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Mayo and Assocla~es, LC <br />• 3.0 PRECIPITATION, PHYSIOGRAPHIC, AND GEOLOGIC SETTING <br />3.1 Precipitation <br />A plot of the Palmer Hydrologic Draught Index (PHDI) for Colorado Division 2 (which <br />includes the West Elk Mine area) is shown on Figure 2 (NCDC, 1998). The PHDI indicates <br />[he long-term climatic trends for the region. The PHDI, which contains monthly values <br />calculated by the National Climatic Data Center (NCDC), indicates the severity of wet or dry <br />periods. The PHDI is computed from climatic and hydrologic parameters including <br />temperature, precipitation, evapotranspiration, soil water recharge, soil water loss, and runoff <br />(Karl, 1986; Guttman, ]991). <br />Because the PHDI takes into account parameters that affect the balance between moisture <br />• supply and moisture demand, the index is a useful tool for evaluating the long-term <br />relationship between climate and groundwater recharge and discharge. The PHDI is useful <br />for evaluating the relationship between climate and variations in the discharge rates of <br />springs and streams. 1'he plot of the PHDI for the mine area indicates extremely wet years in <br />the early and middle 1980's, followed by several years of drought in the late 1980's and early <br />1990's. The 1990's have been characterized by alternating wet and dry periods of short <br />duration. <br />3.2 Physiography <br />The West Elk Mine lease area is located near the northeastern edge of the Colorado Plateau <br />physiographic province. The study area is bounded on the north by [he valley of the North <br />• Fork of the Gunnison River, on the south and west by Mimresota Creek and the Mesaverde <br />Characterization of Groundwater Systems in the V icimty of the West Elk Mine, Somzrset, Colorado <br />29 January 1999 <br />Page 9 <br />