases will not be significant given the very limited <br />area of surface disturbance relative to total drainage basin areas for the potentially affected <br />PSCM Permit App. 2.05 -86 Revision 03/05/10 <br />