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JUL 2 9 RECD <br />raao ion <br />Geotechnical / Emiranmemal En`ineerln` • Materials <br />July 25, 1996 <br />Seneca Coal Company <br />36600 RCR #27 <br />P.O. Drawer D <br />Hayden, CO 81639 <br />Attn: Mr. Mike Altavilla, P.E. <br />Job No. 95-2384 <br />Subject: Embankment Design Review, <br />Poud 010, Yoast Mine, Rout[ County, <br />Colorado. <br />Gentlemen, <br />As requested, we have reviewed the project plans and specifications for the proposed Pond 010 to be <br />conswcted at the Yoas[ Mine in Rout County, Colorado. We previously completed a subsurface <br />investigation for this site and the results of the field and laboratory investigations, as well as some <br />preliminary recommendations for design of the sedimentation pond were given is a report prepared by <br />our office under our job number 941730, dated July 15, 1994. <br />Based on our visit to the project site on this date and our initial review of the project spermrations and <br />plans, we have prepared the following recommendations for this project. <br />1) It appears [hat a keyway, a minimum of 10 feet in width, is proposed for the base of the <br />embankment. Based on [he relatively shallow water [able and [he pervious nature of the <br />bearing soils, we believe that the conswction of the keyway will not prevent the uaderseepage <br />below the dam and the conswction of this keyway will be very difficult. 'T'herefore, we would <br />recommend that the keyway not be coaswcted. <br />2) Due to the relatively high moisttue content of [he subgrade soils exposed a[ the base of [he <br />embankment, we recommend that a layer of Mirafi SOOX or equivalent stabilization fabric be <br />placed beneath the embankment, prior to [he placement of [he fill materials. In addition, the <br />sue of rock fill materials may be required to stabilize the existing soils located in the center of <br />the excavation, in the area where the drainage bottom was situated. The rock fill materials <br />should be placed and rolled into the soft and pttmping areas prior to placement of the fabric <br />and any additional fill materials. <br />3) Based on our review of the places and spedfications, it also appears that a drainage blanket and <br />toe drain will be conswcted along the downstream toe of the embankment. Based on the <br />subsurface conditions encountered io this area, we believe that i[ is imperative that the <br />(970) 879.7888 • Fex (970) 879.7897 <br />29585 U.S. 40 West, Box 775226 • Steamboat Springs, CO 80477 <br />