2011-03-24_REVISION - C1982057 - Laserfiche WebLink

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C-1982-057 TR-73 Engineering-Geotech PAR 24-Mar-2011 Page 3 of 5 • Man-made fill materials (clay, topsoil and rock fragments), placed during reclamation, were encountered to a depth of 19'. The fill materials were typically very soft to loose, and dry to wet. Conclusions and recommendations for repair of the landslide begin on NWCC page 5. Saturation of upper reclaimed fills by perched groundwater at former access ramp fill is the likely failure mechanism; upper fills were placed loosely, and have since become saturated Groundwater will be captured upslope and within the failure, and directed away from failed materials Regrading the remainder of the slide (uphill) to more stable configuration cannot be done until existing fill materials are dewatered Q i ! ill 1111 Y , 111111111111 11111111 A I ... , 1 a. Although not stated directly, the NWCC report seems to imply that relocated Channels PM-2A and PM-2 will now serve the dual purposes of transport of surface water runoff and interception of subsurface water that is flowing into and out of the shrub plot landslide. Please verify that this is or is not the intent of the proposed plan. b. Construction of PM-2 across the toe of the shrub plot landslide may contribute to additional loss of stability in the slide mass due to the removal of any materials now acting as a buttress. Subsequent downhill movement of the mass could encroach upon the PM-2 channel and create a damming effect. Please address the possibility of this scenario occurring. The current application does not propose the construction of any ditches or channels to divert surface or subsurface flow away from the eastern two-thirds of the shrub plot landslide. While regrading the area is not yet feasible, would installation of a cutoff channel be possible with TR-73? Exhibit 20-D.2 Sheet 1 Pond 016 Area Remediation Plan and Road Profile �i I JIMI j I ) I I I a. Page I of the text states that the new road will be approximately 20 feet wide. Please add a typical section for the road to this map, showing the proposed configuration for both cut and fill situations, with roadside ditches and proposed surfacing material and thickness. b. The Division was unable to find details with the TR-73 application that describe how the road will be constructed to comply with the requirements of Section 4.03.2 — Access Roads. Please provide the details and required commitments, or direct the Division to the place in the current permit where these items are already addressed. c. A vertical profile is provided beneath the plan view. The profile is drawn with both horizontal and vertical scales at 1"=100'. Please modify the vertical scale to be I"=20', and add elevation levels at each VP1.