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Portions of the site along the North Creek are designated in Zones A and B. <br /> Zones A and B represent those areas that are affected by the 100-and 500-year <br /> floods, respectively. However, when the North Creek was realigned in 2001 and <br /> 2002, its capacity was significantly increased and the floodplain areas were <br /> eliminated from the landfill footprint. <br /> Rainfall intensities for a 1,000-year storm event for Stockton, California, are <br /> presented in Table 2-1. The intensities were developed from short-duration <br /> depths recorded at Modesto, California, and adjusted for Stockton, California. <br /> TABLE 2-1 <br /> 1 tensi -Duration-Frequencyfor 1,000-Year Return Period <br /> Duration 0.083 0.167 0.25 0.5 1 2 3 6 12 24 <br /> (hr) 5 10 15 30 <br /> min <br /> Intensity 5.06 3.83 3.81 2.34 1.53 0.98 0.78 0.48 0.30 0.17 <br /> in hr) <br /> 2.7 HYDROGEOLOGY <br /> 2.7.1 REGIONAL HYDROGEOLOGY <br /> The Forward Landfill is located in the San Joaquin hydrologic basin. Aquifer <br /> materials within the basin consist predominantly of sand mixed with clay and silt <br /> layers. <br /> Before the early 1960's, groundwater in the area typically flowed to the west. <br /> Since that time, heavy pumping in the Stockton area caused a northerly <br /> component of flow to develop. Salt water intrusion from the west has resulted <br /> in a shift in pumping from west Stockton to east of Stockton, and a resulting <br /> modification in groundwater flow to the northeast. Based on groundwater <br /> elevation contours published by the San Joaquin County Flood Control and <br /> Water Conservation District, the regional groundwater in the vicinity of the site is <br /> now typically 15 to 30 feet below amsl (approximately 55 to 80 feet below <br /> ground surface) and flows to the north-northeast. <br /> GLA (2007) conducted an evaluation of the range of groundwater elevations in <br /> the vicinity of the FL from available resources to assist in assessing the highest <br /> Forward Landfill- Project Description 2-9 BRYAN A.STIRRAT&ASSOCIATES <br /> J:\Allied\Forward\2007.0018 Lateral Expansion\Reports\Proj Descrip\021308 Final Proj Des\Sec 2.doc:2/13/2008) <br />