2010-11-17_PERMIT FILE - C1982056A (2)

Home Browse Search

Where pipeline disturbance traverses steep slopes, additional staked straw wattles will be placed on- contour to limit overland flow following revegetation seeding. Drainage and sediment control for the associated minor surface structures (borehole surface casings and any manhole(s)) will also utilize BMP's including the vegetative filter provided by temporary vegetative stabilization, and berms and/or wattles, as appropriate. The pad and access road for the 6RT Thickener Underflow Borehole installation have been designated as a Small Area Exemption (SAE), and the limited drainage from this area will be controlled by gravel surfacing, staked straw wattles, and reclamation/stabilization of the pad area following well installation. SAE designs for the 6RT Installation are provided in Exhibit 49S, and include upstream and downstream straw bale catch dams for any trenching activities. Temporary drainage and sediment control measures will remain in -place until vegetation is sufficiently established to effectively control runoff, erosion, and sediment loss. As relatively small isolated surface disturbances, the additional disturbance required to construct ditches and sedimentation ponds to intercept, route, and treat runoff from thickener underflow pad and road areas, is not warranted. Similarly, for the associated temporary linear pipeline disturbances, construction of ditches and ponds to control runoff is impractical. Much of the EMD Thickener Underflow Pipeline disturbance will drain naturally to existing Sedimentation Ponds E, F, and G, and the majority of the drainage from pipeline areas is effectively isolated from the nearest drainage (Foidel Creek) by the existing raised railroad bed. The proposed BMP's have proven effective in controlling runoff and sedimentation from similar disturbances. Special design, construction, and operational measures have been incorporated in the design plans to assure that there will be no discharge or mixing of mine water with surface drainage. Following installation of appropriate ASC's for each portion of the project disturbance, available soil materials will be bladed from any new disturbance areas and temporarily windrowed or stockpiled on the upgradient edge of these disturbance areas. Much of the pipeline excavation and borehole pad disturbance will occur in areas that are, or have previously been, disturbed. For the remaining pipeline trench areas, consideration of soil horizon segregation must be balanced with the objective of limiting overall surface disturbance. In the interest of minimizing overall surface disturbance, TCC proposes to not segregate and separately stockpile individual soil horizons for the pipeline trench disturbance, and submits that this approach will not significantly alter soil suitability characteristics, since the differences between the soil horizons is not significant over the areas to be affected by trenching. For the borehole drill -pads, individual soil horizons will be segregated, if present. Generally, to avoid contamination of the windrowed soil material, excavated material will be temporarily placed on the opposite side of the disturbance area. Soil materials will be replaced following completion of pipeline installation. Reseeding of the disturbed areas will be completed during the first appropriate planting period following soil material replacement. When no. longer needed to support ongoing or future mining and related operations, the thickener underflow boreholes will reclaimed by removing the surface manhole structures; plugging and sealing the boreholes, consistent with State Engineer requirements; cutting -off the casings below ground level, and placing a permanent marker; then regarding, replacing soil materials, and reseeding the associated disturbance areas. Pipelines will be abandoned in- place, with the ends of the pipelines cut -off and capped below grade. Field Geotechnical Investigations — TCC occasionally conducts field geotechnical investigations prior to, and as the basis for, design and construction of engineered structures. Geotechnical investigations typically involve shallow soil borings (up to 30 feet) using a hollow -stem auger, and/or excavation of shallow (up to 15 feet) test pits. For both soils borings and test pits, surface disturbance is minimal (no more than 10 x 10 feet for boreholes, and 10 x 15 feet for test pits) and both disturbance and subsequent stabilization occur within a timeframe of less than one day for each MR10 -248 2.05 -84.7 01/07/11