ARCHIVED REPORTS_XR0006124 - Laserfiche WebLink

Home Browse Search

' 2. SITE BACKGROUND • ' 2.1 SITE LOCATION AND LAND USE Former Exxon RS 7-3942 is currently a vacant lot located on the southeast corner of the ' intersection of North Pershing Avenue and Rosemarie Lane (Figure 2) Used oil and three grades of gasoline were stored in four underground storage tanks (USTs), which were removed from the site in July 1986 ' Land use near the site is primarily commercial and residential A Shell service station and a 7-Eleven food and gasoline service store are located on the southwest and northwest corners, ' respectively, of the intersection of North Pershing Avenue and Rosemarie Lane The Chateau Hospital assisted living home is located approximately 200 feet northeast of the site across Rosemarie Lane There is an apartment complex to the east of the site and a commercial ' building to the south Stagg High School is located approximately 1,500 feet southwest of the site ' 2.2 SITE GEOLOGY AND HYDROGEOLOGY ' The geology and hydrogeology of the site were evaluated using existing boring logs from previous site investigations and monitoring data The site is generally underlain by silty-to-clayey sediment to a total depth of approximately 50 feet below ground surface (bgs), '• with laterally generally discontinuous sand to silty sand lenses at approximately 10-20 feet bgs and at approximately 25-35 feet bgs Cross-sections are shown in Appendix A ' As presented on Figure 1, the nearest body of surface water is the Calaveras River, which 1s located approximately 2,000 feet south and upgradient of the site The East Bay Municipal Utilities District's March Lane Aqueduct piping is Iocated approximately 1,000 feet north of the site The groundwater flow direction has generally been to the northeast with a historical average of N53E and an average gradient of 0 006 Historically, groundwater has been encountered at the site at depths ranging from approximately 13 to 41 feet bgs Groundwater has risen approximately 25 feet over time at the site, from -30 55 feet (40 70 feet bgs) 1n October 1992 to -5 24 feet (12 72 feet bgs) in June 2001 The historical onsite groundwater elevation high and low points are also presented on the geologic cross-sections (Appendix A) As presented on these cross-sections, petroleum hydrocarbon impacted soil occurs between approximately 20 and 46 feet bgs Currently groundwater is at approximately 20 feet bgs, which means that these petroleum hydrocarbons entrapped in soil at the site are submerged • f ' GSP"ects1739421MASTERIWPIASR0904LASPTR V5&c 2