ARCHIVED REPORTS XR0013118 - Laserfiche WebLink

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Site Closure Request Pombo Property June 14,2005 1%01 primarily used during the war years(i.e.,early 1940s)to transmit Bunker C from the refinery to railroad hubs in Tracy. The lines extending northwest from Tracy also may have been used to ship crude oil to various markets within the Bay Area until the late 1960s. The lines extending northwest from Tracy were reportedly abandoned in 1970(based on historic OVP drawings and discussions with former Chevron employees)and removed and backfilled where possible. The site is currently zoned as GHC,and is developed with one office building,a storm water retention pond,fire station,and associated parking lots and driveways. 2. Site geology and hydrogeology. The subsurface soil in the project area is predominately silt and clay with isolated sandy lenses,to a depth of at least 25 feet. The water table is approximately 11 feet bgs. Shallow groundwater in the Tracy area is of poor quality in general and prohibited for use as domestic or municipal supply in accordance with the Tracy Municipal Code(Section 11.1.16)for reasons unrelated to the presence of degraded crude oil. 3. Sensitive potential receptors including water supply wells and surface water. A 2,000 foot-radius well survey(SAIC,2005) identified an industrial supply well located northeast(down gradient)of the site, in the general vicinity of boring SB-9 at a presumed distance of approximately 1,000 feet(Figure 5); information regarding well location and well construction was not specified. Soil and groundwater samples collected from boring SB-9 reported no detectable contaminants. Eight other identified wells were all located cross gradient or up gradient to the Pombo Property. 4. Provide a map showing the location of all water supply wells used from municipal,domestic, agriculture,industrial,and other uses within 2,000 feet of the site. All wells identified in the well survey are mapped on Figure 5. 5. Provide scaled site maps of the area showing locations of excavation,sample locations, boring locations,buildings,streets, etc. Figure 2 shows all pertinent site features. 6. Boring logs and cross-sections. Subsurface soils observed during drilling events indicate an upper unit of dark yellowish-brown silts and clays,underlying engineered fill and improved surfaces,extending to depths ranging from approximately 7 to 25 feet bgs. All soil borings were properly abandoned by backfilling with cement grout to ground surface or to grade. Boring logs used in preparing cross-sections are provided as Appendix E;all other boring logs are attached to their respective investigation reports. Cross-sections are provided on Figure 6. 7. Volume of excavated soil. I The soil excavated for the construction of the storm water retention basin was reused on the adjacent parcel as fill material beneath an asphalt parking lot. Additionally,in accordance with the SAIC work plan(2003),excess soil from the soil borings and decontamination fluids were drummed and labeled on site,and properly disposed of in a timely manner by CEMC in accordance with California State and federal regulations. SAIC documentation and available documentation of waste disposal by Geomatrix are provided as Appendix F. 8. Fate of monitoring and remediation wells. There are no monitoring or remediation wells on site. 9. Tables ofgroundwater elevations and depths to water. There are no monitoring or remediation wells on site. 10. Tables of analytical results. 5