2011-02-28_REPORT - C1981028 (5)

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4.1 2010 PRECIPITATION REGIME The climate of the mine and surrounding area is characterized by a wide temperature fluctuation; from below freezing in winter, to very warm in the summer months. Precipitation in the area is provided by weather systems originating in the Gulf of Mexico and is most frequent and reliable during the spring and late summer months (Table 4). Coors Energy Company has collected precipitation data at the mine for a number of years. This data represents the most complete record of precipitation from the mine area. Table 4 presents a summary of precipitation data collected from 1993 through 2010, corresponding with the most recent vegetation monitoring. A review of the data illustrates that precipitation generally is lowest during the late autumn and winter months (October through March), peaks in April through June, and tapers off gradually until late autumn again. The months with the highest average precipitation are May and June. Based on the 1993-2010 data, average yearly precipitation was calculated. At the Keenesburg Mine, precipitation relevant to the growing season occurs from September to the following July. Total cumulative precipitation for the period from September 2009-July 2010 was 14.65 inches, the fourth highest value since 1993. Compared to the corresponding averages, this represents 29.6 percent more precipitation than the average September-July precipitation amount. Cumulative precipitation for the September-December 2009 period was 4.63 inches, 53.8 percent above the average for those months (3.01 inches). Cumulative precipitation from January through July 2010 was 10.02 inches, reflecting an amount 21.9 percent above average precipitation for that time period. April, June, and July 2010 precipitation amounts were significantly above the averages recorded for the mine site, resulting in above average moisture conditions during the 2010 growing season. 4.2 VEGETATION COVER Table 5 presents a historical record of all vegetation cover and total herbaceous production sampling results for monitoring at the mine since 1994. Though a number of the areas are no longer quantitatively monitored (having been released from liability), this information reflects the impact that varying precipitation regimes and stand age have on the vegetation communities at the mine. The total vegetation cover value of Reclamation Area 30 (2006 Reclamation) reflects a decrease of 1.1 percent from the 2009 growing season. As the September-July precipitation from the 2010 growing season was 29.6 percent above average, the decreased vegetation cover cannot be attributed solely to precipitation. August 2010 was very dry, and it is hypothesized that the available moisture from late spring had been used by the cool season species, while warm season perennials, dependant on July and August thunderstorms, received little precipitation during their critical growth period. The following table provides a comparison of the relative cover of species encountered during cover sampling in Reclamation Area 30 between 2009 and 2010. Coors Energy Company Keenesburg Mine Page 12 2010 Revegetation Monitoring Report