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3. Monitoring Results Quarterly groundwater level and quality monitoring commenced in March 1994 to characterize pre- mining groundwater conditions in the area and facilitate the continued evaluation of local groundwater conditions. Also,as part of Teichert's approved plan to dry-pit mine,groundwater level monitoring provides the necessary information to establish and maintain a buffer between the base of mining and groundwater. Mining of the Lone Tree II mining phase began in 1998 and has proceeded to varying depths in different portions of the phase: to an approximate depth of 80 feet in the initial mined area (currently used as a siltation pond)and to the permitted mining depth of 150 feet in the currently mined area. 3.1 Groundwater Levels Groundwater levels observed in the shallow wells have been generally stable since monitoring began in 1994,typically fluctuating seasonally three feet or less,with seasonal high water levels generally observed in late fall and winter, and the seasonal low water levels observed in late spring and summer (Figure 2). Groundwater depths in the shallow aquifer zone have ranged from about 75 feet in the northwest portion of the monitored area to 155 feet in the southeast(Table 1),and the corresponding groundwater elevations range from about 87 to 75 feet,msl(above mean sea level)(Table 2). In the mid to late 1990's, seasonally high groundwater levels rose approximately four to five feet. Since 1998, seasonally high water levels have gradually declined such that groundwater elevation differences across the monitored are have decreased. Individual hydrographs for all network wells are provided in the Appendix. Long-term fluctuations of shallow groundwater levels in the area are depicted by the hydrograph for Well 4S/6E-5A1 (Figure 3),which has been monitored semi-annually by the California Department of Water Resources since 1960. Groundwater levels in this well have fluctuated in a manner reflecting the historical hydrologic conditions: declining slightly during the drought of 1976-77,recovering to the highest observed levels during the wet period of 1983-86, and declining to the lowest observed levels during the drought of 1987-92. As observed in the other shallow network wells,water levels in Well 4S/6E-5A1 slightly recovered subsequent to the 1987-92 drought through 1998, and have since then slightly declined through to the present. Groundwater levels observed in the deep wells are typically lower,and exhibit greater seasonal and annual fluctuation than levels in the shallow wells(Figure 4). Water levels in the deep aquifer zone have ranged in depth from about 190 to 340 feet, with up to 40 to 60 feet of seasonal fluctuation. In the early 2000s, seasonally high groundwater levels in deep zone wells South Tracy#1,Brown's#1, and Brown's New Well declined by up to about 60 feet, and although substantial recovery occurred in recent years, seasonally high water levels are currently lower than during the 1990's. These lower groundwater levels are likely due to an increased demand(pumpage)on the deep aquifer zone from local agricultural interests and industrial operators. For example,pumpage from Teichert's production wells has increased with increased operations at the Vernalis plant. In addition,a number of deep wells are reported to have been installed in the area south and east of the Teichert Vernalis plant(Liese Schadt personal communication with P. Mercurio, Teichert, October 2002). Further,reduced usage of local surface water supplies by local interests,which may have caused a corresponding increase in local groundwater pumpage,has been reported(Liese Schadt personal communication with J. Muller, Teichert, October 2002). ©LUHDORFF& SCALMANINI ,4 CONSULTING ENGINEERS