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4.1 2007 PRECIPITATION REGIME <br />The climate of the mine and surrounding azea is characterized by a wide temperature <br />fluctuation; from below freezing in winter, to very warm in the summer months. <br />Precipitation in the azea is provided by weather systems originating in the Gulf of Mexico <br />and is most frequent and reliable during the spring and late summer months (Table 8). <br />Coors Energy Company has collected precipitation data at the mine for a number of years. <br />This data represents the most complete record of precipitation from the mine area. Table 8 <br />presents a summary of precipitation data collected from 1993 through 2007, corresponding <br />with the most recent vegetation monitoring. A review of the data illustrates that precipitation <br />generally is lowest during the late autumn and winter months (October through Mazch), peaks <br />in April through June, and tapers off gradually until late autumn again. The months with the <br />highest average precipitation are May and June. Based on the 1993-2007 data, average yeazly <br />precipitation was calculated. <br />Cumulative precipitation for the September-December 2006 period was 5.92 inches, 94.1 <br />percent above the average for those months (3.05 inches). The above average total can <br />largely be attributed to the significant snow accumulations in December 2006. <br />Overall total precipitation for 2007 through July was 9.08 inches, reflecting a neazly average <br />amount of precipitation for that time period. As was the case with the September-December <br />2006 period, one month (May 2007) dominated in precipitation received. The May 2007 <br />precipitation total was 4.47 inches, neazly twice the average precipitation amount for that <br />month. <br />At the Keenesburg Mine, precipitation relevant to the growing season occurs from September <br />to the following July. Total cumulative precipitation for the period from September 2006- <br />July 2007 was 15.00 inches, the third highest value since 1993. Compared to the <br />corresponding averages, this represents a value 12.4 percent above the January-July <br />precipitation mean and 34.8 percent above the average September-July precipitation amount. <br />The precipitation regime for this year (2006-2007) reflected nearly normal precipitation <br />amounts and distribution with the notable exceptions of December 2006 and May 2007. <br />Long-lasting snow cover from late December 2006 through late February 2007 contributed to <br />overall cooler temperatures, with little increase in soil moisture due to reduced snow melt and <br />infiltration. Moisture retained in the soil column from the late autumn and early winter <br />months favored very early growth of cool season graminoids and particulazly annual forbs. <br />The significant precipitation amounts in May 2007 contributed to rapid growth of the annual <br />cool season grasses (particulazly Bromus tectorum) and forbs as well as providing significant <br />hold-over moisture for growth of the annual warm season forb, Helianthus annuus. <br />4.2 VEGETATION COVER <br />Table 9 presents a historical record of all vegetation cover and total herbaceous production <br />sampling results for monitoring at the mine since 1994. Though a number of the azeas are no <br />longer quantitatively monitored, this information reflects the impact that varying precipitation <br />regimes and stand age have on the vegetation communities at the mine. In the azeas with <br />Coors Energy Company Keenesburg Mine Page 19 <br />2007 Revegetation Monitoring Report <br />