Laserfiche WebLink
in detectable levels in two samples. Xylenes were detected at 0.007 and 0.10 ppm in samples collected <br /> from 20 and 30 feet, respectively. <br /> 1n a May 25, 1993 letter issued to Mr. Kidd, SJCPHS requested that additional subsurface soil sampling <br /> ' be performed to confirm that soil vapor extraction had effectively removed or significantly reduced <br /> gasoline concentrations in subsurface soils. In response to the SJCPHS's request, SEACOR submitted <br /> a "Work Plan to Conduct Confirmatory Soil Sampling", dated June 16, 1993. In a letter dated July 16, <br /> 1993, SJCPHS conditionally approved the Work Plan. The results of the additional confirmatory soil <br /> sampling requested by SJCPHS are described in this report. <br /> 2.3 PHYSICAL AND HYDROGEOLOGIC SETTING <br /> ' The Site is situated at the southern end of the Sacramento Valley, a subregion of the Central Valle <br /> Y g Y <br /> geomorphic province. The Sacramento Valley is a large asymmetric trough that is bounded by granitic, <br /> metamorphic, and marine sedimentary rocks of pre-Tertiary age. The trough has been filled with as <br /> much as 10 vertical miles of sediment ranging in age from Jurassic to Holocene. Topography in the site <br /> vicinity is relatively flat with a very gentle downward slope towards the southwest. The Site lies at an <br /> approximate elevation of 45 feet above mean sea level. The nearest surface water body is the Mokelunme <br /> River, located approximately 0.75 miles north of the Site. <br /> ' Soils beneath the Site have been investigated to a maximum depth of 59 feet below ground surface. The <br /> Site is underlain by unconsolidated alluvium composed predominantly of sand with lesser and variable <br /> amounts of silt and clay. Soils types encountered consist of alternating layers of brown, yellowish brown <br /> to reddish sand and silty sand. First encountered groundwater occurs in an unconfined condition (water <br /> table) at a depth of approximately 40 to 45 feet bgs. Groundwater elevations measured in wells MW-lA, <br /> MW-2, and MW-3 in January, March, and June 1993 show that the groundwater flow direction is <br /> ' consistently towards the southeast under a hydraulic gradient of 0.008 feet per foot. <br /> CONFIRMA" <br /> 50014-005-01 4 <br />