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raao tons <br />Geo[echnicall Environmental EnQineerin~ • Materials Teann~ <br />Jwy u, 1996 <br />Seneca Coal Company <br />36600 RCR #27 <br />P.O. Drawer D <br />Hayden, CO 81639 <br />Atm: Mr. Mike Al[avilla, P.E. <br />Job iVo. 95-7384 <br />Subject: £mbanitment Design Review, <br />Pond 010, Yoast Mine, Routt County, <br />Colorado. <br />Gentlemen, <br />• <br />~s requested, we have reviewed the project plans and spcci£catioas for the proposed Pond 010 to be <br />constructed at the Yoast Mine in Routt County, Colorado. We previously completed a subsurface <br />investigation for this site and [he reswts o[ the field and laboratory investigations, u well as some <br />preliminary recommendations for design of the sedimentation pond were given in a report prepazed by <br />our office under our job number 94-1730, dated Jwy 15.1994. • <br />Based on our visit to the project site on this dale and our initiw review of the project specifications and <br />plans, we have prepazed the following recommendations for this project. <br />1) [[ appears that a keyway, a minimum of f0 Ceet in width, is proposed Eor the base of the <br />embankment. Based on the relatively shallow water table and the pervious nature of the <br />bearing soils, we believe that the construction of the keyway will not prevent the underseepage <br />below the dam and the construction of [his keyway will be very difficwt. Therefore, we wowd <br />recommend [hat the keyway not be constructed. <br />'_) Due to the relatively high moisture content of the subgrade soils exposed at the base of the <br />embanicmen[, we recommend that a layer of Mirati ~OOX or equivalent stabilization fabric be <br />placed beneath the embankment, prior to the placement of the Fd1 materials. In addition, the <br />use of rock Yill materials may be required [o stabilize the existing soils located in the center of <br />the excavation, in the area where [he drainage bottom was situated. The rock tiB materials <br />shoved be placed and rolled into the soft and pumping areas prior to placement of the Fabric <br />and any additional fill materials. <br />3) Based on our review of [he plans and specifications, it also appears that a drainage blanket and <br />toe drain veil be constructed along [be downstream toe o[ the embankment. Based on the • <br />subsurface conditions encotmtered in this area, we believe that it is imperative that the <br />(970) 879.7888 • Fax (970) 879.7891 <br />29585 U.S. 40 West, Box 775226 • Steamboat Springs. CO 80477 <br />