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CONSULTING ENGINEERS /LAND SURVEYORS <br />2150 Hwy. 6 850, Grand Junction, CO 8150.5-9422.970242-5202 • F/UC970/242.1672 <br />November 24, 2003 <br />Western Water and Land, Inc. <br />746 Horizon Court, Suite 330 <br />Grand Junction, CO 81506 <br />ATTN: Bruce Smith <br />RE: Mine Drainage Detention Dam Stabr7ity Analysis <br />Bruce: <br />As requested, we have reviewed the stability of mine drainage detention facilities which we <br />discussed on October 31, 2003. These facilities consist of a combination of a soil plug and <br />a 4.5 foot high concrete dam upstream from the soil plug. Both the concrete dam and the <br />sail plug have detention capabr7ities and they have each been evaluated sepazately as <br />discussed below: <br />SOIL PLUG: <br />1. The soil phrg material was visually characterized by you as silt and fine sand with <br />angular shale gavels, cobbles and boulders up to 12 inches in sue. A loose bulls <br />density test which you performed indicated a wet density of 99.61bs/cu ft. The <br />native moisture content of the soil phrg material was described as low. Based on <br />this characterization, it was assumed that the native moisture content would be <br />approximately half of the Standazd Proctor Moisture-Density relationship optimum <br />moisture content. Two reference sources were reviewed to estimate strength <br />characteristics for the soil plug material. Both of these sources present typical <br />strength values based on the soil classification. T'he classification of the described <br />material could vary depending on the actual gradation. If more than half of the <br />material consists of gravel, cobbles and boulders, the material would likely be <br />classified as a GM (silty, sandy gravel). If more than half consists of clays, silts and <br />sands the material would likely be classified as SM (silty sand) if the sand sizes <br />dominate, or otherwise as ML (sandy silt). The typical values obtained from the <br />two reference sources cover the range of these classifications and aze shown on an <br />attached tabulation. The strengths obtained from the U.S. Bureau of Reclamation <br />(iJSBR) source' aze too high to be representative of the described material because <br />they aze based on materials compacted to the maximum Standard Proctor dry <br />density. It is seen that the lowest typical tested dry density was about 102 lbs/cu ft <br />which is significantly higher than the measured dry density. However, the USBR <br />information is useful to estimate field moisture content based on the assumption <br />described above. Following is a summary of the characterization moisture contents <br />based on the USBR information along with the resulting dry density based on your <br />test: <br />