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RUG 09 '96 12:24PM PERHODY WSTN SENECR MINE Jp.L p p ^~N~ <br />/ 6nvlr•n,nenel analn••rln( <br />July 75.1996 <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 />Sob No. 95-]384 <br />Subject: F~bsaitment Design Review, <br />Pond O1D, Yoast Mine, Rouu Couary, <br />Colorado, <br />Gentlemen, <br />Act requested, we have reviewed rho project plans and apedficatioas for the proposed Poad 010 to be <br />constructed at the Yoaat Miae in Routt County, Colorado. We previously completed a subsurface <br />utvestigation for thin site and the results of the field and laboratory iaveatigationa, ee well as same <br />preliminary recommettdatioas for design of rho sodimeatatioa pond were given is a report prepared by <br />our office under our job number 94-1730, dated July ]S, 1994. <br />Rased oa our vo;it to the project site on this dale and our initial review of the project spedfitatians sad <br />nlana, we have prepared the following recommendations for this project. <br />1) It appears that a keyway, a minimum of 10 foot in width, is proposed for the base of the <br />embankment Haled on the relatively shallow water table sad the pervious nature of the <br />t~eariag soils, wo be6evC that [he construction of the keyway will not prevent the uadcrseepage <br />bolow the dam and the coasttuction of this keyway will bo very difficult. Therefore, we would <br />rec~++n~*e~d that the keyway not be eonsttueted. <br />7.j Due to the relatively high moisture content of the subgrade soils exposed at the base of the <br />embankment, we recommend that a layer of Mirafi 5000( or equivalent atabiliution fabric be <br />pieced beneath the embaalcmeat, prior to the placement of the Fill materials. In addition, the <br />use of rock fill materials may be required to stabilize the existing soils located in the tearer of <br />the ..xcavation, in rite area where the drainage bottom wan situated. The rock fill materials <br />should be placed and rolled into the soft and pumping arena prior to placement of the fabric <br />and nay additional Fill materials. <br />j Haled on our review of the plena sad apedfirations, it also appears that a drainage blanks[ sad <br />toe drain will be wastructad along the downstream toe of the embankment. Based on the <br />subsurface conditions oncountercd is thin area, we bolieva that it.is impera[ive that the <br />(870) 8797888 • Fa: (870) 878.7881 <br />28585 U.S. 40 Went, Bo: 775228.3teamboat Sprinpa, CO 80477 <br />