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~wFSrEttN <br />wets-trr,-tt <br />INC. <br />A SubsiJiurv <br />lre#ern Fuels <br />A.imaaliorr, /nc. <br />Mr. Dan Mathews <br />Colorado Division of Minerals and Geology <br />2148 Broadway #C-5 <br />Grand Junction, CO 81503 <br />June 10, 1996 <br />Re: Condition of Embankment for Refuse azea RP-4 Sediment Pond. <br />Dear Dan: <br />As requested I performed an inspection of the pond embanlanent of the RP-4 sediment pond the <br />day the cracks were discovered and then again today to re-check my own findings and to try to <br />confirm my theories as to the nature and cause of the cracks. <br />The cracks as investigated were of a greater extent than mentioned in the inspection report. The <br />end of the cracks extended 20 - 30 feet further on either end of the largest sets. The reason this <br />was not immediately appazent was that the cracks had "bridged" over with soil and were not <br />visible until they were dug up. The depth of the bridges were four to six inches on average. The <br />cracks were also measured for depth and presence of moisture. The majority of the cracks were <br />approximately four feet in depth with some of the cracks in the center of the westernmost set <br />reaching nearly eight feet. The cracks were plumbed with a steel measuring tape. The bottoms of <br />the cracks felt to be well defined and dry to the point of dustiness. Rodents in the form of mice, <br />voles and prairie dogs appeared to be using the cracks for refuge. I walked the base of the dam in <br />its entirety and inspected the outlet to the primary spillway. No wet or damp or soft spots were <br />noted, nor did anything appear out of the ordinary. The end of the spillway pipe contained some <br />stagnant water. <br />One would normally assume some sort of rotational failure in an embankment of this nature but <br />this does not seem to be the case in this instance. The presence of the bridges over the cracks at <br />the ends and intermittently over their length doesn't immediately bring to mind a vertical <br />movement that would be associated with a cylindrical or sliding failure of the embankment. Also <br />supporting this, is that upon inspection there does not appear to be any steps or slumping related <br />to this type of failure. <br />The embanlanent appeared to be constructed mainly of the Turley soil series. Researching the <br />USDA SCS Rio Blanco County Soil Survey the Turley series soils are susceptible to moderate <br />shrink-swell action. Tying this to the recent hydrologic history may reveal the cause of the <br />cracking. Starting last spring (95) this area experienced a great deal of rain on a continuing basis. <br />April and May had eighteen days of rain or snow alone .This precipitation along with water <br />Deserndo Aline <br />P.0. Box 1067 <br />Rangelc. Cobndo N16~3 <br />Telephone SOi/6?i~Wil <br />Telecopier t0i/67i-i"9 <br />