PERMFILE104353 - Laserfiche WebLink

Home Browse Search

constructing a sediment pond is not warranted. Sediment contributions from the small disturbed area can effectively be controlled using the stated Best Management Practices (BMP's), and therefore falls under a n SAE, consistent with applicable provisions of Rule 4.05.2(3)(b). The will be no discharge or mixing of mine water with surface drainage from the site. Given the limited site area, agravel-surfaced pad area, the drainage and sediment control measures, and the effectiveness of the BMP's in reducing peak settleable solids concentrations to 0.23 ml/I (modeled results), TCC submits that an SAE is justified for this site. The estimated peak flow and runoff from the site for the 10-year, 24-hour storm event is 1.52 cfs and 0.17 acre-feet, respectively. The peak settleable concentration in the runoff from the proposed Bleeder Shaft pad area is less than natural settleable solids concentrations for runoff from undisturbed lands, given similaz conditions. The upgradient diversion ditches will be triangular ditches designed to safely divert the peak flow from the l0-year, 24- hour storm with a minimum of 1-foot of freeboazd and located as shown on Figure 1, Bleeder Shaft Pad SAE. The shaft pad will be constructed such that it slopes towazd the gravel filter. The check dam and grass filter efficiency was modeled using the SEDCADTM4 check dam and grass filter utility. Exhibit 5 is submitted to demonstrate that application of diversion ditches, drainage collection ditches, wattles, Curlex blankets, and the sump, rock check dam, and grass filter can effectively control and treat runoff from this azea. Thickener Underllow Pipelines and Borehole (TR07-60) -With the exceptions of the surface casing for the Undertlow Borehole and any intermediate access manhole(s), surface disturbance for the Thickener Underflow Pipelines and Borehole will be temporary and surface activities will be limited to pipeline borehole installation activities. During construction, and for the minor surface structures, drainage and sediment control will be provided by Alternative Sediment Controls (ABC's) consisting of combined Best Management Practice (BMP) measures. Construction-related surface disturbance will be limited to soil removal and windrowing from the pipeline trench alignment and borehole pad area, excavation of the trench and temporary stockpiling of excavated material adjacent to the trench, and excavation of temporary pits (within existing disturbance areas) for pipeline boring orjacking operations under the Foidel Creek culvert crossing and railroad spur. Following installation of appropriate ABC's for each portion of the project disturbance, available soil materials will be bladed from any new disturbance areas and temporarily windrowed on the upgradient edge of the disturbance area. 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-pad, individual soil horizons will be segregated. Generally, to avoid contamination of the windrowed soil material, excavated material will be temporarily placed on the opposite side of the disturbance area. BMP's for the construction activities include: • Minimizing the area of surface disturbance • Installation of the Foidel Creek crossing as a bored/jacked pipeline under the existing Foidel Creek road crossing culverts (avoids new surface disturbance of the stream channel and floodplain) • Completion of construction activities during the dry summer period • Placement of staked straw wattles downgradient of all surface disturbance areas to intercept any surface runoff and trap associated suspended solids • Soil replacement and stabilization with temporary revegetation plantings immediately following completion of construction activities Where pipeline disturbance traverses steep slopes, additional staked straw wattles will be placed on contour to limit overland flow following revegetation seeding. Temporary drainage and sediment control measures will remain in-place until vegetation is sufficiently established to effectively control runoff, erosion, and sediment loss. Drainage and sediment control for the minor surface structures (borehole surface casing 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. As a relatively small (0.6 acres) linear surface disturbance, the additional disturbance required to either construct or intercept and route runoff from the disturbed area to a sedimentation pond is not warranted. The proposed BMP's have TR07-60 2.05-84.1 06/04/07