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4. Summary Quarterly groundwater level and quality monitoring of two identified aquifer zones(a shallow and a deep zone)commenced in 1994 and mining of the Lone Tree 11 phase area commenced in 1998. Water level data,collected semi-annually since 1960 by the California Department of Water Resources, are also available for one shallow zone well. The extensive available shallow groundwater level record shows that water levels observed since 1994 are within the range of historically observed levels and relatively stable. Groundwater level elevations in the area ofTeichert's Vernalis plant suggest predominantly southeasterly groundwater flow direction. Groundwater levels observed in the deep wells are typically lower than in the shallow zone, and exhibit greater seasonal and annual fluctuation than groundwater levels in the shallow wells. In the early 2000's, groundwater levels in the deep zone noticeably declined, likely in response to reported increased pumping of local deep irrigation and industrial production wells. In the mid 2000's, substantial recovery of groundwater levels occurred, however, seasonally high water levels remain below those observed in the mid to late 1990s The groundwater quality record documents stable conditions in both the shallow and deep aquifer zones. Shallow groundwater is generally of Ca-Na/HCO,-CI type and deep groundwater is of Ca-Na/HCO,-SO, type. The overall content of soluble minerals is slightly higher in shallow zone groundwater than in deep zone groundwater. Elevated nitrate concentrations in groundwater, documented since pre-mining times to the present, are most likely attributable to historical and ongoing agricultural land use in the area. In summary, the existing data record shows no indication that mining operations have changed groundwater quality to date. g ©LLIa)Qi FF a SCALMANINi CON9LRTING rNOIN[FG9