Laserfiche WebLink
Recommendations: Based on our previous discussions with the CGS and CDRMS and our recent observations made <br />at tine project slide, NWCC believes that the surface drainage ditches t should adequately collect and control the <br />surface drainage in this area. However, we recommend that the eastern most ditch be extended uphill to the southeast <br />approximately 50 to 75 feet so that it can collect and drain the surface water that appears to be ponding directly below <br />(lie head scarp in a depressed area. <br />NWCC also recommends that at least one subsurface trench drain be constructed along the failure area as discussed in <br />the field in 2011. The subsurface trench drain should be located in the vicinity of the eastern most surface drainage <br />ditch. The actual location of this drain should be determined in the field at the time of excavation by a representative <br />of NWCC. The trench drain should extend down through existing fill materials and into the underlying natural soils or <br />bedrock materials so that perched seasonal runoff running along the original pit ramp grade can be intercepted. <br />Intercepted drainage should be daylighted to the drainage ditch situated along the uphill side of the existing-access <br />road. NWCC recommends that the trench drain be a minimum of 2 feet in width and be backfilled with free draining <br />rock and possibly perforated drainage pipe situated at the base of the trench excavation. The requirement for <br />perforated pipe should be determined in the field after the excavation is completed and the type and depth.pf fi•ee <br />draining rock materials has been established. The trench drain should run from the head scarp to the existing haul road <br />along an alignment similar to the surface drains. <br />A second trench drain may be required at the western end of the slide and just east of tine western most surface drainage <br />ditch. We recommend that the location of this trench drain be determined in the field after installation of the first <br />trench drain. .A representative of-NWCC should 'be contacted to observe the excavation of the trench drains and <br />observe the installation of the <br />We appreciate the opportun' <br />this report, or if the can be <br />Sincerely, <br />NWCC, Iti <br />U <br />sx: <br />Brian D. Len,'tEr; <br />� y <br />Sr. Principal E ltieri� ~+ <br />materials. <br />of professional service to you in this matter. If you have any questions regarding <br />service, please contact this office. <br />Job Nmnber. 08 -8099 NWCC, Inc. Pau 2 <br />