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2014-03-07_PERMIT FILE - M2013070
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2014-03-07_PERMIT FILE - M2013070
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Last modified
8/24/2016 5:40:48 PM
Creation date
3/7/2014 3:24:09 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
M2013070
IBM Index Class Name
PERMIT FILE
Doc Date
3/7/2014
Doc Name
Response to Preliminary Adequacy Review
From
Souder, Miller & Associated for Liberty Mining LLC
To
DRMS
Email Name
GRM
Media Type
D
Archive
No
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In accordance with the Manual, the analysis began with a characterization of the developed watershed <br />areas. The project area was analyzed as two distinct watershed areas, see Figures 4 and 5 for the Drainage <br />Basin Delineations for the two areas. Figure 4 depicts the drainage basins/sub- basins, which contribute <br />flows from the undeveloped and undisturbed areas of the site. Figure 5- Drainage Basin Delineation <br />Operation Area, depicts the sub -basin configuration of the operation area. The drainage flows from <br />basins /sub - basins depicted in Figure 4, in particular the northern sub - basins of the undeveloped area, <br />impacts the access road, while the southern sub - basins, sub - basins #1 and #2, of the undeveloped area <br />would contribute flows onto the operation area if left uncontrolled. <br />Analyzing the impacts of stormwater, flows on the access roadway were made assuming that the current <br />alignment of the access roadway would not be altered. The grading /shaping of the access road would be <br />improved to create a crowned section or a cross - sloped section. The use of the section in particular areas <br />was determined by trying to replicate the existing roadway shape in order to minimize changes in flow <br />patterns resulting from roadway improvements. The cross - sloped section for the roadway promotes sheet <br />flow from the hillside above the road, evenly disbursing the flow across the road to minimizing <br />concentrated flow patterns. <br />In areas where flows are collected in a shallow shoulder ditches/swales, located between the hillside slope <br />and the roadway, the roadway section is crowned. The drainage flow in the shallow roadside <br />ditches /swales created by the crowned sections of roadway would become channelized and concentrated <br />as the flow from the hillside is accumulated. The shallow shoulder ditches/swales are short and nun <br />parallel to the road to minimize concentrated flow discharges from the culvert pipes. The short shallow <br />drainage ditches/swales will collect drainage waters from above the road, i.e. uphill of the road, and then <br />directed to culvert pipes crossing the roadway. The culverts are strategically located, based on terrain, to <br />convey water under the roadway. The discharging flow from the culverts located below the roadway will <br />be discharged into a stilling pool wherein the water will be disbursed, altering the flow pattern from a <br />concentrated flow to a sheet flow pattern. The stilling pools will be surrounded by rock check dams to <br />slow and disburse the flow prior to continuing the downhill flow to the Dolores River. This approach to <br />managing the concentrated flows from above the roadway, providing for the flows to be intercepted and <br />removed from the inside /uphill shoulder of the roadway before causing significant erosion damage to the <br />shoulder area. In addition, using this approach will reduce further grading and surface disturbance of the <br />roadway and current shoulder ditch system, which will reduce the need to expose newly cut soil, thereby <br />reducing the potential effects of erosion. This approach also allows concentrated flows to cross the road in <br />a culvert, eliminating erosion damage to and silt creation from the roadway. <br />In areas where a cross sloped roadway section is used, mitigation of possible silt transfer resulting from <br />erosion due to the sheet flow will be controlled by means of waddles, silt fences, straw bails, rock check <br />dams, or other similar measures employed on the downhill side, and uphill side if necessary, of the entire <br />roadway alignment. The proposed road grade /shape generally follows the existing drainage management <br />scheme for the roadway, except that conveyance across the road surface, resulting from existing shoulder <br />ditches /swales, will be modified to cross under the roadway in pipes in lieu of over the roadway in an <br />open channel configuration. In addition, the proposed plan will disburse the currently concentrated flows <br />into a sheet flow pattern. The drainage flow paths in this area would have only minor modifications from <br />the current flow paths established. <br />The second watershed area is that of the Operational Area. This area was analyzed separately because the <br />area will have significant disturbance, i.e. graded and shaped to accommodate the operational aspects of <br />the mine. The analysis considers the impacts to, and the need for, improvements necessary to the <br />management of stormwater runoff from the mine's operation site, see Figure 5- Drainage Basin <br />Delineation for Operations Area for the basins/sub- basins configuration of the Operations Area and <br />Figure b- Mine Operation Area for a depiction of the anticipated uses in the Operational Area. The <br />
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