2008-09-16_PERMIT FILE - C1982056A

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on the classification and engineering characteristics of the on-site soils and bedrock materials. The results • of the field and laboratory investigations are presented herein. This report has been prepared to summarize the data obtained and to present ow conclusions and recommendations for constructing the proposed dam embanl~r-ent and lining the reservoir. Design pazameters and a discussion of geotechnical engineering and geologic considerations related to the construction of the proposed embankment and liner are included. Proposed Construction It is ow understanding that the proposed embankment and reservoir will be constructed to store and treat water that is being pumped from the existing underground mine workings. It is also ow understanding that the surface drainage in the vicinity of the reservoir will be directed away from the pond via the construction of diversion ditches azound the upstream side of the reservoir so that the inflow of surface runoff to the reservoir is minimized. It is also ow understanding that the proposed embankment will be approximately I4 feet high at the highest point and that the soils used to construct the embankment will be obtained from the reservoir area situated upstream of the embankment Based on ow review of the current plans, it also appears that the embankment will be approximately 900 feet in length and will be constructed with a crest width of 12 feet. • Site Conditions The proposed embankment and reservoir will be constructed across an existing drainage swale/channel that is situated south of the 6MN Access Road and east of the 6MN Ventilation Shaft The drainage Swale generally flows in a northwest to southeast direction in this portion of the mine. The drainage swale was dry at the time of this investigation. The proposed dam and reservoir site are currently vacant and undeveloped. The majority of the site is vegetated with grasses, weeds and sage brush. The topography of the site is highly variable with the swale bottom sloping gently down from the west- northwest to the east-southeast The topography of the natural hillsides located above and along the southwest and northeast sides of the Swale bottom are variable and typically range from moderately sloping to strongly sloping (5 to 15 percent). Field Investigation The field investigation for this project was completed on May 29 and 30, 2007. To evaluate the subsurface conditions along the centerline of the proposed embankment six test holes were drilled with an all-terrain mounted drill rig using 4-inch diameter augers. To evaluate the subsurface conditions in proposed borrow area, which is located upstream of the proposed embankment, seven test pits were excavated with a Bobcat 337 trackhoe. The approximate locations of the test holes and test pits are shown in Figure #2. • Job Number: 07-7556 NVVCC, Inc. Page 2