Laserfiche WebLink
Y?AT TR-44 PRELIMINARY ADEQUACY RElllEVll <br />? . As Hated in the cover letter tothe TR-44 application, the primary purpose of the revision <br />plan is to divert potential runoff away from the Pand a? 2 slide area. To provide <br />additional assurance that this purpose would !?e accomplished, we request the <br />following clarifications and?or modi#ications to the proposed plan. <br />a} vile recommend that BAE-? sump be located further to the east slang the ridgeline, at <br />the eastern boundary of the original haul road disturbance. Drainage from the haul road <br />disturbance i not required to be passed through a sedirr?ent pond or SAE treatment <br />structure. Thus, the sump could be located at the east edge of the haul road corridor on <br />the ridgeline, minimizing the drainage area to be ditched and treated. Drainage from the <br />haul road disturbance west of the relocated sump should be diverted to the north, away <br />from the slide, using a series of small berms or water bars. This would eliminate the <br />need to concentrate and collect runoff slang the western end of the ridge, in the vicinity <br />of the slide. <br />b} Due to damage caused to lower sections of Ditch YPM-? by slope movement, it is no <br />longer effective in conveying surface flog away from the slide, and into the sediment <br />pond. If SAE- sump is moved further to the east and water bars are installed across <br />the haul road disturbance corridor as recommended, the upper section of YPM-? an the <br />ridgeline should be regraded and eliminated. <br />c? Please clarify, in the amended narrative of section ?.0 an page ? 4, Attachment 13?? ?, <br />that the existing grater bars that direct runoff to the south, toward the Pond g?2 slide, will <br />be eliminated. <br />?. The proposed sumps would in effect be small impaundr?ent, Please provide a typical <br />sump design drawing and include narrative stating thatthe sumps wauid he <br />suh?ect to P.E. construction certification and annual certification, quarterly <br />operator inspections, and other requirements of Rule 4.05.9. <br />3. Because the sumps would depend an storage to control runoff, the design event should <br />be the ?5?year, ??-hour precipitation event, pursuant to Rule 4.05.g????e}, rather than <br />the ? g year, ?4-hour event. Please amend the application accordingly. <br />4. As an alternative to the impoundment sumps, and to avoid the associated impoundment <br />design, certification, and inspection requirements listed in Items ? and ?, above, a <br />design approach utilizing lama type of sediment filtration structural might be <br />considered. onceptu?lly, this approach would utilize a series of properly sized <br />diversion berms ordips to route flaw off the ridgeline to the north, slang with appropriate <br />sediment filtration structures for each paint of diversion perhaps same combination of <br />rock checks to slag the flow and silt fence or straw wattles to filter sediment}.