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grade aggregate result in the depletion of currently available Portland Cement C6ncrete i� f Y ; resources within the region. PCC-grade aggregate resources in the MRZ-2 areas located within the Corral Hollow Creek, Lone Tree Creek, and Hospital Creek alluvial fans in is f i southwestern San Joaquin County were estimated in 1988 by CDMG to be 584.2 million tons (Jensen and Silva, 1988). The aggregate extraction proposed would represent approximately 5 percent of the estimated resource. Aggregate resources are necessary for construction materials for buildings, bridges, �- canals, and pavements. The demand for aggregate within the Stockton-Lodi Production- Consumption Region (S-LP-CR) for the period 1986 to 2036 was estimated by CDMG to be 112.5 million tons (2.25 million tons per year) to meet aggregate needs. Approximately 40 percent (45 million tons) of the total aggregate demand was historically used as PCC- grade aggregate. At a rate of production of 0.48 millions tons per year, Alternatives 1, 2, j and 3 would provide approximately 21 percent of the estimated aggregate demand and would utilize approximately 5 percent of the estimated resource. This is a less-than- significant impact and an application of this resource that is consistent with its intended l use. , _ Alternative 4: No Project Under the No Project Alternative, the removal of aggregate resources at the project site would not occur. However, aggregate would continue to be extracted at exiting permitted !i sites with the Hospital Creek alluvial fan production region. No mitigation is necessary. " t .I AII_Quarry Excavation Alternatives (1 2, and 3) i` Impact 4.2-6 Elevated GroundwaterLeveIs'Could Affect Post-Reclamation Agriicult: re 4 The borings installed as part of the subsurface investigations for the project site were not completed to depths that would allow evaluation of groundwater conditions below the bottom of the proposed excavation at elevation 85 feet NGVD. One groundwater level measurement within an existing water well at the project site indicated that, at the time of drilling in 1991, the- groundwater-elevation was approximately 75 feet NGVD. The characterization of the expected groundwater table throughout-the project site and potential _ seasonal fluctuation cannot be accurately made on the basis of single data point. Monitoring of a water supply well,located near the project site indicated a range -in groundwater elevation from 43 to 63 feet NGVD. The 1991 water level measurement i apparently suggests that water levels exceed this historic range. However, the expected maximum groundwater levels at the project site cannot be accurately determined on the i basis of the existing data. The potential for groundwater level to rise to elevations which ! j could inundate the mining areas or affect post-reclamation agricultural uses would need FEZ to be established prior to excavating to the maximum depth of proposed mining (85 feet NGVD). This would be a significant impact, Draft Environmental Impact Report 4-21 ER-96-3 5 i