Laserfiche WebLink
RULE 2 - PERMITS <br />Rased on available information. the potential milling- ]'elated impacts to surface water for the PSCM <br />w 111 be localized. temporary. and N\ ill not involve any significant loll` -terin adverse impacts. The <br />hydl'ologlc COIltr01 and Illltl`_ 1011 Measures proposed in corijunctlon with inining and related <br />activities should effectively mitigate any potential adverse hydrologic impacts. <br />In general. probable hydrologic consequences to surface Mater resources resulting from PSCM's <br />operations will be limited by the relatively small surface disturbance area. and will be effectively <br />mitlaated by operation of the drainaoc and sediment control system and ultimate reclamation of <br />mine disturbance areas. Section 2.053. Operations Plan. and Section 2.05.4. Reclamation Plan. <br />outline the extent of proposed 1111nii1g- rclated surface disturbance. Probable surface water impacts <br />and their significance relative to the hydrologic systenl are discussed in the 1o11owing sections. <br />Lxisting and proposed lie\\ inining- related surface disturbance is limited to Millie SUrface facilities <br />areas and involves removal of' vegetation and soil/ substrate materials and grading of disturbance <br />areas for specific inining-related uses. These disturbance activities reduce infiltration potential and <br />evapotranspiration due to elimination of vegetation, and (,encrally 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 arc 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 upgl'adlent areas around areas of disturbance, glades 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 2.053, 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 356.4 <br />acres (including some previously- disturbed areas associated with existing Seneca II facilities), or <br />11.4% and 1.7% 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 />Midterm Review 2.05 -86 Revision 04/2013 <br />