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Bes cline Ground Meter Levels. Alluvial Yater levels. Thirteen monitor wells (YSAL1 through 13) were inst stied by the OSGS to monitor water levels in the alluvium along Sege Creek on the west side of Yoest. Exhibits 7-1 end 7-2 show the alluvial monitor well locations end the potentiometric surface, respectively. The alluvial wells were located such that the Sege Creek eLluviel system is monitored above end below anticipated mining activity. Meter level data for the Sage Creek alluvial wells yes collected by the USGS from October, 1980 through August, 1983 and by Peabody after June, 1990. 4ell YSAL11 ras vandalized prior to 1990, thus no water level data exists subsequent to 1983 for that veil (see Table 7-3). Monthly water level data for these welts, including hydrographs, are presented in Appendix 7-2. Appendix 7-1 contains the well completion information for the Sage Creek alluvial wells. Ground Mater in the Sage Creek alluvial system occurs mainly under unconfined conditions. Wells YSAL10, 11, end 12 have exhibited artesian or flowing artesian conditions for part of their records, but based upon the potentiometric surface map (Exhibit 7-2), only Nell • YSAL10 is considered to be truly artesian at present. The other nine alluvial wells have mean water levels below ground surf ate ranging from 3.10 feet a[ Yell YSAL4 [0 12.50 feet at Yell YSALB. Disregarding the floring portions of their records, Yells YSAL10, 11, and 12 have mean water levels ranging from 3.12 to 5.12 feet below ground surface. Mean saturated thicknesses in those portions of the Sage Creek System monitored range from 7.50 feet et Yell YSALB to 55.90 feet at Yell YSAL4. Table 7-4 presents mean saturated thicknesses for Yoast alluvial wells. It is assumed that ell Sage Creek wells completely penetrate the alluvium at each location. The Sege Creek alluvial reps exhibit measurable seasonal water level changes. The spring is the dominant period for recharge to the Sage Creek alluvial system, as all of the reps monitored show Che shellorest mean water levels during that season. The spring mean water levels range from 1.80 feet at Yell YSALT to 11.44 feet et Yell YSALB. Summer is the next most important season for providing recharge to this system as indicated et 9 out of the 13 yells. The deepect mean eater levels rare observed in the fall and winter months at 11 out of the 13 yells (Yells YSAl4 end 5 shor the greatest deepening during the summer). wean fall and rioter rater levels range from 2.96 feet to 13.71 feet. Mater level • fluctuations at individual wells ere significant, ranging from 4.18 feet et tell YSAL4 to 12.16 feet et Yell YsAL13. Table 7-4 shows the saturated thickness end percent saturation 10