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PROPOSED DECISION - Canadian Strip/Phase II Bond Release <br />August 1, 1991 <br />Page 4 <br />TABLE 2: Summary of Erosional Stability Observations <br /> Identified Possible Erosion <br /> Factor Factor Percentage Condition Class <br /> <br />East Facing Slope N/A N/A 20-40 Slight <br />West Facing Slope <br />Observer 1 14 71 20 Stable <br />Observer 2 38 85 44 Moderate <br />Valley Bottom <br />Observer 3 13 71 18 Slight <br />Observer 4 16 43 37 Slight <br />Northern Part of <br />Property 12 72 17 Stable <br />In summary, modeling shows that post-mining sediment generation is less <br />than in the pre-mining situation throughout the site. Untreated drainage <br />from the disturbed area ceases to contribute additional suspended solids <br />above natural conditions, per Rule 4.05.2(2>. Field observations <br />document that current erosion at the site would not be disruptive to the <br />post-mining land use. <br />The second condition which must be met for Phase II Bond Release regards <br />the successful establishment of vegetation, per Rule 3.03.1(2)(b>. The <br />Division considers that the vegetative cover standard must be met, as <br />this parameter relates directly to erosional stability of a site. <br />Wyoming Fuel Company utilizes a reference area in establishing their <br />vegetation standards. Rule 4.15.7(2)(c) states that sampling should be <br />valid at the 90X confidence level with a 0.10 alpha probability on a <br />one-sided error test. <br />The Canadian Strip Mine has been reclaimed in four phases as identified <br />on Figure 2A of the Bond Release submittal, and Figure 4 of this <br />document. Area I (9.9 acres) was reclaimed in 1979 and reseeded in <br />1980. Area II (4.0 acres) was reclaimed in 1980. Area III (9.2 acres) <br />was reclaimed in 1981. Ponds 1 and 2 covering 5.21 acres were assigned <br />permanent impoundment status in 1991. Area IV (55.13 acres) was <br />reclaimed in 1987. Pond 3 was reclaimed in 1991 and covered 2.01 acres. <br />The total disturbed area at the site equals 87 acres. Vegetation in <br />Areas I, II, and III was sufficiently similar that vegetation sampling <br />was divided into areas reclaimed between 1979 and 1981 (Area I, II, and <br />III) and the area reclaimed in 1987 (Area IV>. <br />