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i~ <br />I' 5.4,1 Groundwater Level Changes Upgradient of the Slurry Wall <br />Figure 16 shows that groundwater level increases ("mounding") have occurred Upgradient of the <br />slurry wall, along the north and west sides of the slurry wall, since it was installed. Groundwater <br />level increases range between 0.4 feet at well S-4 and 4.1 feet at well S-2. The highest <br />groundwater level increases between December 1999 and December 2001 occurred at wells S-2 <br />(4.1 feet) and S-3 (1.9 feet). Groundwater level increases at the other Upgradient wells, S-1, S-4, <br />S-7, and S-8, are generally less than one (1) foot. <br />' The highest groundwater levels that occurred at the Upgradient wells (S-1, S-2, S-3, S-4, S-7, and <br />S-8) during 2001 (Table 1) indicate that none of the wells have sustained a groundwater level of <br />' two (2) feet or less below the natural ground surface. Table 1 shows that the groundwater level at <br />S-2 was measured at 1.86 feet below ground surface on May 9, 2001, however a measurement <br />taken two weeks later, on May 23, 2001, shows that the groundwater level had decreased to 2.66 <br />feet below the ground surface. Groundwater Upgradient of the slurry wall has not, therefore, <br />sustained a level within 2-feet of the ground surface for a period of three weeks, which would <br />require installation of a french drain as set forth in the mining permit. <br />5.4.2 Groundwater Level Changes Downgradient of the Slurry Wall <br />Figure 16 shows that groundwater level decreases have occurred downgradient, along the east <br />' and south sides of the slurry wall, since it was installed. Groundwater level decreases range <br />between 1.4 feet at well S-6 and 4.5 feet at well S-10. The lowest groundwater levels between <br />' December 1999 and December 2001 occurred at wells S-5 (4.3 feet), S-9 (4.2 feet), and 5-10 <br />(4.5 feet). These groundwater level decreases aze caused in part by a groundwater "shadow" <br />along the downgradient edge of the slurry wall. <br />In the area of Mr. Roe's and Dr. Martin's properties, which are about 700 and 1,200 feet <br />' downgradient of the southeastern comer of the slurry wall, groundwater levels have also changed <br />since the slurry wall was installed. Groundwater levels in these areas are about 1.8 feet and 1.4 <br />' feet lower, respectively, compared to pre-slurry wall levels. Although the slurry wall may be <br />partly responsible for some of the observed groundwater level change in the area of the Roe and <br />Martin properties, not all of the change can be attributed to the presence of the slurry wall. <br />' Areally, groundwater levels may also have decreased in response to the past two (2) yeazs of <br />drought conditions in the Fort Collins area as well as local groundwater withdrawals. <br />The lower groundwater level observed at well 5-13 relative to wells L-2 and L-3 may suggest <br />' that local groundwater withdrawal is occurring in the area of well S-13. Groundwater elevation <br />12 <br />